Table_1_Abscisic acid activates desiccation tolerance responses in intertidal seaweed Neoporphyra haitanensis.docx

Intertidal macroalgae have adapted to deal with environmental stresses, in particular desiccation. The phytohormone abscisic acid (ABA) plays an important role in the regulation of a suite of critical responses in plants, including desiccation tolerance. The red alga Neoporphyra haitanensis contains a high level of ABA, but its mechanism of action in N. haitanensis is unknown. In this study, the effect of ABA treatment on the relative water content of thalli during the dehydration-rehydration cycle was evaluated and it was identified that ABA treatment resulted in decreased thalli water loss and an accelerated rehydration process. The effects of addition of ABA upon the activation of antioxidant responses, photosynthetic parameters and gene transcription profiles of N. haitanensis were also evaluated. The results revealed that exogenous ABA regulated the activation of the antioxidant system, including by increasing the activity of antioxidant enzymes, increasing the concentrations of ascorbic acid (AsA) and glutathione (GSH), as well as upregulating the expression of genes encoding antioxidant enzymes and enzymes that synthesize AsA and GSH. ABA treatment also inhibited photosynthesis by reducing light capture and down-regulating the Calvin cycle to save energy; ABA supplementation further simultaneously activated repair mechanisms to avoid excessive DNA and protein damage. The results presented herein demonstrate that ABA plays a crucial role in the regulation of stress tolerance in seaweeds, which may be of great importance when examining the adaptation of this organism to the intertidal environment.

潮间带大型藻类已演化出应对环境胁迫的适应性策略，尤其针对脱水胁迫。植物激素脱落酸（abscisic acid，ABA）在植物调控包括脱水耐性在内的一系列关键胁迫应答过程中发挥重要作用。红藻坛紫菜（Neoporphyra haitanensis）自身含有高水平的脱落酸，但其在该物种中的作用机制尚未明确。本研究首先评估了ABA处理在脱水-复水循环过程中对藻体相对含水量的影响，结果显示ABA处理可降低藻体水分流失速率并加速复水过程。本研究同时还评估了外源ABA添加对坛紫菜抗氧化应答激活、光合参数以及基因转录谱的影响。结果表明，外源脱落酸可调控抗氧化系统的激活：具体包括提升抗氧化酶活性、增加抗坏血酸（ascorbic acid，AsA）与谷胱甘肽（glutathione，GSH）的含量，以及上调编码抗氧化酶以及抗坏血酸与谷胱甘肽合成酶的基因的表达水平。此外，ABA处理还可通过降低光捕获能力、下调卡尔文循环（Calvin cycle）以节约能量，从而抑制光合过程；同时外源ABA补充还能同步激活修复机制，避免DNA与蛋白质受到过度损伤。本研究结果证实，脱落酸在海藻胁迫耐受性调控中发挥关键作用，这对于解析该物种对潮间带环境的适应性机制具有重要意义。