Expression and Accumulation Patterns of Nitrogen-Responsive Lipoxygenase in Soybeans

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Abstract
Gene expression and protein accumulation patterns of nitrogen-responsive lipoxygenase (LOX-NR), as a representative vegetative storage protein, were investigated in nonnodulated soybeans (Glycine max [L.] Merr. cv Wye). The form of available nitrogen (supplied as NH4NO3, NH4+, NO3-, or urea) influenced the mRNA level and the amount of LOX protein, indicating that preferential accumulation of LOX may occur. Soybeans were grown with 0, 2, 5, and 16 mM total nitrogen to determine the extent to which LOX accumulation responded to soil nitrogen levels. Analysis of both mRNA and protein levels was conducted in shoot tips, stems, pod walls, and leaves over the entire life cycle of the plant. A general correlation between increasing available nitrogen level and LOX level was seen in the shoot tip and other organs throughout the soybean life cycle. However, appreciable amounts of LOX-NR mRNA and protein accumulated even when plants were grown under conditions of nitrogen deficiency. The results indicate that LOX may play an important role as a temporary storage site for amino acids in the developing shoot tip. The expression patterns of LOX-NR in plants grown under nitrogen deficiency suggest that these proteins, although responsive to nitrogen status, may not function solely as temporary storage pools for amino acids.