Date of this Version
Plant Physiol. (1994) 105: 1445-1446
Soybean (Glycine max L.) transiently accumulates two abundant vegetative storage proteins, VSP A and VSP B, in vacuoles of above-ground vegetative tissues (Wittenbach, 1983; Staswick, 1990). As older leaves and stems become a source of exported metabolites for developing sinks, the VSPs are preferentially degraded and the resulting metabolites are presumably mobilized in the xylem and phloem stream. A striking feature of these proteins is that VSP gene expression is dramatically increased in mature leaves following the remova1 of reproductive sinks (seed pods) and the amount of these proteins increases accordingly (for review, see Staswick, 1994). Other changes in leaves associated with this shift from a source to a storage organ in response to fruit removal include the elevation of starch, retention of Chl, loss of Rubisco activity, and a delay of visible symptoms of senescence (Wittenbach, 1982).