The mitochondrial glutathione peroxidase GPX3 is essential for H2O2 homeostasis and root and shoot development in rice.

Glutathione (GSH) peroxidases (GPXs: EC 1.11.1.9 and EC1.11.1.12) are non-heme thiol peroxidases that catalyze the reduction of H2O2 or organic hydroperoxides to water, and they have been identified in almost all kingdoms of life. The rice glutathione peroxidase (OsGPX) gene family is comprised of 5 members spread throughout a range of sub cellular compartments. The OsGPX gene family is induced in response to exogenous H2O2 and cold stress. In contrast, they are down regulated in response to drought and UV-B light treatments. Transgenic rice plants have been generated that lack mitochondrial OsGPX3. These GPX3s plants showed shorter roots and shoots compared to non-transformed (NT) plants, and higher amounts of H2O2 mitochondrial release were observed in the roots of these plants cultivated under normal conditions. This accumulation of H2O2 is positively associated with shorter root length in GPX3s plants compared to NT ones. Moreover, GPX3 promoter analysis indicated that it is mainly expressed in root tissue. These results suggest that silencing the mitochondrial OsGPX3 gene impairs normal plant development and leads to a stress-induced morphogenic response via H2O2 accumulation.

Identification and expression analysis of multiple FRO gene copies in Medicago truncatula.

Iron (Fe) is an essential element for plant growth. Commonly, this element is found in an oxidized form in soil, which is poorly available for plants. Therefore, plants have evolved ferric-chelate reductase enzymes (FRO) to reduce iron into a more soluble ferrous form. Fe scarcity in plants induce the FRO enzyme activity. Although the legume Medicago truncatula has been employed as a model for FRO activity studies, only one copy of the M. truncatula MtFRO1 gene has been characterized so far. In this study, we identified multiple gene copies of the MtFRO gene in the genome of M. truncatula by an in silico search, using BLAST analysis in the database of the M. truncatula Genome Sequencing Project and the National Center for Biotechnology Information, and also determined whether they are functional. We identified five genes apart from MtFRO1, which had been already characterized. All of the MtFRO genes exhibited high identity with homologous FRO genes from Lycopersicon esculentum, Citrus junos and Arabidopsis thaliana. The gene copies also presented characteristic conserved FAD and NADPH motifs, transmembrane regions and oxidoreductase signature motifs. We also detected expression in five of the putative MtFRO sequences by semiquantitative RT-PCR analysis, performed with mRNA from root and shoot tissues. Iron scarcity might be a condition for an elevated expression of the MtFRO genes observed in different M. truncatula tissues.

Hypoxia induces H2O2 production and activates antioxidant defence system in grapevine buds through mediation of H2O2 and ethylene.

Paradoxically, in eukaryotic cells, hydrogen peroxide (H(2)O(2)) accumulates in response to oxygen deprivation (hypoxia). The source of H(2)O(2) under hypoxia varies according to the species, organs, and tissue. In non-photosynthetic tissues, H(2)O(2) is mainly produced by activation of NAD(P)H-oxidases or by disruption of the mitochondrial electron transport chain (m-ETC). This study showed that hypoxia, and inhibitors of respiration like potassium cyanide (KCN) and sodium nitroprusside (SNP), trigger the production of H(2)O(2) in grapevine buds. However, diphenyleneiodonium, an inhibitor of NAD(P)H-oxidase, did not reduce the H(2)O(2) levels induced by KCN, suggesting that, under respiratory stress, H(2)O(2) is mainly produced by disruption of the m-ETC. On the other hand, γ-aminobutyric acid (GABA), a metabolite that in plants alleviates oxidative stress by activating antioxidant enzymes, reduced significantly the levels of H(2)O(2) induced by KCN and, surprisingly, repressed the expression of genes encoding antioxidant enzymes such as ASCORBATE PEROXIDASE (VvAPX), GLUTATHIONE PEROXIDASE (VvGLPX), SUPEROXIDE DISMUTASE (VvSOD), and one of the CATALASE isoforms (VvCAT1), while VvCAT2 was upregulated. In contrast to GABA, hypoxia, H(2)O(2), and ethylene increased dramatically the expression of genes encoding antioxidant enzymes and enzymes of the alternative respiratory pathway such as ALTERNATIVE NADH-DEHYDROGENASES (VvaNDs) and ALTERNATIVE OXIDASES (VvAOXs). Hence, it is concluded that H(2)O(2) production is stimulated by respiratory stress in grapevine buds, that H(2)O(2) and ethylene act as signalling molecules and activate genes related to the antioxidant defence system, and finally that GABA reduces H(2)O(2) levels by up-regulating the expression of VvCAT2.

Near-isogenic wheat lines carrying altered function alleles of the Rht-1 genes exhibit differential responses to potassium deprivation.

Most of the elements involved in the integration of signals of low external K(+)-supply into a physiological response pathway remain essentially unknown. The aim of this work was to study the influence exerted by DELLA proteins, which are known to be key components for the control of growth, on plant responses during K(+) deprivation in wheat (Triticum aestivum) by using two sets of near-isogenic lines (NILs) in the Maringa and April Bearded cultivars. After K(+) shortage, the NILs of both cultivars containing the Rht-B1b,Rht-D1b alleles, which encode altered function DELLA proteins, displayed either a slight or no decrease in chlorophyll content, in contrast to the sharp decrease observed in the NILs having the wild type alleles (Rht-B1a,Rht-D1a). That difference was accompanied by a lower relative decrease of biomass accumulation only in the Maringa cultivar. In both cultivars, high chlorophyll retention was coupled with K(+) starvation-induced differences in superoxide dismutase and ascorbate peroxidase activities, which were enhanced in K(+)-starved Rht-B1b,Rht-D1b NILs. In addition, Rht-B1b,Rht-D1b and Rht-B1a,Rht-D1a NILs markedly differed in the accumulation of the major cations Ca(2+), Na(+) and K(+). These results suggest a major role of the Rht-1 genes in the control of physiological responses during K(+) deprivation.

Patterns of activities of root phosphomonoesterase and phosphodiesterase in wetland plants as a function of macrophyte species and ambient phosphorus regime.

Phosphorus (P)-limited plants produce higher amounts of root phosphatases, but research has mostly focused on phosphomonoesterases (PMEs). Because phosphate diesters can form a significant proportion of organic P in wetlands, we aimed to determine whether wetland plants produce both root PMEs and root phosphodiesterases (PDEs), and, if so, what factors influence activities of these enzymes. We measured the activities of root PMEs and PDEs colorimetrically in a wide range of macrophytes from natural and P-enriched wetlands. Hydrolyzable P in sediments was analyzed using commercially available PMEs and PDEs. In all species, both root PMEs and PDEs were always present, and their activities were closely correlated. Sedges and broadleaved emergents had the highest activity of both enzymes, while those of floating-leaved plants were the lowest. Redundancy analysis revealed close association between root enzymes and the proportion of monoesterase- and diesterase-hydrolyzable dissolved unreactive P. Both enzymes were positively correlated with root tissue N : P ratio. Both plant and sediment traits were important when explaining differences in enzyme activities. Although the activities are related to ambient P regime, the relationship was not close enough to use root enzymes as reliable predictors of dissolved unreactive P that is hydrolyzed by sediment phosphomono- and diesterases.

Isoforms of plasma membrane H(+)-ATPase in rice root and shoot are differentially induced by starvation and resupply of NO3⁻ or NH4+.

The goal of this study was to evaluate the effects of nitrogen starvation and resupply in 10 PM H+-ATPase isoforms and the expression of NO3⁻ and NH4+ transporters in rice. The net uptake of both forms of NO3⁻-N or NH4+-N was increased with its resupply. Resupply of NO3⁻ resulted in induction of the following PM H+-ATPase isoforms, OsA1, OsA2, OsA5 and OsA7 in the shoots and OsA2, OsA5, OsA7 and OsA8 in the roots. Resupply of NH4+ resulted in the induction of the following OsA1, OsA3 and OsA7 isoforms in the roots while OsA1 was induced in the shoots. It was observed that increased PM H+-ATPase activity also resulted in increased net uptake of NO3⁻ and NH4+. In the roots, OsNRT2.1 and OsNRT2.2 were induced by NO3⁻ resupply, while OsAMT1.1 and OsAMT1.2 were induced by NH4+ deficiency. The results showed that the expression of PM H+-ATPase isoforms is related to NO3⁻ and NH4+ transporters as well as in which section of the plant it takes place. PM H+-ATPase isoforms OsA2 and OsA7 displayed the strongest induction in response to N resupply, therefore indicating that these genes could be involved in N uptake in rice.

Esterase polymorphism and the analysis of genetic diversity and structure in cactus populations descended from Cereus peruvianus plants regenerated in vitro.

The genetic structure of Cereus peruvianus populations descended from cultivated plants (F(1) populations) and from plants regenerated in vitro (R(1) populations) was analyzed using α- and ß-esterase isozymes in native PAGE. The estimated proportion of polymorphic loci was higher (50%) in the R(1) populations than the F(1) populations (42.85%). The mean observed (0.5599) and expected (0.5620) heterozygosity in R(1) descendents was also higher than the rates in F(1) descendents (H (o) = 0.4142; H (e) = 0.4977). A low level of population differentiation was detected in R(1) descendents (F (st) = 0.05). In contrast, population differentiation was high in F(1) descendents (0.2583). Esterase analysis using PAGE showed that artificial selection by silvicultural management provides high genetic diversity and a large genetic basis for C. peruvianus, whereas in vitro selection from callus tissue culture involves an increase of heterozygosity levels in descendents from somaclones and a low level of interpopulational divergence.

Aluminum-induced oxidative stress in cucumber.

Aluminum (Al) is one of the most abundant elements of the planet and exposure to this metal can cause oxidative stress and lead to various signs of toxicity in plants. Plants are essential organisms for the environment as well as food for humans and animals. The toxic effect of aluminum is the major cause of decreased crop productivity. Thus, the objective of the present study was to analyze the effects of aluminum on the activity of antioxidant enzymes such as catalase (CAT - E.C. 1.11.1.6), superoxide dismutase (SOD - E.C.1.15.1.1) and ascorbate peroxidase (APX - E.C. 1.11.1.11), and on lipid peroxidation, electrolyte leakage percentage (ELP) and chlorophyll and protein oxidation levels in Cucumis sativus L. (cv. Aodai). Seedlings were grown at different concentrations of aluminum ranging from 1 to 2000 microM for 10 days. The increase in ELP and H(2)O(2) production observed in the seedlings may be related to the decreased efficiency of the antioxidant system at higher aluminum concentrations. The antioxidant system was unable to overcome toxicity resulting in negative effects such as lipid peroxidation, protein oxidation and a decrease in the growth of Cucumis seedlings. Aluminum toxicity triggered alterations in the antioxidant and physiological status of growing cucumber seedlings.

Expression of SOD transgene in pepper confer stress tolerance and improve shoot regeneration / Expresión del transgén SOD en el pimiento que confiere tolerancia al estrés y mejora la regeneración de brotes

The objective of this work was to study the stress tolerance and regeneration capability of transgenic pepper plants carrying a sod gene, encoding a tomato chloroplast-localized Cu/Zn SOD protein. The expression of the sod gene was confirmed by enzymatic staining following polyacrylamide gel electrophoresis (PAGE), revealing a ‘novel’ band, which could represent a heterodimeric enzyme. Transgenic T1 and T2 progeny plants were exposed to different oxidative stresses including Methyl viologen (MV) and drought and found to have an increased resistance to oxidative damage. Furthermore, the SOD carrying transgenic pepper plants showed increased levels of regeneration efficiency compared to the wild type pepper plants. Pepper is a recalcitrant species in terms of its in vitro regeneration ability but it could be extremely useful for the development of pharmaceuticals. This approach enables the extent use of pepper for genetic transformation and the production of high valuable products in plants particularly the large fruit varieties.

Biomass growth, micronucleus induction, and antioxidant stress enzyme responses in Vicia faba exposed to cadmium in solution.

Biomass growth, micronucleus induction, and antioxidative stress enzymes (superoxide dismutase, peroxidase, glutathione reductase, and catalase) were investigated simultaneously in the Vicia faba plant exposed to cadmium in solution. The biomass lowest-observed-effect concentration (LOEC) value was 2,000 microM Cd2+. In the shoots, enzymic activities increased without concentration-response relationships. In the roots, after an initial increase, activities of all enzymes showed negative concentration-response relationships. A significant increase in micronucleus induction was observed at 20 microM Cd2+. Regarding sensitivity, our results showed that biomass endpoint was less sensitive than micronucleus induction, which was less sensitive than antioxidative enzyme activities. The increase of antioxidant stress enzyme activities in response to cadmium exposure may be taken as evidence for an enhanced detoxification capacity of V. faba plants toward reactive oxygen species (and derivatives) that might be generated in the stressed plants. Concomitant micronucleus induction may be also interpreted as a consequence of oxidative stress, upholding the view that cadmium-induced DNA damage is, to some extent, via generation of reactive (intermediate) oxygen species.

Onset of in vitro rhizogenesis response and peroxidase activity in Zingiber officinale (Zingiberaceae).

The induction of rooting in microshoots of Zingiber officinale cvs. Suprava, Turia local, Suruchi and V3S18 was achieved on half-strength basal Murashige and Skoog's medium supplemented with 0.5-1.0 mg/l either indole-3-acetic acid (IAA) or indole-3-butyric acid (IBA) and 2% (w/v) sucrose within 7-9 days of culture. Rooting was inhibited when the microshoots were cultured under higher concentration of auxins. The microshoots cultured on medium supplemented with NAA induced large number of thin root hairs with friable calluses within 6-7 days. Peroxidase activity was determined during root induction (0-day to the 10th day at every 2 day interval) from microshoots derived in vitro. The activity was minimum in the inductive phase (primary) and at the maximum level during the root initiative phase. These finding may be useful in monitoring the rooting behaviour in microshoots derived from different subculture and peroxidase activity as a marker for root initiation.