Methyl jasmonate alters N partitioning, N reserves accumulation and induces gene expression of a 32-kDa vegetative storage protein that possesses chitinase activity in Medicago sativa taproots.

Abstract

This study presents the effects of methyl jasmonate (MeJA) on growth, N uptake, N partitioning, and N storage in taproots of non-nodulated alfalfa (cv. Lodi). When compared to untreated plants, addition of 100 micro M MeJA to the nutrient solution for 14 days reduced total growth and modified biomass partitioning between shoots and roots in favour of taproots and lateral roots. MeJA decreased N uptake (after 7 days) and increased N partitioning towards roots after 14 days. This preferential N partitioning to roots was accompanied by increased N storage in taproots as soluble proteins. Compared to total soluble proteins, VSP accumulation occurred earlier (7 days), and was greater (2-fold increase) in plants treated with 100 micro M MeJA. Steady-state transcript levels for two VSPs (32 and 57 kDa) also increased markedly (about 4-fold) in roots of plants treated with 100 micro M MeJA. This suggests that MeJA could act directly (transcriptional regulation) or indirectly (via the changes of N partitioning among alfalfa organs) on N storage as soluble proteins and in particular, VSPs. Because the deduced amino acid sequence of the 32 kDa VSP clone reveals high homology with Class III chitinases, we propose that the 32 kDa VSP may have a role in pathogen defense, in addition to its function as a storage protein.