Band 54, Heft 9-10

Response of chloroplast on the structural level to photodynamic herbicides and high oxygen concentration was compared with symptoms of chloroplast senescence. Based on the present results and those known from the literature a general pattern of response was proposed: the action of most of environmental factors induces the oxidative stress and often gives similar symptoms of structural damage and dysfunctions independent of the primary stressing factor. These alterations consist mostly in swelling of thylakoids, disruption of chloroplast membranes, intensive plastoglobuli accumulation, photodestruction of pigments and inhibition of photosynthesis

Single turn-over xenon flashes induce a thermoluminescence (TL) B-band centred near 35 °C. The far-red illumination of leaves at non-freezing temperatures induces a band peaking at around 45 °C (afterglow or AG-band), together with a downshifted B-band peaking between 15 °C and 28 °C. In control, unfrozen wheat plants, the T max of the B-band induced after 30 s far-red light at 0 °C was approx. 15-18 °C. In maize plants grown under the same conditions, this far-red-induced downshift was not so strong, since the B-band peaked at 28 - 30 °C. Both a decline in the AG-band and a reversal of the downshift of the B-band were observed after short-term freezing in several plant species. There was usually a sudden drop in the AG-band below a critical freezing temperature. However, while in wheat plants a weak TL emission could be seen between 40-50 °C in frozen samples, in cold-sensitive maize plants this was completely suppressed and only the B-band could be detected. In cold-hardened wheat plants the temperature at which the AG-band was suppressed was lower than in non-hardened plants. Drought and short-term heat stress also affect the AG-band. As the AG-band was found to be more sensitive to several types of stresses than the B-band, it can be used as a sensitive stress indicator. However, the behaviour of the AG-band depends on several factors (for example the age of the leaf, etc.), which must be controlled if different species or varieties are to be compared

Changes of thermoluminescence characteristics as well as the O 2 -evolving capacity was analysed in chloroplasts isolated from Nicotiana benthamiana infected with pepper and paprika mild mottle viruses and their chimeric hybrids. The electron transport activity in thylakoids of virus-infected plants was inhibited and could be restored by adding DPC or Ca 2+ which indicated that the virus infection altered the oxygen-evolving complex. In thermoluminescence characteristics of plants infected with either viruses, the first well defined response was a shift in the peak position of the B band from 20 °C to 35 °C corresponding to S 3 (S 2 )Q B - and S 2 Q B - charge recombinations, respectively, which showed an inhibition in the formation of higher S states in the water splitting system. Simultaneously, a new band appeared around 70 °C due to chemiluminescence of lipid peroxidation. Further progress of the viral infection dramatically decreased the intensity of bands originated from charge recombinations with a concomitant increase of the band at 70 °C indicating the general oxidative breakdown of injured thylakoids

In the present study, mung bean (Vigna radiata L.) - a salt susceptible and Indian mustard (Brassica juncea L.) - a salt resistant crop was studied to find out the differences in stress responses of these crops. Seedlings were grown in water soaked cotton under continuous illumination of 35 μmole m -2 s -1 at 26 ± 1 °C. Salinity treatment of 0, 0.5 and 1.0% (w/v) was given to the seedlings at 6 day Photosynthetic pigment content and PS II electron transport activity was reduced under salinity in both mung bean and Indian mustard. The pigment protein pattern of both the crops were similar. Ratio analysis of B and Q thermoluminescence (TL) glow peaks suggested that S 2 Q A - charge recombination was relatively more affected than S 2/3 Q B - charge recombinations

The responses of photosystems (PS) I and II to light stress at 4 °C and 20 °C were studied in leaf discs from three chilling-sensitive plant species, Cucumis sativus, Cucurbita maxima and Nicotiana tabacum, and in the chilling-tolerant Spinacia oleracea. The chilling-sensitive plants were grown at 24 °C under 80 -120 μmol photons m -2 s -1 (Cucumis and Cucurbita) or 30 μmol photons m -2 s -1 (Nicotiana). Spinacia was cultivated outdoors during winter and early spring. The P700 absorbance change around 820 nm served as a relative measure of PSI activity. The potential efficiency of PSII was determined in dark-adapted leaf discs by means of the ratio of variable to maximum chlorophyll (Chl) a fluorescence emission (Fv/Fᴍ). In Cucurbita, Nicotiana and Spinacia, PSI was not or only slightly inhibited by 2 h illumination with 200 μmol m -2 s -1 at 4 °C or with 2000 μmol m -2 s -1 at 20 °C. In leaves of Cucurbita and Nicotiana, exposure to 2000 μmol photons m -2 s -1 at 4 °C resulted in a decline in PSI activity and potential PSII efficiency approximately to the same extent (about 50% within 2 h). In contrast, in Cucumis, both moderate and high light at low temperature caused a PSI inhibition that proceeded considerably faster than the decline in PSII efficiency. Such preferential photoinhibition of PSI was not observed in the other three species tested. In Spinacia, a lower susceptibility of PSI and PSII to photoinhibition at 4 °C was associated with a faster de-epoxidation kinetics of violaxanthin, as compared to the three chilling-sensitive species. In addition, leaves of Spinacia were characterized by a significantly larger pool of xanthophyll-cycle pigments and a higher content of β-carotene based on Chi a+b. When leaves of Cucurbita were preincubated with methylviologen, which catalyzes formation of superoxide anion radicals at the acceptor side of PSI, the decline in potential PSII efficiency under 2000 μmol photons m -2 s -1 at 20 °C and 4 °C was strongly enhanced, whereas the P700 signal was less affected. Our data demonstrate that in the species tested, PSI may be inhibited in vivo besides PSII under light stress, but preferential photoinhibition of PSI is not a general phenomenon in chilling-sensitive plants. At low temperatures, a reduced function of the xanthophyll cycle and of the antioxidative scavenging system might account for enhanced PSI and PSII inhibition in vivo

A study was conducted to analyze the contribution of high irradiance and resulting photoinhibition to the decline in net photosynthesis in the leaves of palm Trachycarpus fortunei during summer and winter as well as at normal growth and low temperatures in field and laboratory conditions, respectively. Fluorescence induction measurements indicated that there was a 10% decrease in the F v /F m ratio in field conditions at midday during both summer and winter, due to the relatively low intensity of incident light resulting from the partial leaf segment folding. Fluorescence parameters completely recovered by the evening hours. In summer the midday decay was due to the decrease of F m which probably represents a rapidly reversible component of photoinhibition by the protective down-regulation of PSII mediated by the xanthophyll cycle. In winter, however, the initial F v /F m ratio was 40% less than as measured in summer and its midday decline was associated with the decrease of F v indicating the partial inactivation of PS II. The net CO 2 assimilation rate followed the pattern of the F v /F m ratio but it could not recover due to the stomatal closure after midday. Comparing the fluorescence and gas exchange measurements we have concluded that the photoinhibition of T. fortunei represented by the F v /F m ratio changes is a regulatory adjustment of PS II efficiency to limiting carbon utilization and to limiting carbon availability imposed by stomatal closure. Leaves photoinhibited under laboratory conditions at growth temperature showed a substantial decrease of 50% in the F v /F m ratio due to the perpendicular exposure, but no apparent changes in D 1 protein content could be detected. Phytotron grown plants exposed to cold stress (6 °C) and low irradiance (250 μmol m -2 s -1 ) under laboratory conditions showed a time related but much slower continuous decrease in F v /F m ratio. After high irradiance the recovery kinetics in the dark at normal growth temperature (28 °C) strongly depended on the extent of the photoinhibition, while after low irradiance complete recovery occurred in 12 hours irrespective of the initial F v /F m value, independently from the time of cold treatment, indicating that at low light and cold treatments only reversible inactive PS IIs were formed

When leaves of atrazine-resistant (AR) and atrazine-sensitive (S) Erigeron canadensis (L.) plants grown at 5 °C were exposed to an elevated temperature (35 °C) for 30 min, the critical (T c ) and peak temperatures (T p ) of the F 0 vs. T curves were considerably higher for the leaves of the S biotype, but not for those of the AR biotype. The temperature dependences of F v /F m and ΔF/F m ′ were not greatly different for the heat-treated cold-acclimated AR biotype, in contrast with the situation for the S plants. This short-term heat treatment resulted in a more significant shift in the optimal thermal interval of CO 2 fixation for the S than for the AR biotypes

Since the early 80’s massive bleaching affects the reef ecosystem. It involves, besides corals, several other species among which large foraminifers, and it corresponds to the loss of their photosynthetic symbionts or the symbionts’ pigments. The cause is unclear, though temperature elevation and strong irradiation have been considered to be primary factors. In this work we investigated in two genera of coral reef foraminifers (Amphistegina lobifera and Amphisorus heimprichii) and in the temperate foraminifer Sorites variabilis the response of photosystem II (PSII) of their symbionts in hospite upon light stress (white light of 550 μE m -2 s -1 and red light of 3200 |μE m -2 s -1 ) and heat stress (up to 32 °C), by means of the Chla fluorescence transients O-J-I-P they exhibit upon illumination. The transients were analysed according to the JIP-test which leads to the calculation of several structural and functional parameters providing a quantification of PSII behaviour. We observed that the various parameters undergo modifications that differ concerning both their extent and their degree of elasticity, thus indicating that different adaptive strategies are employed in response to stress. The most pronounced of these regulatory changes is a wide decrease of the quantum yield of electron transport. However, the extent of the changes, different for the three studied species, was in general smaller when the cultures were kept under low light (70 μE m -2 s -1 ) than in darkness. By the applied stressors, PSII was not damaged and, except for some cells in which an expulsion of symbionts was initiated, no bleaching was observed. This can be well correlated with the observed adaptability of PSII. As a working hypothesis, it is proposed that the decrease of the capacity for electron transport activity might be among the factors triggering bleaching in the field

The effect of extreme temperature on the quantum yield of fluorescence and membrane leakage of Pinus canariensis growing in 5 stands at different altitudes and orientation in Tenerife (Canary Islands, Spain) was determined. Needles were collected from the field and transferred to the laboratory where they were kept in a closed chamber with water-saturated air overnight. Then they were exposed for 30 minutes in plastic bags in a water bath at temperature treatments with steps of 2K between 56 °C and -24 °C and the effect was determined immediately and 24 hours after the treatment by chlorophyll fluorescence and electrolyte leakage. Needles presented incipient damage at temperatures ranging from -5 to -10 °C depending on the altitude and orientation of the stand. The results were more evident when the measurements were done 24 hours after the cold treatment and values were consistent with the electrolyte leakage results. Different resistance to high temperature depending on the altitude and orientation was also found, varying the temperature for incipient damage from 42 to 44 °C detected with the fluorescence parameters but not with the leakage of electrolytes which was not found until 50 °C. The amplitude of thermal limits for photosynthetic efficiency alteration in needles of P. canariensis was relatively narrow and similar to that of evergreen Canarian laurel forest trees

The effect of water stress on gas exchange, water relations and leaf anatomical characteristics have been studied in two olive cultivars (Olea europea, L. cv. ‘Koroneiki’ and cv. ‚Mastoidis’). Photosynthetic rate as well as stomatal conductance were decreased in stressed plants. Osmotic potential (π) declined rapidly in stressed plants indicating their ability for osmoregulation. Bulk modulus of elasticity (ε) was significantly higher in stressed compared to well irrigated plants. The volume fraction of intercellular spaces of the upper palisade parenchyma, the spongy parenchyma as well as the lower palisade parenchyma were significantly lower in stressed compared to well irrigated plants. On the other hand, the density of mesophyll cells in the upper palisade parenchyma, spongy parenchyma and lower palisade parenchyma increased significantly in stressed plants

Chlorophyll fluorescence, gas exchange, water potential and relative water content were measured in the needles of five year old seedlings of Pinus canariensis in order to know their response to mild water stress. Two trial plots of ten plants per plot, of similar age and characteristics were irrigated daily until the experiment was undertaken, then one of the plots was left without watering while the other one was irrigated as before. After a week of treatment, the water potential at midday did not change in any of the irrigated or non-irrigated plants maintaining around -0 .4 MPa, and the relative water content changed from 93% in irrigated to 84% in non-irrigated seedlings. The stomatal conductance decreased 60% in non irrigated plants and as a result CO 2 assimilation decreased by 50% and transpiration was reduced at a higher proportion (70% ), indicating a good control against water loss, before any change in water status in the needles could be observed suggesting an isohydric water economy in this plant

Summer diurnal variations of photosynthesis and α-tocopherol content were measured in relation to natural drought in field-grown rosemary (Rosmarinus officinalis L.) and lemon balm (Melissa officinalis L.) plants. During the summer relative water contents (RWC) of ca. 40% in Rosmarinus officinalis and ca. 30% in Melissa officinalis were attained, indicating severe drought. Both species showed similar diurnal patterns of net CO 2 assimilation rates (A) with a wide plateau of maximum photosynthesis at midday in the absence of drought and one peak of maximum photosynthesis early in the morning under drought conditions. Net CO 2 assimilation rates decreased by ca. 75% due to drought in both species. Melissa officinalis plants showed a significant decrease in the relative quantum efficiency of PSII photochemistry (Φ PSII ), ratio of variable to maximum fluorescence yield (F v /F m ) and chlorophyll content of leaves by ca. 25% under drought conditions at midday. In contrast, Φ PSII , F v /F m and chlorophyll content remained constant throughout the experiment in R. officinalis plants. Although the non-photochemical quenching of chlorophyll fluorescence increased from ca. 1.8 to 3 and the a-tocopherol content rose fifteen fold in both species in response to drought, only R. officinalis plants were able to avoid oxidative damage under drought conditions by the joint increase of carotenoids and α-tocopherol

In this work we study the effect of reduction in relative water content (RW C) on the chlorophyll fluorescence induction kinetics as well as on the membrane integrity, measured as electrolyte leakage, in sun and shade leaves of three Canarian laurel forest trees. No differences were found among the species and type of leaves, when the slow fluorescence kinetic parameters and electrolyte leakage were analyzed, values deviated from the normal ones at 70% and 40% RWC respectively. On the contrary, the photochemical efficiency of PSII was affected at higher values of RWC in sun leaves (90% and 52% RWC depending on the species) than in shade ones (40% RWC). These results indicate that the susceptibility of PSII to water deficit is different depending on species and environmental conditions where the leaves develop

Wounding, Drought, Elicitation, Catalase, Peroxidase The activity of O 2 -scavenging enzymes in bean leaves in different positions and poplar leaves in different leaf storeys was investigated. The effects of wounding, elicitation and drought and the combination of these treatments at various levels were studied. Distal bean leaves showed higher responsiveness than those opposite the treated leaves. Poplar leaves above the treated ones proved to be more active than those in lower storeys. A comparison of the interaction of different stress treatments revealed both synergistic and antagonistic effects on the oxidant-generating rate and anti-oxidant synthesis of damaged and non-damaged plant tissues

Seasonal and diurnal fluctuations were measured in the leaf proline content of three dicot species ( Lim onium gmelini, Lepidium crassifolium and Camphorosma annua), natives to an inland saline area of Hungary. Proline contents were negatively correlated to the mean monthly temperature in all three species. All the investigated species accumulated proline in February and/or March, while increases in temperature were followed by a drop in proline level by the beginning of April/May. Sodium accumulation in the leaves as well as soil water content influenced the amount of proline to a smaller extent than temperature in all of the investigated species. Accumulation of proline did not show significant correlations with the accumulation of sodium in the leaves. Diurnal pattern of leaf proline content changed during the growing season with a decreasing trend at the beginning (April) and increasing trend at the end (August) of the season

The complexity of in vivo toxic effects of Cd on higher plants makes almost impossible an accurate distinction between direct and indirect mechanisms of its action on the photosynthetic apparatus. We, therefore, postulate that multiple Cd effects on plant physiological and metabolic processes may finally be focused on photosynthesis. This would also explain the phenomenon that only a small fraction of Cd entering chloroplasts may cause such disastrous changes in their structure and function. In return, the inhibition of photosynthesis affects numerous metabolic pathways dependent on the primary carbon metabolism

Depending on the physiological process investigated heavy metal phytotoxicity can be either inhibitory or stimulatory. Photosynthesis and its partial light and dark reactions are inhibited; the activity of various enzymes, located in several cell compartiments, is increased. These enzymes are mostly induced since metals affect the transcription activity. They appear to be related to the plant defence against oxidative stress caused by metal phytotoxicity. Careful examination of the time course of this induction reveals differences in response between the metals applied

The effects of toxic concentrations of Cu, Zn and Cd on the fast induction kinetics of fluorescence from photosystem(PS)II were investigated in a comparative way. The fast fluorescence transient from primary leaves of metal-treated bean plants was studied. During several days after metal application, the time course of the changes induced by the different metals was monitored. The results evidenced not only a different time course of the changes in fluorescence related parameters for the three metals, but also different effects on the fluorescence induction kinetics, which could possibly be linked to different mechanisms of action of the metals

The effect of Cd on chlorophyll (Chl) as well as on light-harvesting complex II (LHCII) accumulation, has been examined during the early stages of development in etiolated Phaseolus vulgaris leaves exposed to intermittent light-dark cycles. We found that at the Cd concentrations studied, both Chl and LHCII accumulation were drastically reduced, although the LDS-solubilized total leaf protein level remained unaffected. However, on the basis of total chlorophyll present, the amount of stabilized LHCII was similar in both Cd-treated and nontreated samples. Additionally, the thylakoid-bound protease known to degrade LHCII, was found to be inhibited by Cd treatment both in vivo and in vitro. Finally, Northern hybridization analysis indicated that Cd affects LHCII accumulation by reducing drastically the steadystate level of Lhcb transcripts

Hydroponically cultured cucumber plants supplied with 4 μᴍ Fe chelated either with EDTA or citrate and treated with Cd (10 μᴍ) and Pb (10, 50 μᴍ) from their one- or fourleaf stage were grown up to five-week-old age. The decrease in the chlorophyll content was the most pronounced in plants treated with Cd from a younger age, and in the case of Fecitrate. The chlorophyll a/b ratio of Cd stressed plants was also significantly lowered. In later treated plants the accumulation of chlorophyll was inhibited and the chlorophyll a/b ratio decreased only in the vigorously growing young leaves. Pb treatment had only a slight effect on both parameters. The changes in the chlorophyll-protein pattern of thylakoids were strongly related to their chlorophyll content but the response of each complex was different. Cd reduced the amount of chlorophyll containing complexes in the order of photosystem I > light-harvesting complex II > photosystem Il-core, while light-harvesting complex II appeared somewhat more sensitive than photosystem I in Pb treated plants. In accordance, a decline or blue shift of the long wavelength fluorescence emission band of chloroplasts was observed referring to disturbances also in photosystem I antenna assembly. The accumulation of chlorophyll and chlorophyll-proteins did not show close relationship to the heavy metal content of leaves which was the highest in the first of the intensively expanding leaves in the time of the treatment. The extraordinary sensitivity of photosystem I, and the relative stability of photosystem II under Cd treatment were similar to the case found in iron deficient plants. However, the pattern of chlorophyll content of leaf storeys of Cd treated plants rather followed the changes in their Mn content

Growth parameters of maize seedlings were studied as well as cadmium content in plants in function of the EDTA dose applied to the nutrient medium. No increase in Cd accumulation was found in plants under the influence of EDTA, but this chelating agent was observed to suppress the effect of Cd toxicity on the plant growth

In our previous research, we showed that low Cd concentration increases the effectiveness of the processes leading to activation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). This stimulation was dependent on carbonic anhydrase (CA) activity and resulted in protecting Rubisco activity against Cd toxicity. The aim of the present paper was to test whether this mechanism has any influence on light activation of photosynthesis during the first 2 h of illumination. Both the “activation mechanism” of plant response to Cd-stress conditions and its full efficiency at low Cd concentration were confirmed. The CA-dependent light activation of Rubisco at low Cd level was correlated with accelerated attaining of the maximum Rubisco activity by these plants. The amount of Rubisco was also Cd- and timedependent and varied from continuous accumulation in control plants till reaching the maximum level within 30 minutes for the high Cd concentration. An increase in CA activity that was found to be parallel to the decrease of the amount of CA suggested activation of the enzyme by low Cd concentration

The response of plants to the peroxidizing herbicide oxyfluorfen was investigated. The action of this p-nitrodiphenyl ether is based on inhibition of plastidic protoporphyrinogen oxidase, which leads to accumulation of protoporphyrin IX in the cytosol yielding reactive oxygen species by light activation. The induction of activities of antioxidative enzymes was followed in Nicotiana tabacum plants, var. BelW3. Glutathione reductase activity was elevated by 75% compared to control, monodehydroascorbate reductase by 65% and glutathione 5-transferase by 110% . The mRNA of ascorbate peroxidase and catalase isoform 2 was induced, the catalase isoform 1 was reduced. These findings were confirmed and supported by measuring enzymatic activity changes in photoheterotrophically grown soybean (Glycine max) suspension cultures. To find a possible involvement of compounds regulating oxidative stress response, we investigated the influence of salicylic acid and BTH (benzo(1,2,3)thiadiazole- 7-carbothioic acid 5-methylester), both inducers of pathogen defense, on soybean cell suspension cultures. The specific activities of glutathione reductase, monodehydroascorbate reductase and glutathione 5-transferase increased strongly, comparable to oxyfluorfen treatment. Both compounds protected the cells against oxyfluorfen-induced lipid peroxidation and alleviated the accumulation of protoporphyrin IX

Illumination of acifluorfen-sprayed and 14 h-dark-incubated cucumber seedlings with coolwhite fluorescent light caused overaccumulation of protoporphyrin IX and severe oxidative stress which resulted in seedling death within 72 h. The ratio of variable fluorescence (F v )/ maximum fluorescence (F m ), a measure of the functional status of PSII, declined by 30% , 58% and 85% after 24 h, 48 h and 72 h respectively. When 24 h-light-treated plants were transferred to dark for 24 h the F v /F m ratio was restored to near control levels suggesting a dark recovery from photodynamic damage. The intracellular distribution of protoporphyrin IX that accumulated in the cotyledons of acifluorfen-treated and 1 h-light-exposed plants was 22% within and 78% outside chloroplasts suggesting migration of protoporphyrin IX within one hour of exposure of plants to light. When thylakoid membranes, treated with exogenous protoporphyrin IX, were illuminated there was a reduction in photosystem II activity. Addition of L-histidine, scavenger of singlet oxygen, to illuminated thylakoid+protoporphyrin IX mixture resulted in substantial protection of photosystem II activity suggesting the involvement of singlet oxygen in protoporphyrin IX-mediated photodynamic damage. In illuminated thylakoid+protoporphyrin IX mixture no indication was found for production of superoxide radicals via type I reaction. In cucumber seedlings acifluorfen-induced synthesis of protoporphyrin IX caused severe photodynamic damage mediated by singlet oxygen generated due to type II photosensitization reaction

Physiological examination of resistant and susceptible bean genotypes has shown that the concentration and quantitative ratios of carbohydrates measurable in leaf tissues depend on the age of leaves. During the phases of ontogenesis, the glucose and sucrose levels are the lowest in the primary leaves and highest in the youngest upper leaf. There is a continuous increase in the concentration of both carbohydrates from the oldest to the youngest leaves. The glucose/sucrose quantitative ratio decreases with ageing of the leaves until blooming. Our results indicate that the glucose concentration decreases considerably in the susceptible bean leaves after infection with the bean pathogen Pseudomonas savastanoi pv. phaseolicola. It has been proved that the glucose plays an important role in the formation of the bacterial extracellular polysaccharide (EPS) coat. Because there is a positive correlation between the age-dependent bacterial-resistance and the low sugar (especially glucose) content in older leaves of the originally susceptible bean plant, we think that in the old leaves there is not enough glucose for production of the EPS coat. Lacking EPS coat the bacterial and plant cell walls come in direct contact which permits the induction of hypersensitivity response characteristic of resistance

This article summarises present knowledge of the ecophysiological responses to elevated atmospheric CO 2 of desiccation tolerant (DT) plants. It deals primarily with lichens and bryophytes, as the most prominent groups of DT photosynthetic organisms, but includes some comment on algae and vascular DT plants. Results of research on DT plants are compared with those on desiccation sensitive vascular C 3 plants, the most widely investigated group in the field of global change. Both DT and non-DT plants show an immediate positive response of photosynthesis to elevated CO 2 , but in both groups the longer term effect is generally reduced (or even reversed) by down-regulation or feedback inhibition of photosynthesis, or other limitations on production and growth. In bryophytes and lichens, enhanced short-term photosynthesis may or may not be reflected in increased production; bryophytes have limited source-sink differentiation, and lichens invest excess photosynthate in secondary metabolites. DT plants may gain some advantage from elevated CO 2 at both low and excessive water contents. Neither theoretical considerations nor experimental results suggest that elevated atmospheric CO 2 will lead to any substantial shift in the balance of advantage between DT and non-DT plants

Despite of the downward acclimation of photosynthesis in C. convoluta, increased net photosynthesis and carbon balance can be anticipated in response to elevated atmospheric CO 2 level. CO 2 exchange measurement seems to be more indicative when detecting heavy metal stress than fluorescence parameters. Among these, the relative fluorescence decrease ratio (RFd690) shows damage first, suggesting that the primary attack site for heavy metal ions is CO 2 fixation and reaction centres are harmed last. Long-term elevated CO 2 ameliorates partly this damage by improving C-balance to a greater extent in the heavy-metal stressed lichens

This study has investigated the effects of elevated CO 2 and elevated O 3 , both singly and in combination, on the yield of spring wheat (Triticum aestivum L., cv. Minaret). Plants were grown in open-top chambers and exposed to three CO 2 concentrations (ambient, 510 and 680 ppmv) and two O 3 concentrations (ambient and ambient +50 or +90 ppbv) either from anthesis onwards or for the full growing season. To date, experiments that have investigated the interactive effects of these gases have shown a variety of responses, ranging from an amelioration of the damaging effects of high O 3 to a greater sensitivity to O 3 at elevated CO 2 . The effects on grain yield and yield com ponents were determined. Our results confirm that elevated CO 2 provides some protection to a wheat crop against the damaging effects of O 3 on grain yield. However, the level of protection varies from one growing season to the next and also appears to be related particularly to the timing of exposure to elevated O 3

Young sessile oak (Quercus petraea) trees were exposed for one vegetation period in closed environmental chambers in a crossed factorial study on effects to varied CO 2 concentrations, ozone concentrations and irrigation treatments. Elevated CO 2 concentrations (ambient + 350 (μmol mol -1 ) caused a significant increase in biomass production, alterations in leaf anatomy and chloroplast ultrastructure as well as an increase in leaf starch content, as compared to ambient CO 2 concentrations. The effects of elevated O 3 concentrations and drought stress were far less distinct. The leaf starch content was influenced by CO 2 and O 3 in a synergistic manner

Tropospheric ozone has been recognised as a limiting factor for plant growth since late fifties of our century. The decrease in the rate of light saturated net photosynthesis (A sat ) was shown to be the major effect of ozone in leaves with negative consequences for plant growth and the development of plant communities. The reasons for the ozone-induced decrease in A sat are still under investigation. Possible mechanisms are an increasing stomatal limitation, an increase in mesophyll limitation including a reduction of the CO 2 fixation in the Calvin cycle and an impairment of the photochemical reactions in the grana membranes of chloroplasts. We conclude from the reviewed literature and from our own experiments that a decrease in carboxylation efficiency (CE) seems to be an early event caused by ozone leading to a decrease in A sat . The loss in current photochemical capacity (F v /F m ) appears with a lag phase of many days and therefore the loss is thought to be a secondary effect due to a decreased demand of ‘assimilatory power’

Grafting is an easy way to produce a new seedling, which can tolerate against various stresses. During the acclimation after grafting, however, the seedlings still suffer a severe water stress. It is well known that water stress produces active oxygen to oxidize ascorbic acid. The concentration of ascorbic acid in the leaves was analyzed by HPLC equipped with an electrochemical detector. The column used was SP-120-5-ODS-BP (DAISO, JAPAN) and elution was performed with 0.1 ᴍ phosphate buffer, pH 3.0. After grafting the seedlings were acclimated under a 6-hr light/dark regimen. The content of ascorbic acid increased gradually during 2 days compared with control. The ascorbate peroxidase showed about constant activity, so the increase of ascorbic acid may be due to its requirement to cure the grafting

Effects of different concentrations of glucose, sucrose and the natural growth regulator, triacontanol were studied under the unfavourable stress conditions of micropropagation of two woody plants, Sorbus rotundifolia L. and Primus x davidiopersica ‘Piroska’. After 4 - 6 weeks of cultures, the number and length of shoots, the photosynthetic activity as well as the chlorophyll, carotenoid and anthocyanin contents were investigated. As shown by the growth parameters, the optimal carbohydrate concentration was between 1.5-2.5% , whereas in higher concentrations, a definite inhibition could be observed. A similar response was found in changes of the anthocyanin content in Prunus x davidiopersica ‘Piroska’, but this effect was less pronounced with the photosynthetic pigments in both species. The Fv/Fm ratio representing the quantum yield of photosynthesis was low due to the inhibitory effect of stress and altered significantly by changing the carbohydrate concentrations. In all cases, the addition of 2 - 4 μg triacontanol/1 further enhanced the stimulating effect of the optimal carbohydrate concentrations, which indicated the specific importance of the appropriate hormone balance under such stress conditions

Optimization of nitrogen supply in a tomato plant is stepwise assessed, from chloroplast characteristics to whole crop performance. Experiments are reported in which important key processes are quantified in relation to the nitrogen content of leaves. Interactions of N effects with leaf aging and canopy light distribution are analyzed. A simulation model that integrates this knowledge is constructed. The results of three nitrogen partitioning scenarios for Rubisco suggest that optimization of the distribution of Rubisco between leaf layers is less important for plant productivity than within-leaf optimization of the photosynthetic apparatus

Reflectance spectra allow the early detection of stressors causing differences in pigment content as well as changes of leaf tissue structure and photosynthetic activity. The reflectance decreased with increasing Chl content in greening bean leaves. In stressed leaves, in turn, the reflectance increased with decreasing Chl content. This also caused a shift of the red reflection rise (“red edge”) to shorter wavelengths (“blue shift”) associated with a blue shift of the inflection point of the red edge. The contribution of the red and far-red Chl fluorescence to the reflectance signal at the red edge of the spectrum and the shift of the wavelength position of the inflection point are demonstrated and discussed