根系质外体屏障在老芒麦适应干旱逆境中的作用机制初探

Apoplastic barriers are important strategy for plant to adapt to the environmental stresses such as drought. As two types of root apoplastic barriers, suberin lamellae and casparian strip provide the main resistance of radial transport of water via transcellular and apoplastic pathway, which is likely to play a vital role in drought tolerance. However, little was known on the functional mechanism because plants used in the very small number of researches were the drought-sensitive plants such as Arabidopsis and rice. In this project, a xero-mesophyte Elymus sibiricus, which has developed roots, was taking as material, the following experiments would be done: through comprehensive evaluation on drought-resistance of 10 Elymus sibiricus accessions and cultivars, a drought-tolerant variety, a moderately tolerant variety and a sensitive variety were selected to compare the difference under drought stress, including investigating the growth phenotype, photosynthetic capacity, root hydraulic conductivity (Lpr), apoplastic water transport traced by PTS fluorescence, suberin monomer contents by GC-MS, and the development of suberin lamellae and casparian strip by histochemical staining technique. The results would contribute to clarifying the function of root apoplastic barriers in the drought tolerance of plants, and therefore, provide important genetic resources and theoretical instructions for improving crops and herbages.

质外体屏障是植物适应干旱等极端环境的重要策略之一。作为根系质外体屏障的两大主要类型，木栓层和凯氏带分别是根系水分跨细胞途径和质外体途径径向运输的重要阻力来源，很可能在植物抗旱性中发挥着重要作用。但目前学术界对根系质外体屏障在植物抗旱中的研究很少，且主要以拟南芥、水稻等对干旱敏感的植物为对象，因此对其在抗旱性中的作用缺少全面的了解。本项目拟以根系发达的旱中生牧草老芒麦为研究材料，通过对10份老芒麦优良种质进行抗旱性综合评价，筛选强抗旱种质、中度抗旱种质和干旱敏感种质各一份，进一步比较干旱胁迫下的生长表型、光合性能、根系水力学导度(Lpr)等差异，采用PTS荧光示踪质外体途径水分运输，GC-MS测定木栓质单体含量，结合组织化学染色观察木栓层和凯氏带的发育，以解析根系质外体屏障在植物抗旱性中的作用，为农作物和优良牧草抗旱性的遗传改良提供理论依据。

本研究以根系发达的旱中生牧草老芒麦为研究材料，通过对52份老芒麦优良种质进行抗旱性综合评价，筛选强抗旱种质和干旱敏感种质各一份，进一步比较两种质干旱胁迫下的水分状况、光合性能、根系水力学导度(Lpr)、质外体途径溶质运输、木栓质单体含量、木栓层和凯氏带发育等差异，以解析根系质外体屏障在植物抗旱性中的作用。本项目取得了以下主要进展和成果：(1) 通过隶属函数综合评价，从52份老芒麦种质资源中筛选出一份抗旱性最强种质(drought tolerant, DT)和一份抗旱性最弱种质(drought sensitive, DS)； (2) 干旱胁迫下，老芒麦通过维持体内良好的水分状况，光合作用及清除活性氧等能力，从而减轻干旱胁迫对叶片的伤害；(3) 老芒麦根的伸长生长和侧根数量的增加对其抗旱性具有重要作用；(4) 老芒麦根系没有外皮层，在受到干旱胁迫时可诱导根内皮层凯氏带和木栓层形成和增厚；(5) 老芒麦根系木栓质主要由阿魏酸、对羟基肉桂酸、未取代脂肪酸、w-OH酸及a, w-二酸组成；其根内皮层木栓层比地上部角质层响应干旱胁迫更及时灵敏；(6) 老芒麦通过根系质外体屏障影响养分的吸收和回流，从而增强老芒麦抗旱性；(7) 通过转录组测序及qRT-PCR实验，初步探究了根系质外体屏障相关基因在老芒麦响应干旱胁迫时的作用，为后续研究其抗旱性的分子机制奠定了基础；(8) 在模式植物拟南芥中，利用木栓质合成缺陷突变体cyp86a1发现，脂肪族木栓质能通过限制Na+的内流、K+的外排，同时限制水分向介质中回流，赋予植物耐盐性；(9) 开展了老芒麦抗寒性综合评价，从43份老芒麦中筛选到一份强抗寒种质和一份低温敏感种质，初步研究了其生理机制，为深入研究老芒麦抗寒机理奠定了基础。