Effect of elevated carbon dioxide on nitrogen assimilation and mobilization in wheat and rye genotypes of different ploidy levels

Abstract

Two wheat genotypes differing in ploidy level viz. PBW 343 (hexaploid) and PDW 274 (tetraploid), and rye genotype WSP 540-2 (diploid) were grown under elevated CO2 (EC: 550 ± 50 ppm) and ambient CO2 (AC: 380 ppm) to study the changes in nitrogen assimilatory pathway enzymes. Elevated CO2 increased nitrate reductase (NR) activity in flag leaves of the three genotypes at milk stage, and activity was highest in rye (diploid). At dough stage, hexaploid and tetraploid genotypes showed higher NR activity in plants grown under EC. Elevated CO2 resulted in higher expression of NR gene (NIA1). Activity of glutamine synthetase (GS) in flag leaves was higher in all the three genotypes under EC at milk stage but the activity declined at dough stage. The expression of GS1 increased in flag leaves of plants grown under EC at both milk and dough stages, while the expression of GS2 declined during the reproductive stages, especially in ears of EC grown plants. Nitrate content decreased in leaf tissues of all the three genotypes by 90 DAS in EC grown plants. This indicated enhanced nitrate assimilation in leaves by NR under EC at reproductive stage. However, lower GS2 expression and lower GS activity during late reproductive phase (dough stage) indicated inhibition of consequent steps.