Effects of Boron on Proton Transport and Membrane Properties of Sunflower (Helianthus annuus L.) Cell Microsomes

Abstract

Boron deficiency and toxicity inhibit ATP-dependent H+ pumping and vanadate-sensitive ATPase activity in sunflower roots and cell suspensions..The effects of boron on H+ pumping and on passive H+ conductance, as well as on fluorescence anisotropy in KI-washed microsomes isolated from sunflower (Helianfhus annuus 1. cv Enano) cell suspensions, have been investigated. Boron deficiency reduced the total and vanadate-sensitive ATPase activities as well as the vanadate-sensitive ATP-dependent H+ pumping without affecting the amount of antigenic ATPase protein as measured by immunoblotting with an Arabidopsis fhaliana plasma membrane anti-H+-ATPase polyclonal antibody. Kinetic studies revealed that boron deficiency reduced Vmax of vanadate-sensitive ATPase activity with little change in the apparent K,,, for MgZ+-ATP. Proton leakage was greater in microsomal vesicles isolated from cells grown without boron and incubated in reaction medium without added boron, and this effect was reversed by addition of boron to the reaction medium. Fluorescence anisotropy indicated that diphenyl hexatriene and 1-(4-trimethylammoniumphenyI)-6-phenyl-1,3,5-hexatriene probes were immobilized to a greater extent in microsomes from cells grown without boron than in those from cells grown with 100 p~ H3B03. The apparent decrease of membrane fluidity in microsomes from cells grown without boron was reversed by the addition of boron to the reaction medium. Taken together these data suggest that inhibition of H+ gradient formation in microsomes from sunflower cells grown in the absence of boron could be due to the combined effects of reduced H+-ATPase activity and increased passive conductance across the membrane, possibly resulting from increased membrane rigidity.Although the essentiality of B in plants is well known, its mechanism of action is not clearly established. Impaired membrane function could underlie many responses to Bdeficient conditions (Parr and Loughman, 1983). In this regard, it was shown that B induced hyperpolarization of sunflower (Helianthus annuus) cell membranes and increased membrane permeability to K+ (Schon et al., 1990). B also affected H+ efflux in young sunflower seedling roots (Roldin et al., 1992) and in carrot cell cultures (Blaser-Grill et al., 1989). In addition, a requirement for B in the stimulation of Supported by grant PB 87-0324 from Direccibn General de Present address:

Transcriptional Profiling Reveals Adaptive Responses to Boron Defi ciency Stress in Arabidopsis

“…The suppressed expression of the H + -ATPase genes under conditions of B defi ciency could directly affect the transmembrane transport and growth by cell elongation. A previous study reported that B defi ciency changed the activity of H + -ATPase but not the abundance of the protein (Ferrol et al, 1993). In contrast, Camacho-Cristóbal and González-Fontes (2007) reported results similar to ours insofar as they also found that B deficiency reduced the level of a plasmalemma H + -ATPase transcript (PMA2) in tobacco roots.…”

Boron deficiency decreases plasmalemma H+-ATPase expression and nitrate uptake, and promotes ammonium assimilation into asparagine in tobacco roots

“…In the present work we show a rapid decrease of root PMA2 transcript levels under boron deWciency (Fig. 3a), which could imply a drop in the plasmalemma H + -ATPase activity (Schon et al 1990;Ferrol et al 1993) and, as a consequence, a lower nitrate uptake (Fig. 2).…”

“…2). In experi- ments with cultures of sunXower cells Ferrol et al (1993) suggested that the regulation of plasmalemma H + -ATPase by boron treatment was due to changes in its activity rather than in the amount of this protein. In addition, in the present work we have observed a strong transcriptional regulation of plasmalemma H + -ATPases by boron deWciency in tobacco roots (Fig.…”

Essential and Toxic Effects of Macro‐, Trace and Ultratrace Elements for Higher Plants, Interactions and Requirement

“…The effect on H + pump achievement (ion uptake!) demonstrated in membrane vesicles from B-sufficient and B-deficient sunflower roots may be explained in this way (Ferrol et al 1993). Other functions of B are independent of this, and concern especially the binding of 6-phosphogluconic acid; this leads to a preferred conversion of D-glucose from photosynthesis into cellulose, hemicelluloses, pectins, and lignins.…”