Mechanism and Inheritance of Continuous Light-Tolerance in Cucurbita moschata

在许多物种中，植物在连续光照下表现出黄化等伤害症状。另一方面，有些物种没有表现出任何伤害，即使在连续的光照下也能很好地生长。本研究以耐光和感光品种为材料，研究了南瓜连续耐光的机理和遗传规律，并对耐光和感光品种进行了正反交。在倒数F_1代中，以叶绿素浓度表示的黄化程度为中亲值。耐×敏品种F2的叶绿素浓度介于耐性值和敏感值之间，没有明显的分离现象。在敏感的F_2植株的F_3代中，一个敏感群和一个耐性群以大约9：1的比例分离。这些结果表明，水稻对连续光的耐性受两个或两个以上涉及隐性基因的等位基因控制，连续光伤害仅发生在幼叶上。我们假设成熟的叶片感觉到连续的光，这一信息诱导了新叶的伤害。为了检验这一假设，我们覆盖了部分植物。在连续光照下，成熟叶片遮盖12h/d，膨大叶片不会受到伤害。敏感接穗嫁接到成熟叶片的耐性砧木上，其膨大的叶片未发生连续的光伤害。这些结果表明，在连续光照下，敏感品种的展开叶片产生了一定的伤害诱导物，且连续耐光品种的超氧化物歧化酶和过氧化氢酶活性的提高速度比敏感品种快。这些结果表明，抗氧化物酶活性的快速升高参与了植物对连续光照的耐受机制。

In many species, plants show injury symptoms such as chlorosis under continuous light. On the other hand, some species do not show any injury and grow well even under continuous light. In this study, we examined the mechanisms and inheritance of continuous light-tolerance using tolerant and sensitive cultivar in Cucurbita moschata.Reciprocal crosses were conducted for tolerant and sensitive cultivar. In the reciprocal F_1, the degree of chlorosis expressed as chlorophyll concentration was mid-parent value. The chlorophyll concentration of F_2 from tolerant × sensitive cultivar ranged from tolerant value to sensitive value and there was no distinct segregation. In the F_3 progeny from a sensitive F_2 plant, one sensitive and one tolerant group were segregated in approximately 9:1 ratio. These results suggested that continuous-light tolerance was controlled by two or more alleles involving recessive genes.Continuous light-injury occurred only on young, expanding leaves. We hypothesized that mature leaves sense continuous light, and this information induces the injury of new leaves. To examine this hypothesis, we covered plants partially. Injury did not occur on expanding leaves under continuous light when mature leaves were covered for 12 hr/day. Continuous light-injury did not occur on the expanding leaves of sensitive scion grafted to tolerant rootstock with mature leaves. These results indicated that the expanded leaf of sensitive cultivar produced some injury-inducer under continuous light.The activities of superoxide dismutase and catalase in continuous light-tolerant cultivar increased more rapidly than those in sensitive cultivar. These results suggested that a rapid increase in the antioxidant enzymatic activities was involved in the mechanism of tolerance to continuous light.