Relation Between Ca and Sr Transport Rates, as Determined Simultaneously in Isolated Segments of Vetch, Barley, and Pine Roots

摘要

Root segments of vetch, barley, and pine were exposed to nutrient containing 85Sr and 45Ca tracers. Transport in both vetch and barley usually declined before an elapsed time of 24 hours unlike corn, which maintains its steady state beyond 24 hours. Pine was radically different in that it showed no difference between acropetal and basipetal transport rates and had very low rates. Sr transport in all plants studied to date followed that of Ca and the ratio Sr/Ca transported was equal to the ratio Sr/Ca in the nutrient. In vetch, stable Ca transport was reduced to one-fifth when Sr concentration was increased from 0.5 mM to 2.5 mM. Yet stable Sr transport did not change, indicating that the effect on transport was not due to competitive inhibition. A similar effect was less pronounced in barley, but could not be detected in pine. The magnitude of the transport rates varied considerably between the various species, corn being greatest followed by barley, vetch, and pine in decreasing order. Transport did not correlate with root weight or surface area; it amounted to from 0.03 to 0.60 nanomoles per hour in these experiments as compared to 7 nanomoles per hour previously established in corn (in all cases, 55 mm segments, sectioned 10 mm from apex). (Author)