Translocation of Photosynthetically Assimilated C14 in Straight-Necked Squash

Abstract

The mature primary leaf blade of Cucurbita melopepotroticollis, was exposed to C14O2 (58.8% C14) for 15 seconds and the C14 translocated was measured as a function of time using chemical methods and tissue autoradiography. Five minutes after assimilation C14-stachyose, moving with a velocity in excess of 290 cm/hour, was detected in the petiole. The rate of export reached a maximum at about 15 minutes then decelerated and approached zero at 3 hours when 55% of the total C14 assimilated had been exported mainly as stachyose and sucrose. Translocates moved simultaneously toward the root and upper plant in the bicollateral phloem tissue. The most rapidly expanding organs of the plant received the greatest quantity of translocates. A radial movement of C14 occurred from the phloem throughout the plant. Concurrent bidirectional movement in the phloem was observed in leaves during a particular period of their development and in the stem. Young leaves began to translocate sugars after reaching approximately 1/2 their mature size at which stage they commenced the biosynthesis of stachyose.