Control of chlorophyll synthesis by phytochrome : III. Does phytochrome regulate the chlorophyllide esterification in mustard seedlings?

The rate of chlorophyllide esterification in mustard cotyledons can be increased by a pretreatment with 5 min red light applied 24 h prior to the protochlorophyll(ide)→chlorophyll(ide) photoconversion at 60 h after sowing. Simultaneously the red light pulse pretreatment leads to a decrease of the total amount of chlorophyll(ide) a in darkness. It has been proven that phytochrome (Pfr) is the photoeffector for both. Since the amounts of esterified chlorophyllide are determined by the ratio [chlorophyll a]/[chlorophyllide a+chlorophyll a] it is assumed that Pfr increases the rate of esterification indirectly via stimulating the decrease of chlorophyll(ide) a. The regulation of chlorophyll synthesis by Pfr does not seem to involve a control of esterification. The duration of the chlorophyllide esterification differs from the duration of the Shibata shift although both are greatly shortened by the red light pulse pretreatment. The effect of 5 min red light on the duration of the esterification is fully reversible by 5 min far-red light while the reversibility with respect to the Shibata shift is lost within 2 min [Jabben, M. and H. Mohr, Photochem. Photobiol. 22, 55-58 (1975)]. We conclude that the control of the chlorophyllide esterification and the control of the Shibata shift cannot be traced back to the same initial action of Pfr.