Abstract
Heat stress is a major environmental stress that limits plant growth and yield worldwide. The present study was carried out to explore the physiological mechanism of heat tolerant to provide the theoretical basis for heat-tolerant breeding. The changes of leaf morphology, anatomy, nitrogen assimilation, and carbohydrate metabolism in two wucai genotypes (WS-1, heat tolerant; WS-6, heat sensitive) grown under heat stress (40°C/30°C) for 7 days were investigated. Our results showed that heat stress hampered the plant growth and biomass accumulation in certain extent in WS-1 and WS-6. However, the inhibition extent of WS-1 was significantly smaller than WS-6. Thickness of leaf lamina, upper epidermis, and palisade mesophyll were increased by heat in WS-1, which might be contributed to the higher assimilation of photosynthates. During nitrogen assimilation, WS-1 possessed the higher nitrogen-related metabolic enzyme activities, including nitrate reductase (NR), glutamine synthetase (GS), glutamate synthase (GOGAT), and glutamate dehydrogenase (GDH), which were reflected by higher photosynthetic nitrogen-use efficiency (PNUE) with respect to WS-6. The total amino acids level had no influence in WS-1, whereas it was reduced in WS-6 by heat. And the proline contents of both wucai genotypes were all increased to respond the heat stress. Additionally, among all treatments, the total soluble sugar content of WS-1 by heat got the highest level, including higher contents of sucrose, fructose, and starch than those of WS-6. Moreover, the metabolism efficiency of sucrose to starch in WS-1 was greater than WS-6 under heat stress, proved by higher activities of sucrose phosphate synthase (SPS), sucrose synthase (SuSy), acid invertase (AI), and amylase. These results demonstrated that leaf anatomical alterations resulted in higher nitrogen and carbon assimilation in heat-tolerant genotype WS-1, which exhibited a greater performance to resist heat stress.
Highlights
Heat stress due to high temperature is a serious threat to crop production and quality worldwide [1]
Compared to their respective controls, the stem diameter, fresh and dry weight of WS-1 were significantly declined by 10.47%, 8.37%, and 44.29% under heat stress, respectively; the above indexes were decreased by 11.87%, 17.67%, and 57.14% in WS-6
The present study focused on the response of plant morphology, leaves anatomy characteristics, nitrogen and carbohydrate metabolism in wucai exposed to high temperature
Summary
Heat stress due to high temperature is a serious threat to crop production and quality worldwide [1]. Transitory or constantly high temperatures could cause an array of morpho-anatomical, physiological, and biochemical changes in plants, which affected plant growth, development, and even phenology and might lead to a drastic decline in economic yield [2,3]. In recent years, this issue has become more urgent due to the global warming. Yuan et al / Influence of heat stress in two wucai genotypes using various genetic approaches has become the effective way to mitigate the heat stress For this purpose, the thorough understanding of physiological responses to heat, mechanisms of heat tolerance, and possible strategies are imperative in vegetable production. Disturbance of fundamental processes such as carbon and nitrogen assimilation, respiration, and transpiration may reduce overall metabolic efficiency and result in vegetative developmental defects [7,8]
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