Role of Glutathione-Ascorbate Cycle and Photosynthetic Electronic Transfer in Alternative Oxidase-Manipulated Waterlogging Tolerance in Watermelon Seedlings

Alternative oxidase (AOX) has been documented to mitigate the oxidative stress caused by abiotic stresses. However, it remains unknown how AOX regulates the antioxidant system and photosynthesis under waterlogging. To address this issue, we used two watermelon (Citrullus lanatus L.) cultivars (waterlogging tolerant cultivar ‘YL’ and sensitive cultivar ‘Zaojia8424’) as materials and the AOX inhibitor salicylhydroxamic acid (SHAM) to investigate the effects of AOX on photosynthesis and reactive oxygen species metabolism under waterlogging. We found that waterlogging decreased leaf photosynthesis and quantum yield of photosynthesis in watermelon, and the waterlogging tolerant cultivar ‘YL’ showed higher expression level of ClaAOX than the sensitive cultivar ‘Zaojia8424’. Net photosynthesis rate was higher in ‘YL’ than ‘Zaojia8424’. Moreover, waterlogging induced photoinhibition in ‘Zaojia8424’ but not in ‘YL’. Meanwhile, waterlogging promoted the accumulation of superoxide and peroxide hydrogen, and triggered oxidative damage. ‘YL’ suffered from less severe oxidative damage due to increased contents of ascorbate, a higher ratio of reduced glutathione (GSH) to oxidized glutathione (GSSG), a higher activity of ascorbate peroxidase (APX) and catalase (CAT), and enhanced levels of CAT and APX expression, relative to ‘Zaojia8424’. However, the alleviation of photosynthesis and oxidative damage, increased content of ascorbate and higher GSH/GSSG ratio were abolished by SHAM. Our results suggested that photosynthetic electronic transfer and glutathione-ascorbate cycle are involved in waterlogging tolerance mediated by the AOX pathway in watermelon.

Nitrate Increases Cadmium Accumulation in Sweet Sorghum for Improving Phytoextraction Efficiency Rather Than Ammonium

Sweet sorghum has potential for phytoextraction of cadmium (Cd) owning to its large biomass and relatively high Cd tolerance. Nitrogen affects both growth and Cd concentrations in plants. However, different forms of nitrogen effects on Cd accumulation in sweet sorghum to improve efficiency of Cd phytoremediation is still elusive. In this study, nitrate substantially promoted both dry weight and Cd concentrations in leaves, stems + sheaths and roots of sweet sorghum when compared with ammonium. As a result, Cd accumulation in nitrate-supplied sweet sorghum was around 3.7-fold of that in ammonium-supplied plants under unbuffered pH condition, while the fold was about 2.2 under buffered pH condition. We speculated pH values and Cd species in the growth medium to some extent contributed to increased Cd accumulation as affected by nitrate. Net photosynthesis rate and Fv/Fm of nitrate-treated plants under Cd stress were higher than that of ammonium-treated plants when the pH was unbuffered. Responses of antioxidant capacity in roots to Cd stress with nitrate application were stronger than that with ammonium supplementation. Taken together, nitrate is more suitable than ammonium for Cd phytoextraction by using sweet sorghum, which is able to enhance at least double efficiency of phytoextraction.

Features Of Photosynthesis And Water Regime Of Quercus Pubescens Willd. Under The Conditions Of Autumn Drought Of The Southern Coast Of The Crimea

The objective of the research is to determine the optimal zones and thresholds of soil moisture, temperature, illumination, limiting photosynthesis and transpiration of Quércus pubéscens Willd. and allowing the introduction of the species to other regions. The dependences of the net photosynthesis rate (Pn) and the transpiration rate (E) on stomatal conductivity (gs), leaf temperature (Tl), and soil moisture (Ws) are shown. The ratio of the processes of photosynthesis and respiration, under the influence of soil drought, allowed us to define their optimal values: Ws = 26 – 28%, Pn = 16 –18 μmol/m2c, Rt = 2 – 4 μmol/m2c. The relationship between the net photosynthesis rate, total respiration, and leaf temperature allowed us to determine the temperature maximum of net photosynthesis (the thermal compensation point): Pn = Rt = 2.0 μmol/m2c at Tl = 37ºC. It was found that in the absence of soil drought, the proportion of respiratory costs (Rt/Pg) from true photosynthesis is 20 – 23%, and with soil moisture of 8 – 10% increases to 55 – 58%.

Local and Systemic Changes in Photosynthetic Parameters and Antioxidant Activity in Cucumber Challenged with Pseudomonas syringae pv lachrymans

We studied changes in gas exchange, photochemical activity and the antioxidant system in cucumber leaves locally infected with Pseudomonas syringae pv lachrymans and in uninfected systemic ones. Infection-induced declined net photosynthesis rate and the related changes in transpiration rate, the intracellular CO2 concentration, and prolonged reduction in maximal PSII quantum yield (Fv/Fm), accompanied by an increase in non-photochemical quenching (NPQ), were observed only in the infected leaves, along with full disease symptom development. Infection severely affected the ROS/redox homeostasis at the cellular level and in chloroplasts. Superoxide dismutase, ascorbate, and tocopherol were preferentially induced at the early stage of pathogenesis, whereas catalase, glutathione, and the ascorbate–glutathione cycle enzymes were activated later. Systemic leaves retained their net photosynthesis rate and the changes in the antioxidant system were partly like those in the infected leaves, although they occurred later and were less intense. Re-balancing of ascorbate and glutathione in systemic leaves generated a specific redox signature in chloroplasts. We suggest that it could be a regulatory element playing a role in integrating photosynthesis and redox regulation of stress, aimed at increasing the defense capacity and maintaining the growth of the infected plant.

Accumulation of Airborne Toxic Elements and Photosynthetic Performance of Lolium multiflorum L. Leaves

In this study, we aimed to investigate the accumulation of airborne trace elements in Lolium multiflorum leaves concerning photosynthetic activity parameters. Five sites for four 28-day series of plant exposition were selected. The concentration of trace elements in leaves was measured after each series, while photosynthetic activity parameters were measured three times during each series. Net photosynthesis rate (PN) and stomatal conductance (gs) were mostly negatively associated with all analyzed trace elements, unlike to CO2 concentrations (Ci). Arsenic was found with opposite trend in two exposure series. The high accumulation of Cd and Pb in plants recorded at two sites was mostly related to lowest PN and gs. Similar tendency for PN was found at sites and series with the highest Cr and Ni content in plants. L. multiflorum revealed a medium-level accumulation of trace elements and a low tolerance of the photosynthetic process to the presence of trace elements in ambient air.

Possibility of Increasing the Growth and Photosynthetic Properties of Precocious Walnut by Grafting

Plant growth characteristics after grafting are mainly dependent on photosynthesis performance, which may be influenced by grafting combinations with different rootstocks and scions. In this study, we used one-year-old walnut grafts to investigate the grafting compatibility between precocious (‘Liaoning 1’, L) and hybrid (‘Zhong Ning Sheng’, Z) walnut, as well as rootstock and scion impact on the growth and photosynthetic properties of walnut trees. The results showed that grafting compatibility between the two varieties is high, with survival rates upward of 86%. Overwintering survival of grafted seedlings was as high as 100%, which indicated that the allopolyploid had good resistance to low-temperature stress. The homograft of the hybrid walnut had the highest net photosynthesis rate (18.77 μmol·m−2s−1, Z/Z) and growth characteristics, which could be due to its higher transpiration rate and stomatal conductance, whereas the homograft of precocious walnut presented the lowest net photosynthesis rate (15.08 μmol·m−2s−1, L/L) and growth characteristics. Significant improvements in the net photosynthesis rate (15.97 and 15.24 μmol·m−2s−1 for L/Z and Z/L, respectively) and growth characteristics of precocious walnut were noticed during grafting of the hybrid walnut, which could have been contributed by their transpiration rate. The results of this study serve as a guide for the selection and breeding of good rootstock to improve plant growth characteristics and photosynthetic efficiency. We conclude that good rootstock selection improves plant growth potential and could play an important role in sustainable production.

Application of Anti-Transpirant to Control Sugar Accumulation in Grape Berries and Alcohol Degree in Wines Obtained from Thinned and Unthinned Vines of cv. Falanghina (Vitis vinifera L.)

In the last few decades, the accumulation of sugar in grape berries and hence the alcohol degree of wines has been affected by increasing global temperatures. In order to limit plant photosynthetic activity, it is possible to apply anti-transpirant on field, reducing sugar accumulation in berries. In this contest, our aim was to evaluate the efficiency of the application of a di-1-p-menthene-based natural anti-transpirant (Vapor Gard®, VG) on Falanghina vines during 2013 and 2014. Plants were treated at veraison stage with VG and compared with water-sprayed ones for control. The experimental design included also bunch thinned (BT) plants treated with VG or water. The effect of VG and/or BT on grapes was evaluated through physiological measurements on vines and chemical analyses on berries and wines. Moreover, wine sensory profiles were produced. The results we obtained show that by applying anti-transpirant it is possible to induce a significant reduction of net photosynthesis rate (25%–40%) and stomatal conductance (40%–60%) on leaves, a lower sugar accumulation in berries (2 °Brix) and a consequent reduction of alcohol in the obtained wine (0.9%–1.6% vol.). These results suggest that anti-transpirant sprays could be a useful tool in reducing cost of yield manipulation, improving ripeness and reducing wine alcohol, without affecting the wine sensory profile.

Investigating the variations of soil fertility and Sorghum bicolor L. physiological performance under plantation of some Acacia species

Taking the importance of agricultural production sustainability with limited resources to use efficiency in an arid area, afield experiment was designed to investigate the effect of three, Acacia trees (Acacia nilotica, A. seyal, and A. tortilis) planting combination on soil fertility and Sorghum bicolor L. growth and physiological performance. The sorghum planted in 7 strips between 14 rows of Acacia trees planting combinations and one treeless strip as control. Acacia species plantations significantly increase soil fertility in terms of available nitrogen (N), phosphorus (P), potassium (K) and organic carbon (OC) contents as compared to control, highest level of N and P content (59.01 ± 1.45 and 58.77 ± 1.10 mg/kg) was reported in strip between rows of A. tortilis. Although the highest net photosynthesis rate (P_n) and stomatal conductance (g_s) recorded in plants grown between rows of pure A. torilis, and rows of A. torilis–A. seyal, but different Acacia significantly enhanced sorghum growth and physiology with reference to net photosynthesis rate, stomatal conductance and chlorophyll fluorescence (chlF). The results stated linear relation between soil nutrients (N, P, K), P_n, and chlF increasing soil fertility improve physiological performance of sorghum. In conclusion, the three Acacia improve soil fertility and sorghum growth. Generally, this plantation trial can be environment-friendly alternative agricultural practices in Saudi Arabia or any area with a similar ecological condition to amend the soil and improve crop performance.

Ethylene-insensitive Arabidopsis mutants etr1-1 AND ein2-1 have decreased freezing tolerance

The freezing tolerance of Arabidopsis thaliana (L.) Heynh. was studied in relation to functioning of the ethylene signaling pathway. Constitutive freezing tolerance was compared in wild-type plants (ecotype Col-0) and ethylene-insensitive mutants etr1-1 and ein2-1. For the first time it was established that ethylene-insensitive mutants had by 25-30% lower net photosynthesis rate, the decreased content of soluble sugars and, as a result, lower freezing tolerance. Our work provides evidence that perception and transduction of ethylene signal are necessary for constitutive tolerance of Arabidopsis to low temperature.

Physiological responses of garden roses to hot and humid conditions

Garden roses do not grow well under hot and humid conditions. The objective of this study was to investigate the physiological responses of ‘Marie Curie’ and ‘Lapjau’ to high temperatures and relative humidity. The study included temperatures of 25/18°C (day/night) and 35/28°C (day/night), and relative humidity of 70% and 100%. ‘Marie Curie’ was more tolerant to heat stress than ‘Lapjau’ based on relative electrolyte leakage (REL), malondialdehyde (MDA), and activities of superoxide dismutase (SOD). The heat tolerance of cultivars also was confirmed by the levels of chlorophyll content and the net photosynthesis rate. Both cultivars were more stressed under more water vapour deficit than saturated vapour at 35/28°C (day/night), while at 25/18°C (day/night) the cultivars were more stressed under saturated humidity condition than at 70% relative humidity. In conclusion, combined hot and saturated humidity does not necessarily result in increased stress over separated heat or humidity elevations to the garden roses. Rose growers can use this information in regions where hot and humid conditions concur.