UV-B辐射增强对元阳梯田红米原花色素合成与沉积的影响及机理

Enhanced ultraviolet-b (UV-B) radiation on earth surface is one of the important issues in the research on global climate change. Proanthocyanidin is a UV-B radiation absorbing material, contributes to plant defense UV-B radiation. However, studies focused on response of the proanthocyanidin in plant leaves or petals to UV-B radiation. The study report is very limited on the effects of enhanced UV-B radiation on the proanthocyanidin synthesis and accumulation in grains. The red rice of Yuanyang Terraces is colored by the proanthocyanidin contained in the seed husk. It is worthy to study the red rice response to UV-B radiation. Therefore, in this project the red rice variety Baijiaolaojing of Yuanyang Terrace will be selected as a study object under enhanced UV-B radiation at in situ field and indoor conditions. The research objects include: (1) To determine the effects of enhanced UV-B radiation on the composition (catechin, epicatechin, oligomeric and poly proanthocyanidin) and content of the proanthocyanidin in the red rice, and on the caryopsis morphology and proanthocyanidin deposition. (2) To clarify the response of the activity of key enzymes and its coding gene expression in the biosynthesis of proanthocyanidin in the red rice to enhanced UV-B radiation. (3) To expound the mechanisms of enhanced UV-B radiation on the synthesis and accumulation of proanthocyanidin in the red rice of Yuanyang Terraces at cellular, enzyme and molecular level. The results will provide a new understanding of the effects of enhanced UV-B radiation on the proanthocyanidins metabolism in plant grains, and enrich the theory of UV-B radiation influencing the synthesis and deposition of plant proanthocyanidin.

地表UV-B辐射增强是全球气候变化研究的重要问题之一。原花色素是一类UV-B辐射吸收物质，有助于植物防御UV-B辐射，但研究集中在植物叶片或花瓣上，有关UV-B辐射对籽粒原花色素合成和累积的影响，报道不多。元阳梯田红米因其种皮内所含的原花色素而呈色，其对UV-B辐射的响应值得关注。因此，本项目拟以元阳梯田红米水稻品种白脚老粳为研究对象，大田原位种植和室内条件下，模拟UV-B辐射增强，研究UV-B辐射对梯田红米原花色素组分特征（儿茶素、表儿茶素、寡聚原花色素和多聚原花色素）、含量、颖果形态结构与原花色素沉积的影响，明确红米原花色素合成代谢关键酶活性及其编码基因表达对UV-B辐射增强的响应，解析UV-B辐射影响梯田红米原花色素合成与累积的细胞、酶学及分子机理。研究结果为丰富UV-B辐射影响植物果实原花青素代谢提供新的认识，丰富UV-B辐射影响植物原花色素合成与沉积的理论。

项目以元阳梯田传统水稻品种白脚老粳为试验材料，模拟不同强度（0、2.5、5.0和7.5 kJ·m-2·d-1）UV-B辐射和水稻不同生长时期进行UV-B辐射增强处理，开展大田原位种植和室内试验，测定水稻籽粒发育过程中原花青素含量、原花青素分布、调控合成关键酶活性（苯丙氨酸解氨酶、查尔酮异构酶、二氢黄酮醇4-还原酶、无色花色素合成酶、花青素还原酶）和组分特征（儿茶素、表儿茶素、原花青素A2、原花青素B2、原花青素C1）的变化，并利用代谢组学和转录组学技术研究籽粒次生代谢过程；将UV-B辐射处理后的红米喂食衰老模型小鼠，比较小鼠生长、结构（脑部海马区）和抗氧化指标（过氧化氢酶活性、超氧化物歧化酶活性、丙二醛含量）的变化。研究结果表明：（1）UV-B辐射增强，使得籽粒原花青素在水稻籽粒中呈现由外到内逐渐减少的规律，主要聚集在果皮和胚乳表层。（2）UV-B辐射显著提高籽粒中原花青素B2的含量，UV-B辐射增强2.5、5.0 kJ·m-2·d-1显著提高籽粒中原花青素C1的含量，随水稻籽粒发育，儿茶素、表儿茶素、原花青素B2和原花青素C1的含量逐渐降低。（3）水稻正常营养过程受抑制，将能量分配至次生代谢产物合成过程，通过合成黄酮类物质以实现保护的作用。UV-B辐射通过调控metabolic process、catalytic activity和celluar process，影响籽粒中次生代谢产物的生物合成、糖代谢和氨基酸代谢。（4）UV-B辐射对水稻籽粒的抗氧化效果排序为：5.0 kJ·m-2·d-1UV-B辐射处理的水稻籽粒>自然光照下的水稻籽粒>2.5 kJ·m-2·d-1UV-B辐射处理的水稻籽粒>7.5 kJ·m-2·d-1辐射处理的水稻籽粒。因此，水稻响应UV-B辐射增强的过程主要通过改变籽粒原花青素合成和组分特征、调控原花青素合成酶活性、籽粒代谢物质和基因表达的过程，来增强自身防御能力，为水稻防御机制提供了新的认识。初步阐释UV-B辐射增强对水稻次生代谢过程的分子机理，对进一步的认识水稻次生代谢过程具有重要的意义。该项目已发表论文11篇，培养博士生1人，硕士生5人。课题组人员参加了5次国际、国内学术会议。