Biochemical dynamics of soybean paraveinal mesophyll cell vacuoles and identification of cysteine proteases associated with these dynamics

A critical determinant of plant productivity is the reallocation of nitrogen from the vegetative organs to the developing seed. In this nutrient recycling process, vegetative storage proteins (VSPs) and specific vegetative lipoxygenases (VLXs) play a major role as nitrogen reserves that can be mobilized to meet the needs of growing seed and tissues. VLXs and VSPs in soybeans accumulate in vacuoles of the paraveinal mesophyll (PVM) cell layer prior to their degradation. When these VLXs and VSPs are mobilized, PVM vacuoles convert from storage to lytic forms, which is reversed upon sink limitation. Additionally, cysteine protease activity is induced by removal of sink limitation, suggesting a putative role of cysteine proteases in the mobilization of VLXs and VSPs in the PVM vacuole.