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

Helianthus annuus L. plants were grown with the shoots at normalair temperature and with the roots in nutrient solution at 10,20 or 30 °C. The higher the root temperature the greaterthe growth of the leaves, resulting in higher production ofphotosynthates. Irrespective of growth conditions an equilibriumwas established between the maintenance respiratory activityof shoot and roots. A constant proportion of the photosynthateproduced was used in respiration. The results are discussedin relation to a thermodynamic theory of stability of biologicalsystems. It is suggested that changes in energy partition betweenmaintenance and growth, and then in relative growth rates ofshoots and roots during an adaptation period, represent a majorhomeostatic mechanism. shoots, roots, maintenance respiration, growth, relative growth rate, respiration, adaptation, sunflower, Helianthus annuus L.