Sugar transport and nitrate reductase activity rate in roots affect plant adaptation to cold and warm climate plants

Nitrogen metabolism in the root is controlled by 2 fluxes: 1) nitrate intake from the external solution. 2) Transport of sugar from the leaves. Nitrate reduction to ammonium or direct ammonium uptake produce ammonia in the root cell. When the rate of sugar transport to root cells is slower than their sugar consumption for respiration, ammonia will accumulate and the root cells will die from ammonia toxicity. In nature, plants can be defined with regard to the activity of their root nitrate reductase. High N concentration inside the root and high root temperatures reduce root sugar content to the point of root death. Low N concentration at a continuous supply could help maintain plant roots alive, both in nature and in glasshouse plants grown in containers. I propose here, based on published works and our own studies, that plant roots die with increase in root temperature in the presence of nitrate or ammonium due to the depletion of sugar in the root cell by increased rate of root cell respiration. The rate of sugar supply to the root is species dependent. The rate of sugar respiration in the root is a function of root temperature. It is suggested here that the fraction of root nitrate reductase activity out of total nitrate reduction in the plant is responsible for the survival of plants between temperate and hot climates