Starch synthase activityand grain growth in wheat cultivars under elevated temperature: A comparison of responses

Wheat (Triticum aestivum L.) cvs. HD 2285 and C 306 (relatively tolerant) and HD 2329 and HD 2428 (susceptible type) were exposed during grain development period to 5–7°C higher temperature in a normal glasshouse and 8°C higher than control in temperature control glasshouse of phytotron facility. There was more severe depression in grain growth under elevated temperature in phytotron experiment and was associated with greater decrease in the activity of soluble starch synthase (SSS) in the grains. Furthermore, relatively tolerant cultivars showed less decrease compared to susceptible cultivars in grain growth and also showed less decrease in SSS activity. Such parallelism in the effect of elevated temperature on grain growth and SSS activity and relatively tolerant cultivars showing less depression, further suggests that soluble starch synthase is the key component imparting sensitivity to high temperature for grain growth in wheat. The study suggested that thermotolerance for grain growth in wheat could possibly be improved through incorporation of thermostable form of this enzyme.