Chlorophyll biosynthesis and metabolism analyses of reciprocal interspecific hybrid between Cucumis hystrix and C. sativus

The reciprocal interspecific hybrids between Cucumis hystrix and C. sativus were used to analyze chlorophyll biosynthesis and metabolism by measuring their chlorophyll (Chl) contents, chlorophyllase (Chlase) activities and chlorophyll biosynthesis precursors’ contents in order to reveal the mechanisms of yellow leaves involved. The results showed that the contents of Chl a, Chl b and total chlorophyll in the leaves of HC and CH were significantly lower than those of their parents in the experiment. Nevertheless, the Chlase activities of HC and CH were the nearly comparable to their parents. The content of protochlorophyllide (Pchlide) in HC accumulated distinctly, whereas the content of Chl a decreased. The result suggested that the biosynthesis of Chl in HC was blocked at the step of converting Pchlide to Chl a. The content of δ-aminolevulinic acid (ALA) and porphobilinogen (PBG) in CH promoted rapidly, yet uroporphyrinogen (Urogen Ⅲ) content reduced remarkably, and the contents of coproporphyrinogen Ⅲ, protoporphyrin IX, Mg-protoporphyrin IX and protochloro-phyllide were all decreased accordingly. The result displayed that the biosynthesis of Chl in CH was blocked at the step of converting PBG to Urogen Ⅲ. Simultaneously, we discovered the novel phenotypes of yellow leaves in HC and CH were induced by different mechanism, which further confirmed the reciprocal differences in the interspecific hybridization between C. hystrix and C. sativus.