Stimulation of ATPase activity in barley (Hordeum vulgare) root plasma membrane after treatment of intact tissues and cell free extracts with triacontanol.

Ca2+- and Mg2+-dependent ATPase activity (EC 3.6.1.3) in a plasma membrane-enriched fraction increased rapidly after in vivo application of physiologically active concentrations of triacontanol (TRIA) to the roots of barley (Hordeum vulgare L. cv. Conquest) seedlings. Ca2+- and Mg2+-dependent ATPase activity was 64 and 85% higher, respectively, in the roots of seedlings germinated in the presence of growth- promoting concentrations of TRIA compared to controls. The increase in vivo was concentration dependent, with the greatest increase obtained at 2.3 nM TRIA. Maximal stimulation of ATPase activity of excised tissue treated with TRIA coincided with the temperature at which the barley was grown. At this temperature the plasma membrane is primarily in a mixed gel/liquid crystalline state. Pretreatment of barley roots with cyclohexamide did not alter ATPase stimulation by TRIA. Two to three times more [14C]-TRIA (mg membrane protein)-1 was found associated with plasma membrane-enriched vesicles treated with TRIA than with vesicles enriched for mitochondrial membranes or for vesicles enriched for tonoplast, Golgi and rough endoplasmic reticulum. Both Ca2--and Mg2+-dependent ATPase activity increased by 40-60% within 30 min of the addition of 2.3 nM TRIA to cell-free extracts of barley roots. The addition of octacosanol, the C28 analogue of TRIA, to cell-free extracts did not affect metal-dependent ATPase activity. Consistent with many studies in the green-house, simultaneous additions of equimolar amounts of TRIA and octacosanol to cell-free extracts resulted in inhibition of ATPase stimulation by TRIA. TRIA may directly affect plasma membrane function in barley roots. [ABSTRACT FROM AUTHOR]