Metabolic activity of cotton roots in response to temperature

Abstract

Root growth, under genetic control, responds to numerous environmental stimuli. The occurrence of below optimal soil temperatures for root growth of cotton ( Gossypium hirsutum L.) at planting time may delay seedling establishment and reduce seasonal crop productivity. The present study assessed cotton root growth and metabolism at various temperatures to determine if observed temperature responses were related to developmental changes in seedling growth. Studies monitoring seedling root 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 reduction showed that the temperature optima of root metabolism at 10 days after planting (DAP) was lower than that obtained from the measure of accumulated root growth at 10 DAP. The differences in the temperature optima appear to be associated with dynamic changes in seedling development which may be related to changes in stored seed reserves. Metabolic temperature responses are broad during peak seed reserve mobilization and become narrow with the depletion of available reserves. Measurement of root length or root number at 10 DAP would reflect a composite of narrow and broad metabolic temperature sensitivities. Because root development is linked to this composite of metabolic temperature responses, the temperatures providing the maximum root size at 10 DAP are actually higher than the optimum temperature for metabolism under the non-saturating substrate levels associated with the majority of the growing season. Evaluation of cotton root growth responses to shoot and root temperatures within or below cotton's thermal kinetic window revealed enhanced root growth when the roots temperatures were within the thermal kinetic window. These findings provide new insights for evaluation of the temperature characteristics of root growth.