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Elymus nutans Griseb. is a dominant forage in the Qinghai–Tibetan Plateau. However, the combined cold and drought (CD) stress is a major problem inhibiting its growth, development, and yield. Here, the responses of morphological, photosynthetic, osmoregulation levels, and signal transduction under cold, drought, and CD stress were explored. Both cold- and drought-stressed plants showed varying degrees of damage. In addition, CD stress led to more severe damage than single stress, especially in total biomass, photosynthetic capacity, and electron transfer efficiency. The total biomass, net photosynthetic rate, and maximal quantum yield of photosystem II (PSII) photochemistry reduced by 61.47%, 95.80%, and 16.06% in comparison with the control, respectively. Meanwhile, CD stress was accompanied by lower chlorophyll contents, down-regulated expression level of key photosynthetic enzymes (EnRbcS, EnRbcL, and EnRCA), stomatal closure, disrupted chloroplast ultrastructure, and reduced starch content. Furthermore, CD stress induced some adaptability responses in cold- and drought-tolerant E. nutans seedlings. The combined stress provoked alterations in both cold- and drought-related transcription factors and responsive genes. EnCBF12, EnCBF9, EnCBF14, and EnCOR14α were significantly up-regulated under cold or drought stress, and the transcript level of EnCBF3 and EnCBF12 was even 2.94 and 12.59 times higher than control under CD treatment, which indicated the key role of transcription factors activation in coping with CD stress. In addition, the content of soluble sugar, reducing sugar, proline, glycine betaine, and other osmolytes was significantly improved under CD stress. Therefore, we demonstrated that exposure to CD stress led to severe morphological and photosynthetic damage and revealed the acclimation to the cold and drought stress combination via osmotic adjustment and transcription factors activation in the Tibetan wild E. nutans. [ABSTRACT FROM AUTHOR]

Rice is widely planted and serves as staple food in the world, but it is often exposed to acid rain and rice blast (Pyricularia oryzae). In this work, we analyzed the effects of co-exposure to simulated acid rain (SAR) and P. oryzae on the photosynthetic growth of rice seedlings. We found that the growth, photosynthesis, and chloroplast ultrastructure of rice seedlings were damaged under single treatments of P. oryzae and strong acid rain (pH 2.0) but increased under medium acidity acid rain (pH 4.0). Similarly, when plants were exposed to both P. oryzae and acid rain, pH 4.0 mitigated the changes of growth, photosynthetic characteristics, and chloroplast ultrastructure induced by P. oryzae, but pH 2.0 aggravated these changes. In addition, we found that significant differences in chlorophyll content (chlorophyll a and chlorophyll b) correlated with transpiration rate (Tr) under the combined stress of acid rain and P. oryzae at pH 4.0 and pH 2.0. Medium-acidity acid rain alleviated the harm caused by P. oryzae on rice growth by enhancing synergistic regulatory mechanisms of photosynthetic traits to increase plant resistance tolerance. The effect of P. oryzae on photosynthetic traits of rice was regulated by acidity of acid rain.

This paper aims to elucidate the effects of exogenous brassinolide (BL) on maize germination and seedling growth under chilling stress. The cold-resistant maize hybrid Tiannong 9 and the cold-sensitive hybrid Tianhe 1 were soaked at the germination stage (6 °C) and leaves were sprayed at seedling stage (4 °C), with BL at concentrations of 0, 0.01, 0.1, and 1 mg/L. The germination rate of the maize seeds and the changes in seedling biomass, antioxidant, photosynthetic, and plant endogenous hormone systems and chloroplast ultrastructures were determined. The results showed that the optimum concentration of BL to alleviate chilling stress in maize seedlings was 0.1 mg/L. This rate effectively increased the germination rate and plant biomass of maize and significantly increased the superoxide dismutase (SOD) peroxidase (POD) and catalase (CAT) activities, the net photosynthetic rate (Pn), stomatal conductance (gs) and transpiration rate (Tr), and seedling auxin (IAA), gibberellin (GA3) and trans zeatin nucleoside (t-ZR) contents under chilling stress. In addition, BL significantly reduced the malondialdehyde (MDA) content, abscisic acid (ABA) content, and intercellular carbon dioxide concentration (Ci). In the comparison of mesophyll cells, the chloroplast membrane of the treatment group was tightly attached to the stroma, and some of the plasma membranes were dissolved, but the overall structure of the chloroplast was relatively complete, and the osmiophilic granules were relatively few. The exogenous application of BL can effectively alleviate the damage caused by a low temperature in maize, maintain the normal characteristics of seedlings in chilling environments, and ensure the development and growth of plant tissue in the later stage.

Rice is widely planted and serves as staple food in the world, but it is often exposed to acid rain and rice blast (Pyricularia oryzae). In this work, we analyzed the effects of co-exposure to simulated acid rain (SAR) and P. oryzae on the photosynthetic growth of rice seedlings. We found that the growth, photosynthesis, and chloroplast ultrastructure of rice seedlings were damaged under single treatments of P. oryzae and strong acid rain (pH 2.0) but increased under medium acidity acid rain (pH 4.0). Similarly, when plants were exposed to both P. oryzae and acid rain, pH 4.0 mitigated the changes of growth, photosynthetic characteristics, and chloroplast ultrastructure induced by P. oryzae, but pH 2.0 aggravated these changes. In addition, we found that significant differences in chlorophyll content (chlorophyll a and chlorophyll b) correlated with transpiration rate (Tr) under the combined stress of acid rain and P. oryzae at pH 4.0 and pH 2.0. Medium-acidity acid rain alleviated the harm caused by P. oryzae on rice growth by enhancing synergistic regulatory mechanisms of photosynthetic traits to increase plant resistance tolerance. The effect of P. oryzae on photosynthetic traits of rice was regulated by acidity of acid rain. [ABSTRACT FROM AUTHOR]

Salt stress is one of the primary abiotic stresses that negatively affects agricultural production. Melatonin, as a useful hormone in plants, has been shown to play positive roles in crop improvement to abiotic stress conditions. However, it remains unclear whether spraying melatonin could reduce the halotolerance gap between tomato genotypes with different salt sensitivities. Here, plant growth, H2O2 content, electrolyte leakage, antioxidant system, gas exchange, pigment content, and chloroplast ultrastructure of salt sensitive genotype (SG) and resistant genotype (RG) at CK (control), M (spraying melatonin), S (salt), and SM (spraying melatonin under salt stress) were investigated. The results showed that the weight, height, and stem diameter of the plant at SM from both genotypes significantly increased compared with S. The plant undergoing SM from both genotypes showed significantly decreased H2O2 but increased activity of SOD, APX, GR, and GSH, as well as net photosynthetic rate and Fv/Fm, as compared with S. The ratio between SM and S (SM/S) of SG was significantly higher than that of RG in terms of plant height and stem diameter, whereas antioxidant parameters, H2O2 content, and electrolyte leakage showed no difference between RG and SG in SM/S. The SM/S of SG in terms of photosynthetic parameters and pigment content were significantly higher than that of RG. Chloroplast ultrastructure showed remarkable changes under salt stress, whereas spraying melatonin reduced the destruction of chloroplasts, especially for SG. We concluded that spraying melatonin reduces the halotolerance gap between SG and RG by photosynthesis regulation instead of the antioxidant mechanism. This indicated that the positive roles of melatonin on tomato plants at salt stress depend on the genotype sensitivity. [ABSTRACT FROM AUTHOR]

This paper aims to elucidate the effects of exogenous brassinolide (BL) on maize germination and seedling growth under chilling stress. The cold-resistant maize hybrid Tiannong 9 and the cold-sensitive hybrid Tianhe 1 were soaked at the germination stage (6 °C) and leaves were sprayed at seedling stage (4 °C), with BL at concentrations of 0, 0.01, 0.1, and 1 mg/L. The germination rate of the maize seeds and the changes in seedling biomass, antioxidant, photosynthetic, and plant endogenous hormone systems and chloroplast ultrastructures were determined. The results showed that the optimum concentration of BL to alleviate chilling stress in maize seedlings was 0.1 mg/L. This rate effectively increased the germination rate and plant biomass of maize and significantly increased the superoxide dismutase (SOD) peroxidase (POD) and catalase (CAT) activities, the net photosynthetic rate (Pn), stomatal conductance (gs) and transpiration rate (Tr), and seedling auxin (IAA), gibberellin (GA3) and trans zeatin nucleoside (t-ZR) contents under chilling stress. In addition, BL significantly reduced the malondialdehyde (MDA) content, abscisic acid (ABA) content, and intercellular carbon dioxide concentration (Ci). In the comparison of mesophyll cells, the chloroplast membrane of the treatment group was tightly attached to the stroma, and some of the plasma membranes were dissolved, but the overall structure of the chloroplast was relatively complete, and the osmiophilic granules were relatively few. The exogenous application of BL can effectively alleviate the damage caused by a low temperature in maize, maintain the normal characteristics of seedlings in chilling environments, and ensure the development and growth of plant tissue in the later stage. [ABSTRACT FROM AUTHOR]