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High cytosolic concentrations of Na+ inhibit plant growth and development. To maintain low cytosolic concentrations of Na+ , higher plants use membrane-bound transporters that drive the efflux of Na+ or partition Na+ ions from the cytosol, either to the extracellular compartment or into the vacuole. Bryophytes also use an energy-dependent Na+ pumping ATPase, not found in higher plants, to efflux Na+ . To investigate whether this transporter can increase the salt tolerance of crop plants, Oryza sativa has been transformed with the Physcomitrella patens Na+ pumping ATPase (PpENA1). When grown in solutions containing 50 mm NaCl, plants constitutively expressing the PpENA1 gene are more salt tolerant and produce greater biomass than controls. Transgenics and controls accumulate similar amounts of Na+ in leaf and root tissues under stress, which indicates that the observed tolerance is not because of Na+ exclusion. Moreover, inductively coupled plasma analysis reveals that the concentration of other ions in the transformants and the controls is similar. The transgenic lines are developmentally normal and fertile, and the transgene expression levels remain stable in subsequent generations. GFP reporter fusions, which do not alter the ability of PpENA1 to complement a salt-sensitive yeast mutant, indicate that when it is expressed in plant tissues, the PpENA1 protein is located in the plasma membrane. PpENA1 peptides are found in plasma membrane fractions supporting the plasma membrane targeting. The results of this study demonstrate the utility of PpENA1 as a potential tool for engineering salinity tolerance in important crop species.

Uncinula necator, the causal agent of grapevine powdery mildew, was found to elevate the activity of the pathogenesis-related (PR) proteins, chitinase and β-1,3-glucanase in leaves and berries of a number of susceptible grapevine (Vitis vinifera) cultivars. The increase in hydrolytic activity was directly related to the severity of powdery mildew infection on both leaves and berries but no systemic induction was observed in uninfected tissues. A number of cDNA clones encoding various PR proteins, including chitinases (PR-2), β-1,3-glucanases (PR-3) and thaumatin-like (TL) proteins (PR-5), were isolated and their expression in response to powdery mildew infection examined. PR genes encoding extracellular proteins were most strongly induced in infected leaves, including an acidic class III chitinase (VvChi3), a basic class I glucanase (VvGlub) and a thaumatin-like protein (VvTl2). A basic class I chitinase (VvChi1b) was also detected, but only in severely infected leaves. A similar pattern of PR gene induction was observed in mildew-infected preveraison berries, with the exception of VvChi1b, which was not detected. Chitinase and β-1,3-glucanase enzyme activities were also found to be highly induced in leaves and preveraison berries by ethephon treatment. The pattern of chitinase gene induction by ethephon, however, was markedly different for mildew infection, with no apparent induction of VvChi3 but a marked increase in the transcript level of an acidic class IV chitinase, VvChi4. These results demonstrate that the leaves and preveraison berries of grapevine respond to environmental and stress-related stimuli by the expression of specific PR genes but that the induction of these genes during pathogen invasion does not afford complete protection of these tissues against Uncinula necator. The following abbreviations have been used: Tris: 2-amino-2-(hydroxymethyl)-1,3-propanediol; EDTA: ethylenediaminetetra-acetic acid; PVPP: polyvinylpolypyrrolidone. The GenBank accession numbers for VvChi1b and VvGlub are AF053341 and AF053750, respectively.