Heterologously expressed protein phosphatase calcineurin downregulates plant plasma membrane H+-ATPase activity at the post-translational level.

To investigate the effects of calcineurin expression on cellular ion homeostasis in plants, we have obtained a transgenic cell culture of tomato, expressing constitutively activated yeast calcineurin. Transgenic cells exhibited reduced growth rates and proton extrusion activity in vivo. We show that reduction of plasma membrane H+-ATPase activity by expression of calcineurin is the basis for the observed phenotypes.

A novel intracellular K+/H+ antiporter related to Na+/H+ antiporters is important for K+ ion homeostasis in plants.

In this study we have identified the first plant K+/H+ exchanger, LeNHX2 from tomato (Lycopersicon esculentum Mill. cv. Moneymaker), which is a member of the intracellular NHX exchanger protein family.

Involvement of endogenous salicylic acid content, lipoxygenase and antioxidant enzyme activities in the response of tomato cell suspension cultures to NaCl.

•   The effects of salt stress and adaptation on salicylic acid (SA) content and on antioxidant and lipoxygenase (LOX) enzyme activities were studied in tomato (Lycopersicon esculentum cv. Pera) cells. •   NaCl-adapted cells were obtained from calli adapted to 100 mm NaCl by successive subcultures in medium supplemented with 100 mm NaCl.

Enhanced H+/ATP coupling ratio of H+-ATPase and increased 14-3-3 protein content in plasma membrane of tomato cells upon osmotic shock.

Modulation of proton extrusion and ATP-dependent H+ transport through the plasma membrane in relation to the presence of 14-3-3 proteins in this membrane in response to osmotic shock was studied in tomato (Lycopersicon esculentum Mill. cv. Pera) cell cultures.

Tolerance to NaCl induces changes in plasma membrane lipid composition, fluidity and H+-ATPase activity of tomato calli.

Two tomato (Lycopersicon esculentum Mill. cv. Pera) callus lines tolerant to NaCl were obtained by successive subcultures of NaCl-sensitive calli in 50 and 100 mM NaCl-supplemented medium.

The arabidopsis Na+/H+ exchanger AtNHX1 catalyzes low affinity Na+ and K+ transport in reconstituted liposomes.

In saline environments, plants accumulate Na(+) in vacuoles through the activity of tonoplast Na(+)/H(+) antiporters. The first gene for a putative plant vacuolar Na(+)/H(+) antiporter, AtNHX1, was isolated from Arabidopsis and shown to increase plant tolerance to NaCl. However, AtNHX1 mRNA was up-regulated by Na(+) or K(+) salts in plants and substituted for the homologous protein of yeast to restore tolerance to several toxic cations.

Time-course of lipoxygenase, antioxidant enzyme activities and H O accumulation during the early stages of Rhizobium-legume symbiosis.

•  The involvement of lipoxygenase and antioxidant enzyme activities as well as hydrogen peroxide (H O ) accumulation are reported during early infection steps in alfalfa (Medicago sativa) roots inoculated either with a wild type Sinorhizobium meliloti or with a mutant defective in Nod-factor synthesis (Nod C ). •  Compatibility between M. sativa and Rhizobium correlates, at least in part, with an increase in the activities of these enzymes, particularly catalase and lipoxygenase, during the preinfection period (up to 12 h).

Plasma membrane H-ATPase activity is involved in adaptation of tomato calli to NaCl.

A tomato (Lycopersicon esculentum Mill. cv. Pera) callus culture tolerant to NaCl was obtained by successive subcultures of NaCl-sensitive calli in medium supplemented with 50 mM NaCl.