Mitteilungen der Gesellschaft für Pflanzenbauwissenschaften Band 23

Mitt. Ges. Pflanzenbauwiss. 23: 244 (2011)
Plasma membrane H + -ATPase is regulated
by boron nutrition in maize shoot
Ammara Fatima, Stefan Hanstein, Britta Pitann and Sven Schubert
Institute of Plant Nutrition, Justus-Liebig-University Gießen. E-Mail: Ammara.Fatima@agrar.unigiessen.de
Introduction
The essentiality of boron (B) for normal plant growth was first described in the
beginning of the 20 th century. In recent years, many functions of B in plant cells have
been proposed, including cell-wall synthesis and structure, maintaining membrane
function, as well as supporting metabolic activities. Currently, the only direct evidence
for the role of B in plants involves cross-linking of the pectin rhamnogalacturonan II
(RGII) in the cell wall (O’Neill et al., 2004). However, increasing evidence suggests
one or more functions of B in plasma membrane function and/or structure. It is
unclear, whether B directly interacts with membrane proteins or indirectly modifies
membrane properties with subsequent changes in enzymatic activities. The present
study investigates the role of B in H +_ ATPase hydrolytic and pumping activity of
plasma membrane from maize.
Materials and Methods
Plants were grown with 0 and 10 µM B in hydroponics under controlled conditions.
Plasma membranes were isolated with two-phase partitioning and membrane H + -
ATPase hydrolytic and pumping activity was measured in plasma membranes
isolated from maize shoot as described by Yan et al. ( 2002).
Results and Discussion
Boron supply in the nutrient medium significantly improved plant growth parameters:
Young shoot fresh and dry biomass, leaf area and plant height. We found that the
hydrolytic activity of H + -ATPase was not affected. However, a significant increase
was observed in active H + -pumping activity of plasma membrane H + -ATPase from Btreated
shoots. To investigate whether B produced qualitative or quantitative enzyme
changes. We determined the kinetic parameters and activation energy, which
remained unaffected by B. Then the enzyme concentration of plasma membrane
ATPase was measured by means of western blot analysis. The results showed that B
significantly increased enzyme concentration. To gain a deeper insight into the effect
of boron on H + -ATPase, we analyzed the relative expression of MHA isoforms
(MHA1, MHA2, MHA3, and MHA4) of plasma membrane H + -ATPase by means of
real-time PCR. We were able to identify only MHA1 and MHA3. Boron application upregulated
relative expression of MHA3. The increase in pumping activity of plasma
membrane H + -ATPase induced by boron attributed to enhanced enzyme
concentration in the plasma membrane and up-regulation of MHA3.
References
O’Neill, M.A., Ishii,T. Albersheim, P., Darvill, A.G. 2004: Rhamnogalacturonan II: Structure and function
of a borate crosslinked cell wall pectic polysaccharide. Annu. Rev. Plant Biol. 55:109.
Yan, F., Zhu, Y., Müller, C., Zörb, C., Schubert, S. 2002: Adaptation of H+-pumping and plasma membrane
H+-ATPase activity in proteoid roots of white lupin under phosphate deficiency. Plant Physiol.
129:50-63.