BACKGROUND AND AIMS Proteases are responsible for protein degradation during leaf senescence, allowing nutrients to be redirected to sink tissues. In a previous work, we reported that sulphur deficiency produced a delay in the leaf senescence of barley (Hordeum vulgare L.) plants, both at vegetative and reproductive stages. In this work we analyse the effect of sulphur deficiency on the expression of several genes coding for proteases of different catalytic groups, which have been strongly associated with leaf senescence. METHODS Four independent experiments were performed in order to impose low sulphur availability conditions: one of steady-state sulphur deficiency during vegetative stage and three of sulphur-starvation during vegetative and reproductive stages. KEY RESULTS Sulphur deficiency inhibited or reduced the senescence associated induction of seven of the eight proteases analysed. Their induction, as well as senescence and phloem amino acid remobilization, could be achieved with senescence inductors such as methyl-jasmonate (a hormonal stimulus) and darkness, but with different rates of induction dependent on each gene. Sulphur deficiency also exerted an opposite effect on the gene expression of two cysteine-proteases (HvSAG12 and HvLEGU) as well as on one serine-protease (HvSUBT) according to leaf age and plant phenological stages. All three genes were induced in green leaves but repressed in senescent ones of sulphur deficient plants at the vegetative stage. At the reproductive stage both cysteine-proteases were only repressed in senescent leaves while the serine-protease was induced in green and senescent leaves by sulphur deficiency. CONCLUSIONS Our results highlight the relevance of adequate sulphur nutrition in order to ensure leaf senescence onset and proteases' genes induction, which will consequently impact on grain protein composition and quality. In addition our results provide evidence that leaf age, plant developmental stage and the nature of the stress modulate the sulphur responses.

中文翻译：

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根据大麦（Hordeum vulgare L.）物候阶段，硫有效性对衰老相关蛋白酶基因的调节


背景和目的 蛋白酶负责叶片衰老过程中的蛋白质降解，使营养物质重新定向至库组织。在之前的工作中，我们报道了缺硫导致大麦（Hordeum vulgare L.）植物在营养阶段和生殖阶段的叶子衰老延迟。在这项工作中，我们分析了缺硫对编码不同催化组蛋白酶的几种基因表达的影响，这些基因与叶片衰老密切相关。方法为了施加低硫有效性条件，进行了四项独立实验：其中一项是营养阶段稳态缺硫，三项是营养和生殖阶段缺硫。主要结果 硫缺乏抑制或减少了所分析的八种蛋白酶中的七种与衰老相关的诱导。它们的诱导以及衰老和韧皮部氨基酸的再动员可以通过衰老诱导剂如茉莉酸甲酯（一种激素刺激物）和黑暗来实现，但诱导率取决于每个基因。根据叶龄和植物物候阶段，缺硫还对两种半胱氨酸蛋白酶（HvSAG12 和 HvLEGU）以及一种丝氨酸蛋白酶（HvSUBT）的基因表达产生相反的影响。所有这三个基因都在绿叶中被诱导，但在营养阶段缺硫植物的衰老叶子中受到抑制。在繁殖阶段，两种半胱氨酸蛋白酶仅在衰老叶片中受到抑制，而丝氨酸蛋白酶在绿叶和衰老叶片中因缺硫而被诱导。 结论我们的结果强调了充足的硫营养的相关性，以确保叶片衰老的开始和蛋白酶基因的诱导，从而影响谷物蛋白质的组成和质量。此外，我们的结果提供了证据表明叶龄、植物发育阶段和胁迫性质调节硫反应。