Photochemical Activity Of Photosystem Research Articles

Effect of Low Light on Photosynthetic Performance of Tomato Plants-Ailsa Craig and Carotenoid Mutant Tangerine.

The effects of a five-day treatment with low light intensity on tomato plants-Ailsa Craig and tangerine mutant-at normal and low temperatures and after recovery for three days under control conditions were investigated. The tangerine tomato, which has orange fruits, yellowish young leaves, and pale blossoms, accumulates prolycopene rather than all-trans lycopene. We investigated the impact of low light at normal and low temperatures on the functioning and effectiveness of photosynthetic apparatuses of both plants. The photochemical activities of Photosystem I (PSI) and Photosystem II (PSII) were assessed, and the alterations in PSII antenna size were characterized by evaluating the abundance of PSII-associated proteins Lhcb1, Lhcb2, CP43, and CP47. Alterations in energy distribution and interaction of both photosystems were analyzed using 77K fluorescence. In Aisla Craig plants, an increase in thylakoid membrane fluidity was detected during treatment with low light at a low temperature, while for the tangerine mutant, no significant change was observed. The PSII activity of thylakoids from mutant tangerine was more strongly inhibited by treatment with low light at a low temperature while low light barely affected PSII in Aisla Craig. The obtained data indicated that the observed differences in the responses of photosynthetic apparatuses of Ailsa Craig and tangerine when exposed to low light intensity and suboptimal temperature were mainly related to the differences in sensitivity and antenna complexes of PSII.

Impact of Light with Different Spectra on the Photosynthetic Activity of Cucumber Plants under Fusarium Wilt

The photosynthetic activity of 28-day-old cucumber plants of the Kustovy variety formed under LED illumination with the predominance of red light (RL) or far red light (FRL) and infected with the fungus Fusarium oxisporum sp. (F.ox.) was studied. The predominance of RL or FRL contributed to an increase in the content of chlorophyll and carotenoids per dry leaf weight compared to the plants grown under white light (WL). In the infected plants grown under WL and RL regimes, an increase in the total content of chlorophyll and carotenoids was observed relative to healthy plants, and a decrease in the same parameters for FRL was noted. In healthy cucumber leaves grown under RL and FRL regimes, an increase in the activity of photosystem (PS)1 and PS2 in comparison with WL was observed. Infection of cucumber plants grown under WL did not cause any changes in the functional parameters of PS2 against the background of a slight reduction in PS1 complexes. Under RL and FRL regimes, a decrease in the photochemical activity of PS 1 and PS 2 in infected leaves was noted. The activity of ascorbate peroxidase - one of antioxidant enzymes in chloroplasts decreased in healthy cucumber leaves under RL and FRL compared to WL and increased in infected leaves compared to the healthy ones under all light regimes, especially strongly under RL. The results obtained demonstrate different response mechanisms for cucumber chloroplasts to the infection with a fungal pathogen, depending on the light conditions of growing.

Comparison of Protective Reactions of Rape Seeds to Chloride Salination at Exposure to Epibrassinolide before or during Salt Stress.

We compared the defensive response of rape plants to treatment with 24-epibrassinoldide (10 nM, EBL) before the onset of salt stress (preadaptation stage) and under conditions of chloride salination (150mM NaCl). It is shown that salt stress inhibits some growth parameters by 30-35%. EBL, regardless of the plant treatment method, showed a pronounced protective effect, first of all, at the level of the assimilating surface, the main photosynthetic pigments, and the photochemical activity of photosystem II. It was established for the first time that the pretreatment of plants with EBL followed by salt stress is accompanied by suppression of NaCl-induced accumulation of proline and an increase in superoxide dismutase activity, whereas the addition of a hormone under salt stress increases the content of carotenoids, which leads to a decrease in the level of lipid peroxidation.

Role of Ascorbate and Ascorbate–Glutathione Cycle for Photosynthetic Protection in Selected Indigenous Rice Landraces Under Drought Stress

From precise drought tolerance screening of local rice landraces of Koraput, six rice landraces were identified as superior drought tolerant capacity in our earlier study. However, little information is available on their physiological response of redox regulation and photochemical activity under drought stress. The present work evaluates their redox regulations driven by ascorbate–glutathione cycle and photochemical activity of photosystem II under simulated drought stress by polyethylene glycol 6000. Leaf chlorophyll content, electron transport rate and effective quantum yield of PSII were significantly higher in studied indigenous rice genotypes in comparison with susceptible check variety under drought condition. Further, greater quantities of ascorbate and elevated levels of ascorbate–glutathione cycle enzyme activities were observed under drought treatment in studied indigenous rice genotypes in compared with susceptible IR64. The findings suggested that maintenance of better photochemical activity in studied rice genotypes under water-deficit condition may be due to improved redox regulation of ascorbate and efficient ascorbate regeneration pathways. This study thus shows a new light into drought stress response of indigenous rice of Koraput with global implications.

The Inhibitory Effect of New Antimony(III)-Based Organometallic Complexes on the Photochemical Activity of Photosystem II and the Activity of Chloroplast Carbonic Anhydrase and Glutathione Reductase

Complexes of some metals are known to be inhibitors of various physiological processes in photosynthesizing organisms. In order to search for new efficient inhibitors, six novel antimony(III) complexes are synthesized and studied for inhibition of the photochemical activity of photosystem II (PSII) and key chloroplast enzymes, such as carbonic anhydrase and glutathione reductase. It is found that several complexes efficiently inhibit the carbonic anhydrase activity of PSII but inhibit the photochemical activity of this photosystem less efficiently. All the complexes inhibit the activity of chloroplast glutathione reductase.

He–Ne laser illumination ameliorates photochemical impairment in ultraviolet-B stressed-wheat seedlings via detoxifying ROS cytotoxicity

The protective effect and physiochemical mechanism of He-Ne laser illumination on photochemical impairment were evaluated by investigating chlorophyll fluorescence characteristics, photochemical activities of two photosystems, reactive oxygen species (ROS) levels and antioxidant enzyme activities in UV-B stressed-wheat (Triticum aestivum L.) seedlings. The results showed that enhanced UV-B stress significantly inhibited plant growth, reduced photosynthetic pigment content and antioxidant enzyme activities, while increased intracellular ROS levels. Meanwhile, UV-B stress also altered chlorophyll fluorescence characteristics and photochemical activities of seedlings. However, He-Ne laser illumination markedly improved photochemical activities and photosynthetic efficiency of two photosystems through detoxifying excessive ROS productions. Illumination with white fluorescent lamps (W), red light (R), or red light, then far-red light (R + FR) had not alleviated the inhibitory effect of UV-B stress on plant growth, suggesting that He-Ne laser illumination might be responsible for UV-B-stressed seedlings due to its regulation for intracellular ROS levels and plant oxidant/antioxidant balance. Furthermore, the laser alone also showed a positive impact on photochemical activities of photosystem I and photosystem II in plants.

Photosynthesis and sucrose metabolism in leaves of Arabidopsis thaliana aos, ein4 and rcd1 mutants as affected by wounding

We have investigated the influence of mechanical wounding of Arabidopsis rosette leaves on photochemical activity of photosystem II, gas exchange, sugar content and sucrose metabolism in wild-type plants and mutants impaired in hormonal balance. The aos (jasmonate deficiency), rcd1 (reduced sensitivity to ABA, ethylene, and methyl-jasmonate), and ein4 (ethylene insensitivity) mutants have been used. Generally, mechanical injury led to dynamic changes in metabolism, especially in sugar and carotenoid contents. Whereas all mutants showed lower photosynthesis and respiration in comparison to the wild-type plants, leaf wounding caused a decrease in respiration in aos and ein4, and an increase in respiration in wild type. The mechanical injury triggered an increase of the activities of sucrose hydrolysing enzymes, such as sucrose synthase (SuSy) and several types of invertases, which was most evident in case of rcd1 and aos plants. This was correlated with injury-related changes in soluble sugars in the mutants, but not in wild-type plants where sugar content was not significantly affected by wounding. The results confirm the key role of stress hormones, such as jasmonate and ethylene, in mediating stress responses after wounding. The outcome of the experiments also underlines important roles of SuSy and invertase in regeneration of injured tissues, most probably by providing precursors for cell wall biosynthesis and by modulating sugar-signalling in plant cells.

Fluorescence induction changes in bean leaves after heat treatment

The regularities in the alterations of chlorophyll a fluorescence induction curves of bean leaves after short (15 min) heating in the range of temperatures from 24 to 45°C were determined. A dramatic decrease in the relative f luorescence quenching (F P –F T )/F T , as well as the F v /F m ratio, were observed after heating at temperatures above 38°C, which indicates a decrease in the photochemical activity of photosystem II. The effect of an increase in the resistance of the photosynthetic apparatus to the temperature of 43°C after preheating at 37°C was demonstrated.

The fluorescent indices of bean leaves treated with sodium fluoride

It is shown that the treatment of bean leaves with NaF in concentration of 10(-2) M resulted in the alteration of fluorescent indices registered by the method of pulse fluorimetry. Fluorescent parameters F(0) and F(m) decreased, but the ratio F(v)/F(m) = (F(m) - F(0))/F(m), characterizing the maximal photochemical activity of photosystem II remained invariable. Photochemical fluorescence quenching (qP) was higher than in control during the first minutes of illumination with the actinic light, and it markedly decreased with the following illumination. Nonphotochemical quenching (qN), in contrary, decreased at the beginning of illumination, and then increased. Photosynthetic activity as characterizing by the ratio (F(M) - F(T))/F(T) reduced after the leaf treatment with NaF. Results obtained are interpreted proceeding, on the one hand, from the influence of NaF on redistribution of excitation energy between photosystem II and photosystem I and its inhibitory effect on the ATPase complex and Kalvin-Benson cycle, on the other.

Characterization of the structural changes and photochemical activity of photosystem I under Al3+ effect

The photochemical activity of photosystem I (PSI) as affected by Al3+ was investigated in thylakoid membranes and PSI submembrane fractions isolated from spinach. Biophysical and biochemical techniques such as oxygen uptake, light induced absorbance changes at 820nm, chlorophyll fluorescence emission, SDS–polyacrylamide gel electrophoresis, and FTIR spectroscopy have been used to analyze the sites and action modes of this cation on the PSI complex. Our results showed that Al3+ above 3mM induces changes in the redox state of P700 reflected by an increase of P700 photooxidation phase and a delay of the slower rate of P700 re-reduction which reveals that Al3+ exerted an inhibitory action at the donor side of PSI especially at plastocyanin (PC). Furthermore, results of P700 photooxidation monitored in the presence of DCMU with or without MV suggested that the same range of Al3+ concentrations impairs the photochemical reaction centers (RC) of PSI, as shown by the decline in the amount of active population of P700, and disrupts the charge separation between P700 and the primary electron acceptor A0 leading to the inhibition of electron transfer at the acceptor side of PSI. These inhibitory actions were also accompanied by an impairment of the energy transfer from light harvesting complex (LHCI) to RC of PSI, following the disconnection of LHCI antenna as illustrated by an enhancement of chlorophyll fluorescence emission spectra at low temperature (77K). The above results coincided with FTIR measurements that indicated a conformational change of the protein secondary structures in PSI complex where 25% of α-helix was converted into β-sheet, β-antiparallel and turn structures. These structural changes in PSI complex proteins are closely related with the alteration photochemical activity of PSI including the inhibition of the electron transport through both acceptor and donor sides of PSI.

Evaluation of Spring Wheat (20 Varieties) Adaptation to Soil Drought during Seedlings Growth Stage

The effect of soil drought (10 days) on the growth of plants, the accumulation of water and leakage of electrolytes, gas exchange, the contents of chl a + b and carotenoids in leaves and photochemical activity of photosystem II was studied at the seedling stage by transient fluorescent analysis in 20 of the popular varieties of polish spring wheat. Drought caused a particularly strong reduction in vigor of growth of seedlings, net photosynthesis rate and triggered an increase in electrolyte leakage from the leaves. Certain varieties during the drought demonstrated relatively intense CO2 assimilation at low water loss through transpiration. The varieties tested were significantly different in terms of tolerance to drought of the processes of gas exchange and seedlings development. Photochemical processes in PSII showed high tolerance to drought and at the same time low differentiation among varieties. The results obtained suggested that tolerance of growth parameters to drought and CO2 assimilation at the seedling stage may alleviate consequent depression of final yield of the grain.

Differential distribution of pigment-protein complexes in the Thylakoid membranes of Synechocystis 6803

Thylakoids in Synechocystis 6803, though apparently uniform in appearance in ultrastructure, were found to consist of segments which were functionally dissimilar and had distinct proteomes. These thylakoid segments can be isolated from Synechocystis 6803 by successive ultracentrifugation of cell free extracts at 40,000×g (40k segments), 90,000×g (90k segments) and 150,000×g (150k segments). Electron microscopy showed differences in their appearance. 40k segments looked feathery and fluffy, whereas the 90k and 150k thylakoid membrane segments appeared tiny and less fluffy. The absorption spectra showed heterogeneous distribution of pigment-protein complexes in the three types of segments. The photochemical activities of Photosystem I (PSI) and Photosystem II (PSII) showed unequal distributions in 40k, 90k and 150k segments which were substantiated with low temperature fluorescence measurements. The ratio of PSII/PSI fluorescence emission at 77K (λ(ex) = 435nm) was highest in 150k segments indicating higher PSII per unit PSI in these segments. The chlorophyll fluorescence lifetimes in the membranes, determined with a time-correlated single-photon counting technique, could be resolved in three components: τ(1) (=) <40ps, τ(2) (=) 425-900ps and τ(3) (=) 2.4-3.2ns. The percentage contribution of the fastest component (τ(1)) decreased in the order 40k > 90k > 150k segments whereas that of the other two components showed a reversed trend. These studies indicated differential distribution of pigment-protein complexes in the three membrane segments suggesting heterogeneity in the thylakoids of Synechocystis 6803.

Functional plasticity of photosynthetic apparatus and its resistance to photoinhibition in Plantago media

Morphological and functional characteristics of Plantago media L. leaves were compared for plants growing at different light regimes on limestone outcrops in Southern Timan (62°45′N, 55°49′E). The plants grown in open areas under exposure to full sunlight had small leaves with low pigment content and high specific leaf weight; these leaves exhibited high photosynthetic capacity and elevated water use efficiency at high irradiance. The maximum photochemical activity of photosystem II (Fv/Fm) in leaves of sun plants remained at the level of about 0.8 throughout the day. The photosynthetic apparatus of sun plants was resistant to excess photosynthetically active radiation, mostly due to non-photochemical quenching of chlorophyll fluorescence (qN). This quenching was promoted by elevated deepoxiation of violaxanthin cycle pigments. Accumulation of zeaxanthin, a photoprotective pigment in sun plant leaves was observed already in the morning hours. The plant leaves grown in the shade of dense herbage were significantly larger than the sun leaves, with pigment content 1.5–2.0 times greater than in sun leaves; these leaves had low qN values and did not need extensive deepoxidation of violaxanthin cycle pigments. The data reveal the morphophysiological plasticity of plantain plants in relation to lighting regime. Environmental conditions can facilitate the formation of the ecotype with photosynthetic apparatus resistant to photoinhibition. Owing to this adjustment, hoary plantain plants are capable of surviving in ecotopes with high insolation.

UV-B induced stress responses in three rice cultivars

UV-B responses of three rice (Oryza sativa L.) cultivars (Sasanishiki, Norin 1 and Surjamkhi) with different photolyase activity were investigated. Carbon dioxide assimilation data support that Sasanishiki was less sensitive to UV-B than Norin 1 and Surjamkhi. UV-B radiation sharply decreased the content of Rubisco protein in Surjamkhi and has no effect in Sasanishiki. The photochemical activities of photosystem (PS) 1 and PS 2 was slightly affected by UV-B treatment. The content of H2O2 and the activities of antioxidant enzymes, catalase (CAT), peroxides (POX) and superoxide dismutase (SOD) were enhanced after UV-B treatment. The activities of CAT and POX isoenzymes in Sasanishiki were more enhanced by UV-B radiation than those in Norin 1 and Surjamkhi.

Effect of Pb ions on superoxide dismutase and catalase activities in leaves of pea plants grown in high and low irradiance

The role of irradiance on the activity of antioxidant enzymes: superoxide dismutase (SOD) and catalase (CAT) was examined in the leaves of Pisum sativum L. plants grown under low (LL) or high (HL) irradiance (PPFD 50 or 600 µmol m−2 s−1) and exposed after detachment to 5 mM Pb (NO3)2 for 24 h. The activities of both enzymes increased in response to LL compared with HL and no effect of Pb ions was observed. Photosystem (PS) 1 and PS 2 activities were also investigated in chloroplasts isolated from these leaves. LL lowered PS 1 electron transport rate and changes in photochemical activity of PS 1 induced by Pb2+ were visible only in the chloroplasts isolated from leaves of LL grown plants. PS 2 activity was influenced similarly by Pb ions at both PPFD. This study demonstrates that leaves of HL grown plants were less sensitive to lead toxicity than those from LL grown plants. Changes in electron transport rates were the main factors responsible for the generation of reactive oxygen species in the chloroplasts and as a consequence, in induction of antioxidant enzymes.

Photosynthesis and photoinhibition in two xerophytic shrubs during drought

Seasonal changes in water relations, net photosynthetic rate (P(N)), and fluorescence of chlorophyll (Chl) a of two perennial C(3) deciduous shrubs, Ipomoea carnea and Jatropha gossypifolia, growing in a thorn scrub in Venezuela were studied in order to establish the possible occurrence of photoinhibition during dry season and determine whether changes in photochemical activity of photosystem 2 (PS2) may explain variations of PN in these species. Leaf water potential (psi) decreased from -0.2 to -2.1 MPa during drought in both species. The PN decreased with y in T carnea and J. gossypifolia by 64 and 74%, respectively. Carboxylation efficiency (CE) decreased by more than 50 and 70% in I. carnea and J gossypifolia, respectively. In I. carnea, relative stomatal limitation (L(s)) increased by 17% and mesophyll limitation (L(m)) by 65% during drought, while in J. gossypifolia Ls decreased by 27% and L. increased by 51%. Drought caused a reduction in quantum yield of PS2 (theta(PS2)) in both species. Drought affected the capacity of energy dissipation of leaves, judging from the changes in the photochemical (q(P)) and non-photochemical quenching (NPQ) coefficients. Photo-inhibition during drought in I. carnea and J gossypifolia was evidenced in the field by a drop in the maximum quantum yield of PS2 (F(v)/F(m)) below 0.8 and also by non-coordinated changes in phi(PS2) and quantum yield of non-photochemical excitation quenching (Y(n)). Total soluble protein content on an area basis increased with psi but the ribulose-1,5-bisphosphate carboxylase/oxygenase content remained unchanged. A reduction of total Chl content with drought was observed. Hence in the species studied photoinhibition occurred, which imposed an important limitation on carbon assimilation during drought.

Retardation of photo-induced changes in Photosystem I submembrane particles by glycinebetaine and sucrose.

The protective role of co-solutes (glycinebetaine and sucrose) against photodamage in isolated Photosystem (PS) I submembrane particles illuminated (2000 muE m(-2) s(-1)) for various time periods at 4 degrees C was studied. The photochemical activity of PS I in terms of electron transport measured as oxygen uptake and P700 photooxidation was significantly protected. A photoinduced enhancement of oxygen uptake observed during the first hours of strong light illumination attributed to denaturation or dissociation of membrane-bound superoxide dismutase [Rajagopal et al. (2003) Photochem. Photobiol 77: 284-291] was also retarded by glycinebetaine and sucrose. Chlorophyll photobleaching resulting in a decrease of absorbance and a blue-shift of the absorbance maximum in the red was greatly delayed in the presence of co-solutes. This phenomenon was also observed in the chlorophyll-protein (CP) complexes of PS I particles exposed to strong illumination separated on non-denaturing poly-acrylamide gels. In this case, a decrease in the absorbance of the CP1b band coinciding with an increase of CP1a during the course of illumination and ascribed to oxidative cross-linking (Rajagopal et al. 2003) was also retarded. Our results, thus, clearly demonstrated for the first time that co-solutes could minimize the alteration of photochemical activity and chlorophyll-protein complexes against photodamage of PS I submembranes particles.

Effect of membrane fluidity on photoinhibition of isolated thylakoids membranes at room and low temperature.

The relationship between thylakoid membrane fluidity and the process of photoinhibition at room and low (4 degrees C) temperature was investigated. Two different membrane perturbing agents--cholesterol and benzylalcohol were applied to manipulate the fluidity of isolated pea thylakoids. The photochemical activity of photosystem I (PSI) and photosystem II (PSII), polarographically determined, were measured at high light intensity for different time of illumination at both temperatures. The exposure of cholesterol- and benzylalcohol-treated thylakoid membranes to high light intensities resulted in inhibition of both studied photochemical activities, being more pronounced for PSII compared to PSI. Time dependencies of inhibition of PSI and PSII electron transport rates for untreated and membranes with altered fluidity were determined at 20 degrees C and 4 degrees C. The effect is more pronounced for PSII activity during low-temperature photoinhibition. The data are discussed in terms of the determining role of physico-chemical properties of thylakoid membranes for the response of photosynthetic apparatus to light stress.

Morphological and Physiological Differences in Synechococcus elongatus during Continuous Cultivation at High Iron, Low Iron, and Iron Deficient Medium

Thermophilic unicellular cyanobacterium Synechococcus elongatus Nag. var. thermalis Geitl. strain Kovrov 1972/8 was cultivated in continuous flow reactor to simulate conditions occurring in nature in regions with low iron concentration. Two degrees of iron deprivation were established: (a) low iron (LI) conditions (9.0 µM Fe) when cells still maintained maximal growth rate but already exhibited changes in photosynthetic apparatus, and (b) iron deficient (ID) conditions (0.9 µM Fe) when cell growth rate decreased and extensive morphological and functional changes were observed. A decrease in the cellular content of phycobilin antenna was observed in both ID and LI cells and an increase of carotenoid concentration only in the ID culture. Morphologically, ID cells showed a decrease in the amount of phycobilins and in the number of thylakoid membranes. This suggests that S. elongatus responds to decrease in iron availability by substitution of the phycobilisomes by antennae containing chlorophyll (Chl) and carotenoids. Photochemical activity of photosystem (PS) 2, determined as Fv/Fm ratio was similar in high iron (HI) and LI cultures and approximately five times lower in ID culture. On the other hand, the activity of the whole electron transport chain showed the opposite tendency: the relative rates of the CO2-dependent oxygen evolution in HI : LI : ID cultures were approximately 1 : 2 : 4. Thus in nutrient stress the photosynthetic apparatus preserved its activity despite the decrease in the amount of both Chl-binding complexes and thylakoid membranes.

Electrokinetic properties of thylakoids in in vitro cultured Gypsophila paniculata plants

In vitro cultured Gypsophila paniculata L. plants were used as a model to evaluate the effect of some cytokinins and anticytokinins on thylakoid surface charge. Influence of the cytokinins N-6-furfurylaminopurine (kinetin) and N1-(2-chloro-4-pyridyl)-N2-phenylurea (4-PU-30), cytokinin antagonists 2-chloro-4-cyclobutylamino-6-ethylamino-1,3,5-triazine and N-(4-pyridyl)-O-(4-chlorophenyl) carbamate on the pigment content, surface charge density (s ), fluorescence induction kinetics and millisecond-delayed light emission was studied. Our results showed that the chlorophyll (a+b) content significantly decreased after the 1st and the 2nd month of G. paniculata growth in the presence of the cytokinins kinetin and 4-PU-30. In our model system, cytokinins enhanced the number of open lateral buds and, as a consequence, more shoots per explant. Hence, chlorophyll synthesis was not inhibited but so-called ‘dilution of the pigments’ was available. Anticytokinins inhibited the formation of more than one shoot, and the chlorophyll content was not influenced significantly. The phenylurea cytokinin 4-PU-30 and anticytokinins increased the electrophoretic mobility, zeta potential and surface charge density of thylakoids after a longer time of treatment. Making thylakoid membranes more negatively charged, phenylurea cytokinin and anticytokinins increased the aggregation of the complexes and the energization of the membrane. Our results showed that plant growth regulators decreased the primary photochemical activity of photosystem II (estimated by the ratio Fv/Fm) and delayed fluorescence intensity in the 1st month. However, no significant changes were observed in these parameters in the 2nd month.