Soil Drench Treatment with ?-Aminobutyric Acid Increases Drought Tolerance of Potato

The non-protein amino acid β-aminobutyric acid (BABA) is known to be a priming agent for a more efficient activation of cellular defence responses and a potent inducer of resistance against biotic and abiotic stresses in plants. Nevertheless, most of the studies on priming have been carried out in Arabidopsis. In potato, the effect of BABA was demonstrated only on biotic stress tolerance. We investigated the effect of BABA on the drought tolerance of potato and found that soil drenched with BABA at a final concentration of 0.3 mM improves the drought tolerance of potato. Water loss from the leaves of the primed plants is attenuated and the yield is increased compared to the unprimed drought-stressed plants. The metabolite composition of the tubers of the BABA-treated plants is less affected by drought than the tuber composition of the non-treated plants. Nitric oxide and ROS (reactive oxygen species) production is increased in the BABA-treated roots but not in the leaves. In the leaves of the BABA-treated plants, the expression of the drought-inducible gene StDS2 is delayed, but the expression of ETR1, encoding an ethylene receptor, is maintained for a longer period under the drought conditions than in the leaves of the non-treated, drought-stressed control plants. This result suggests that the ethylene-inducible gene expression remains suppressed in primed plants leading to a longer leaf life and increased tuber yield compared to the non-treated, drought-stressed plants. The priming effect of BABA in potato, however, is transient and reverts to an unprimed state within a few weeks.     

Abscisic acid-deficient plants do not accumulate proteinase inhibitor II following systemin treatment

The role of systemin inPin2 gene expression was analyzed in wild-type plants of potato (Solanum tuberosum L.) and tomato (Lycopersicon esculentum Mill.), as well as in abscisic acid (ABA)-deficient tomato (sitiens) and potato (droopy) plants. The results showed that systemin initiates Pin2 mRNA accumulation only in wildtype tomato and potato plants. As in the situation after mechanical wounding,Pin2 gene expression in ABA-deficient plants was not activated by systemin. Increased endogenous levels of jasmonic acid (JA) and accumulation of Pin2 mRNA were observed following treatment with α-linolenic acid, the precursor of JA biosynthesis, suggesting that these ABA mutants still have the capability to synthesize de novo JA. Measurement of endogenous levels of ABA and JA showed that systemin leads to an increase of both phytohormones (ABA and JA) only in wild-type but not in ABA-deficient plants.     

Spatial control of developmental regulatory genes inAspergillus nidulans

ThebrlA andabaA genes ofAspergillus nidulans regulate stages of conidiophore development and are themselves regulated during development.brlA⁻ mutants produce conidiophore stalks devoid of vesicles, sterigmata, and spores.abaA⁻ mutants produce most of the conidiophore structures but fail to form conidia. To assess the spatial expression of these two genes, we fused the 5′ flanking region ofbrlA orabaA to theEscherichia coli lacZ gene.A. nidulans transformants with a single copy of either fusion gene integrated at a defined heterologus locus (argB) expressedβ-galactosidase during conidiophore development, parallelingbrlA andabaA mRNA accumulation. Controls lacking the fusion genes produced little or noβ-galactosidase activity. A method forin situ detection ofβ-galactosidase was devised. Hyphae or conidiophores were permeabilized by treatment with chloroform vapors and stained with 5-bromo-4-chloroindolyl-β-d-galactoside.β-Galactosidase activity was detected in specific conidiophore cell types.brlA- andabaA-directedβ-galactosidase accumulated in vesicles, sterigmata, and immature conidia. This procedure should be applicable for determining cellular specificities of gene expression in fungi for which transformation systems exist.     

Functional Characterization of Dihydroflavonol-4-Reductase in Anthocyanin Biosynthesis of Purple Sweet Potato Underlies the Direct Evidence of Anthocyanins Function against Abiotic Stresses

Dihydroflavonol-4-reductase (DFR) is a key enzyme in the catalysis of the stereospecific reduction of dihydroflavonols to leucoanthocyanidins in anthocyanin biosynthesis. In the purple sweet potato (Ipomoea batatas Lam.) cv. Ayamurasaki, expression of the IbDFR gene was strongly associated with anthocyanin accumulation in leaves, stems and roots. Overexpression of the IbDFR in Arabidopsis tt3 mutants fully complemented the pigmentation phenotype of the seed coat, cotyledon and hypocotyl. Downregulation of IbDFR expression in transgenic sweet potato (DFRi) using an RNAi approach dramatically reduced anthocyanin accumulation in young leaves, stems and storage roots. In contrast, the increase of flavonols quercetin-3-O-hexose-hexoside and quercetin-3-O-glucoside in the leaves and roots of DFRi plants is significant. Therefore, the metabolic pathway channeled greater flavonol influx in the DFRi plants when their anthocyanin and proanthocyanidin accumulation were decreased. These plants also displayed reduced antioxidant capacity compared to the wild type. After 24 h of cold treatment and 2 h recovery, the wild-type plants were almost fully restored to the initial phenotype compared to the slower recovery of DFRi plants, in which the levels of electrolyte leakage and hydrogen peroxide accumulation were dramatically increased. These results provide direct evidence of anthocyanins function in the protection against oxidative stress in the sweet potato. The molecular characterization of the IbDFR gene in the sweet potato not only confirms its important roles in flavonoid metabolism but also supports the protective function of anthocyanins of enhanced scavenging of reactive oxygen radicals in plants under stressful conditions.     

Ectopic Expression of Sweet Potato Cysteine Protease SPCP3 Alters Phenotypic Traits and Enhances Drought Stress Sensitivity in Transgenic Arabidopsis Plants

In this report sweet potato cysteine protease SPCP3 cDNAs, with or without the corresponding granulin-like domain, were overexpressed in transgenic Arabidopsis plants. Transgenic Arabidopsis plants with ectopic expression of full-length SPCP3 exhibited slight promotion of earlier floral transition from vegetative to reproductive growth and a higher percentage of yellowing siliques per plant. Transgenic progeny seeds showed similar patterns of germination rates and germination curves but lower germination percentages compared to those of wild-type control seeds. During drought treatment, photochemical F _v/F _m values and relative water content of transgenic plants were significantly reduced compared to those of wild-type controls. Transgenic Arabidopsis plants with ectopic expression of sweet potato SPCP3 with or without the corresponding C-terminal granulin-like domain exhibited similar drought-stress sensitivity patterns. Drought stress also enhanced SPCP3 gene expression, photochemical F _v/F _m reduction, and wilting in sweet potato detached leaves. Based on these data, we conclude that sweet potato granulin-containing cysteine protease SPCP3 is a functional gene, and its ectopic expression alters phenotypic traits and enhances drought-stress sensitivity in transgenic Arabidopsis plants. The presence of the C-terminal granulin-like domain has no significant influence on SPCP3-mediated drought-stress sensitivity in transgenic Arabidopsis plants.     

Metallothioneins 1 and 2 Have Distinct but Overlapping Expression Patterns in Arabidopsis

The spatial and temporal expression patterns of metallothionein (MT) isoforms MT1a and MT2a were investigated in vegetative and reproductive tissues of untreated and copper-treated Arabidopsis by in situ hybridization and by northern blotting. In control plants, MT1a mRNA was localized in leaf trichomes and in the vascular tissue in leaves, roots, flowers, and germinating embryos. In copper-treated plants, MT1a expression was also observed in the leaf mesophyll and in vascular tissue of developing siliques and seeds. In contrast, MT2a was expressed primarily in the trichomes of both untreated and copper-treated plants. In copper-treated plants, MT2a mRNA was also expressed in siliques. Northern-hybridization studies performed on developing seedlings and leaves showed temporal variations of MT1a gene expression but not of MT2a expression. The possible implications of these findings for the cellular roles of MTs in plants are discussed.