Adaptation and Functional Balance Between Shoot and Root Activity of Sunflower Plants Grown at Different Root Temperatures

Abstract

Helianthus annuus L. plants were grown with the shoots at normal air temperature and with the roots in nutrient solution at 10, 20 or 30 °C. The higher the root temperature the greater the growth of the leaves, resulting in higher production of photosynthates. Irrespective of growth conditions an equilibrium was established between the maintenance respiratory activity of shoot and roots. A constant proportion of the photosynthate produced was used in respiration. The results are discussed in relation to a thermodynamic theory of stability of biological systems. It is suggested that changes in energy partition between maintenance and growth, and then in relative growth rates of shoots and roots during an adaptation period, represent a major homeostatic mechanism.