Kousei Yamashita

Stimulation of H+ extrusion and plasma membrane H+-ATPase activity of barley roots by ammonium-treatment

Abstract H+ extrusion and the plasma membrane H+-ATPase activity were analyzed using barley roots exposed to ammonium. H+ extrusion from roots was enhanced 4 h after the addition of 5 mol m-3 ammonium to the medium. However, the stimulation of the plasma membrane H+-ATPase activity occurred at least 8 h after the addition of ammonium. Furthermore, this stimulation was found to be caused by the increase in the content of H+-ATPase proteins based on the results of immunoassay. These results indicate that H+ was actively extruded to the medium through the increase in the amount of plasma membrane H+-ATPase proteins, when barley roots were exposed to ammonium for more than 8 h. Thus, it is assumed that in the long term exposure to ammonium nitrogen, ammonium-induced stimulation of the H+-ATPase activity may be important to maintain intracellular pH in root cells under the acidic conditions associated with the uptake of ammonium.

Stimulation of plasma membrane h+-transport activity in barley roots by salt stress

Abstract Plasma membrane vesicles were prepared from barley roots (Hordeum vulgare cv. Kikaihadaka) using the phase partitioning method. H+ -transport activity could be measured without membrane inversion treatment, since the plasma membrane vesicles showed a latency value of approximately 50% for the activity. Following the exposure to NaCl, alterations of the plasma membrane H+ -ATPase and H+ -transport activity were investigated. After barley roots were treated with 200 mol m−3 NaCl for 1 d, both plasma membrane H+-ATPase activity and H+ -transport activity assayed in the presence of nitrate were reduced as compared with those of control roots. However, in the salinized roots, the H+ -transport activity measured with chloride was higher than that of control roots, though the H+-ATPase activity was lower. These results suggest that the permeability of the plasma membrane to chloride may increase by salt stress.

Salt stress-induced enhancement of anion efflux and anion transport activity in plasma membrane of barley roots

Abstract Extract In salinized land, high external concentration of salts (generally sodium and chloride) reduces the growth and yield of many plants. Although the mechanisms controlling these phenomena have not been fully elucidated, it appears that excessive accumulation of ions within cells is one of the major contributory factors (Greenway and Munns 1980).

Effect of sodium chloride stress on the plasma membrane ATPase of barley roots: Probable cause for decrease in ATPase activity

Abstract The regulation of plasma membrane ATPase activity by salt stress was investigated in barley roots. The plasma membrane fractions were prepared from the roots treated with or without 200 mM sodium chloride (NaCl) for one day. After salt treatment, ATPase activity reduced by 20 to 30% as compared with that of control roots. No significant changes in the content of total phospholipid and sterol were detected in the plasma membrane fraction by salt stress. After extraction of most of the phospholipids in the plasma membrane vesicles with a solution containing 1% (W/V) octylglucoside and 1% (W/V) Triton X‐100, the ATPase activity in salt‐stressed roots was lower than that of control roots. After reconstitution of detergent‐extracted protein into liposome, the reduction of ATPase activity by salt stress did not recover. Based on immunoblott analysis, the relative amount of H+‐ATPase in plasma membrane fraction prepared, from NaCl‐stressed roots was smaller than that of control roots. These results indi...

Characterization of ferric chelate reductase in plasma membranes isolated from cucumber roots

Plasma membrane (PM)-bound ferric chelate reductase (FeCh-R) is thought to be activated in the roots of nongraminaceous plants under Fe deficiency and to participate in the ferric reduction for uptake. Purified PM-vesicles were obtained from the roots of cucumber (Cucumis sativus L.) plants grown in the absence or in the presence of Fe. The increase of PM-bound FeCh-R activity under Fe deficiency did not exceed 10% compared to Fe sufficient roots. In both Fe-deficient and control plants, FeCh-R activity showed stable maximal values in the presence of Triton X-100 at concentrations over 0.03%. Preincubation of PM-vesicles with 0.03% Triton X-100 in the absence of substrates resulted in marked reduction of FeCh-R activity with time. The effect of Triton X- 100 on FeCh-R activity was completely alleviated by adding NADH, FAD or both during the preincubation, only partly alleviated by Fe citrate, and not alleviated by FMN. The stimulation of FeCh-R activity by FAD was concentration dependent with maximum effect at FAD concentrations over 100 nM. Our results indicate that a FAD-containing protein may be important for the integrity of transplasma membrane reductase involved in Fe reduction.

Enhancement of nitrate efflux and the plasma membrane hydrogen ion‐transport activity of barley roots by nitrate treatment

The effect of nitrate (NO 3 ) on the activities of hydrogen (H + )-ATPaSe and H + -transport in the plasma membrane vesicles isolated from barley (Hordeum vulgare L. cv. Kikaihadaka) roots was investigated. After treatment with 10 mM NO 3 for longer than 24 h, both activities of H + -ATPase and H + -transport assayed in the presence of chloride (Cl) were stimulated less than 20%. While H + -transport activity was approximately two times higher in NO 3 - grown roots than in control roots when assayed in the presence of NO 3 instead of Cl. This result suggests that NO 3 is permeable in the plasma membrane vesicles isolated from NO 3 -grown roots rather than that of the control, and thereby stimulate H + -transport activity through the collapse of positive potentials established by H + -ATPase. Furthermore, NO 3 efflux from roots was markedly enhanced after 48 h of the exposure to NO 3 . Taken together, NO 3 efflux may be mediated by the permeability to NO 3 which is induced by NO 3 .

Increase of ATP-dependent H+ pump activity of tonoplast of barley roots by aluminium stress: Possible involvement of abscisic acid for the regulation

Aluminium (Al) stress increases ATP-dependent H+ transport activity of tonoplast-enriched membrane vesicles prepared from barley roots. Also, Al stress significantly increased ABA content in roots. Treatment of roots with abscisic acid (ABA), as in the case of Al stress, increased ATP-dependent H+ transport activity of tonoplastenriched membrane vesicle preparations. Vanadate treatment, which is expected to reduce the plasma membrane H+-ATPase activity as does Al stress, increased both ABA content in roots and the H+ transport activity of tonoplast membrane vesicles. Any treatment with Al, ABA and vanadate increased nitrate-inhibitible ATPase activity of prepared membrane vesicles. These results suggest that the increase of ABA in Al-stressed roots may play a key role in the activation of H+-pump of the tonoplast.