ON THE POLARITY OF PHYTOCHROME CONTROLLED LEAF UNFOLDING IN DARK-GROWN SEEDLINGS OF TRITICUM AESTIVUM*

Abstract— The apical ends of sections cut from etiolated primary wheat leaves show a higher degree of phytochrome-mediated leaf unfolding than the basal ends, regardless of the position of the segment in the leaf. It could be clarified that this polarity is not the result of a stable gradient within the intact dark grown leaf. Partial irradiation experiments have shown that leaf unfolding can be induced much more effectively by an irradiation of the apical half of a section than of the basal half. Though only the basal end of the sections was incubated with gibberellic acid (GA₃) in darkness, the degree of the GA₃-induced leaf unfolding was highest at the apical end of these non-irradiated segments. The results suggest that in each separate leaf section a new gradient of a still unknown “unfolding-factor” is established.