Phytochrome decay in seedlings under continuous incandescent light

✍ Scribed by R. E. Kendrick; C. J. P. Spruit

• Book ID: 104750046
• Publisher: Springer-Verlag
• Year: 1972
• Tongue: English
• Weight: 452 KB
• Volume: 107
• Category: Article
• ISSN: 0032-0935
• DOI: 10.1007/bf00386395

✦ Synopsis

Under continuous high intensity incandescent light the decay of phytochrome in Amaranthus seedlings deviates from the predicted first order rate characteristic of the Pfr/Ptotal ratio maintained. This deviation takes the form of a slower decay than would be predicted and is only observed at high intensities. Experiments are presented to test the hypothesis that this reduced rate of decay is the result of a high level of phytochrome intermediates maintained under high intensity incandescent light. Accumulation of intermediates under these conditions has been demonstrated using a quasi-continuous measuring speetrophotometer. They are weakly absorbing and their concentration increases with light intensity. Although they form Pfr in darkness, it is proposed that they do not decay. The model predicts that in a sample cuvette, where a light intensity gradient exists, there is more probability of a phytochrome molecule being present as Pfr at the back of the euvette: the region of lowest light intensity. Under conditions which favour phytochrome decay, a preferential loss of phytochrome should result at the back of the cuvette and an increasingly higher proportion of the remaining phytochrome will consequently be measured as intermediate as the experiment progresses. The results confirm the hypothesis and in addition, after 60 min incandescent light, demonstrate an accumulation of intermediates which form Pfr with a longer half-life than at the begining of the experiment. Pisum epieotyl hooks show no such intermediate accumulation or preferential decay at the back of the cuvette, which is in agreement with the observed first order phytoehrome decay under high intensity incandescent light. A scheme is presented explaining the results on the basis of the decay process.