Hajime Ohno

Activation of sucrose-metabolizing enzymes and stimulation of sucrose uptake by auxin and sucrose in eggplant (Solanum melongena L.)

Summary Tissue segments prepared from ovaries and fruits of eggplant (Solanum melongena L.) were incubated in the presence of auxin and sucrose, and activities of sucrose-metabolizing enzymes were determined. Activities of cell-wall-bound and soluble acid invertases increased in response to exogenous indole-3-acetic acid (IAA) and 4-chlorophenoxyacetic acid (4-CPA), whereas activities of sucrose synthase (SS) and sucrose phosphate synthase (SPS) were not influenced by auxin. On the other hand, SS activity increased in response to added sucrose, whereas the activities of acid invertase and SPS were not influenced by sucrose. The effects of IAA on uptake of sugars into ovary tissues were also examined. The uptake of sucrose, glucose, and fructose by carrier-mediated transport was stimulated clearly by IAA. These results indicate that IAA stimulates both the activation of acid invertase and the uptake of sugars, and an increased concentration of sucrose stimulates activation of SS. The sink activity increased in these ways may thus trigger fruit growth.

Changes in content of indole-3-acetic acid and in activities of sucrose-metabolizing enzymes during fruit growth in eggplant (Solanum melongena L.)

Summary Changes in the content of endogenous indole-3-acetic acid (IAA) and in activities of sucrose-metabolizing enzymes during fruit set were investigated in eggplant ( Solanum melongena L.). When fruit growth was stimulated by pollination or treatment with 4-chlorophenoxyacetic acid (4-CPA), IAA content increased during fruit set. Intra- and extra-cellular fractions were separated by washing fruit tissue segments with 0.5 mol · L −1 NaCl. Invertase from both fractions had an optimum at pH 5. The activity in the intra-cellular fraction (soluble acid invertase) was much higher than that in the extra-cellular fraction (cell-wall-bound acid invertase). However, fruit mass and IAA content did not increase in unpollinated fruit. Activities of all the sucrose-metabolizing enzymes also increased during fruit set, when fruits were treated by pollination or 4-CPA. Time courses of change in activity of soluble acid invertase and sucrose phosphate synthase (SPS) were quite similar to that of the relative growth rate of the fruit. In contrast, changes in activity of cell-wall-bound acid invertase and sucrose synthase (SS) were not clearly associated with fruit growth. The increase in activity of soluble acid invertase was accompanied by the increase in endogenous IAA content. These results suggest a possible involvement of IAA in the synthesis of soluble acid invertase that may induce fruit growth.