No abstract

The plasma membrane (PM) H(+)-ATPase has been proposed to play important transport and regulatory roles in plant physiology, including its participation in auxin-induced acidification in coleoptile segments. This enzyme is encoded by a family of genes differing in tissue distribution, regulation, and expression level. A major expressed isoform of the maize PM H(+)-ATPase (MHA2) has been characterized. RNA gel blot analysis indicated that MHA2 is expressed in all maize organs, with highest levels being in the roots. In situ hybridization of sections from maize seedlings indicated enriched expression of MHA2 in stomatal guard cells, phloem cells, and root epidermal cells. MHA2 mRNA was induced threefold when nonvascular parts of the coleoptile segments were treated with auxin. This induction correlates with auxin-triggered proton extrusion by the same part of the segments. The PM H(+)-ATPase in the vascular bundies does not contribute significantly to auxin-induced acidification, is not regulated by auxin, and masks the auxin effect in extracts of whole coleoptile segments. We conclude that auxin-induced acidification in coleoptile segments most often occurs in the nonvascular tissue and is mediated, at least in part, by increased levels of MHA2.

The complete sequencing of the genome of Saccharomyces cerevisiae indicated that this organism contains five genes encoding aldehyde dehydrogenases. YOR374w and YER073w correspond to the mitochondrial isoforms and we propose as gene names ALD4 and ALD5, respectively. YPL061w has been described as the cytoplasmic constitutive isoform and named ALD6. We characterize here the tandem‐repeated ORFs YMR170c and YMR169c as the cytoplasmic stress‐inducible isoforms, with gene names ALD2 and ALD3, respectively. The expression of ALD2 and ALD3 is dependent on the general‐stress transcription factors Msn2,4 but independent of the HOG MAP kinase pathway. ALD3 is induced by a variety of stresses, including osmotic shock, heat shock, glucose exhaustion, oxidative stress and drugs. ALD2 is only induced by osmotic stress and glucose exhaustion. A double null mutant, ald2 ald3, exhibited unchanged sensitivity to any of the above stresses. The only phenotype detected in this mutant was a reduced growth rate in ethanol medium as compared to the wild type. Copyright © 1999 John Wiley & Sons, Ltd.