EFFECTS OF WATER STRESS ON NUTRIENT QUALITY AND ACCUMULATION OF PROTEIN IN RICE GRAINS

Abstract

Aims Soil drying is an important factor threatening rice production in China, and there has been much recent research on the development of grain yield and quality in rice grown under shortages of water. The objective of this study is to examine the effects of soil moisture and N supply levels on rice grain N accumulation and nutrient quality. Methods We conducted a pot study using three rice cultivars and varying in N content to examine physiological characteristics for N accumulation and distribution to grains during the grain-filling period in response to water stress and N supply exposure at heading stage. Important findings The activities of glutamine synthetase (GS) and glutamate synthase (GOGAT) involved in N metabolism were enhanced by mild water stress at 10-20 DAA (days after anthesis) under normal N level, and abilities to synthesize amino acids were improved, which promoted the accumulation of N and elevated the protein content in grains. However, the activities of GS and GOGAT were negatively affected by mild water stress with exposure to high N level, which resulted in decreased synthesis of amino acids. The dynamic changes of the ratio of protein to grain weight presented a “V type during grain-filling. Water stress improved the ratio of protein to grain weight from 15 DAA to harvest under normal N level, but the ratio was decreased by water stress under higher N level when compared with well-watered treatments. Changes of four component parts of protein subjected to water stress varied with nitrogen levels and cultivars. Compared to well-watered treatment, the water-stressed treatment had higher contents of prolamine and glutelin under normal N level, but the contents of prolamine and glutelin subjected to water stress were significantly less than those in the well-watered treatment under higher N level. Water stress affected the lysine content of grains, and varied with cultivars and N supplies. Lysine contents of `Shanyou63' under two N levels were decreased by water stress, but were increased in `Yangdao6'. The variation observed in enzymes involved in N metabolism and partitioning at grain filling to grains of the rice imposed by water stress at heading indicated that plant genotypes influence N accumulation and protein components of grains and subsequent nutrient quality.