Synthesis and Apparent Turnover of Acid Invertase in Relation to Invertase Inhibitor in Wounded Sweet Potato Root Tissue

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Abstract
Previously we showed that acid invertase activity increased and then decreased rapidly in wounded sweet potato (Ipomoea batatas Liam.) root tissue, and that the tissue contained a heat-stable, proteinaceous inhibitor with a molecular weight of about 19,500 daltons. In response to wounding of sweet potato root tissue, inhibitor activity decreased during the increase in invertase activity but later increased slightly when invertase activity declined. Cycloheximide treatment did not affect the decrease in inhibitor activity that occurred during the early incubation stage, but did inhibit the increase in inhibitor activity that occurred during the late incubation stage. Intrinsic invertase activity, which was assayed after removing the inhibitor, increased and then decreased after wounding, as apparent activity did. The degradative rate of acid invertase in root discs, when assayed by intrinsic activity, was roughly the same during both the early and late incubation stages after wounding, and the degradative rate of the enzyme during the late incubation stage was unaffected by cycloheximide treatment. These results suggest that in sweet potato root discs, enzyme synthesis occurs during the early incubation stage, and ceases during the late incubation stage; however, the enzyme undergoes constant degradation. The change in acid invertase activity after wounding seems to be controlled in root tissue by the interactions of inhibitor-binding and turnover of the enzyme protein.