Differences in nutrient remobilization characteristics and relationship to senescence and grain nutrient content among rice varieties

Abstract

During leaf senescence, essential nutrients are remobilized to sink tissues such as developing seeds and grains. Nutritional contents in the grains of crop plants may be influenced by the extent of the nutrient remobilization process, which may be influenced by the leaf senescence programming. To test these hypothetical relationships in rice plants, nutrient remobilization characteristics of three macro-elements—nitrogen (N), phosphorus (P), and potassium (K)—were examined among ten rice genetic backgrounds including nine representative Thai rice varieties and one Indian variety. Greenness colorations and the N, P, and K contents of flag leaves of the field-grown rice plants were quantified at 0, 7, 14, 21, and 28 days after flowering. Rice varieties that exhibited a stay-green trait or high nutrient remobilization efficiency were identified. On average, the N, P, and K remobilization efficiencies were 50%, 27%, and 22%, respectively, suggesting a poor remobilization process in rice compared to other crop plants. No significant relationship (P < 0.05) was found between the nutrient remobilization rates or efficiencies and the leaf greenness reduction efficiencies among the rice varieties. Furthermore, no significant relationship (P < 0.05) was found between the N, P, and K contents in mature rice grains and the nutrient remobilization rates and efficiencies, or the initial nutrient content stored in flag leaves. Further studies using a larger number and broader range of rice varieties and examining other characteristics of the leaf senescence and nutrient remobilization processes may be needed to verify this lack of association.