THE LIPOXYGENASE ISOZYMES IN SOYBEAN [GLYCINE MAX(L) MERR] LEAVES - CHANGES DURING LEAF DEVELOPMENT, AFTER WOUNDING, AND FOLLOWING REPRODUCTIVE SINK REMOVAL

The levels of individual lipoxygenase isozymes in soybean [Glycine max (L.) Merr.] leaves were assessed during leaf development, after mecha nical wounding, and in response to reproductive sink removal. Native i soelectric focusing followed by immunoblotting was employed to examine individual lipoxygenase isozymes. In leaves of all ages, two distinct classes of lipoxygenase isozymes were detected. One class of lipoxyge nase isozymes had nearly neutral isoelectric points (pls) ranging from pH 6.8 to 7.2. The other class of lipoxygenase isozymes had acidic pl s ranging from pH 4.7 to 5.6. During leaf development, all of the neut ral lipoxygenase isozymes and most of the acidic isozymes were present in greatest abundance in the youngest leaves examined and declined in amount as leaf age increased. However, four acidic lipoxygenase isozy mes (pl = 4.70, 4.80, 4.90, 4.95) were more abundant in intermediate-a ge leaves than in either the youngest or oldest leaves examined. Follo wing mechanical wounding of leaves, these same four acidic isozymes al so increased in abundance both locally and systemically in leaves from wounded plants. Unlike the specific effects of wounding on the lipoxy genase isozymes in leaves, reproductive sink removal stimulated a gene ral increase in most of the acidic lipoxygenase isozymes in leaves.