ABSTRACT
Marrow (Cucurbita pepo L.) is one of the most important vegetables in Egypt. Arsenate (AsO43−) and arsenite (AsO33−) are the primary chemical forms occurring in soils. Soil microorganisms conform these compounds by oxidation/ reduction or methylation/de-methylation reactions ( Christophersen et al., 2009). Arsenate is one of the ubiquitous environmental contaminants with heavy pollution from mining, industrial and agricultural activities. Bioavailability, uptake and phytotoxicity of arsenic (As) to plants are influenced by factors such as As concentration in soil, As species, plant species, soil properties, like redox potential, drainage conditions, pH and soil phosphorus content. Arsenate is toxic to plants and reduce the activities of its enzyme (Kim et al., 2009). ROSs may be generated through the conversion of arsenate to arsenite. This may result in damage to proteins, DNA, and lipids. Arsenate increases lipid peroxidation, SOD activity and phytochelatins production correlated with increasing arsenate concentrations (El-Shora & Lamiaa, 2009). The scavenging system controlling reactive oxygen species (ROS) comprises non-enzymatic antioxidants (e.g. glutathione (GSH), ascorbate, carotenoids) and enzymatic antioxidative systems (e.g. superoxide dismutase (SOD), peroxidase (POD), catalase, GSH reductase) (Liu et al., 2007). The influence of increased concentrations of arsenate on photosynthesis, pigment content, antioxidative capacity superoxide dismutase (SOD), guaiacol peroxidase (GPX), guaiacol peroxidase (GPX), and Ascorbate peroxidase (APX). Also, the effect of arsenate on GSH, ascorbate, carotenoids in the shoots was investigated in order to achieve a better understanding of the biochemical mechanisms of defense against As stress in plants.
