Nutrition supply affects the activity of pathogenesis-related β-1,3-glucanases and chitinases in wheat

Abstract

Nitrogen (N) is an essential mineral for plants and both its deficiency and excess causes serious problems in agriculture. As stress-inducible defense is costly, N conditions likely affect the trade-off between the growth and defense. Previous studies identified a few defense-related enzymes dependent on N nutrition. Chitinases (EC 3.2.1.14) and glucanases (EC 3.2.1.39) are typical plant defense enzymes belonging to the group of pathogenesis-related (PR) proteins with multiple functions in plants. Since a comprehensive study on the impact of N nutrition on their activity is missing, we studied their profiles and activities at isoforms level in wheat plants grown hydroponically at N doses corresponding to limited (0, 0.75 and 5.25 mM N), optimal N (7.5 mM N) as well as excess (15, 30 and 35 mM N) N supply in the form of nitrate. Our results show that several isoforms of both enzymes in wheat leaves and/or shoots clearly depended on N supply, while their activities rather depended on organ type. Furthermore, glucanases and chitinases appeared to be regulated in an opposite way. The activities of particular chitinases and glucanases correlated with a proline content that has multiple functions in plants. Proline typically accumulated with increasing the N supply when certain excessive N doses induced the gene for proline synthase (P5CS) in shoots and that for ornithine aminotransferase (OAT) in roots. This work points to a N-dependent activity of several defense-related compounds suggesting the possibly of altered plant defense potential under various N regimes.