Control by Phytochrome of 14C-Sucrose Incorporation into Buds of Etiolated Pea Seedlings

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Abstract
When etiolated pea epicotyls are excised immediately above the cotyledons and dipped basally into C14-sucrose, their terminal buds respond to red light by increased growth (IG) and enhanced incorporation of sucrose (EIS). Both phenomena are phytochrome controlled, showing typical kinetics, reversal by far-red light, escape from photochemical control and limitation to leaf tissues. EIS is of greater magnitude, occurs more rapidly and is saturated by lower energies of red light than IC, suggesting its possible importance as a controlling reaction in phytochrome-mediated growth. Both IG and EIS are best shown in the presence of a long epicotyl derived from a 5 to 6-day-old seedling in the presence of about 0.1 [image] unlabeled sucrose in the medium. Enhanced incorporation is the highest with sucrose: fructose, glucose, maltose and ribose were less effective in that order. Both levels of incorporation and red light effects are poor for labeled tyrosine, phenlalanine. valine, acetic acid, cinnamic acid and [alpha]-keto-glutaric acid. The possible connection between carbohydrates and phyto-chrome-mediated photomorphogenesis is considered.