1. State Key Laboratory of Crop Stress Biology in Arid Areas and College of Agronomy; Northwest A&F University; Yangling Shaanxi 712100 China
2. Department of Plant Biology and Crop Science; Rothamsted Research; Harpenden Herts AL5 2JQ UK
3. Institute of Water Saving Agriculture in Arid Regions of China; Northwest A&F University; Yangling Shaanxi 712100 China