Development of Vacuolar Membranes during Elongation of Cells in Mung Bean Hypocotyls

概要

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The development of vacuolar membrane in the elongating hypocotyls of the mung bean was investigated. The hypocotyls from 3-day-old seedlings were dissected into the dividing, elongating and mature regions. The diameter of protoplasts prepared from the mature regions was about 3-fold greater than the diameter of those from the dividing region. The activity of inorganic pyrophosphatase, an enzyme associated with the vacuolar membrane, was detectable even in the dividing region. The level of pyrophosphatase was quantified by slot-blot analysis with the pyrophosphatase-specific antibody. The relative amount of pyrophosphatase per cell, calculated on the basis of DNA content, increased about 4-fold during cell maturation. When the densities of vacuolar membranes were compared by sucrose density gradient centrifugation, there was no marked difference among the preparations from three regions. Furthermore, most of the major proteins were common to the three purified preparations of vacuolar membranes. From the results, it appears that most components of vacuolar membrane may be synthesized de novo and added to the existing membrane during cell elongation. Furthermore, it is proposed that the H^+-pyrophosphatase may actively hydrolyze its substrate to maintain the internal acidity of expanding vacuoles, because pyrophosphate was present at a concentration of more than 70 μM in the dividing and elongating regions.
日本植物生理学会の論文