ROLE OF THE ROOT IN THE TRANSLOCATION OF PRODUCTS OF PHOTOSYNTHESIS IN SUGAR BEET, SOYBEAN, AND PUMPKIN

Abstract

The influence of root function on the export of ¹⁴C-labelled products from leaves of sugar beet, soybean, and pumpkin plants was examined with reference to the concept of a circulatory mechanism for translocation. When roots were placed on demineralized water for periods up to 10 days, oxygen uptake rates were reduced. In sugar beet, this was accompanied by an apparent stimulation of about 21% in the quantity of labelled sugar exported from the leaf. In soybean and pumpkin the quantity of export was not altered, but the distribution of exported ¹⁴C in the plant was modified to favor a decrease in the proportion recovered from the young parts and an increase in that from the stem and root. The absence of nutrient in the root medium did not result in any significant changes in the pattern of slow metabolism of the sugar translocated to the roots of sugar beet or soybean. In the pumpkin, the proportion of radioactivity recovered in the amino acids was lower, and glyceric acid accumulated in the fed leaf. When portions of the sugar beet root were excised 30 min before assimilation of ¹⁴CO₂ by a leaf, the quantity of labelled sucrose exported during a 30-min interval was reduced to about 25% of normal, but the apparent velocity of translocation was not altered and the reduction in quantity could be eliminated by extending the time allowed for export. These results led to the conclusion that the root does not exert a controlling influence on translocation, but that it can contribute to the efficiency of the process.