Inhibition of zeaxanthin formation and of rapid changes in radiationless energy dissipation by dithiothreitol in spinach leaves and chloroplasts

Dithiothreitol, which completely inhibits the de-epoxidation of violaxanthin to zeaxanthin, was used to obtain evidence for a causal relationship between zeaxanthin and the dissipation of excess excitation energy in the photochemical apparatus in Spinicia oleracea L. In both leaves and chloroplasts, inhibition of zeaxanthin formation by dithiothreitol was accompanied by inhibition of a component of nonphotochemical fluorescence quenching. This component was characterized by a quenching of instantaneous fluorescence (F_o) and a linear relationship between the calculated rate constant for radiationless energy dissipation in the antenna chlorophyll and the zeaxanthin content. In leaves, this zeaxanthin-associated quenching, which relaxed within a few minutes upon darkening, was the major component of nonphotochemical fluorescence quenching determined in the light, i.e. it represented the `high-energy-state' quenching. In isolated chloroplasts, the zeaxanthin-associated quenching was a smaller component of total nonphotochemical quenching and there was a second, rapidly reversible high-energy-state component of fluorescence quenching which occurred in the absence of zeaxanthin and was not accompanied by F_o quenching. Leaves, but not chloroplasts, were capable of maintaining the electron acceptor, Q, of photosystem II in a low reduction state up to high degrees of excessive light and thus high degrees of nonphotochemical fluorescence quenching. When ascorbate, which serves as the reductant for violaxanthin de-epoxidation, was added to chloroplast suspensions, zeaxanthin formation at low photon flux densities was stimulated and the relationship between nonphotochemical fluorescence quenching and the reduction state in chloroplasts then became more similar to that found in leaves. We conclude that the inhibition of zeaxanthin-associated fluorescence quenching by dithiothreitol provides further evidence that there exists a close relationship between zeaxanthin and potentially photoprotective dissipation of excess excitation energy in the antenna chlorophyll.     

The Xanthophyll Cycle Modulates the Kinetics of Nonphotochemical Energy Dissipation in Isolated Light-Harvesting Complexes, Intact Chloroplasts, and Leaves of Spinach

We analyzed the kinetics of nonphotochemical quenching of chlorophyll fluorescence (qN) in spinach (Spinacia oleracea) leaves, chloroplasts, and purified light-harvesting complexes. The characteristic biphasic pattern of fluorescence quenching in dark-adapted leaves, which was removed by preillumination, was evidence of light activation of qN, a process correlated with the de-epoxidation state of the xanthophyll cycle carotenoids. Chloroplasts isolated from dark-adapted and light-activated leaves confirmed the nature of light activation: faster and greater quenching at a subsaturating transthylakoid pH gradient. The light-harvesting chlorophyll a/b-binding complexes of photosystem II were isolated from dark-adapted and light-activated leaves. When isolated from light-activated leaves, these complexes showed an increase in the rate of quenching in vitro compared with samples prepared from dark-adapted leaves. In all cases, the quenching kinetics were fitted to a single component hyperbolic function. For leaves, chloroplasts, and light-harvesting complexes, the presence of zeaxanthin was associated with an increased rate constant for the induction of quenching. We discuss the significance of these observations in terms of the mechanism and control of qN.     

Zeaxanthin Synthesis, Energy Dissipation, and Photoprotection of Photosystem II at Chilling Temperatures

When leaves of a mangrove, Rhizophora mangle, were exposed to an excess of light at chilling temperatures, synthesis of zeaxanthin through violaxanthin de-epoxidation as well as nonphotochemical fluorescence quenching were markedly reduced. The results suggest a protective role of energy dissipation against the adverse effects of high light and chilling temperatures: leaves of R. mangle that had been preilluminated in 2% O₂, 0% CO₂ at low photon flux density and showed a high level of zeaxanthin, and leaves that had been kept in the dark and contained no zeaxanthin, were both exposed to high light and chilling temperatures (5°C leaf temperature) in air and then held under control conditions in low light in air at 25°C. Measurements of chlorophyll a fluorescence at room temperature showed that the photochemical efficiency of PSII and the yield of maximum fluorescence of the preilluminated leaf recovered completely within 1 to 3 hours under the control conditions. In contrast, the fluorescence responses of the predarkened leaf in high light at 5°C did not recover at all. During a dark/light transient in 2% O₂, 0% CO₂ in low light at 5°C, nonphotochemical fluorescence quenching increased linearly with an increase in the zeaxanthin content in leaves of R. mangle. In soybean (Glycine max) leaves, which contained a background level of zeaxanthin in the dark, a similar treatment with excess light induced a level of nonphotochemical fluorescence quenching that was not paralleled by an increase in the zeaxanthin content.     

Light Response of CO(2) Assimilation, Dissipation of Excess Excitation Energy, and Zeaxanthin Content of Sun and Shade Leaves

Intact attached sun leaves of Helianthus annuus and shade leaves of Monstera deliciosa and Hedera helix were used to obtain light response curves of CO₂ uptake, the content of the carotenoid zeaxanthin (formed by violaxanthin de-epoxidation), as well as nonphotochemical quenching (q_NP), and the rate constant of radiationless energy dissipation (k_D). The latter two parameters were calculated from the decrease of chlorophyll a fluorescence at closed photosystem II traps in saturating pulses in the light. Among the three species, the light-saturated capacity of CO₂ uptake differed widely and light saturation of CO₂ uptake occurred at very different photon flux densities. Fluorescence quenching and zeaxanthin content exhibited features which were common to all three species: below light-saturation of CO₂ uptake nonphotochemical quenching occurred in the absence of zeaxanthin and was not accompanied by a decrease in the yield of instantaneous fluorescence. Nonphotochemical quenching, q_NP, increased up to values which ranged between 0.35 and 0.5 when based on a control value of the yield of variable fluorescence determined after 12 hours of darkness. As light saturation of CO₂ uptake was approached, q_NP showed a secondary increase and the zeaxanthin content of the leaves began to rise. This was also the point from which the yield of instantaneous fluorescence began to decrease. The increase in zeaxanthin was paralleled by an increase in the rate constant for radiationless energy dissipation k_D, which opens the possibility that zeaxanthin is related to the rapidly relaxing “high-energy-state quenching” in leaves.     

Physiological and biochemical responses of resistant and susceptible wheat to injury by Russian wheat aphid

We examined the physiological and biochemical responses of resistant ('Halt' and 'Prairie Red') and susceptible ('TAM 107') wheat, Triticum aestivum L., to injury by the Russian wheat aphid, Diuraphis noxia (Mordvilko). Photosynthetic capacity was evaluated by measuring assimilation/internal CO2 (A/Ci) curves, chlorophyll fluorescence, chlorophyll, and nonstructural carbohydrate content. Total protein and peroxidase specific activity also were determined. No significant differences were detected in chlorophyll concentration between aphid-infested and control TAM 107 plants. The aphid-infested resistant cultivars had similar or significantly higher chlorophyll concentrations compared with their respective control plants. Measurements over time showed that infested Halt plants had delays in photosynthetic senescence, Prairie Red plants had photosynthetic rate changes that were similar to control plants, and TAM 107 plants displayed accelerated photosynthetic senescence patterns. The photochemical and nonphotochemical quenching coefficients were significantly higher in infested Halt plants compared with their respective control plants on day 3. Infested TAM 107 plants had significantly higher photochemical quenching compared with control plants at all times evaluated, and they had significantly higher nonphotochemical quenching on day 3. Throughout the experiment, infested Prairie Red plants exhibited photochemical and nonphotochemical quenching coefficient values that were not significantly different from control plants. Total protein content was not significantly different between aphid-infested and control plants for all cultivars. Differences between physiological responses of infested susceptible and resistant cultivars, particularly temporal changes in photosynthetic activity, imply that resistant Halt and Prairie Red wheat tolerate some impacts of aphid injury on photosynthetic integrity.     

Dynamic changes in photosynthesis and chlorophyll fluorescence in Nicotiana tabacum infested by Bemisia tabaci (Middle East–Asia Minor 1) nymphs

Bemisia tabaci Middle East–Asia Minor 1 (MEAM1) is a worldwide pest. To determine whether MEAM1 nymphs produce the same symptoms in different host plants, we measured the plant growth and chlorophyll content of tobacco and cotton plants that were infested by MEAM1 nymphs. Furthermore, to investigate the spatial and temporal changes in photosynthesis caused by MEAM1 nymphs, the net photosynthetic rate (Pn) and chlorophyll a fluorescence of local and systemic tobacco leaves were assayed at 8, 11, 14, and 20 days after MEAM1 adult removal, which represent the stages of 1st, 2nd, 3rd, and 4th instar nymphs, respectively. The results showed that MEAM1 nymph infestation reduced the plant height and internode length of tobacco at 14 and 20 days, as well as the dry weight of infested and systemic tobacco leaves. However, MEAM1 nymph infestation did not affect the plant height or internode length of cotton. Also, the dry weight and chlorophyll and carotenoid content of infested and systemic leaves of cotton plants were not influenced by MEAM1 nymph infestation. However, the contents of chlorophyll a and b and carotenoids in infested tobacco leaves decreased over time; the chlorophyll a content of systemic tobacco leaves decreased at 11, 14, and 20 days. The chlorophyll and carotenoid contents in infested and systemic leaves of cotton plants were not influenced by MEAM1 nymph infestation. In addition, the Pn of infested tobacco leaves decreased at 14 and 20 days, while the Pn in systemic tobacco leaves decreased after 11 days. The greatest decrease in performance index on absorption basis (PI _ABS ) of infested and systemic tobacco leaves occurred on day 14. The fluorescence intensity at 2 ms (J peak) and 300 μs (K peak) increased on day 14, which indicates that 3rd instar nymphs caused serious damage to the primary photochemical reactions and donor side of PSII. These results suggest that MEAM1 nymph infestation had different effects on tobacco and cotton plants. The infestation caused spatial and temporal changes in photosynthesis in tobacco plants. The lower chlorophyll a content may have been related to the lower net photosynthetic rate of systemic and infested tobacco leaves. The decreased stability of the oxygen-evolving complex and the reaction center of PSII and the decrease in electron transport were the main reasons for the decrease in the level of photosynthesis in tobacco leaves caused by MEAM1 nymphs during various stages of infestation.     

Physiological response of Nannochloropsis sp. to saline stress in laboratory batch cultures

In the present paper, we investigated the physiological response of the marine microalga Nannochloropsis sp. to salt stress (13, 27, 54, and 81 g L^?1 NaCl). Increasing the sodium chloride concentration caused up to a 70 % decrease in the chlorophyll a concentration, cell growth, and net photosynthesis rate. The chlorophyll a fluorescence measurements indicated a strong reduction in the effective quantum yield of photosystem II (?60 %) and an increase in nonphotochemical quenching when the cells were exposed to NaCl concentrations greater than 27 g L^?1 (control). In contrast, the specific lipid content increased up to 80 % when the sodium chloride concentration was increased from 27 to 54–81 g L^?1. These results are relevant for the outdoor cultivation of this microalga using open photobioreactors, in which microalgae are subjected to strong changes in salinity concentration caused by water evaporation.     

Topography of photosynthetic activity of leaves obtained from video images of chlorophyll fluorescence

The distribution of photosynthetic activity over the area of a leaf and its change with time was determined (at low partial pressure of O₂) by recording images of chlorophyll fluorescence during saturating light flashes. Simultaneously, the gas exchange was being measured. Reductions of local fluorescence intensity quantitatively displayed the extent of nonphotochemical quenching; quench coefficients, q_N, were computed pixel by pixel. Because rates of photosynthetic electron transport are positively correlated with (1 − q_N), computed images of (1 − q_N) represented topographies of photosynthetic activity. Following application of abscisic acid to the heterobaric leaves of Xanthium strumarium L., clearly delineated regions varying in nonphotochemical quenching appeared that coincided with areoles formed by minor veins and indicated stomatal closure in groups.     

Zeaxanthin and the Induction and Relaxation Kinetics of the Dissipation of Excess Excitation Energy in Leaves in 2% O(2), 0% CO(2)

The relationship between the carotenoid zeaxanthin, formed by violaxanthin de-epoxidation, and nonphotochemical fluorescence quenching (q_NP) in the light was investigated in leaves of Glycine max during a transient from dark to light in 2% O₂, 0% CO₂ at 100 to 200 micromoles of photons per square meter per second. (a) Up to a q_NP (which can vary between 0 and 1) of about 0.7, the zeaxanthin content of leaves was linearly correlated with q_NP as well as with the rate constant for radiationless energy dissipation in the antenna chlorophyll (k_D). Beyond this point, at very high degrees of fluorescence quenching, only k_D was directly proportional to the zeaxanthin content. (b) The relationship between zeaxanthin and k_D was quantitatively similar for the rapidly relaxing quenching induced in 2% O₂, 0% CO₂ at 200 micromoles of photons per square meter per second and for the sustained quenching induced by long-term exposure of Nerium oleander to drought in high light (B Demmig, K Winter, A Krüger, F-C Czygan [1988] Plant Physiol 87: 17-24). These findings suggest that the same dissipation process may be induced by very different treatments and that this particular dissipation process can have widely different relaxation kinetics. (c) A rapid induction of strong nonphotochemical fluorescence quenching within about 1 minute was observed exclusively in leaves which already contained a background level of zeaxanthin.     

An analysis of the chlorophyll-fluorescence transients from pea leaves generated by changes in atmospheric concentrations of CO2 and O2

Removal of CO₂ from pea leaves, which were either grown in a glasshouse at 15°C or in a controlled environment at 23°C, produced an initial increase in chlorophyll fluorescence emission followed by a slow decrease to steady state. From estimations of the redox state of Q, using a nondestructive in vivo technique, the contributions of photochemical and nonphotochemical quenching processes to these fluorescence transients were determined. The fluorescence changes observed on removal of CO₂ from the two types of pea leaves were mainly attributable to changes in nonphotochemical quenching although markedly different changes in photochemical quenching were also observed. When leaves grown at 23°C were depleted of CO₂, Q immediately became more reduced, whereas in leaves grown at 15°C Q, unexpectedly, became more oxidised. On return of CO₂ to the leaves these phenomena were reversed, i.e., in leaves grown at 23°C Q became more oxidised and in the 15°C grown leaves Q became more reduced. Increased electron transport to O₂ may account for the oxidation of Q on depletion of CO₂ from 15°C grown leaves. The generation of fluorescence transients on removal and return of CO₂ to the leaf required the presence of oxygen. The fast fluorescence kinetics observed on exposure of the leaf at steady state to a second saturating irradiation suggest that O₂ may accept electrons directly from Photosystem II at a site between Q and B.     

Variations in light energy dissipation in <Emphasis Type="Italic">Woodfordia fruticosa</Emphasis> leaves during expansion

Young leaves of tropical trees frequently appear red in color, with the redness disappearing as the leaves mature. During leaf expansion, plants may employ photoprotective mechanisms to cope with high light intensities; however, the variations in anthocyanin contents, nonphotochemical quenching (NPQ), and photorespiration during leaf expansion are poorly understood. Here, we investigated pigment contents, gas exchange, and chlorophyll (Chl) fluorescence in Woodfordia fruticosa leaves during their expansion. Young red leaves had significantly lower Chl content than that of expanding or mature leaves, but they accumulated significantly higher anthocyanins and dissipated more excited light energy through NPQ. As the leaves matured, net photosynthetic rate, total electron flow through PSII, and electron flow for ribulose-1,5-bisphosphate oxygenation gradually increased. Our results provided evidence that photorespiration is of fundamental importance in regulating the photosynthetic electron flow and CO₂ assimilation during leaf expansion.     

Leaf chloroplast ultrastructure and photosynthetic properties of a chlorophyll-deficient mutant of rice

Leaf chloroplast ultrastructure and photosynthetic properties of a natural, yellow-green leaf mutant (ygl1) of rice were characterized. Our results showed that chloroplast development was significantly delayed in the mutant leaves compared with the wild-type rice (WT). As leaves matured, more grana stacks formed concurrently with increasing leaf chlorophyll (Chl) content. Except for the lower intercellular CO₂ concentration, the ygl1 plants had a higher leaf net photosynthetic rate, stomatal conductance, and transpiration rate than those of the WT plants. Under equal amounts of Chl, the excitation energy of PSI and PSII was much stronger in the mutant than that in the WT. The ygl1 plants showed higher nonphotochemical quenching and lower photochemical quenching. They also exhibited higher actual photochemical efficiency of PSII with a higher electron transport rate. Under the light of 200 μmol(photon) m^?2 s^?1, the ygl1 mutant showed lesser deepoxidation of violaxanthin in the xanthophyll cycle than WT, but it increased substantially under strong light conditions. In conclusion, the photosynthetic machinery of the ygl1 remained stable during leaf development. The plants were less sensitive to photoinhibition compared with WT due to the active xanthophyll cycle. The ygl1 plants were efficient in both light harvesting and conversion of solar energy.     

Changes in the photosynthetic characteristics of cotton leaves infested by invasive mealybugs tended by native ant species

Herbivore injury has a direct effect on the growth and performance of host plants through photosynthetic suppression. However, changes in plant photosynthesis affected by ant tending of hemipteran sap feeders remain poorly understood. We investigated the effects of an invasive mealybug (Phenacoccus solenopsis) tended by native ants (Paratrechina longicornis) on the chlorophyll content and chlorophyll fluorescence characteristics of cotton (Gossypium hirsutum) leaves under greenhouse conditions. The results showed that the relative chlorophyll content of the infested cotton leaves significantly decreased after 10 days, and the chlorophyll contents were reduced by 26.4 and 34.9 % after 20 days in the without and with ant treatments compared to the control, respectively. In addition, the light utilization efficiency and maximum relative electron transport rate were reduced by 53.0 and 51.3 % compared to the control, respectively. However, no significant differences in these factors were found between the without and with ant treatments. The light saturation coefficient, describing the capacity of a sample to resist glare, exhibited no significant difference among treatments. The number of tending P. longicornis ants increased with P. solenopsis numbers, and the P. solenopsis numbers decreased after 20 days compared to the without ant treatment. We suggest that the tending ants may enhance the feeding ability of individual mealybugs in spite of the decreased number of mealybugs in this situation. Additionally, P. longicornis decrease the relative chlorophyll content of infested cotton leaves and may accelerate the damage caused by P. solenopsis to plants over time.     

Seasonal Changes in Primary Photosynthetic Events during Low Temperature Adaptation of <Emphasis Type="Italic">Pinus sylvestris</Emphasis> in Central Yakutia

The methods of chlorophyll fluorescence induction and HPLC were used to study the influence of autumnal temperature decrease on photochemical electron-transport activity of photosystem II (PSII), nonphotochemical quenching of excessive excitation energy, and the composition of pigments in the firstyear needles of Pinus sуlvestris L. trees grown naturally in Central Yakutia. In the period from the beginning of September to October 10, the chlorophyll content was reduced by half, while the Chl a/b ratio increased from 2.9 to 4.3–4.5, indicating the degradation of peripheral antenna complexes. The decrease in average daily temperature to 4.9–6.4°C led to a transient increase in the quantum yield of nonphotochemical quenching (ΔpH-dependent parameter φNPQ). These changes were accompanied by a slow accumulation of unregulated zeaxanthin fraction insensitive to illumination conditions. The further decrease in average daily temperature to near-zero levels was paralleled by a sharp increase in zeaxanthin content, while the pH-dependent quenching was replaced with the constitutive quenching (parameter φ_f,D) because of the supposed structural reorganization of PSII. These processes were accompanied by a fast decrease in PSII functional activity, which was mostly due to the impairment of plastoquinone photochemical reduction. Freezing temperatures (from–3.6 to–12.1) destructed the oxygen-evolving complex in PSII and completely inactivated the PSII reaction centers. It is concluded that the largest changes in the condition of photosynthetic apparatus occur at a near-zero temperature range and proceed until complete inactivation of PSII under the action of freezing temperatures.     

Photosynthetic characteristics and antioxidant enzyme system in high-chlorophyll rice Gc mutant

The physiological photosynthetic characteristics and antioxidant enzyme system of the high-chlorophyll rice (Oryza sativa L.) mutant (Gc) and its wild type (Zhenshan 97B) were compared and analyzed. Resulting data showed that the total chlorophyll (Chl) and Chl b contents in the Gc mutant were significantly increased by 19.0 and 81.7%, respectively, while the increase in Chl a and thylakoid membrane protein contents was insignificant. The net photosynthetic rate (P _N) was significantly higher in the mutant; stomatal conductance, intercellular CO₂ concentration, and transpiration rate decreased significantly, and water-use efficiency increased significantly, indicating the higher photochemical efficiency of the mutant. The chlorophyll fluorescence parameters: electron transport rate and effective quantum yield of PSII photochemistry of the mutant were significantly higher than those of Zhenshan 97B. The nonphotochemical quenching of the mutant under light adaptation increased by 52.3%. The enzymatic activity of superoxide dismutase, peroxidas, and catalase in the mutant roots and leaves were all higher than those for the wild-type plants. It is believed that the higher activity of antioxidant enzymes in the mutant may be an important factor making difficult the photo-inactivation of Chl, and thus, increasing the content of Chl, especially Chl b.     

Photochemical heat-shock response in common bean leaves as affected by previous water deficit

The heat sensitivity of photochemical processes was evaluated in the common bean (Phaseolus vulgaris) cultivars A222, A320, and Carioca grown under well-watered conditions during the entire plant cycle (control treatment) or subjected to a temporal moderate water deficit at the preflowering stage (PWD). The responses of chlorophyll fluorescence to temperature were evaluated in leaf discs excised from control and PWD plants seven days after the complete recovery of plant shoot hydration. Heat treatment was done in the dark (5 min) at the ambient CO₂ concentration. Chlorophyll fluorescence was assessed under both dark and light conditions at 25, 35, and 45°C. In the dark, a decline of the potential quantum efficiency of photosystem II (PSII) and an increase in minimum chlorophyll fluorescence were observed in all genotypes at 45°C, but these responses were affected by PWD. In the light, the apparent electron transport rate and the effective quantum efficiency of PSII were reduced by heat stress (45°C), but no change due to PWD was demonstrated. Interestingly, only the A222 cultivar subjected to PWD showed a significant increase in nonphotochemical fluorescence quenching at 45°C. The common bean cultivars had different photochemical sensitivities to heat stress altered by a previous water deficit period. Increased thermal tolerance due to PWD was genotype-dependent and associated with an increase in potential quantum efficiency of PSII at high temperature. Under such conditions, the genotype responsive to PWD treatment enhanced its protective capacity against excessive light energy via increased nonphotochemical quenching.     

The relationship between photosynthesis and a mastoparan-induced hypersensitive response in isolated mesophyll cells

The G-protein activator mastoparan (MP) was found to elicit the hypersensitive response (HR) in isolated Asparagus sprengeri mesophyll cells at micromolar concentrations. The HR was characterized by cell death, extracellular alkalinization, and an oxidative burst, indicated by the reduction of molecular O₂ to O₂⁻. To our knowledge, this study was the first to monitor photosynthesis during the HR. MP had rapid and dramatic effects on photosynthetic electron transport and excitation energy transfer as determined by variable chlorophyll a fluorescence measurements. A large increase in nonphotochemical quenching of chlorophyll a fluorescence accompanied the initial stages of the oxidative burst. The minimal level of fluorescence was also quenched, which suggests the origin of this nonphotochemical quenching to be a decrease in the antenna size of photosystem II. In contrast, photochemical quenching of fluorescence decreased dramatically during the latter stages of the oxidative burst, indicating a somewhat slower inhibition of photosystem II electron transport. The net consumption of O₂ and the initial rate of O₂ uptake, elicited by MP, were higher in the light than in the dark. These data indicate that light enhances the oxidative burst and suggest a complex relationship between photosynthesis and the HR.     

Chlorophyll fluorescence quenching and violaxanthin deepoxidation of FBPase antisense plants at low light intensities and low temperatures

Genetically modified potato (Solanum tuberosum L. cv. Desiree) and tobacco (Nicotiana tabacum cv. Samsun N.N.) plants were used to analyze the effects exerted by the chloroplastic (cp) fructose- 1,6-bisphosphatase (FBPase) on the regulation of light energy discrimination at the level of photosystem II. The cp-FBPase activity was progressively inhibited by an mRNA antisense to this FBPase. The chlorophyll fluorescence quenching parameters of these transgenic plants were compared to those of wild-type and transgenic plants that were acclimated to low temperatures. In particular various lines of the transgenic potato and tobacco plants were exposed to a temperature treatment of 10 and 20°C for 10 days. Light intensities were kept low to reduce photoinhibition so that we could analyze exclusively the effects of a modification in the carbon fixation cycle on the chlorophyll fluorescence quenching parameters. The photon flux densities (PFDs) employed at the level of the middle leaves of all plants were set to two different values of 10 μmol m^?2 s^?1 and 50 μmol m^?2 s^?1. Subsequent to this 10-day acclimation the chlorophyll-fluorescence parameters of all plants were measured. Photoinhibition as expressed by the F_y/F_m ratio was minor in plants subjected to a PFD of 10 μmol m^?2 s^?1. Higher photon fluence rates of 50 μmol m^?2 s^?1 at temperatures of 10°C gave rise to a significant reduction in the F_y/F_m ratios obtained from the transgenic plants which were characterized by a restriction in cp-FBPase capacity to 20% of normal activity. Furthermore, a progressive inhibition of the cp-FBPase activity induced an amplified nonphotochemical quenching of chlorophyll fluorescence with in the genetically manipulated species (except at 10°C and 50 μmol m^?2 s^?1). The increase in nonphotochemical quenching depended upon light and temperature. Photochemical quenching of light quanta within the antisense plants declined relative to that in the wild type. To further characterize the mechanisms producing higher levels of nonphotochemical fluorescence quenching. we analyzed several of the xanthophyll cycle pigments. The deepoxidation state of the xanthophyll cycle pigments in potato plants increased with attenuating FBPase activities under all conditions. For tobacco plants, this elevation of the deepoxidation state was only observed at a PFD of 50 μmol m^?2 s^?1.     

Qualitative and Quantitative Evaluation of Gall Induced by <Emphasis Type="Italic">Pseudophacopteron alstonium</Emphasis> Yang et Li 1983 (Hemiptera: Psyllidae: Phacopteronidae) as Plant Parasite,in <Emphasis Type="Italic">Alstonia scholaris</Emphasis> Leaves

Alstonia scholaris (Dr C. Alston, 1685–1760) (Family Apocynaceae) (Chattim tree), commonly known as devil tree, is an evergreen tropical tree. The tree is native to India and also found in Sri Lanka, Southern China, throughout Malaysia to northern Australia. This plant is seriously damaged by formation of tumor like galls across the Kolkata city,West Bengal which affects its ornamental and medicinal value. Gall is formed by ovipositing adults of Pseudophacopteron alstonium Yang et Li 1983 (Hemiptera: Psyllidae: Phacopteronidae) and results in destruction of host plant. The nymphal stage undergoes moulting through first instar to third instar to reach the adult within galls. It is observed that highly infested leaves can bear 60–80 galls. The gallmaker Pseudophacopteron sp. stresses the host organ, and the host counters it with physiological activities supplemented by newly differentiated tissues. In infested leaves, chlorophyll and carbohydrate contents decreased sequentially with the age of the gall. There were no significant changes in protein and total amino acid content in gall tissue. But total lipid content was highest in mature galled leaves. Increased phenolic content after psylloid herbivory, which exerted oxidative stress on the host plants, was observed in gall infested leaves as compared to fresh ungalled leaves of Alstonia scholaris. Moisture content was highest in ungalled healthy leaves than the young galled, mature galled and perforated galled leaves.     

Chlorophyll Fluorescence Quenching During Photosynthetic Induction in Leaves of Abutilon striatum Dicks. Infected with Abutilon Mosaic Virus,Observed with a Field-Portable Imaging System

A portable Chi fluorescence imaging system was used to characterise nonuniform Chi fluorescence quenching in Abutilon striatum leaves infected with phloem-localised abutilon mosaic virus. The instrument was used to observe fluorescence emission at intervals during induction transients, and to map nonphotochemical quenching during saturating pulses applied in the course of these transients. Two symptom types were distinguished: yellow vein-associated motifs that showed lower maximum Chi fluorescence than nearby green tissues, but virtually zero nonphotochemical quenching, and vein-defined mosaics (pale green) that initially showed normal maximum Chi fluorescence but strongly impaired nonphotochemical quenching. Mature vein-defined mosaics (yellow to white areas) resembled vein-associated symptoms with zero nonphotochemical quenching. Islands of apparently healthy green tissue enclosed by mosaic symptoms showed slower nonphotochemical quenching than controls. Possible effects of localised carbohydrate accumulation, thought to follow from infection by the phloem-limited virus, on photosynthetic processes as well as the synthesis and stability of chloroplast protein complexes, are discussed in the context of symptom development.