ABSTRACT
Low temperature is one of the major environmental constraints which reduce plant development and crop productivity. Plants are able to adapt to low-temperature stress through activation of reactive oxygen scavenging systems. Salicylic acid (SA) is one component of a complex signaling pathway modulate the plant responses to environmental stresses including low temperature stress. In this study, we evaluated the effectiveness of salicylic acid (SA) pretreatment on antioxidant system in Egyptian clover under low temperature stress. Antioxidants play important role in enhancing low temperature tolerance in plants. Berseem (var. BL-42 and BL-10) seeds were germinated for three days at 25°C after hydro-priming or SA priming (25, 50, 75, 100 and 125 µg/mL) for 4 hours. After germination of three days, one set of Petri plates was exposed to low temperature (LT) stress (5°C) for five days and other set was retained at 25°C. Physiological and biochemical parameters were observed in root and shoot samples after seven days of germination. Higher vigor index was obtained at 50 and 75 µg/mL of SA pretreatment. Low temperature treatment upregulates antioxidant enzyme (CAT, APX, GR, GPX and SOD) activities but LT+SA treatment further enhanced the antioxidant potential of clover seedlings. SA pretreatment @ 50 to 100 µg/mL concentrations resulted in upregulation of non-enzymatic antioxidants at both 25°C and 5°C. Total protein, proline and total phenol were differentially affected by different SA treatments under LT stress. SA alleviated the adverse effect of LT stress by decreasing lipid peroxidation and H2O2 content in berseem seedlings. Results have shown that SA pretreatment ameliorated LT stress in clover by upregulating antioxidants and biochemical metabolites.
ABSTRACT
In the present study, cultural and nutritional conditions for enhanced production of xylanase by a local soil isolate of Trichoderma viride, using various lignocellulosic substrates in submerged culture fermentation have been optimized. Of the lignocellulosics used, maize straw was the best inducer followed by jowar straw for xylanase production. The highest activity achieved was between 14 to 17 days of fermentation. A continuous increase in xylanase production was observed with increasing level of lignocellulosics in the medium and highest activity was observed with maize straw at 5 percent level. Xylanase production with higher levels of lignocellulosics (3 to 5 percent) of maize, jowar and barseem was found to be higher as compared to that with commercial xylan as carbon source. Sodium nitrate was the best nitrogen source among the six sources used. Maximum xylanase production was achieved with initial medium pH of 3.5-4.0 and incubation temperature of 25ºC.The enzyme preparation was effective in bringing about saccharification of different lignocellulosics. The xylanase production could be further improved by using alkali treated straw as carbon source.
Neste estudo, otimizou-se as condições culturais e nutricionais para produção aumentada de xilanase por uma cepa local de Trichoderma viride isolada de solo, empregando-se vários substratos lignocelulósicos, em fermentação submersa. Entre os substratos utilizados, o melhor indutor de produção de xilanase foi palha de milho, seguido de palha de sorgo. A atividade mais alta foi obtida entre 14 e 17 dias de fermentação. Com palha de milho observou-se um aumento contínuo na produção de xilanase com o aumento da concentração dos substratos lignocelulósicos no meio, sendo que a melhor atividade foi obtida com 5 por cento de palha de milho. A produção de xilanase com níveis mais altos de (3 a 5 por cento) de milho, sorgo e forragem verde (barseem) foi mais levada do que com xilana comercial como fonte de carbono. Entre as fontes de nitrogênio testadas, a melhor foi nitrato de sódio. Produção máxima de xilanase foi obtida quando o pH inicial do meio foi 3,5 4,0 e a temperatura de incubação 25ºC. A enzima foi eficiente na sacarificação de diferentes substratos lignocelulósicos. A produção de xilanase poderia ser aumentada empregando-se álcali ao invés de palha tratada como fonte de carbono.