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Abstract：
BACKGROUND: Brassinosteroids (BRs) are a new group of plant hormones and play important roles in plant growth and development. However, little information is available if BRs could regulate spikelet development in rice (Oryza sativa L.) especially under soil-drying conditions. This study investigated whether and how BRs mediate the effect of soil-drying on spikelet differentiation and degeneration in rice. A rice cultivar was field-grown and exposed to three soil moisture treatments during panicle development, that is, well-watered (WW), moderate soil-drying (MD) and severe soil-drying (SD).
RESULTS: Compared with the WW treatment, the MD treatment enhanced BRs biosynthesis in young panicles, increased spikelet differentiation and reduced spikelet degeneration. The SD treatment had the opposite effects. Changes in expression levels of key rice inflorescence development genes (OsAPO2 and OsTAW1), ascorbic acid (AsA) content, and activities of enzymes involved AsA synthesis and recycle, and amount of nonstructural carbohydrates (NSC) in young panicles were consistent with those in BRs levels, whereas hydrogen peroxide (H2O2) content showed opposite trend. Knockdown of the BRs synthesis gene OsD11 or application of a BRs biosynthesis inhibitor to young panicles markedly decreased OsAPO2 and OsTAW1 expression levels, BRs and AsA contents, activities of enzymes involved AsA synthesis and recycle, NSC amount in rice panicles and spikelet differentiation but increased the H2O2 content and spikelet degeneration compared to the control (the wide type or application of water). The opposite effects were observed when exogenous BRs were applied.
CONCLUSIONS: The results suggest that BRs mediate the effect of soil-drying on spikelet differentiation and degeneration, and elevated BRs levels in rice panicles promote spikelet development under MD by enhancing inflorescence meristem activity, AsA recycle and NSC partitioning to the growing panicles.
RESULTS: Compared with the WW treatment, the MD treatment enhanced BRs biosynthesis in young panicles, increased spikelet differentiation and reduced spikelet degeneration. The SD treatment had the opposite effects. Changes in expression levels of key rice inflorescence development genes (OsAPO2 and OsTAW1), ascorbic acid (AsA) content, and activities of enzymes involved AsA synthesis and recycle, and amount of nonstructural carbohydrates (NSC) in young panicles were consistent with those in BRs levels, whereas hydrogen peroxide (H2O2) content showed opposite trend. Knockdown of the BRs synthesis gene OsD11 or application of a BRs biosynthesis inhibitor to young panicles markedly decreased OsAPO2 and OsTAW1 expression levels, BRs and AsA contents, activities of enzymes involved AsA synthesis and recycle, NSC amount in rice panicles and spikelet differentiation but increased the H2O2 content and spikelet degeneration compared to the control (the wide type or application of water). The opposite effects were observed when exogenous BRs were applied.
CONCLUSIONS: The results suggest that BRs mediate the effect of soil-drying on spikelet differentiation and degeneration, and elevated BRs levels in rice panicles promote spikelet development under MD by enhancing inflorescence meristem activity, AsA recycle and NSC partitioning to the growing panicles.
摘要：
背景：油菜素类固醇（BRs）是一类新的植物激素，在植物生长发育中起着重要作用。然而,如果BRs可以调节水稻（OryzasativaL.）的小穗发育，尤其是在土壤干燥条件下，则几乎没有信息。这项研究调查了BRs是否以及如何介导土壤干燥对水稻小穗分化和退化的影响。水稻品种是田间种植的，并在穗部发育过程中暴露于三种土壤水分处理，也就是说,浇水充足(WW)，中度土壤干燥(MD)和重度土壤干燥(SD)。
结果：与WW治疗相比，MD治疗增强了幼穗BRs的生物合成，小穗分化增加，小穗退化减少。SD处理具有相反的效果。水稻花序发育关键基因(OsAPO2和OsTAW1)表达水平的变化,抗坏血酸（AsA）含量，以及与AsA合成和再循环相关的酶的活性，幼穗中非结构性碳水化合物（NSC）的含量与BRs水平一致，而过氧化氢(H2O2)含量则呈相反趋势。敲除BRs合成基因OsD11或对幼穗应用BRs生物合成抑制剂显着降低了OsAPO2和OsTAW1的表达水平，BRs和AsA含量，涉及AsA合成和回收的酶活性，与对照相比，水稻穗和小穗分化中的NSC量增加了H2O2含量和小穗变性（广泛的类型或施用水）。当应用外源BR时观察到相反的效果。
结论：结果表明，BRs介导了土壤干燥对小穗分化和退化的影响，水稻圆锥花序中BRs水平的升高通过增强花序分生组织活性促进MD下小穗发育，AsA再循环和NSC分配到生长的圆锥花序。
结果：与WW治疗相比，MD治疗增强了幼穗BRs的生物合成，小穗分化增加，小穗退化减少。SD处理具有相反的效果。水稻花序发育关键基因(OsAPO2和OsTAW1)表达水平的变化,抗坏血酸（AsA）含量，以及与AsA合成和再循环相关的酶的活性，幼穗中非结构性碳水化合物（NSC）的含量与BRs水平一致，而过氧化氢(H2O2)含量则呈相反趋势。敲除BRs合成基因OsD11或对幼穗应用BRs生物合成抑制剂显着降低了OsAPO2和OsTAW1的表达水平，BRs和AsA含量，涉及AsA合成和回收的酶活性，与对照相比，水稻穗和小穗分化中的NSC量增加了H2O2含量和小穗变性（广泛的类型或施用水）。当应用外源BR时观察到相反的效果。
结论：结果表明，BRs介导了土壤干燥对小穗分化和退化的影响，水稻圆锥花序中BRs水平的升高通过增强花序分生组织活性促进MD下小穗发育，AsA再循环和NSC分配到生长的圆锥花序。
