Mobilization of nitrogen reserves during regrowth of defoliated Trifolium repens L. and identification of potential vegetative storage proteins

Although it is well established that carbon reserves contributeto shoot regrowth of leguminous forage species, little informationis available on nitrogen reserves except in Medicaqo sativaL. and Trifolium subterraneum L. In this study, reserves werelabelled with ¹⁵N to demonstrate the mobilization of endogenousnitrogen from roots and stolons to regrowing leaves and newstolons during 24 d of regrowth in white clover (Thfolium repensL.). About 55% and 70%, respectively, of the nitrogen contentsof these organs were mobilized to support the regrowth of leaves.During the first 6 d, nitrogen in regrowing leaves came mainlyfrom N reserves of organs remaining after defoliation. Afterthese first 6 d of regrowth, most of the shoot nitrogen wasderived from exogenous nitrogen taken up while the contributionof nitrogen reserves decreased. After defoliation, the buffer-solubleprotein content of roots and stolons decreased by 32% duringthe first 6 d of regrowth. To identify putative vegetative storageproteins, soluble proteins were separated using SDS-PAGE ortwo-dimensional electrophoresis. One protein of 17.3 kDa instolons and two proteins of 15 kDa in roots seemed to behaveas vegetative storage proteins. These three polypeptides, initiallyfound at high concentrations, decreased in relative abundanceto a large extent during early regrowth and then were accumulatedagain in roots and stolons once normal growth was re-established. Key words: White clover, regrowth, ¹⁵N-labelled, vegetative storage proteins, electrophoresis