Decrease In Photosynthesis Research Articles

Effect of 28-homobrassinolide on the drought stress-induced changes in photosynthesis and antioxidant system of Brassica juncea L.

To investigate the effect of exogenously applied 28-homobrassinolide (HBL) on drought-stressed plants, photosynthesis and antioxidant systems were examined in Indian mustard (Brassica juncea L.). Seedlings of Indian mustard were subjected to drought stress for 7 days at the 8–14 (DS1)/15–21 (DS2) days’ stage of growth and then returned to normal conditions of growth. These seedlings were sprayed with HBL (0.01 μM) at the 30-day stage and were sampled at 60 days to assess the changes in growth, photosynthesis and antioxidant enzymes. Plants exposed to stress at either of the stages of growth exhibited a significant decrease in growth and photosynthesis. The exposure of plants to stress at an earlier stage (DS1) was more inhibitory than that at a later stage (DS2). However, the follow-up treatment with HBL significantly improved the values of these parameters and also overcame the inhibitory effect of water stress. The activity of antioxidant enzymes [catalase (E.C. 1.11.1.6), peroxidase (E.C. 1.11.1.7) and superoxide dismutase (E.C. 1.15.1.1)] and proline content in leaves exhibited an increase in response to both the treatment factors, where their interaction had an additive effect. It was, therefore, concluded that the elevated antioxidant system, at least in part, was responsible for amelioration of the drought stress.

Directed Biosynthesis of Phytotoxic Alkaloids in the Cyanobacterium Nostoc 78–12A

Nostocarboline, a chlorinated and N-methylated carbolinium alkaloid, displays potent and selective inhibition of photoautotrophic organisms as well as the malaria parasite Plasmodium falciparum, while showing very low toxicity to bacterial and fungal pathogens, rat myoblasts and crustaceans. New derivatives of nostocarboline incorporating Br, F or methyl substituents have been obtained through precursor-directed biosynthesis in Nostoc 78-12A (identical to Nostoc sp. ATCC 43238) by feeding this cyanobacterium with differently substituted tryptophan derivatives or 6-Br-norharmane (eudistomin N). These experiments substantiate the biosynthetic hypothesis and validate the inherent flexibility of the corresponding enzymes for metabolic engineering. The new derivatives inhibit the growth of the toxic-bloom-forming cyanobacterium Microcystis aeruginosa PCC 7806 above 1 microM. The mode of action of nostocarboline was investigated by using chlorophyll-a fluorescence imaging, and it was demonstrated that a decrease in photosynthesis precedes cell death, thus establishing the phytotoxic properties of this alkaloid.

Physiology and proteomics of the water‐deficit stress response in three contrasting peanut genotypes

Peanut genotypes from the US mini-core collection were analysed for changes in leaf proteins during reproductive stage growth under water-deficit stress. One- and two-dimensional gel electrophoresis (1- and 2-DGE) was performed on soluble protein extracts of selected tolerant and susceptible genotypes. A total of 102 protein bands/spots were analysed by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS) and by quadrupole time-of-flight tandem mass spectrometry (Q-TOF MS/MS) analysis. Forty-nine non-redundant proteins were identified, implicating a variety of stress response mechanisms in peanut. Lipoxygenase and 1l-myo-inositol-1-phosphate synthase, which aid in inter- and intracellular stress signalling, were more abundant in tolerant genotypes under water-deficit stress. Acetyl-CoA carboxylase, a key enzyme of lipid biosynthesis, increased in relative abundance along with a corresponding increase in epicuticular wax content in the tolerant genotype, suggesting an additional mechanism for water conservation and stress tolerance. Additionally, there was a marked decrease in the abundance of several photosynthetic proteins in the tolerant genotype, along with a concomitant decrease in net photosynthesis in response to water-deficit stress. Differential regulation of leaf proteins involved in a variety of cellular functions (e.g. cell wall strengthening, signal transduction, energy metabolism, cellular detoxification and gene regulation) indicates that these molecules could affect the molecular mechanism of water-deficit stress tolerance in peanut.

Photosynthesis, fluorescence, shoot biomass and seed weight responses of three cowpea ( Vigna unguiculata (L.) Walp.) cultivars with contrasting sensitivity to UV-B radiation

Current and projected increases in ultraviolet-B (UV-B) radiation (280–320 nm) may alter crop production. An experiment was conducted to study the influence of UV-B radiation on photosynthetic CO 2 assimilation, photosystem II (PSII) photochemistry, pigments, UV-B absorbing compounds, vegetative and reproductive growth responses of three cowpea cultivars, California Blackeye (CB)-5, CB-27, and Mississippi Pinkeye (MPE). Cowpea cultivars were subjected to four levels of biologically effective UV-B radiation of 0 (control), 5, 10 and 15 kJ m −2 d −1 from 8 days after emergence (DAE) to maturity of the crop in sunlit, controlled environment chambers. Increase in UV-B radiation caused a decrease in maximum light-saturated photosynthesis ( A max) in all the three cultivars, but the magnitude of decrease varied, 12% in MPE, 37% in CB-27, and 43% in CB-5 at 15 kJ of UV-B. The lower damaging effect of UV-B on A max in MPE was supported by a smaller decrease in maximum rate of Rubisco activity ( V cmax) coupled with higher levels of light-saturated rate of electron transport ( J max) compared to other sensitive cultivars, CB-5 and CB-27. The tolerance nature of MPE was further evidenced by less or no effect of UV-B on photosynthetic electron transport rate (ETR), photochemical quenching ( q P), and quantum yield of PSII photochemistry ( Φ PSII) compared to CB-5 and CB-27 across the UV-B treatments. Further, maximal electron transport rates (ETR max) estimated at saturated light substantially decreased with increase in UV-B in CB-5 and CB-27, while there was no or less influence on MPE. All cultivars showed linear relationship between Φ PSII and quantum yield of CO 2 fixation ( Φ C O 2 ) derived from light–response curves and internal-CO 2-response curves of chlorophyll a (Chl a) fluorescence. MPE maintained significantly higher concentration of UV-B absorbing compounds compared to the CB-5 and CB-27 across UV-B levels. Plants grown at elevated UV-B radiation produced significantly lower plant and seed dry weights in both the sensitive cultivars (CB-5 and CB-27) while the effect on MPE was minimal. This study revealed that the current and projected UV-B radiation could significantly decrease the growth and yield of sensitive cowpea cultivars, possibly caused by reduction in the photosynthetic efficiency of plants. In general, MPE showed more tolerance to UV-B radiation based on most of the parameters studied as compared to the CB-5 and CB-27.

The effects of hydrogen peroxide on metabolism in the coral Goniastrea aspera

Coral metabolism reflects the physiological condition of a coral colony. We studied coral metabolism using a continuous-flow, complete mixing (CFCM) experimental system. Small-size Goniastrea aspera coral colonies were incubated in the CFCM system with and without hydrogen peroxide (H 2O 2) added to the supplied seawater (0 µM H 2O 2 for 12 days; 0, 0.3, 3.0, and 30 µM H 2O 2 for 3 days, for each treatment) Without addition of H 2O 2, coral metabolism, including photosynthesis (gross primary productivity) and calcification, was relatively stable and there were no significant metabolic changes, suggesting that, without H 2O 2 added to the CFCM system, the corals did not suffer significant stress from the experimental system over a 12-day incubation period. When H 2O 2 was added, large decreases in photosynthesis and calcification were observed. The non-parametric Mann–Whitney U-test showed that there were statistically significant differences in photosynthesis after addition of 3.0 µM and 30 µM H 2O 2, compared with the control. We also found statistically significant differences in net calcification after addition of 30 µM H 2O 2. Thus, the incubation experiments suggest that higher H 2O 2 concentrations in seawater clearly influence coral metabolism. However, the results also suggest that the current seawater H 2O 2 level in Okinawa is not likely to pose significant acute effects on the metabolic activities of corals.

Early stage toxicity of excess copper to photosystem II of Chlorella pyrenoidosa–OJIP chlorophyll a fluorescence analysis

Acute toxicity of excess Cu on the photosynthetic performance of Chlorella pyrenoidosa was examined by using chlorophyll a fluorescence transients and JIP-test after exposure to elevated Cu concentrations for a short time period. High Cu concentration resulted in a significant suppression in photosynthesis and respiration. The absorption flux (ABS/RC) per PSII reaction center increased with increasing Cu concentration, but the electron transport flux (ET0/RC) decreased. Excess Cu had an insignificant effect on the trapping flux (TR0/RC). The decline in the efficiency, with which a trapped exciton can move an electron into the electron transport chain further than Q(A)-(Psi0), the maximal quantum yield of primary photochemistry (Phi0), and the quantum yield of electron transport (Phi(E)0) were also observed. The amount of active PSII reaction centers per excited cross section (RC/CS) was also in consistency with the change of photosynthesis when cells were exposed to excess Cu concentration. JIP-test parameters had a good linear relationship with photosynthetic O2 evolution. These results suggested that the decrease of photosynthesis in exposure to excess Cu may be a result of the inactivation of PSII reaction centers and the inhibition of electron transport in the acceptor side.

Photodegradation product of sulcotrione and the physiological response of maize ( Zea mays) and white mustard ( Sinapis alba)

One of the strategies for decreasing the consumption of herbicides consists in improving their uptake and efficiency. It was suggested that the photodegradation of herbicides due to sunlight results in a greater demand of herbicides to be introduced into the environment in order to ensure the plant protection activity. Moreover, an ecotoxicological effect of the photoproducts needs to be clarified. The physiological response of Zea mays and Sinapis alba (weed) to sulcotrione and its main photoproduct, called chromone (xanthene-1,9-dione-3,4-dihydro-6-methylsulfonyl), was evaluated under controlled conditions in a growth chamber. The dose-response effects were determined on Z. mays and S. alba. Using the sulcotrione (doses ranging from 1 to 9 mg per plant), the physiological parameters indicated a decrease of photosynthesis for the S. alba species while the Z. mays species were only slightly affected. On the contrary, the chromone had no herbicide activity on both species. The sulcotrione is known to block 4-hydroxyphenyl pyruvate dioxygenase (HPPD) enzyme. The differences between the parent herbicide and the photoproduct could be ascribed to drastic structural modifications. We have shown that the chromone probably do not block the HPPD active site.

Seasonal dynamics of CO2 exchange during primary succession of boreal mires as controlled by phenology of plants

Vegetation succession in mires is rather well identified using the paleoecological approach. Recently, the ecological succession concept has been extended to ecosystem functions, e.g., carbon dioxide (CO2) dynamics. Although a strong link between mire vegetation and carbon dynamics is well acknowledged, the successional changes in mire ecosystem functions have remained practically unstudied, especially under the same climatic control. To study the patterns and dynamics of CO2 exchange during mire succession, we measured CO2 exchange and vegetation dynamics over 2 growing seasons along a mire chronosequence on the land uplift coast of the Bay of Bothnia in western Finland. The study showed a decrease in photosynthesis during mire succession that was linked to compositional change in vegetation, i.e., replacement of sedge and herb dominance with the dominance of dwarf shrubs and Sphagna. Similarly, the study revealed decreased variation in gross photosynthesis (PG) and ecosystem respiration (RE) over a growing season, which resulted in lower levels of seasonal CO2 dynamics at older stages. The observed successional trend in phenology and CO2 dynamics was largely a consequence of the gradual decrease in the abundance of plant groups with efficient photosynthesis and green area production.

Elevated atmospheric CO2 concentration ameliorates effects of NaCl salinity on photosynthesis and leaf structure of Aster tripolium L.

This study investigated the interaction of NaCl-salinity and elevated atmospheric CO2 concentration on gas exchange, leaf pigment composition, and leaf ultrastructure of the potential cash crop halophyte Aster tripolium. The plants were irrigated with five different salinity levels (0, 25, 50, 75, 100% seawater salinity) under ambient and elevated (520 ppm) CO2. Under saline conditions (ambient CO2) stomatal and mesophyll resistance increased, leading to a significant decrease in photosynthesis and water use efficiency (WUE) and to an increase in oxidative stress. The latter was indicated by dilations of the thylakoid membranes and an increase in superoxide dismutase (SOD) activity. Oxidative stress could be counteracted by thicker epidermal cell walls of the leaves, a thicker cuticle, a reduced chlorophyll content, an increase in the chlorophyll a/b ratio and a transient decline of the photosynthetic efficiency. Elevated CO2 led to a significant increase in photosynthesis and WUE. The improved water and energy supply was used to increase the investment in mechanisms reducing water loss and oxidative stress (thicker cell walls and cuticles, a higher chlorophyll and carotenoid content, higher SOD activity), resulting in more intact thylakoids. As these mechanisms can improve survival under salinity, A. tripolium seems to be a promising cash crop halophyte which can help in desalinizing and reclaiming degraded land.

Patterns of resistance and resilience of the stress-tolerant coral Siderastrea radians (Pallas) to sub-optimal salinity and sediment burial

The coastal lagoons of south Florida, U.S., experience fluctuating levels of sedimentation and salinity and contain only a subset of the coral species found at the adjacent reefs of the Florida Reef Tract. The dominant species within these habitats is Siderastrea radians, which can reach densities of up to 68 colonies m - 2 and is commonly exposed to salinity extremes (< 10 psu to > 37 psu) and chronic sediment burial. In this study, we document the patterns of resistance and resilience of S. radians to sub-optimal salinity levels and sediment burial in a series of short-term, long-term, acute, chronic, single-stressor, and sequential-stressor experiments. S. radians displayed remarkable patterns of resistance and resilience and mortality was documented only under prolonged (≥ 48 h) continuous exposure to salinity extremes (15 and 45 psu) and chronic sediment burial. A reduction in photosynthetic rates was documented for all salinity exposures and the decrease in photosynthesis was linearly related to exposure time. Negative impacts on photosynthetic rates were more severe under low salinity (15 psu) than under high salinity (45 psu). Corals exposed to intermediate, low-salinity levels (25 psu), exhibited initial declines in photosynthesis that were followed by temporary increases that may represent transient acclimatization patterns. The impacts of sediment burial were influenced by the duration of the burial period and ranged from a temporary reduction in photosynthesis to significant reductions in growth and tissue mortality. The maintenance of P/R ratios > 1 and the rapid (< 24 h) recovery of photosynthetic rates after burial periods of 2-24 h indicates that S. radians is able to resist short-term burial periods with minor physiological consequences. However, as burial periods increase and colonies become covered at multiple chronic intervals, sediment burial resulted in extended photosynthetic recovery periods, reduced growth, and mortality. Under normal conditions (i.e., no salinity stress), S. radians was very effective at clearing sediments, and > 50% of the colonies' surface area was cleared within 1 h. However, clearing rates were influenced by physiological status, and prior exposure to sub-optimal salinity significantly reduced the clearing rates of stressed colonies. The response of S. radians to disturbance documented in this study characterizes this species as highly stress-tolerant and provides an explanation for its present high abundance in both reef and marginal environments. Moreover, the key life-history attributes of S. radians, such as brooding reproductive strategy, small colony size, high stress-tolerance, and high recruitment rates, suggest the potential for this species to replace reef-building taxa under increased disturbance scenarios in Florida and elsewhere in the region.

Interactive effects of NaCl salinity and elevated atmospheric CO 2 concentration on growth, photosynthesis, water relations and chemical composition of the potential cash crop halophyte Aster tripolium L.

This study was aimed at obtaining detailed information about the interaction of NaCl-salinity and elevated atmospheric CO 2 concentration in the potential cash crop halophyte Aster tripolium. Plants were irrigated with 5 different salinity levels (0, 25, 50, 75 and 100% sws) under ambient and elevated (520 ppm) CO 2. Under saline conditions leaf water potential decreased to a value below the one of the nutrient solution. Osmotic adjustment was mainly due to the accumulation of sodium and chloride (includer type). However, the salt was unequally distributed within the plants. K/Na selectivity was high in the lateral roots and low in the petioles, so that these organs served as “salt filters” which prevented an excessive salt accumulation and ion toxicity in the leaf blades and in the main root, the storage organ for organic substances. Despite some signs of ion toxicity and nutrial imbalance, these factors do not seem to be predominantly responsible for the limited salinity tolerance of A. tripolium. In order to maintain a positive water balance the salt treated plants increased stomatal resistance. But at the same time stomata closure led to a significant decrease in photosynthesis and thus in WUE. The impaired assimilation rate contributed to the significant growth depression (50% reduction of the maximum yield between 50% and 75% sws), together with the higher energy consumption needed for various salinity tolerance mechanisms, e.g. for an enhanced synthesis of compatible solutes (proline, carbohydrates) and stress-induced proteins. Elevated atmospheric CO 2 concentration led to a significant increase in photosynthesis and in WUE. The latter indicates, together with a higher water potential, that the water relations of the plants had improved. By reducing stomatal resistance energy gain was maximized. The additional supply with energy-rich organic substances was not employed for producing more biomass but for increasing the investment in salinity tolerance mechanisms, e.g. for an enhanced synthesis of proline, carbohydrates and proteins. These mechanisms led to a higher survival rate under saline conditions, i.e. to an improved salt tolerance. The results of the study indicate that A. tripolium is a promising cash crop halophyte which will probably benefit from rising atmospheric CO 2 concentrations in future.

Botryticides affect grapevine leaf photosynthesis without inducing defense mechanisms

The effects of the two botryticides, fludioxonil (fdx) and fenhexamid (fhd), were investigated on grapevine leaves (Vitis vinifera L. cv. Pinot noir) following photosynthesis and defense mechanisms. Treatments were carried out in vineyard at the end of flowering. Phytotoxicity of both fungicides was evaluated by measuring variations of leaf photosynthetic parameters and correlated expression of photosynthesis-related genes. Results demonstrated that similar decrease in photosynthesis was caused by fdx and fhd applications. Moreover, the mechanism leading to photosynthesis alteration seems to be the same for both fungicides. Stomatal limitation to photosynthetic gas exchange did not change following treatments indicating that inhibition of photosynthesis was mostly attributed to non-stomatal factors. Nevertheless, fungicides-induced depression of photosynthesis was related neither to a decrease in Rubisco carboxylation efficiency and in the capacity for regeneration of ribulose 1,5-bisphosphate nor to loss in PSII activity. However, fdx and fhd treatments generated repression of genes encoding proteins involved in the photosynthetic process. Indeed, decreased photosynthesis was coupled with repression of PsbP subunit of photosystem II (psbP1), chlorophyll a/b binding protein of photosystem I (cab) and Rubisco small subunit (rbcS) genes. A repression of these genes may participate in the photosynthesis alteration. To our knowledge, this is the first study of photosynthesis-related gene expression following fungicide stress. In the meantime, defense responses were followed by measuring chitinase activity and expression of varied defense-related genes encoding proteins involved in phenylpropanoid synthesis (PAL) or octadecanoid synthesis (LOX), as well as pathogenesis-related protein (Chi4C). No induction of defense was observed in botryticides-treated leaves. To conclude, the photosynthesis is affected without any triggering of plant defense responses.

Leaf cold acclimation and freezing injury in C3 and C4 grasses of the Mongolian Plateau

The scarcity of C4 plants in cool climates is usually attributed to their lower photosynthetic efficiency than C3 species at low temperatures. However, a lower freezing resistance may also decrease the competitive advantage of C4 plants by reducing canopy duration, especially in continental steppe grasslands, where a short, hot growing season is bracketed by frost events. This paper reports an experimental test of the hypothesis that cold acclimation is negligible in C4 grasses, leading to greater frost damage than in C3 species. The experiments exposed six C3 and three C4 Mongolian steppe grasses to 20 d chilling or control pre-treatments, followed by a high-light freezing event. Leaf resistance to freezing injury was independent of photosynthetic type. Three C3 species showed constitutive freezing resistance characterized by <20% leaf mortality, associated with high photosynthetic carbon fixation and electron transport rates and low leaf osmotic potential. One freezing-sensitive C4 species showed the expected pattern of chilling-induced damage to photosynthesis and >95% leaf mortality after the freezing event. However, three C3 and two C4 species displayed a cold acclimation response, showing significant decreases in osmotic potential and photosynthesis after exposure to chilling, and a 30–72% reduction of leaf freezing injury. This result suggested that down-regulation of osmotic potential may be involved in the cold acclimation process, and demonstrated that there is no inherent barrier to the development of cold acclimation in C4 species from this ecosystem. Cold acclimation via osmoregulation represents a previously undescribed mechanism to explain the persistence of C4 plants in cool climates.

Independently silencing two photosynthetic proteins in Nicotiana attenuata has different effects on herbivore resistance.

Insect attack frequently down-regulates photosynthetic proteins. To understand how this influences the plant-insect interaction, we transformed Nicotiana attenuata to independently silence ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCase) activase (RCA) and RuBPCase and selected lines whose photosynthetic capacity was similarly reduced. Decreases in plant growth mirrored the decreases in photosynthesis, but the effects on herbivore performance differed. Both generalist (Spodoptera littoralis) and specialist (Manduca sexta) larvae grew larger on RCA-silenced plants, which was consistent with decreased levels of trypsin protease inhibitors and diterpene glycosides and increased levels of RuBPCase, the larvae's main dietary protein. RCA-silenced plants were impaired in their attack-elicited jasmonate (JA)-isoleucine (Ile)/leucine levels, but RuBPCase-silenced plants were not, a deficiency that could not be restored by supplementation with Ile or attributed to lower transcript levels of JAR4/6, the key enzyme for JA-Ile conjugation. From these results, we infer that JA-Ile/leucine signaling and the herbivore resistance traits elicited by JA-Ile are influenced by adenylate charge, or more generally, carbon availability in RCA- but not RuBPCase-silenced plants. Growth of generalist larvae on RuBPCase-silenced plants did not differ from growth on empty vector controls, but the specialist larvae grew faster on RuBPCase-silenced plants, which suggests that the specialist can better tolerate the protein deficiency resulting from RuBPCase silencing than the generalist can. We conclude that the plant-herbivore interaction is more influenced by the particular mechanisms that reduce photosynthetic capacity after herbivore attack than by the magnitude of the decrease, which highlights the value of understanding defense mechanisms in evaluating growth-defense tradeoffs.

Consequences of nitrogen deficiency induced by low external N concentration and by patchy N supply in Picea abies and Thuja occidentalis

We examined the responses of two coniferous species Picea abies and Thuja occidentalis to decreased nitrogen availability. Plants were grown for 2 months in inorganic substrate irrigated by nutrient solution. Nitrogen availability was reduced either by lower N concentration in the nutrient solution or by a patchy supply of a high N concentration to only one side root isolated in a split-root setup where the rest of the root system received all nutrients except N. At the end of cultivation we measured rates of net photosynthetic CO2 uptake, net nitrogen and water uptake, some structural characteristics (dry mass of fine roots, dry mass and area of needles) and the total N content of needles. For a more detailed analysis of the distribution of the newly acquired N within the shoot, 15N was administered to subsets of plants in each of the three treatments. Low N availability resulted in lower specific leaf area in Thuja but not in Picea. The decrease of net photosynthesis at lower N supply was greater in Picea than in Thuja. Photosynthetic nitrogen use efficiency, however, linearly decreased with increasing N content only in Thuja. Patchy N supply caused uneven distribution of newly acquired labeled nitrogen and total N but did not result in significantly greater heterogeneity in the rate of photosynthesis among branches both in Picea and in Thuja plants. We conclude that both examined species possess mechanisms that reduce adverse effects of patchy N supply and restricted nitrogen transport in xylem to some parts of crown on their photosynthetic carbon assimilation.

Interpreting the decrease in leaf photosynthesis during flowering in mango

Little is known about the effect of flowering on leaf photosynthesis. To understand why net photosynthesis (A(net)) is lower in Mangifera indica L. leaves close to inflorescences than in leaves on vegetative shoots, we measured nitrogen and carbohydrate concentrations, chlorophyll a fluorescence and gas exchange in recently matured leaves on vegetative terminals and on floral terminals of 4-year-old trees. We used models to estimate photosynthetic electron fluxes and mesophyll conductance (g(m)). Lower A(net) in leaves close to developing inflorescences was attributable to substantial decreases in stomatal conductance and g(m), and also in photosynthetic capacity as indicated by the decrease in the light-saturated rate of photosynthetic electron transport (J(max)). The decrease in J(max) was the result of decreases in the amount of foliar nitrogen per unit leaf area, and may have been triggered by a decrease in sink activity as indicated by the increase in the hexose:sucrose ratio. Parameters measured on leaves close to panicles bearing set fruits were generally intermediate between those measured on leaves on vegetative shoots and on leaves close to inflorescences, suggesting that the changes in A(net) associated with flowering are reversible.

Effects of simulated deposition of acid mist and iron ore particulate matter on photosynthesis and the generation of oxidative stress in Schinus terebinthifolius Radii and Sophora tomentosa L.

Particulate matter is a natural occurrence in the environment, but some industries, such as the iron ore sector, can raise the total amount of particles in the atmosphere. This industry is primarily a source of iron and sulfur dioxide particulates. The effects of the pollutants from the iron ore industries on representatives of restinga vegetation in a Brazilian coastal ecosystem were investigated using physiological and biochemical measures. Two species, Schinus terebinthifolius and Sophora tomentosa, were exposed to simulated deposition of acid mist and iron ore particulate matter in acrylic chambers in a greenhouse. Parameters such as gas exchange, fluorescence emission, chlorophyll content, total iron content, antioxidant enzyme activity and malondialdehyde content were assessed in order to evaluate the responses of the two species. Neither treatment was capable of inducing oxidative stress in S. terebinthifolius. Nevertheless, the deposition of iron ore particulates on this species increased chlorophyll content, the maximum quantum efficiency of photosystem II and the electron transport rate, while iron content was unaltered. On the other hand, S. tomentosa showed a greater sensitivity to the treatments. Plants of S. tomentosa that were exposed to acid mist had a decrease in photosynthesis, while the deposition of iron particulate matter led to an increase in iron content and membrane permeability of the leaves. The activities of antioxidant enzymes, such as catalases and superoxide dismutase, were enhanced by both treatments. The results suggested that the two restinga species use different strategies to overcome the stressful conditions created by the deposition of particulate matter, either solid or wet. It seems that while S. terebinthifolius avoided stress, S. tomentosa used antioxidant enzyme systems to partially neutralize oxidative stress. The findings also point to the potential use of S. tomentosa as a biomarker species under field conditions.

Effect of cadmium on photosynthesis, nutrition and growth of mungbean

Contamination of soils with cadmium is a major threat to ecosystems. Root uptake of cadmium from contaminated soils induces physiological changes such as a decrease in plant growth. Plant species and varieties show differential physiological mechanisms of cadmium tolerance. Here, we studied the effect of cadmium chloride on leaf chlorosis, gas exchange attributes and some essential nutrients in the shoots of selected tolerant and sensitive mungbean (Vigna radiata) varieties at the seedling, vegetative and reproductive growth stages. Our results show that elevated concentrations of cadmium led to accumulation of cadmium in the shoot and roots, intervein chlorosis of leaves and loss of pigments. Tolerant mungbean showed steady-state contents of potassium, magnesium, manganese and iron, and photosynthetic pigments at all growth stages. A decrease in the net photosynthesis, increase in substomatal CO2 level and a decline in the ratio of net photosynthesis and substomatal CO2 level revealed that cadmium prevented CO2 fixation by Rubisco. Correlations of shoot cadmium concentration and chlorosis with its nutrient and pigment content, although negative in both varieties, were closer in the tolerant but absent, or weaker if present, in the sensitive mungbean. Most nutrients had close association with the content of photosynthetic pigments of tolerant mungbean, which indicated their involvement in maintaining steady levels of pigments. This finding indicates the involvement of nutrients and pigments in cadmium tolerance. In conclusion, cadmium tolerance in mungbean was attributed to low cadmium uptake and its accumulation in the shoot, leaf chlorosis, improved pigment, nutrient levels and carboxylation efficiency of Rubisco throughout the mungbean phenology. Based on these findings the tolerant mungbean can be grown in moderately cadmium-contaminated soils.

Effects of heat stress on gas exchange and photosystem II (PSII) photochemical activity of Phillyrea angustifolia exposed to elevated CO2 and subsaturating irradiance

Gas exchange and chlorophyll a fluorescence measurements were performed simultaneously on leaves of Phillyrea angustifolia L. to assess the effects of heat stress (30 min at 40 °C) on photosynthesis and photosystem II (PSII) photochemical efficiency of plants grown at ambient CO2 and exposed to an elevated CO2 concentration (800 µmol·mol–1) and 300 µmol photons·m–2·s–1. No significant difference was found in the heat-induced decreases of net photosynthesis (PN), quantum yield of PSII electron transport (ΦPSII), and maximum PSII photochemical efficiency (Fv/Fm) between plants exposed to ambient and elevated CO2 concentrations, showing that elevated CO2 was not able to reduce the potential for photoinhibition at high temperatures under moderate light conditions. The heat-induced decrease of PN was higher than that of ΦPSII indicating that reductive power was more utilized in non-assimilatory processes than in CO2 fixation at both CO2 treatments. This result suggested that impairment of the Calvin cycle rather than electron transport inhibition was the main cause of the limitation in CO2 fixation.

Paraheliotropism in Robinia pseudoacacia L.: an efficient strategy to optimise photosynthetic performance under natural environmental conditions

We assessed the contribution of leaf movements to PSII photoprotection against high light and temperature in Robinia pseudoacacia. Gas exchange and chlorophyll a fluorescence measurements were performed during the day at 10:00, 12:00, 15:00 and 18:00 hours on leaves where paraheliotropic movements were restrained (restrained leaves, RL) and on control unrestrained leaves (UL). RL showed a strong decrease of net photosynthesis (A(n)), stomatal conductance (g(sH2O)), quantum yield of electron transport (PhiPSII), percentage of photosynthesis inhibited by O2 (IPO) and photochemical quenching (q(P)) in the course of the day, whereas, a significant increase in C(i)/C(a) and NPQ was observed. Contrary to RL, UL had higher photosynthetic performance that was maintained at elevated levels throughout the day. In the late afternoon, A(n), g(sH2O), PhiPSII and q(P) of RL showed a tendency to recovery, as compared to 15:00 hours, even if the values remained lower than those measured at 10:00 hours and in UL. In addition, contrary to UL, no recovery was found in F(v)/F(m) at the end of the study period in RL. Data presented suggest that in R. pseudoacacia, leaf movements, by reducing light interception, represent an efficient, fast and reversible strategy to overcome environmental stresses such as high light and temperature. Moreover, paraheliotropism was able to protect photosystems, avoiding photoinhibitory damage, leading to a carbon gain for the plant.