Effects of Photoperiod, Low Temperature and N Nutrition on VSP Accumulation in Taproot of Alfalfa

In Medicago sativa L., vegetative storage protein (VSP), specifically accumulated in taproot, are strongly involved in nitrogen storage. How the accumulation of such VSPs is regulated remains largely unknown. Experiments were designed with non-nodulated alfalfa to determine if length of the photoperiod, a decrease of temperature, or high availability of mineral nitrogen may induce the accumulation of VSPs. 15N labelling was used to quantify nitrogen uptake and its further relative translocation within the plant while VSPs accumulation was analysed by ELISA quantification. Results showed that environmental factors such as shortening daylength or low temperature changed biomass allocation within the plant by reducing shoot growth. As a consequence, short days promoted the relative N allocation to taproot whereas VSP accumulation showed a higher trend. On the other hand, low temperature, changes in N source or availability in the nutrient solution, may lead to a higher influx of nitrogen and a higher soluble protein relative concentration in taproot while VSP abundance remained low