The translocation of sugars in Cucurbita melopepo. V. The effect of leaf blade temperature on assimilation and transport

Abstract

The primary leaf blades of Cacurbita were exposed to 14CO2 for 15 s at different temperatures between 0 and 55° and the assimilation, metabolism, and translocation of 14C studied for periods of 5 min to 1 h. There was little significant change in net assimilation between 15 and 45°, but at 10° or lower and at 55° there was an appreciable decrease. The qualitative pattern of 14C incorporation into the ethanol-soluble fraction of the blade remained undisturbed by a temperature change from 0 to 45° but the rate of incorporation was significantly reduced at the lower temperatures. Sucrose, stachyose, and raffinose were predominantly labeled throughout except at 55° when 14C-malate predominated. Translocation from the blade was more sensitive to temperature change. At 15° and below, movement became restricted. At 5° or lower, and at 55° transport was almost completely inhibited. Between 25 and 45° there was little change in transport rate. Sucrose, stachyose, and raffinose were the major compounds translocated throughout the temperature range permitting movement. At lower blade temperatures development of the 14C-gradient in the petioles and the 14C distribution reflected the diminished rate of 14C assimilation and mobilization in the blades. The response of 14C translocation from the leaf blade to temperature change closely resembled that previously obtained in other transporting regions of the plant.