PHYTOCHROME-MEDIATED THRESHOLD CONTROL OF HYPOCOTYL GROWTH IN PARTLY DE-ETIOLATED MUSTARD (Sinapis alba L.) SEEDLINGS |
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Authors: | Heidemarie Oelze-Karow Hans Mohr |
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Affiliation: | Biologisches Institut II der Universität, Schänzlestrasse 1, D-7800 Freiburg i.Br., W. Germany |
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Abstract: | Abstract— Hypocotyl elongation in etiolated mustard ( Sinapis alba L.) seedlings is known to be controlled by phytochrome (Pfr) through a threshold mechanism. The Pfr threshold value required to suppress hypocotyl growth was low (3 times 10−2% Pfr, based on total phytochrome in the hypocotyl at 36 h after sowing = 100%). In the present study the question was addressed whether the threshold control by Pfr of hypocotyl elongation also operates in light-pretreated, partly de-etiolated seedlings after transfer to darkness. The experimental results show that this is the case. Calculation of the threshold level in far-red light pretreated seedlings led to a very low value (3 times 10−7%) compared to etiolated seedlings (3 times 10−2%). In red light pretreated seedlings the threshold level was calculated to be 9 times 10−7%. Since the light pretreatment affected the rate of degradation of phytochrome strongly (half-life of Ptot in continuous red light was found to be 35 min in far-red pretreated instead of 47 min in etiolated material), the difference in threshold level between far-red and red pretreated material cannot be interpreted unambiguously. However, the conclusion can be drawn that light nretreatment strongly increases the degradation rate of Pfr and decreases the threshold level. |
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