Phytochrome Control of Cell Wall-bound Hydroxyproline Content in Etiolated Pea Epicotyls

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Abstract
The red light inhibition of growth of the intact pea (Pisum sativum L. cv. Alaska) 3rd internode was correlated with an increase in the content of cell wall-bound hydroxyproline. These changes were detected 3 h after irradiation, and possibly at 1 h. Far red light reversed the effects of red light. The iron chelator .alpha.,.alpha.''-dipyridyl reversed the red light effects on both growth and hydroxyproline content. Using segments incubated in vitro, no phytochrome-mediated change in hydroxyproline content could be observed, perhaps because of an overwhelming wounding response. If plants were irradiated in situ and grown for 8 h before excision and incubation of segments, some enhancement of hydroxylation by red light was detectable both colorimetrically and radioisotopically. The red light inhibition of segment growth was reversed by .alpha.,.alpha.''-dipyridyl. These results are examined in reference to the role of extension in normal and induced growth cessation.