METABOLIC-ACTIVITY OF COTTON ROOTS IN RESPONSE TO TEMPERATURE

Root growth, under genetic control, responds to numerous environmental stimuli. The occurrence of below optimal soil temperatures for root g rowth of cotton (Gossypium hirsutum L.) at planting time may delay see dling establishment and reduce seasonal crop productivity. The present study assessed cotton root growth and metabolism at various temperatu res to determine if observed temperature responses were related to dev elopmental changes in seedling growth. Studies monitoring seedling roo t growth revealed distinct temperature optima for the cotton seedling. Analysis of the temperature characteristics of in vivo mitochondrial electron transport measured by 2,3,5-triphenyltetrazolium chloride red uction showed that the temperature optima of root metabolism at 10 day s after planting (DAP) was lower than that obtained from the measure o f accumulated root growth at 10 DAP. The differences in the temperatur e optima appear to be associated with dynamic changes in seedling deve lopment which may be related to changes in stored seed reserves. Metab olic temperature responses are broad during peak seed reserve mobiliza tion and become narrow with the depletion of available reserves. Measu rement of root length or root number at 10 DAP would reflect a composi te of narrow and broad metabolic temperature sensitivities. Because ro ot development is linked to this composite of metabolic temperature re sponses, the temperatures providing the maximum root size at 10 DAP ar e actually higher than the optimum temperature for metabolism under th e non-saturating substrate levels associated with the majority of the growing season. Evaluation of cotton root growth responses to shoot an d root temperatures within or below cotton's thermal kinetic window re vealed enhanced root growth when the roots temperatures were within th e thermal kinetic window. These findings provide new insights for eval uation of the temperature characteristics of root growth.