Rice tillering, which determines the panicle number per plant, is an important agronomic trait for grain production. In higher plants, ascorbic acid (Asc) plays a major role in ROS-scavenging activity. l-Galactono-1, 4-lactone dehydrogenase (GalLDH, EC1.3.2.3) is an enzyme that catalyzes the last step of Asc biosynthesis in plants. Previously, we have reported that homozygous L-GalLDH-suppressed transgenic rice plants (GI) display a reduced tiller number and a lower level of foliar carotenoids (Car) compared with wild type. Strigolactones (SL), which play an important role in the suppression of shoot branching, are synthesized in the roots of rice plant using Car as substrates. In this paper, the relationship between Asc, SL, the accumulation of H2O2, changes in antioxidant capacity, enzyme activities, and gene transcriptions related to the synthesis of SL were analyzed in transgenic rice plants for L-GalLDH suppressed (GI-1 and GI-2) and overexpressing (GO-2). The results showed that the altered level of Asc in the L-GalLDH transgenic rice plants leads to a change in redox homeostasis, resulting in a marked accumulation of H2O2 and decreased antioxidant capacity in GI-1 and GI-2, but lower H2O2 content and increased antioxidant capacity in GO-2. Meanwhile, the altered level of Asc also leads to altered enzyme activities and gene transcript abundances related to SL synthesis in L-GalLDH transgenics. These observations support the conclusion that Asc influences tiller number in the L-GalLDH transgenics by affecting H2O2 accumulation and antioxidant capacity, and altering those enzyme activities and gene transcript abundances related to SL synthesis.

中文翻译：

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L-galactono-1, 4-lactone脱氢酶抑制或过表达的转基因水稻中独脚金内酯的合成受内源抗坏血酸的影响

水稻分蘖决定了单株的穗数，是粮食生产的重要农艺性状。在高等植物中，抗坏血酸 (Asc) 在 ROS 清除活动中起主要作用。l-Galactono-1, 4-lactone dehydrogenase (GalLDH, EC1.3.2.3) 是一种催化植物 Asc 生物合成最后一步的酶。此前，我们曾报道纯合 L-GalLDH 抑制的转基因水稻植物 (GI) 与野生型相比，分蘖数减少，叶类胡萝卜素 (Car) 水平较低。独脚金内酯 (SL) 在抑制枝条分枝方面发挥重要作用，以 Car 为底物在水稻根部合成。本文从 Asc、SL、H2O2 的积累、抗氧化能力的变化、酶的活性、在转基因水稻植物中分析了与 SL 合成相关的基因转录，以确定 L-GalLDH 被抑制（GI-1 和 GI-2）和过度表达（GO-2）。结果表明，L-GalLDH 转基因水稻植株 Asc 水平的改变导致氧化还原稳态的变化，导致 H2O2 显着积累，GI-1 和 GI-2 的抗氧化能力降低，但 H2O2 含量和增加 GO-2 的抗氧化能力。同时，Asc 水平的改变也导致与 L-GalLDH 转基因中 SL 合成相关的酶活性和基因转录本丰度的改变。这些观察结果支持 Asc 通过影响 H2O2 积累和抗氧化能力影响 L-GalLDH 转基因的分蘖数的结论，