水稻生育后期外源赤霉素调控稻草饲用品质的机理研究

Utilizing rice (Oryza sativa L.) straw as roughage is a significant solution to the rice straw burning in South China where roughage shortage exists in the same time due to the poor feeding quality of rice straw. According to our previous investigation results, spraying exogenous gibberellic acid (GA) during late growth period could increase the levels of digestible nutrients such as nonstructural carbohydrates and crude protein in rice straw, thus improving its feeding quality. However, the regulation mechanism was not sure. This study is to investigate the regulation mechanism of spraying GA during late growth period in accumulating digestible nutrients in the straw. Three sink-source types (sink-limited type, source-limited type and sink-source coordinated type)of rice varieties will be used in this study. The contents of endogenous plant hormones (such as GA, 3-indole acetic acid, cytokinin and abscisic acid ), the dynamics of the photosynthetic characteristics of leaves (superoxide dismutase and peroxidase activities, and malondialdehyde and chlorophyll contents), and the sucrose-starch related enzymes activities (such as those of sucrose synthase, ADPG pryophosphorylase, Q-enzyme, α -amylase and β- amylase) in leaf and stem will be investigated after spraying GA during late growth period. The activity of gibberellin-binding proteins in cell membrane of leaf and stem will also be analyzed. The total RNAs will be isolated from stem and leaf for DNA microarray hybridization to select differently expressed sequences with or without GA treatment. Then we would use qRT-PCR quantification technique to verify DNA microarray hybridization results ,and clarify and analyze the function of the selected sequences. The significantly differently expressed sequences and the gibberellin-binding proteins activity would be taken correlation analysis with the physiological traits to clarify the regulation mechanism of exogenous GA on the feeding quality of rice straw during late growth period, so as to provide theoretical basis in production.

改善稻草饲用品质、提高稻草饲用率将能有效减少我国南方农区稻草的废弃焚烧量，同时缓解该区域草食畜牧业中粗饲料严重短缺的现状。本人前期研究表明生育后期喷施外源赤霉素（GA）能显著提高稻草中糖分和粗蛋白含量，改善饲用品质，但机理尚不清楚。本项目拟利用不同库源类型的水稻品种，在生育后期进行外源GA 处理，定期取样，分析茎叶中各种内源激素含量、叶片光合能力（超氧化物歧化酶、过氧化物歧化酶活性，叶绿素和丙二醛含量）及光合产物转运代谢相关酶（蔗糖合成酶、ADPG 焦磷酸化酶、Q-酶、α,β-淀粉酶）活性的变化，研究外源GA对水稻生长发育的影响；同时测定茎叶细胞膜上GA受体的活性，并利用基因芯片技术筛选在GA处理后表达差异显著的基因，通过qRT-PCR技术对芯片结果进行验证，并对选中基因进行初步分类和功能分析；最后将GA受体活性、基因表达与生理指标进行相关分析，明确生育后期外源GA调控稻草饲用品质的机理。

改善稻草饲用品质、提高稻草饲用率将能有效缓解我国南方农区稻草大量废弃焚烧，同时该区域草食畜牧业中粗饲料严重短缺的矛盾。本人前期研究表明生育后期喷施外源赤霉素（GA）能显著改善稻草饲用品质，但调控机理尚不清楚。. 本研究首先选择出GA调控效果显著的处理时间及浓度，开花后15天喷施45 g/ha的GA。外施GA后籼稻品种两优培九和粳稻品种南粳44衰老进程放缓；但是籼稻和粳稻品种间存在显著差异：两优培九GA处理组稻草的单茎绿叶面积增加幅度极显著高于南粳44（P<0.01），稻草中的NSC和粗蛋白（CP）增加幅度显著高于南粳44（P<0.05），叶片中的MDA含量显著低于对照（P<0.05），SOD和POD活性显著高于对照（P<0.05），且增加幅度高于南粳44，叶片中的GA含量和GA/ABA比值均显著高于对照（P<0.05），且高于南粳44。这说明水稻生育后期喷施外源GA能显著改善稻草饲用品质，主要通过减少MDA的积累量，提高SOD和POD活性，提高内源GA含量及GA/ABA比值来实现，但对衰老进程较快的籼稻品种两优培九的效果优于粳稻品种南粳44。. 利用表达谱测序技术筛选出GA处理后表达差异显著的基因：两优培九GA处理后，对照组和GA处理组有28个基因表达发生显著变化，其中表达上调的有9个，下调的有19个。表达差异显著的基因主要属于亚油酸代谢、α-亚麻酸的代谢、戊糖、葡萄糖醛酸转换、植物病原物相互作用、淀粉和蔗糖代谢、氨基糖和核苷酸糖代谢、嘌呤代谢等途径。粳稻品种南粳44GA处理后有11个基因的表达发生显著差异，其中9个基因表达上调，2个基因表达下调。差异表达基因主要集中在类黄酮生物合成、黄酮和黄酮醇的生物合成、昼夜节律-植物等途径上。. 本研究对水稻生育后期GA调控稻草饲用品质的机理进行研究，为通过栽培措施改善现有水稻品种的稻草饲用品质提供理论依据，对提高稻草饲用率的新途径进行探索。另外，对外源GA调控稻草饲用品质过程中表达显著差异的基因进行筛选和初步分类，为进一步的基因功能分析和克隆奠定基础。