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The aim of this work was to investigate the role of the antioxidant enzymes in salt tolerance comparing the salt-sensitive (Pérola) and a salt-tolerant (Pitiúba) cultivar of cowpea [Vigna unguiculata (L.) Walp.]. Salt stress (100 mM NaCl for 8 d) reduced the leaf growth rate more in the sensitive cultivar. The salt-induced decrease in the relative water content, Na + accumulation and increase in leaf electrolyte leakage was similar in both cultivars. Salt stress induced a higher increase in the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX) and phenol peroxidase (POX) in the tolerant cultivar than in sensitive one.

ABSTRACT(Activities of antioxidant enzymes and root growth inhibition in cowpea seedlings exposed to diff erent salt levels). Phenol peroxidase (POX) is a dual enzyme that is involved with hydrogen peroxide scavenging and lignin biosynthesis, contributing to growth inhibition by secondary wall thickening. In order to relate growth inhibition to salt-induced oxidative modulation, the activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and POX were evaluated in cowpea roots under salinity. Four-day-old seedlings of the Pitiúba and Pérola cultivars were exposed to 0, 25, 50, 75 and 100 mM NaCl in germination paper under controlled conditions. Aft er two days of treatment, root length was reduced under 100 mM NaCl by 56 and 26% in Pitiúba and Pérola, respectively, which was associated with enhanced electrolyte leakage and cell death in the root apex. NaCl salinity did not trigger lipid peroxidation, indicating that cell death was probably due to membrane damage instead of oxidative stress. Salt stress reduced the activity of SOD, CAT and APX and increased the POX activity, demonstrating that this enzyme plays a role in oxidative protection in cowpea roots exposed to NaCl salinity. In conclusion, salt-induced growth inhibition in cowpea roots could be attributed, at least in part, to a coordinate action involving an increase in POX activity and a drop in CAT and APX activities. Atividade de enzimas antioxidantes e inibição do crescimento radicular de feijão caupi sob diferentes níveis de salinidade

In order to identify salt tolerance indicators, several physiological variables were evaluated in two contrasting cashew (Anacardium occidentale L.) rootstocks in response to salt stress. The tolerant CCP 09 genotype showed better growth performance after two weeks under a large range of NaCl salinity (50, 100, 150 and 200 mM). The NaCl treatments induced a significant drop in transpiration as a consequence of an increased stomatal resistance in both genotypes. No significant differences in Na + , Cl -, and K + concentrations were found in both roots and leaves regardless of rootstocks. The tolerant genotype exhibited lower relative water content and less negative leaf osmotic potential as compared with the sensitive genotype and, therefore, these variables could not be related to salt tolerance. Salt stress caused more significant changes in protein and amino acid concentrations in roots than in leaves. Among the physiological indicators, leaf membrane damage was closely associated with the differences in salt tolerance between the two cashew genotypes. Furthermore, under NaCl salinity the tolerant rootstock showed greater ability to accumulate compatible organic solutes (amino acids, proline and soluble sugars) in leaves in addition to maintaining the soluble sugar concentration in roots as compared with the sensitive rootstock. Key words: Anacardium occidentale, organic solutes, salt stress, salt tolerance, sodium and chloride partitioning, sodium-to-potassium ratio Mudanças em indicadores fisiológicos associados com a tolerância ao estresse salino em dois porta-enxertos contrastantes de cajueiro: Com o objetivo de identificar marcadores fisiológicos de tolerância ao estresse salino, diversas variáveis fisiológicas foram avaliadas em dois porta-enxertos de cajueiro (Anacardium occidentale L.) apresentando contraste na tolerância à salinidade. O genótipo tolerante (CCP 09) apresentou melhor crescimento sob todas as concentrações de NaCl (50, 100, 150 e 200 mM), após duas semanas. O tratamento salino reduziu severamente a transpiração, como conseqüência do aumento substancial da resistência estomática nos dois genótipos. Os dois portaenxertos não apresentaram diferenças significativas nas concentrações de Na + , Cl -e K + nos tecidos de raízes e folhas. O genótipo tolerante, em comparação com o sensível, apresentou menor conteúdo relativo de água e maior (menos negativo) potencial osmótico foliar, de maneira que essas variáveis não devem estar associadas com a tolerância ao sal na espécie em questão. O estresse salino induziu mudanças significantemente maiores nas concentrações de proteína e aminoácidos em raízes do que em folhas, sugerindo que a raiz foi o órgão mais sensível ao sal. Entre os indicadores fisiológicos avaliados, o dano de membrana foi o que mais bem se associou com a diferença de tolerância ao estresse salino entre os dois genótipos. Em adição, o porta-enxerto tolerante apresentou maior acúmulo de solutos orgânicos (aminoácidos, prolina e açúcares solúveis) em folhas, além de manter, em maior e...

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