Abstract
Maintaining an appropriate balance of carbon to nitrogen metabolism is essential for rice growth and yield. Glutamine synthetase is a key enzyme for ammonium assimilation. In this study, we systematically analyzed the growth phenotype, carbon-nitrogen metabolic status and gene expression profiles in GS1;1-, GS1;2-overexpressing rice and wildtype plants. Our results revealed that the GS1;1-, GS1;2-overexpressing plants exhibited a poor plant growth phenotype and yield and decreased carbon/nitrogen ratio in the stem caused by the accumulation of nitrogen in the stem. In addition, the leaf SPAD value and photosynthetic parameters, soluble proteins and carbohydrates varied greatly in the GS1;1-, GS1;2-overexpressing plants. Furthermore, metabolite profile and gene expression analysis demonstrated significant changes in individual sugars, organic acids and free amino acids, and gene expression patterns in GS1;1-, GS1;2-overexpressing plants, which also indicated the distinct roles that these two GS1 genes played in rice nitrogen metabolism, particularly when sufficient nitrogen was applied in the environment. Thus, the unbalanced carbon-nitrogen metabolic status and poor ability of nitrogen transportation from stem to leaf in GS1;1-, GS1;2-overexpressing plants may explain the poor growth and yield.
Highlights
Nitrogen is an essential macronutrient required for plant growth and development, and it is a major limiting factor in determining plant productivity and crop yield [1,2,3,4]
Our results showed a significant (P,0.05) decrease in the root length and plant height, root and shoot dry weight in GS1;1, GS1;2-overexpressing plants when compared to wildtype plants at both the tillering and heading stages under the 06N, 0.16N, 16N and 56N conditions (Fig. 1)
Our results showed significant (P,0.05) decreases in the carbon/nitrogen ratio, in the stem, in the GS1;1, GS1;2-overexpressing plants when compared to wildtype plants
Summary
Nitrogen is an essential macronutrient required for plant growth and development, and it is a major limiting factor in determining plant productivity and crop yield [1,2,3,4]. Amino acids and the resulting proteins, in particular enzymes, are essential for most cellular activities [5] In addition to their independent utilization, the coordination and optimal functioning of the metabolic pathways for nitrogen and carbon assimilation in plants are critical for determining plant growth and, biomass accumulation [6,7]. Maintaining an appropriate balance or ratio of carbohydrates to nitrogen metabolites in the cell, which is referred to as the ‘‘carbon/nitrogen balance,’’ is important for the regulation of plant growth, development and yield production [5,8,9,10]
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