Regulation of Acyl Carrier Protein Messenger RNA Levels during Seed and Leaf Development

We have examined the expression of acyl carrier protein (ACP) mRNA levels and ACP activity in leaves, where fatty acids function primarily in membrane synthesis, and in developing soybean seeds, where fatty acids are primarily used for oil storage. An RNA probe transcribed from a synthetic spinach ACP-I gene hybridized on Northern blots to ACP mRNA from both seed and leaf tissue from soybean, spinach, and rapeseed. In each species, the ACP transcript from leaf was slightly larger than that from seed. Both the amounts of ACP protein and the levels of ACP mRNA were substantially higher in young leaf tissue of spinach and soybean when compared to mature leaf tissue. Light-grown spinach leaves also contained higher ACP activity and accumulated more ACP mRNA than dark-grown leaves. ACP mRNA levels measured in developing soybean seeds peaked at 20 days after flowering then decreased 10-fold by 70 days after flowering. In each tissue, the developmental changes in ACP protein levels can be accounted for by changes in ACP mRNA abundance. Comparison of the relative prevalence of mRNA and protein for ACP and lectin in soybean seeds suggests a major difference in mRNA translational efficiency and/or protein stability for these two proteins.