Photomorphogenesis of the ein mutant of Brassica rapa.

Several phytochrome-controlled processes have been examined in etiolated and light-grown seedlings of a normal genotype and the elongated internode (ein/ein) mutant of rapid cycling Brassica rapa. Etiolated ein seedlings displayed a selective deficiency in response to prolonged red light with respect to inhibition of hypocotyl elongation, expansion of cotyledons and synthesis of anthocyanin. In contrast to normal seedlings, light-grown ein seedlings did not show a growth promotion in response to end-of-day far-red irradiation. Additionally, whereas the first internode of light-grown normal seedlings showed a marked increase in elongation in response to reduced red:far-red ratio, ein seedlings showed only a small elongation response. Immunochemical analysis has demonstrated that the ein mutant lacks a detectable phytochrome B-like protein. Furthermore, analysis at the DNA level has demonstrated the presence of a lesion within the promoter region of the PHYB gene of ein. Both physiological and molecular evidence strongly suggest, therefore, that EIN=PHYB. In common with other photoreceptor mutations, the ein mutation has been shown to be semi-dominant. EIN/ein heterozygote seedlings contain about 50% of the level of immunodetectable phytochrome B of equivalent normal, EIN/EIN seedlings. Etiolated seedlings of the EIN/ein heterozygote show a responsiveness to red light almost exactly intermediate between that of ein/ein and EIN/EIN homozygotes. The response of the EIN/ein heterozygote both to low red:far-red ratio light and to end-of-day far-red light treatments is also intermediate between that of the homozygotes EIN/EIN and ein/ein A range of other phytochrome-controlled responses have been examined in normal and ein seedlings which have further elucidated the roles played by phytochrome B in rapid cycling B. rapa, whilst shedding light on the actions of other phytochrome species. Finally, a method for the transformation of rapid cycling B. rapa has been investigated, demonstrating the potential for the creation of transgenic phytochrome mutants in rapid cycling B. rapa.