Impact of elevated temperatures and carbon dioxide on development and composition of soybean seed

Soybean (Glycine max L.) was grown in sunlit, controlled environment chambers under diel sinusoidal temperatures of 28/18, 32/22, 36/26, 40/30 and 44/34°C (day/night, maximum/minimum), and two concentrations of carbon dioxide ([CO₂]), 350 and 700 μmol mol−1 , imposed over the entire crop life cycle. Under elevated temperature, single seed growth was delayed by two weeks and growth rates decreased. There was no effect of [CO₂] on seed growth. The weight per seed decreased linearly with increasing temperature. Almost all mature seed from plants grown at 40/30°C were shriveled, whereas no shriveled seed were observed at 28/18°C.; The number of cells per cotyledon was highest at 32/22°C and decreased at higher temperatures. Few nuclei were visible in one week old cotyledon cells from plants grown at 40/30°C compared to numerous nuclei visible in cotyledon cells from plants grown at 28/18°C. When grown at 40/30°C, seed cells appeared highly vacuolated with few plastids or organelles. This implies a problem in nuclear and/or plastid duplication during the cell division phase.; The harvested seed were analyzed for oil, fatty acids, total nitrogen, phosphorus and carbohydrates. Oil concentration was highest at 32/22°C and decreased at higher temperatures. The ratio of oleic acid to linolenic acid concentration increased with increasing temperature. Nitrogen and phosphorus concentration increased up to 40/30°C and then decreased dramatically. Total nonstructural carbohydrates decreased with increasing temperatures. Most changes in seed development and composition were linked to temperatures above 32/22°C, but there were no [CO₂] effects.; Changes in gene expression due to temperatures of 28/18 or 40/30°C at two levels of [CO₂] were documented through the differential display of RNA. Twelve candidate genes were differentially regulated by these environmental treatments. Of the 12, four were verified through northern blot analysis. The transcript (mRNA) for α-tubulin was not present in seeds grown at 700 μmol mol−1 [CO₂]. Transcripts for β-glucosidase and chitinase class III were present only in seeds from 28/18°C, and mRNA for MAP-kinase kinase was present in seeds from 40/30°C but not from 28/18°C.