Reduction In Photosynthesis Research Articles

Antioxidant Activity and Photosynthesis Efficiency in Melissa officinalis Subjected to Heavy Metals Stress

The aim of this study was to assess influence of cadmium and zinc treatments on antioxidant activity combined with the photosynthesis efficiency in a popular herb lemon balm (Melissa officinalis L.). Plants were grown under greenhouse conditions by the pot method. The Mn, Cu, Cd, and Zn contents in soil and plants were measured by HR-CS FAAS. The activity of net photosynthesis, stomatal conductance, transpiration rate, intercellular CO2, and index of chlorophyll in leaves were determined for all investigated species. Reduction of the net photosynthesis was observed for cultivations subjected to either Zn or Cd treatments. Phenolic contents were determined by the chemical Folin-Ciocalteu method, while enhanced voltammetric analysis was applied to assess the antioxidant properties of plant extracts. Both of these approaches yielded similar results. Herbal extracts had exceptional antioxidant capacities and were good scavengers of free radicals and reactive oxygen species. Structural similarity of cadmium and zinc facilitated their mutual structural exchange and prompted substantial expansion of phenolics under the mixed Zn and Cd treatments.

Identification of key responsive leaf traits for ozone tolerance in six modern indica and japonica rice cultivars (Oryza sativa L.) over two years

Increasing ozone concentrations cause rice yield loss in many polluted regions, it renders the use of ozone-tolerant rice cultivars to mitigate its negative effects. To evaluate the sensitivity of rice cultivars to ozone, however, simple diagnostic procedures, such as alterations in leaf properties, have not been systematically established. As a result, a comparative investigation on the upper leaf properties of three indica and three japonica modern rice cultivars was carried out in Yangzhou, China, utilizing an ozone fumigation platform. From the start of tillering until the end of harvest in the growing seasons of 2016 and 2017, the plants were subjected to 100 ppb of ozone for 8 h each day, as well as control conditions (approximately 10 ppb). At 20 days after heading, eighteen leaf characteristics, including leaf SPAD, chlorophyll (CHL), morphological parameters, malondialdehyde (MDA), antioxidants content, and antioxidative enzyme activity, were evaluated. The results demonstrated that ozone stress accelerated leaf senescence, as shown by an increase in MDA content and faster reductions in pigment quantities (SPAD value, CHL), light-saturated photosynthesis (Asat) and stomatal conductance (gs). Ozone considerably reduced leaf area, length, and dry weight (DW), but did not affect stomatal density (SD) and dry weight per unit area (WPA). Ozone stress significantly enhanced total ascorbate (ASA), but enzyme activity of superoxide dismutase (SOD), peroxidase (POD), and hydrogen peroxidase (CAT) showed a trend of decrease. Analysis of variance (ANOVA) demonstrated a substantial interaction impact between ozone and year on the majority of leaf attributes, which may be ascribed to the high temperatures during the heading stage in 2016. The ozone-induced changes in leaf characteristics of the indica cultivar, such as leaf SPAD value, CHL, area, Asat, gs, MDA, and CAT, were greater than those of the japonica cultivar, demonstrating a substantial interaction between rice type and ozone. In combination with grain yield, this study demonstrated that the yield response differences across rice cultivars under ozone stress were closely related to the major leaf characteristics, including leaf pigments, Asat, gs, and MDA. These findings provide a significant theoretical basis for selecting ozone-tolerant rice cultivars and implementing cultivation strategies to reduce ozone’s negative impact on rice yield.

Comparative Study of Cypripedium Plant Photosynthetic Characteristics from Changbai Mountain

This study reports on extensive and in-depth investigations into the morphological, photosynthetic, and physiological indices of 10 different types of Cypripedium plant introduced from Changbai Mountain. It is an important prerequisite for the ex situ conservation of Cypripedium plants to provide new insights into their photosynthesis. This result can not only promote the production of vegetative plants but also promote the production of plants with lots of flowers and the physiological characteristics of Cypripedium plants for promoting the artificial introduction and cultivation of wild resources. A critical comparison of the results showed that high light intensity is one of the causes of the reduction in photosynthesis in the samples. Cypripedium macranthum had the most morphological advantages, while Cypripedium guttatum, the smallest plant type, had the lowest plant morphogenesis. Photoinhibition began daily at 12:00 pm and reached a second peak at 14:00 pm in all 10 types. C. macranthum, Cypripedium ventricosum, and Cypripedium calceolus had greater photosynthetic capacity than the other types. Using principal component analysis, the order of photosynthetic physiological characteristics of the 10 Cypripedium plants was CCMY > CVPP > CCRY > CMPP > CVRR > CSPY > CMWW > CMLL > CMDD > CGWW. These results lay the groundwork for future research on Cypripedium resource distribution and artificial conservation.

Trehalose and NO work together to alleviate Cd toxicity in pepper (Capsicum annuum L.) plants by regulating cadmium sequestration and distribution within cells and the antioxidant defense system

The response of plants to trehalose (TR) and nitric oxide (NO) has been tested in different stressful conditions, but the contribution of endogenous TR to plant tolerance to cadmium stress (Cd-S) induced by NO is still unclear. Ten days after germination, among the pepper seedlings, half were immersed for 12 h in a solution containing 15.0 mM TR or 0.6 mM sodium citrate (SC), an inhibitor of trehalose-6-phosphate phosphatase (TPP). Then, the plants were exposed to control (no addition of Cd) or Cd-S (0.1 mM CdCl2) up to two additional weeks. Throughout the stress period, both treatments were combined with sodium nitroprusside (SNP; 0.1 mM), a NO donor, supplied through the nutrient solution. Plants exposed to Cd-S experienced a substantial reduction in plant growth, photosynthesis, and leaf water relation parameters, but an increase in oxidative stress parameters, free proline, phytochelatins (PCs), and the activities of catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), glutathione reductase (GR), and ascorbate peroxidase (APX). The detrimental effects of Cd-S on the afore-mentioned traits were reversed by the supplementation of SNP, which in turn significantly increased the endogenous NO and TR levels, and leaf calcium (Ca2+) and potassium (K+), and reduced the leaf H2O2, MDA, and Cd contents as well as membrane leakage. SNP raised the amounts of GSH and PCs in Cd-S- plants, thereby modulating Cd sequestration to render it nontoxic. The treatment of SNP encouraged Cd build-up in the cell walls of root and leaf in order to prevent Cd from being transported to other vital cell organelles to safeguard them from metal toxicity. The supplementation of SC, a scavenger of TPP, eliminated TR content, thereby reversing the positive effect of SNP on Cd-S plants. Exogenous application of TR together with SNP+SC reversed the negative effect of SC. This suggests that TR is necessary for NO to be effective in improving the pepper plant Cd-S tolerance.

The Effects of Water Stress on Cotton Leaf Area and Leaf Morphology

The most important effect of water stress on plants is that it reduces leaf area and leads to changes in leaf morphology. Decreased leaf area results in reduces crop yield through the reduction in photosynthesis. This study investigates the effects of the decrease in leaf area on seed cotton yield, evapotranspiration (ET), water use efficiency (WUE), and leaf geometry in cotton plants under water stress in different growth periods. The cotton plant was divided into three different growth periods (vegetative period (VP), flowering and boll growth period (FB), and boll opening (BO) period), and irrigation water was applied at field capacity level during the periods of full irrigation (T), while non-irrigation was applied during the water stress periods (O). In the experiment, 6 different irrigation strategies were based on: OOO, TTT, OTO, TOO, OTT, and TOT. In each treatment, five leaves were taken from three plants in every replicate during three growth periods, and the leaf area and geometric lengths of each leaf were measured. Seed cotton yield, evapotranspiration, and WUE decreased significantly depending on the severity and duration of the water stress to which the cotton was exposed. Physiologically, cotton leaves under water stress in the first stage of growth tended to increase the leaf lobe numbers while reducing the leaf area. Therefore, there were more leaf lobes numbers measured in OOO than in other treatments. Irrigation in the vegetative growth period was more effective in increasing the leaf area than the other growth periods.

L-Arginine Alleviates the Reduction in Photosynthesis and Antioxidant Activity Induced by Drought Stress in Maize Seedlings.

Maize (Zea mays L.) is one of the most important food crops in the world. Drought is currently the most important abiotic factor affecting maize yield. L-arginine has emerged as a nontoxic plant growth regulator that enhances the tolerance of plants to drought. An experiment was conducted to examine the role of L-arginine in alleviating the inhibitory effects of drought on the photosynthetic capacity and activities of antioxidant enzymes when the plants were subjected to drought stress. The results showed that the biomass of maize seedlings decreased significantly under a 20% polyethylene glycol-simulated water deficit compared with the control treatment. However, the exogenous application of L-arginine alleviated the inhibition of maize growth induced by drought stress. Further analysis of the photosynthetic parameters showed that L-arginine partially restored the chloroplasts' structure under drought stress and increased the contents of chlorophyll, the performance index on an adsorption basis, and Fv/Fm by 151.3%, 105.5%, and 37.1%, respectively. Supplementation with L-arginine also reduced the oxidative damage caused by hydrogen peroxide, malondialdehyde, and superoxide ions by 27.2%, 10.0%, and 31.9%, respectively. Accordingly, the activities of ascorbate peroxidase, catalase, glutathione S-transferase, glutathione reductase, peroxidase, and superoxide dismutase increased by 11.6%, 108.5%, 104.4%, 181.1%, 18.3%, and 46.1%, respectively, under drought. Thus, these findings suggest that L-arginine can improve the drought resistance of maize seedlings by upregulating their rate of photosynthesis and their antioxidant capacity.

Impact of heat priming on heat shock responses in Origanum vulgare: Enhanced foliage photosynthetic tolerance and biphasic emissions of volatiles

Climate change enhances the frequency of heatwaves that negatively affect photosynthesis and can alter constitutive volatile emissions and elicit emissions of stress volatiles, but how pre-exposure to mildly warmer temperatures affects plant physiological responses to subsequent severe heat episodes remains unclear, especially for aromatic plants with high and complex volatile defenses. We studied the impact of heat shock (45 °C/5 min) applied alone and after exposure to moderate heat stress (35 °C/1 h, priming) on foliage photosynthesis and volatile emissions in the aromatic plant Origanum vulgare through 72 h recovery period. Heat stress decreased photosynthesis rates and stomatal conductance, whereas the reductions in photosynthesis were primarily due to non-stomatal factors. In non-primed plants, heat shock-induced reductions in photosynthetic activity were the greatest, but photosynthetic activity completely recovered by the end of the experiment. In primed plants, a certain inhibition of photosynthetic activity remained, suggesting a sustained priming effect. Heat shock enhanced the emissions of volatiles including lipoxygenase pathway volatiles, long-chained fatty acid-derived compounds, mono- and sesquiterpenes, geranylgeranyl diphosphate pathway volatiles, and benzenoids, whereas different heat treatments resulted in unique emission blends. In non-primed plants, stress-elicited emissions recovered at 72 h. In primed plants, volatile emissions were multiphasic, the first phase, between 0.5 and 10 h, reflected the primary stress response, whereas the secondary rise, between 24 and 72 h, indicated activations of different defense metabolic pathways. Our results demonstrate that exposure to mild heat leads to a sustained physiological stress memory that enhances plant resistance to subsequent severe heat stress episodes.

Diurnal changes in the stomatal, mesophyll, and biochemical limitations of photosynthesis in well-watered greenhouse-grown strawberries

The diurnal variations in the factors of photosynthesis reduction under well-watered greenhouse conditions remain poorly understood. We conducted diurnal measurements of gas exchange and chlorophyll fluorescence in strawberries (Fragaria × ananassa Duch.) for three sunny days. Quantitative limitation analysis was also conducted to investigate the diurnal variations of photosynthetic limitations [stomatal (SL), mesophyll (MCL), and biochemical limitation (BL)]. Under well-watered greenhouse conditions, a photosynthesis reduction was observed, and the respective limitations exhibited different diurnal changes based on the environmental stress severity. The main limitation was SL, varying between 11.3 and 27.1% around midday, whereas MCL and BL were in 4.3-14.2% and 1.7-8.5%, respectively, under relatively moderate conditions. However, both SL (11.2-34.2%) and MCL (4.8-26.4%) predominantly limited photosynthesis under relatively severe conditions, suggesting that stomatal closure was the main limitation and that the decline in mesophyll conductance was not negligible under strong environmental stress, even under well-watered greenhouse conditions.

Influence of cosmic rays on environmental ecosystems

AbstractIt is presented a model to consider the effect of high energy cosmic rays on three types of terrestrial ecosystem: coastal macroalgae, lakes, and forests. The model includes insights into muon dosimetry based in the stopping power of muons while traveling in water and soft biological tissues. It is shown that a muon from secondary cosmic rays could deposit in cells an energy much higher than that deposited by ultraviolet photons coming from the Sun. Consequently, drastic short‐term reductions of photosynthesis are obtained if energetic astrophysical phenomena such as gamma ray bursts and neutron star mergers happen in our astronomical neighborhood, while radiational solar storms also cause considerable inhibition of photosynthesis.

Physiological and anatomical responses of Eugenia dysenterica to glyphosate

Abstract Brazil is among the countries that most use pesticides in the world. These chemicals cause undesirable changes in ecosystems, particularly the contamination of non-target native forest species through drift. The nuisances caused by pesticides go beyond environmental damage and include public health problems. The objective of this work was to evaluate the effects of glyphosate on leaf gas exchange, photosynthetic pigments and morphoanatomy of seedlings of Eugenia dysenterica. The visual toxicity, physiological and morphoanatomical characteristics of E. dysenterica, when exposed to concentrations of 0, 550, 1110 and 2220 g a.e. ha-1 of glyphosate, were analyzed. The results indicate that the herbicide caused toxicity in the leaves in all treatments. Reductions in photosynthesis (A), stomatal conductance (gs), and transpiration (E) at 47 DAA, were also identified. Glyphosate caused damage to the anatomical structures of E. dysenterica leaves. From the data analyzed it is possible to affirm that plants of E. dysenterica are sensitive to the action of glyphosate. Visible symptoms such as chlorosis and necrosis in the leaf edge are indicators that can be used by rural communities as a warning of the risk of contamination.

Nitric Oxide- and Sulfur-Mediated Reversal of Cadmium-Inhibited Photosynthetic Performance Involves Hydrogen Sulfide and Regulation of Nitrogen, Sulfur, and Antioxidant Metabolism in Mustard

This study aimed to test the role of hydrogen sulfide (H2S) in the responses regarding the nitric oxide- (NO) and sulfur (S)-mediated improvement in photosynthesis and growth under cadmium (Cd) stress in mustard (Brassica juncea L. cv. Giriraj), and integrate the mechanisms of S, nitrogen (N), and antioxidant metabolism. The plants grown with Cd (200 mg Cd kg−1 soil) exhibited reduced assimilation of S and N and diminished photosynthetic performance, which was associated with higher Cd accumulation-induced excess reactive oxygen species (ROS) production. The application of 100 μM of sodium nitroprusside (SNP, a NO donor) together with a more prominent concentration of S resulted in increased photosynthetic S- and N-use efficiency, production of non-protein thiols and phytochelatins, efficiency of enzymatic (superoxide dismutase, ascorbate peroxidase, and glutathione reductase), non-enzymatic antioxidants (ascorbate and glutathione) limiting Cd accumulation and, thus, reduced oxidative stress (superoxide radical, hydrogen peroxide, and thiobarbituric acid reactive species content). The benefit of NO together with S was manifested through a modulation in H2S production. The use of 100 μM of hypotaurine (HT; H2S scavenger) or 100 μM of cPTIO (2-4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) in plants treated with NO plus S reversed the action of NO plus S, with a higher reduction in photosynthesis and growth with the use of HT, suggesting that H2S plays a significant role in the NO- and S-mediated alleviation of Cd stress. The interplay of NO and ES with H2S may be used in augmenting the photosynthesis and growth of Cd-grown mustard plants.

Morphoanatomical, Physiological, and Biochemical Indicators in Lactuca sativa L. Germination and Growth in Response to Fluoride

Fluoride is one of the main phytotoxic environmental pollutants, and high concentrations (10-30 mg L-1) are commonly detected in surface and groundwater. Little, however, is known about the effects of this pollutant on crops that require irrigation during their development, which, in addition to phytotoxicity, may cause negative human health effects. Thus, the aim of this study was to characterize the effects of potassium fluoride (KF) on the germination of lettuce seeds and identify the physiological and anatomical markers of this pollutant's action on plants exposed to it during growth. Initially, lettuce seeds were sown in gerboxes and soaked in solutions containing 0 mg L-1, 10 mg L-1, 20 mg L-1, and 30 mg L-1 KF. Plants grown in a greenhouse were treated daily with KF irrigation at the same KF concentrations for 40 days. KF exposure reduced the germination rate and germination speed index of lettuce seeds at 20 mg L-1 and 30 mg L-1, resulting in compromised root development at the highest KF concentration. Lettuce plants displayed a slight photosynthesis reduction and a significant photochemical efficiency decrease after exposures to all KF concentrations. Lower chlorophyll contents and nitrogen balance indices were observed in plants exposed to 30 mg L-1 KF. On the other hand, increases in phenolic compounds and malondialdehyde were noted with increasing KF concentrations. Lettuce plants can, therefore, accumulate fluoride in leaves when irrigated with KF-rich water. The investigated physiological and biochemical variables were proven to be adequate fluoride action biomarkers in lettuce plants and may become an important tool in the study of olericulture contaminants.

Nitric Oxide and Salicylic Acid Regulate Glutathione and Ethylene Production to Enhance Heat Stress Acclimation in Wheat Involving Sulfur Assimilation.

Phytohormones have a role in stress adaptation. The major mechanism underlying the role of exogenously-sourced nitric oxide (NO; as sodium nitroprusside, SNP: 50.0 µM) and salicylic acid (SA; 0.5 mM) in the presence of 2.0 mM SO4-2 was assessed in heat stress (HS; 40 °C for 6 h daily for 15 days) tolerance in wheat (Triticum aestivum L. cv. HD-3226). The cultivar HD-3226 possessed high photosynthetic sulfur use efficiency (p-SUE) among the six cultivars screened. Plants grown under HS exhibited an increased content of reactive oxygen species (ROS; including superoxide radical and hydrogen peroxide) and extent of lipid peroxidation with a consequent reduction in photosynthesis and growth. However, both NO and SA were found to be protective against HS via enhanced S assimilation. Their application reduced oxidative stress and increased the activity of antioxidant enzymes. NO or SA supplementation along with S under HS recovered the losses and improved photosynthesis and growth. The use of SA inhibitor (2-aminoindane-2-phosphonic acid; AIP) and NO scavenger (cPTIO) confirmed that the mitigating effects of SA and NO involved induction in S assimilation.

Impact of Cadmium Stress on Growth and Physio-Biochemical Attributes of Eruca sativa Mill.

Plants may experience adverse effects from Cadmium (Cd). As a result of its toxicity and mobility within the soil-plant continuum, it is attracting the attention of soil scientists and plant nutritionists. In this study, we subjected young Eruca sativa Mill. seedlings to different levels of Cd applications (0, 1.5, 6 and 30 µmol/L) via pot experiment to explore its morpho-physio-biochemical adaptations. Our results revealed a significant Cd accumulation in leaves at high Cd stress. It was also demonstrated that Cd stress inhibited photosynthetic rate and pigment levels, ascorbate peroxidase (APX), guaiacol peroxidase (GPX), catalase (CAT), and superoxide dismutase (SOD) enzyme activities, and increased malondialdehyde (MDA) levels. Conversely, the concentration of total ascorbate (TAS) increased at all levels of Cd application, whereas that of ascorbic acid (ASA), and dehydroascorbate (DHA) increased at 1.5 (non-significant), 6, 30 and 6 µmol/L (significant), though their concentrations decreased non-significantly at 30 µmol/L application. In conclusion, Cd-subjected E. sativa seedlings diverted much energy from growth towards the synthesis of anti-oxidant metabolites and osmolytes. However, they did not seem to have protected the E. sativa seedlings from Cd-induced oxidative stress, causing a decrease in osmotic adjustment, and an increase in oxidative damage, which resulted in a reduction in photosynthesis and growth. Accordingly, we recommend that the cultivation of E. sativa should be avoided on soil with Cd contamination.

Effect of free ammonia shock on Chlorella sp. in wastewater: Concentration-dependent activity response and enhanced settleability

The unstable microbial activity and unsatisfactory settling performance impede the development and implementation of microalgal wastewater treatment, especially in high-ammonium wastewater in the presence of free ammonia (FA). The shock of FA due to the nutrient fluctuation in wastewater was demonstrated as the primary stress factor suppressing microalgal activities. Recent study has clearly revealed the inhibition mechanism of FA at a specific high level (110.97 mg/L) by inhibiting the genetic information processing, photosynthesis, and nutrient metabolism. However, the effects of various FA shock concentrations on microalgal activities and settling performance remain unknown, limiting the wastewater bioremediation efficiencies improvement and the process development. Herein, a concentration-dependent shock FA (that was employed on microalgae during their exponential growth stages) effect on microalgal growth and photosynthesis was observed. Results showed that the studied five FA shock concentrations ranging from 25 to 125 mg/L significantly inhibited biomass production by 14.7–57.0%, but sharp reductions in photosynthesis with the 36.0–49.0% decreased Fv/Fm values were only observed when FA concentration was above 75.0 mg/L. On the other hand, FA shock enhanced microalgal settling efficiency by 12.8-fold, which was believed to be due to the stimulated intra- and extracellular protein contents and thereby the enhanced extracellular polymer substances (EPS) secretion. Specifically, FA shock induced 40.2 ± 2.3% higher cellular protein content at the cost of the decreased carbohydrates (22.6 ± 1.3%) and fatty acid (39.0 ± 0.8%) contents, further improving the protein secretion by 1.21-fold and the EPS production by 40.2 ± 2.3%. These FA shock-induced variations in intra- and extracellular biomolecules were supported by the up-regulated protein processing and export at the assistance of excessive energy generated from fatty acid degradation and carbohydrates consumption. In addition, FA shock significantly decreased the biomass nutritional value as indicated by the 1.86-fold lower essential amino acid score and nearly 50% reduced essential to non-essential amino acids ratio, while slightly decreased the biodiesel quality. This study is expected to enrich the knowledge of microalgal activities and settling performance in response to fluctuant ammonium concentrations in wastewater and to promote the development of microalgal wastewater treatment.

The Impact of Polymer on the Productivity and Photosynthesis of Soybean under Different Water Levels

In order to practice sustainable and resource-efficient agriculture, the use of new technologies such as water-retaining polymers is essential. The objective of this study was to evaluate the effect of a polymer incorporated into the soil on gas exchange and yield under different water regimes (WR) in three soybean cultivars. The experiment was conducted at Embrapa Cerrados under field conditions in 2016 and 2017, using three different cultivars (BRS 5980IPRO, NA 5909RG and BRS 7280RR). Soybean cultivars were submitted to four water regimes (representing 30%, 50%, 83% and 100% of evapotranspiration replacement, namely WR1, WR2, WR3 and WR4). No beneficial results were observed in 2016 with Polymer. Most of the reductions in photosynthesis and transpiration by adding the polymer can be attributed to stomatal control, but such reductions did not influence productivity. In 2017, the yield was higher using Polymer in WR4 and WR3 by 40 to 20%, depending on the cultivar. Under severe stress (WR2 and WR1), reduced gas exchange was obtained with Polymer, but the yield was not reduced. These results indicate that Polymer contributed to the prolongation of photosynthetic activity during the reproductive phase of soybean and may represent a potential strategy for increasing yield under moderate drought stress.

Cell wall ester modifications and volatile emission signatures of plant response to abiotic stress.

Growth suppression and defence signalling are simultaneous strategies that plants invoke to respond to abiotic stress. Here, we show that the drought stress response of poplar trees (Populus trichocarpa) is initiated by a suppression in cell wall derived methanol (MeOH) emissions and activation of acetic acid (AA) fermentation defences. Temperature sensitive emissions dominated by MeOH (AA/MeOH <30%) were observed from physiologically active leaves, branches, detached stems, leaf cell wall isolationsand whole ecosystems. In contrast, drought treatment resulted in a suppression of MeOH emissions and strong enhancement in AA emissions together with volatiles acetaldehyde, ethanol, and acetone. These drought-induced changes coincided with a reduction in stomatal conductance, photosynthesis, transpiration, and leaf water potential. The strong enhancement in AA/MeOH emission ratios during drought (400%-3500%) was associated with an increase in acetate content of whole leaf cell walls, which became significantly 13 C2 -labelled following the delivery of 13 C2 -acetate via the transpiration stream. The results are consistent with both enzymatic and nonenzymatic MeOH and AA production at high temperature in hydrated tissues associated with accelerated primary cell wall growth processes, which are downregulated during drought. While the metabolic source(s) require further investigation, the observations are consistent with drought-induced activation of aerobic fermentation driving high rates of foliar AA emissions and enhancements in leaf cell wall O-acetylation. We suggest that atmospheric AA/MeOH emission ratios could be useful as a highly sensitive signal in studies investigating environmental and biological factors influencing growth-defence trade-offs in plants and ecosystems.

Moderate photoinhibition of PSII and oxidation of P700 contribute to chilling tolerance of tropical tree species in subtropics of China

In the subtropics, a few tropical tree species are distributed and planted for ornamental and horticultural purposes; however, the photosynthesis of these species can be impaired by chilling. This study aimed to understand how these species respond to chilling. Light-dependent and CO₂ assimilation reactions of six tropical tree species from geographically diverse areas, but grown at a lower subtropical site in China, were monitored during a chilling (≤ 10°C). Chilling induced stomatal and nonstomatal effects and moderate photoinhibition of PSII, with severe effect in <i>Ixora chinensis</i>. <i>Woodfordia fruticosa</i> was little affected by chilling, with negligible reduction of photosynthesis and PSII activity, higher cyclic electron flow (CEF), and oxidation state of P700 (P700⁺). Photoinhibition of PSII thus reduced electron flow to P700, while active CEF reduced oxidative damage of PSI and maintained photosynthesis during chilling. Studied parameters revealed that coupling between light-dependent and CO₂ assimilation reactions was enhanced under chilling.

Limited effects of shade on physiological performances of cocoa (Theobroma cacao L.) under elevated temperature

Shade is one of the recommended management solutions to mitigate the effects of heat stress, which is a major challenge for cocoa production globally. Nevertheless, there are limited studies to verify this hypothesis. Here, we evaluate the effects of heat and shade on cocoa physiology using experimental plots with six-month old potted seedlings in a randomized complete block design. Infrared heaters were applied for one month to increase leaf temperatures by an average of 5–7 ºC (heat treatment) compared with no heat (unheated treatments), and shaded plants were placed under a shade net removing 60% of the light compared with no shade (sun treatments). Plants under heat treatments in sun and in shade showed severe reduction in photosynthesis. Measurements of chlorophyll fluorescence and photosynthetic light response curves indicated that heat caused damages at photosystem II and additionally resulted in lower rates of maximal photosynthesis. Temperature optima for photosynthesis were at 31–33 ºC with only small differences between treatments, and as light saturation was reached at low PAR levels of 325 – 380 µmol m −2 s −1 in shade and 427 – 521 µmol m −2 s −1 in sun, ambient rates of photosynthesis were comparable between sun and shade treatments. Heat treatments resulted in decreased concentrations of chlorophyll and changed pigment composition, reduced specific leaf areas, and plant biomass. While shade may benefit cocoa seedlings, our results indicate that the positive effects may not be sufficient to counteract the negative effects of increased temperatures on cocoa physiology. • Heat is imposed on six-month old cocoa seedlings and shade is provided. • Heat treated plants show severe reduction in photosynthesis and damages at photosystem II. • Heat decreases chlorophyll concentrations and pigment composition. • Shade improves cocoa physiology but has limited effects on heat.

Evaluation of Photosynthetic Roles of Different Canopy Strata and Capitulum on Seed Yield and its Components of Spring Safflower (Carthamus tinctorius L.)

The main source of seed filling results from the photosynthesis of the green tissue closest to the seed sinks in the capitula. To evaluate the role of different leaf strata and capitula in seed yield and its components of Safflower genotypes, a field study was performed as a factorial experiment based on RCBD in 3 replicates in East Azarbaijan Agricultural and Natural Resources Research and Education Center in 2008. The used factors in this experiment were: two Safflower genotypes including (Mahalli Esfahan and Goldasht) and defoliation in five levels: defoliation of plants in lower 1/3, middle 1/3, upper 1/3 of the stem, capitulum covered with aluminum paper and control (without defoliation). The results showed that defoliation did not affect plant height and number of pods. But, there was a highly significant difference between strata in terms of number of seeds per pod, number of seeds per plant, 1000 seeds weight, oil percentage and oil yield. The interaction of genotype×strata treatments in seeds yield and harvest index was significant. Among the defoliation treatment levels in both genotypes, the highest decrease in the seed yield compared to the control were observed in the upper 1/3 defoliation levels, whereas the lowest decrease was observed in the lower 1/3 defoliation level. The rate of seed yield reduction in Mahalli Esfahan was higher than Goldasht. The change in Goldasht seed yield was mostly due to changes in the number of seeds per plant and the number of seeds in the head. In addition, net photosynthesis, strata leaf area, and photosynthesis contribution of the upper strata compared to the lower ones were higher, and removal of the upper strata had the highest effect on seed yield through the reduction in the total photosynthesis of the whole plant. Also, covering the capitulum caused a significant decrease in the seed yield. So, head photosynthesis has a major contribution to Safflower seed yield.