Silicon uptake in rice and cucumbers

The study of silicon uptake in rice (Oryza sativa L. cv. Ml02) revealed an energy dependent, carrier-mediated system of silicon transport. This uptake system saturated at approximately 2 mM external Si and displayed a Vmax of 18.5 umol.g root-1.h"1 and a Km of 0.578 mM. Transport was found to not rely on transpiration rates. Studies of the effect of temperature, anoxia and KCN showed that the silicon uptake system was as strongly dependent on metabolic energy as potassium and several other major macronutrients, though it responded more slowly to such treatments than did potassium. The uptake system showed the characteristics of a derepressible system of uptake, in which plants deprived of silicon showed markedly enhanced rates of uptake as compared with plants grown in the presence of adequate silicon levels. The study of the kinetics of uptake in cucumbers (Cucumis sativus cv. Corona) revealed the possibility that, rather than passively absorbing silicon, the plants possess a low affinity saturable system responsible for the uptake of silicon, with a Km of 0.84 mM and a Vmax of 12.5 umol.g root-1.h-1. This system, however, did not appear to have a derepressible system of uptake such as was the case for rice. In the light of the growing body of information pointing to the importance of silicon as a plant nutrient, this study provides physiological evidence of silicon accumulation by two plant species and lays the foundation for fuller physiological and biochemical studies which may resolve the question of the essentiality of this element in plants.Science, Faculty ofBotany, Department ofGraduat