Purification and Characterization of a Soybean Leaf Storage Glycoprotein

Abstract

Removing the pods from soybean (G. max [L.] Merr. cv. Wye) plants induces a change in leaf function which is characterized by a change in the leaf soluble protein pattern. The synthesis of at least 4 polypeptides (.apprx. 27, 29, 54, and 80 kildoaltons) is enhanced, and these polypeptides accumulate to levels comprising over 50% of the soluble protein. Heat girdling the petiole also causes the accumulation of these polypeptides, suggesting that the signal for changing leaf function may be associated with inhibition of phloem transport. The 27 and 29 kilodalton polypeptides are glycosylated and were purified to greater than 90% by (NH4)2SO4 fractionation, concanavalin A affinity, and gel filtration chromatography. These peptides apparently comprise a single protein. Mouse antiserum was prepared against this glycoprotein and was used to check for cross-reactivity with seed proteins and to quantitate changes with leaf development. No cross-reactivity was observed with seed soluble proteins from several stages of development. Quantitation showed the highest content in podded plants at, and shortly following, flowering, with levels subsequently declining in conjunction with seed growth. In depodded plants, the level of glycoprotein continued to increase following flowering and accounted for 45% of the soluble leaf protein by 4 wk after depodding.