Project Number: 6615-11000-007-00
Project Type: Appropriated

Start Date: Jan 20, 2005
End Date: Jan 19, 2010

Objective:
Identify mechanisms of heat tolerance at ambient and elevated CO2 among cultivars of soybean, dry bean, grain sorghum, and maize showing different pollen development, reproductive growth, yield, and seed quality sensitivities to heat stress. Determine if yield failures under high temperatures are mediated by low oxygen in reproductive tissues. Determine photosynthetic mechanisms of C4 plant responses to increased CO2, and to increased CO2 under elevated temperatures and/or water deficit.

Approach:
Selected soybean, sorghum, and maize cultivars will be grown at current doubled CO2 in Gainesville ambient and +4.5 Celsius sections of temperature-gradient greenhouses to identify heat tolerant cultivars. For grain sorghum and maize in sunlit controlled-environment chambers, procedures will be used to identify heat-sensitive points in pollen sugar transport and/or starch metabolism, and to identify genes that are sensitive to heat in the sucrose'starch pathway in developing pollen. Microprobes will be used to determine oxygen in soybean and dry bean pods and seeds as affected by temperature and ambient oxygen. Seeds produced from all studies will be analyzed for phytochemicals of interest for human nutrition. Measurements of leaf gas exchange, enzyme activities, and metabolic products will be used to test hypotheses that positive C4 plant response to high CO2 results from enhanced photosynthesis in early stages of leaf development.