Submergence-induced leaf senescence may alter chlorophyll metabolism. The objective of this study was to characterize chlorophyll biosynthesis and degradation in contrasting perennial ryegrass (Lolium perenne) in response to submergence stress and recovery. The light-green and fast-growing accession PI238938 and the darker-green and slow-growing cultivar BrightStar SLT were exposed to 0, 6 h, 1-, 3-, and 7-d of submergence stress and 1- and 5- d of de-submergence, respectively. Plant growth of PI238938 were more severely inhibited by submergence stress and recovery. Both accessions showed increased leaf malondialdehyde under stress and recovery, but reduced chlorophyll (Chl) concentrations were observed at 3- and 7-d of stress and at recovery. The reduction in Chl was more severe in BrightStar SLT at 7 d of stress. The concentration of 5-aminolevulenic acid was unaffected by stress but increased at 1d of recovery. Activities of 5-aminolevulinic acid dehydratase (ALAD) involved in Chl biosynthesis remained unchanged under stress and recovery, while the activities of Chl degrading enzymes chlorophyllase (CHL) and pheophytinase (PPH) increased at 3 d or 7 d of stress, and returned to the control level after recovery in both accessions. The downregulation of Chl-biosynthetic genes CHLI, POR, and CHLP and the upregulation of Chl-degrading genes CLH, PPH, and SGR were observed in both accessions under most of the stress periods. BrightStar SLT exhibited much lower expressions of the Chl-biosynthetic genes PBGD, CHS, and CHID under stress, while PI238938 had remarkably higher expressions of genes involved in Chl breakdown including CLH, PPH, PAO, RCCR, and SGR, and the expressions of these genes remained at a higher level at 1 d of recovery. The results indicated that submergence-induced leaf senescence and declines in Chl were associated with downregulation of more Chl-biosynthetic genes in slow-growing genotype and upregulation of more Chl-degrading genes in fast-growing genotype of perennial ryegrass.

中文翻译：

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生长习性不同的多年生黑麦草种质中叶绿素代谢和基因表达对淹没胁迫的响应和随后的恢复

淹没诱导的叶片衰老可能会改变叶绿素代谢。本研究的目的是表征对比多年生黑麦草 (Lolium perenne) 响应淹没压力和恢复的叶绿素生物合成和降解。浅绿色和快速生长的种质 PI238938 和深绿色和生长缓慢的品种 BrightStar SLT 暴露于 0、6 h、1-、3-和 7-d 淹没胁迫以及 1-和 5- d的去淹没，分别。PI238938 的植物生长受到淹没胁迫和恢复的更严重抑制。两个种质在胁迫和恢复下均显示出增加的叶丙二醛，但在胁迫 3 天和 7 天以及恢复时观察到叶绿素 (Chl) 浓度降低。在应激第 7 天，BrightStar SLT 中 Chl 的减少更为严重。5-氨基乙酰丙酸的浓度不受应激的影响，但在恢复后第1天增加。参与 Chl 生物合成的 5-氨基乙酰丙酸脱水酶 (ALAD) 的活性在胁迫和恢复下保持不变，而 Chl 降解酶叶绿素酶 (CHL) 和脱镁叶绿素酶 (PPH) 的活性在胁迫 3 d 或 7 d 时增加，并恢复到两个种质恢复后的控制水平。在大多数胁迫时期，在这两个种质中都观察到了 Chl 生物合成基因 CHLI、POR 和 CHLP 的下调以及 Chl 降解基因 CLH、PPH 和 SGR 的上调。BrightStar SLT 在胁迫下表现出低得多的 Chl 生物合成基因 PBGD、CHS 和 CHID 的表达，而 PI238938 具有显着更高的 Chl 分解相关基因的表达，包括 CLH、PPH、PAO、RCCR 和 SGR，这些基因的表达在恢复1 d时保持在较高水平。结果表明，淹水诱导的叶片衰老和 Chl 下降与多年生黑麦草慢速生长基因型中更多 Chl 生物合成基因的下调和快速生长基因型中更多 Chl 降解基因的上调有关。