In vitro binding of IAA to plasma membrane-rich fractions containing Mg^<++>-activated ATPase from mung bean hypocotyls

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Cell homogenates of dark-grown mung bean hypocotyls were fractionated into six fractions (L-0, L-1 to L-5) by stepwise sucrose density-gradientcentrifugation. The majority (ca. 84%) of Mg^<++>_activated ATPase activity of the 10,000 × g pellet was localized in the L-0 (1.03≦d≦1.14) and L-1 (1.14≦d≦1.16) fractions. Over 40% of the vesicular membrane in the L-0 fraction and 60% of the L-1 fraction could be stained with phosphotungstic acid (PTA)-chromic acid, a selective staining for the plant plasma membrane. In vitro binding of ^<14>C-IAA to the fraction components was the greatest in the L-1 fraction among the six. The binding of ^<14>C-IAA to the L-1 fraction in vitro was markedly interfered with by the presence of a high concentration of cold IAA (2 × 10^<-4> M). However, it was not affected by the IAA analogues IPA, IBA and IAN. This indicates that IAA highly specifically binds to the L-1 fraction. In vitro specific binding of ^<14>C-IAA to L-1 and L-0 was decreased with an increasing acidity from pH 8.0 to 5.0. In vitro binding of ^<14>C-IAA to L-1 and L-5 was urther enhanced when these fractions were isolated from sections pretreated with 10^<5> M Cold IAA for 60 min.
日本植物生理学会の論文