Impact of High Temperature Stress on Carbohydrate Metabolism in Developing Microspores of Grain Sorghum.
Mukesh Jain1, Andrew Funk1, P.V. Vara Prasad2, L. Hartwell Allen Jr.3, Kenneth J. Boote1, and Prem S. Chourey3. (1) University of Florida, Agronomy Department, Gainesville, FL 32611-0500, (2) Kansas State University, Agronomy Department, 2004 Throckmortran Hall, Manhattan, KS 66506, (3) USDA-ARS, 2005 SW 23rd Street, Gainesville, FL 32608
High temperature stress prior to flowering and during flowering is known to decrease seed-set and yields in grain sorghum [Sorghum bicolor L. (Moench)]. However, the mechanisms through which seed-set is decreased are not well understood. The objective of this research was to understand the impact of high temperature stress during pollen development and pollen maturation on carbohydrate metabolism and transcript profiles of developing microspores, pollen viability and percent seed-set in grain sorghum. Plants of sorghum cultivar DK28E were grown in natural sunlit outdoor controlled environment growth chambers at near-optimum temperature (30/20°C; daytime maximum/nighttime minimum) or at elevated temperature (36/26°C) during various stages of pollen development (10 d or 5 d prior to panicle emergence) for the duration 5 to 10 days. At panicle initiation stage, developing and developed pollen grain samples were collected to determine carbohydrate content and transcript profiles. Similarly, after the completion of the stress period data on pollen viability and percentage seed set was estimated. The results showed that high temperature stress significantly decreased pollen germination and resulted in lower seed-set percentage. High temperature stress also caused significant changes in carbohydrate metabolism and transcript profiles of developing microspores particularly those related to cell wall invertase (CWI). There was a significant decrease in steady-state transcript levels of CWI and other downstream genes involved in sugar to starch metabolism. In addition transcriptional changes in levels of some crucial regulatory genes (SnRK1 and HxK) and transcriptional factors (MADS-1, MADS-1 and hexose transporters) were observed under high temperature stress. These data suggest the high temperature stress influences the sugar signals and related gene expression profiles, and transport of sugars to developing pollen, ultimately leading to lower seed-set and lower yields.