Vegetative Storage Proteins in White Clover ( Trifolium repens L.): Quantitative and Qualitative Features

Abstract

The kinetic pattern of protein mobilization in roots, stolons and nodules of white clover ( Trifolium repens cv. Grasslands Huia) was studied over a regrowth period following complete defoliation. Defoliation led to a significant decrease in soluble protein in stolons and roots during the first days of regrowth as compared with uncut plants. Protein degradation was also observed in nodules of both uncut and defoliated plants. Two of the proteins characterized (15 and 17.3 kDa), which accumulate mainly in perennial tissues, have previously been referred to as Vegetative Storage Proteins (VSPs). Using plants inoculated with either efficient (potentially functional) or inefficient Rhizobium strains, the 15 kDa VSP appeared to be located exclusively in the nodules, and it cross-reacted positively with antibodies raised against soybean leghaemoglobin. Nevertheless, the kinetics of its hydrolysis-accumulation following defoliation clearly supported the view that it may play a role in nitrogen storage. The 17.3 kDa protein was shown to accumulate in response to exposure to low temperature, and exhibited a seasonal pattern of relative accumulation under field conditions. Results are discussed in terms of the putative role that this VSP may play in overwintering of clover.