Effects of environmental factors and endogenous signals on N uptake, N partitioning and taproot vegetative storage protein accumulation in Medicago sativa

Abstract

Our objectives were to study the regulation of N partitioning within tissues of non-nodulated alfalfa (Medicago sativa L.) and N storage in taproots as vegetative storage proteins (VSP) of 15, 19, and 32 kDa and β-amylase (57 kDa) by environmental (photoperiod, temperature, N availability) and endogenous factors (methyl jasmonate). When compared to long-day conditions (LD, 16 h day/8 h night), short-day (SD, 8 h day/16 h night), exposure to low temperature (5˚C) or application of methyl jasmonate (MeJA, 100 M ) for 35 d reduced the biomass shoot/ root ratio and modified the source–sink relationships for N. SD and MeJA treatments resulted in partitioning of N to taproots and a concomitant accumulation of VSPs. In comparison with LD, SD treatment also stimulated β-amylase gene expression 2.5-fold. Although low temperature increased the N partitioning to root tissues and the accumulation of soluble proteins in taproot, VSP concentration and β-amylase mRNA levels remained low. Increasing N concentration from 1 to 5 mM KNO₃ doubled the total dry matter but did not affect the N partitioning within the plant, VSP accumulation, or ‚ β-amylase expression. These results suggested that short photoperiod can result in preferential N allocation toward taproots with a concomitant induction of VSP accumulation.