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损伤症状，如褪绿。另一方面，有些品种即使在连续光照下也不会出现任何损伤，生长良好。本研究利用南瓜的耐光品种和感光品种进行了连续耐光性的正反交试验，研究了南瓜连续耐光性的遗传机制。在F_1的反交中，以叶绿素浓度表示的黄化程度为中亲值。耐感品种F_2的叶绿素含量变化范围在耐感值和敏感值之间，没有明显的分离。在F_2代的F_3代中，一个敏感群体和一个耐受群体以约9：1的比例分离。这些结果表明，耐连续光性受两个或两个以上的隐性基因控制，持续光伤害只发生在幼嫩的展开叶上。我们假设，成熟的叶片感觉到连续的光，这一信息诱导新叶的伤害。为了验证这一假设，我们覆盖了部分植物。在连续光照下，成熟叶片覆盖12小时/天时，扩展叶片上没有发生损伤。敏感接穗嫁接到成熟叶片的耐病砧木上，其展开叶片不发生持续光损伤。结果表明，连续光照下，敏感品种的展开叶片产生一定的伤害诱导物，耐光品种的超氧化物歧化酶和过氧化氢酶活性比敏感品种的活性提高更快。这些结果表明，抗氧化酶活性的迅速增加参与了对连续光的耐受机制。

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.