Abstract
BackgroundWater spinach (Ipomoea aquatica) is an important heat-resistant leafy vegetable that can survive under long-time heat stress condition. However, the physiological characteristics and molecular changes in its response to heat stress are poorly understood.ResultsIn this study the selected water spinach cultivars with different thermo resistance and their physiological response to heat stress were examined. Under prolonged heat stress, plant growth was inhibited in all tested cultivars. This inhibition was accompanied by the reduction of photosynthetic performance. The reactive oxygen species system in terms of superoxide and hydrogen peroxide contents, as well as antioxidant polyphenols, were evaluated. The results showed that prolonged heat stress caused reduced antioxidant capacity, but the role of antioxidant capacity in a prolonged thermotolerance was not predominant. Transcriptomic analysis of the water spinach subjected to heat stress revealed that 4145 transcripts were specifically expressed with 2420 up-regulated and 1725 down-regulated in heat-sensitive and heat-tolerant cultivars treated with 42 °C for 15 days. Enrichment analysis of these differentially expressed genes showed that the main metabolic differences between heat-sensitive and heat-tolerant cultivars were the carbohydrate metabolism and phenylpropanoid biosynthesis. The results of carbohydrate profiles and RT-qPCR also suggested that heat stress altered carbohydrate metabolism and associated changes in transcriptional level of genes involved in sugar transport and metabolic transition.ConclusionsThe prolonged heat stress resulted in a reduced antioxidant capacity while the role of antioxidant capacity in a prolonged thermotolerance of water spinach was not predominant. Transcriptome analysis and the measurement of carbohydrates as well as the gene expression evaluation indicated that the response of the metabolic pathway such as carbohydrate and phenylpropanoid biosynthesis to heat stress may be a key player in thermo resistance.
Highlights
Water spinach (Ipomoea aquatica) is an important heat-resistant leafy vegetable that can survive under long-time heat stress condition
It has been reported that heat tolerant plants have stronger scavenging reactive oxygen species (ROS) genes compared with heat sensitive ones [8] and that enhancing the activity of antioxidant enzymes could improve the tolerance of plant to heat stress [9]
Compared with the cultivars cultured at 25 °C, the content of chlorophyll a (Fig. 1e) in all cultivars decreased after heat exposure
Summary
Water spinach (Ipomoea aquatica) is an important heat-resistant leafy vegetable that can survive under long-time heat stress condition. The physiological characteristics and molecular changes in its response to heat stress are poorly understood. Heat stress occurs when plants exposed to temperatures above the optimal for growth for some time. Reactive oxygen species (ROS) were produced and accumulated in different organisms which would cause the oxidative stress in plants. The transcription factors related to growth and development were repressed by long-term heat stress in swichgrass (Panicum virgatum) [12] while a large amount of transcription factors were induced by short-term heat stress in wheat (Triticum aestivum) [13]. The common genes identified in short-term and long-term heat stress are related with protein folding and unfolding [12,13,14]
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