Mechanism and Inheritance of Continuous Light-Tolerance in Cucurbita moschata

2004 Fiscal Year Final Research Report Summary

• Project/Area Number: 15580023
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Horticulture/Landscape architecture
• Research Institution: OKAYAMA UNIVERSITY
• Principal Investigator: MURAKAMI Kenji Okayama University, The Graduate School of Natural Science and Technology, Lecturer, 大学院・自然科学研究科, 講師 (40200266)
• Co-Investigator(Kenkyū-buntansha): MASUDA Masaharu Okayama University, Faculty of Agriculture, Professor, 農学部, 教授 (90026617)
• Project Period (FY): 2003 – 2004
• Keywords: antioxidant enzyme / chlrosis / continuous light-injury / expanding leaves / mature leaves

Research Abstract

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.