Sugar Uptake and Translocation in the Castor Bean Seedling I. Characteristics of Transfer in Intact and Excised Seedlings'

sugar present in the endosperm was predominantly, and in the cotyledon almost exclusively, sucrose. Anatomical features were described which contribute to the efficiency of the cotyledons as organs of absorption and transmittal of sucrose to the embryonic axis, where hexoses are much more prevalent. The ability of the cotyledons to absorb sucrose survived removal of the endosperm from the seedling. A series of experiments is described in which the cotyledons of such excised seedlings were immersed in sucrose-:"C and measurements made of uptake and of translocation to various parts of the seedling. Increasing rattes of absorption were observed as the sutcrose concentration was raised to 0.5 M and these rates were maintained for several hours. Removal of the embryonic axis (hypocotyl plus roots) drastically altered both the response to suicrose concentration and the time couirse of absorption by the cotyledons. More than 80 % of the stugar normally entering the cotyledons from the endosperm is transmitted to the embryonic axis and this extensive turnover was seen also in ptulse/chase experiments with excised seedlings. The cotyledons of excised seedlings absorbed sucrose against high apparent concentration gradients. The absorption was stimtulated by phosphate and had a pH optimtum at abolut pH 6.4. It was inhibited by arsenate, azide and 2,4-dinitrophenol.