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

When etiolated pea epicotyls are excised immediately above the cotyledons and dipped basally into (14)C-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 tissue. EIS is of greater magnitude, occurs more rapidly and is saturated by lower energies of red light than IG, 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 m unlabeled sucrose in the medium.Enhanced incorporation is most dramatic with sucrose; lesser effects are shown with fructose, glucose, maltose and ribose in that order. Both level of incorporation and red light effects are poor for labeled tyrosine, phenylalanine, valine, acetic acid, cinnamic acid and alpha-ketoglutaric acid. The possible connection between carbohydrates and phytochrome-mediated photomorphogenesis is considered.