Mechanism and Inheritance of Continuous Light-Tolerance in Cucurbita moschata

在许多物种中，植物在持续光照下表现出黄化等损伤症状。另一方面，有些品种即使在连续光照下也没有任何伤害，生长良好。以耐光敏感品种瓜为材料，研究了瓜连续耐光性的遗传机制。对耐敏感品种进行了正交杂交。在倒数F_1中，以叶绿素浓度表示的黄化程度为亲本中值。耐敏感品种的F_2叶绿素浓度从耐受性值到敏感性值不等，没有明显的分离。在F_2敏感植株的F_3后代中，一个敏感组和一个耐受组的分离比例约为9:1。这些结果表明，水稻的连续耐光性受两个或多个涉及隐性基因的等位基因控制。持续的光害只发生在幼嫩、膨大的叶片上。我们假设成熟叶片感知到持续的光，而这种信息诱导了新叶的伤害。为了验证这一假设，我们将植物部分覆盖。在连续光照条件下，成熟叶片覆盖12小时/天，膨大叶片未发生损伤。敏感接穗嫁接到成熟叶片的耐受性砧木上，膨胀叶片不发生连续光害。这些结果表明，在连续光照下，敏感品种展开叶片产生了一定的伤害诱导剂。连续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提高得更快。这些结果表明，抗氧化酶活性的快速增加参与了耐连续光的机制。

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.