Molecular Mechanisms of Proline-Mediated Tolerance to Toxic Heavy Metals in Transgenic Microalgae

Pro has been shown to play an important role in ameliorating environmental stress in plants and microorganisms, including heavy metal stress. Here, we describe the effects of the expression of a mothbean Δ(1)-pyrroline-5-carboxylate synthetase (P5CS) gene in the green microalga Chlamydomonas reinhardtii. We show that transgenic algae expressing the mothbean P5CS gene have 80% higher free-Pro levels than wild-type cells, grow more rapidly in toxic Cd concentrations (100 μM), and bind fourfold more Cd than wild-type cells. In addition, Cd-K edge extended x-ray absorption fine structure studies indicated that Cd does not bind to free Pro in transgenic algae with increased Pro levels but is coordinated tetrahedrally by sulfur of phytochelatin. In contrast to P5CS-expressing cells, Cd is coordinated tetrahedrally by two oxygen and two sulfur atoms in wild-type cells. Measurements of reduced/oxidized GSH ratios and analyses of levels of malondialdehyde, a product of the free radical damage of lipids, indicate that free Pro levels are correlated with the GSH redox state and malondialdehyde levels in heavy metal–treated algae. These results suggest that the free Pro likely acts as an antioxidant in Cd-stressed cells. The resulting increased GSH levels facilitate increased phytochelatin synthesis and sequestration of Cd, because GSH–heavy metal adducts are the substrates for phytochelatin synthase

Abiotic stress effects on the antioxidative response profile of Albizia julibrissin Durazz. (Fabaceae)

Abiotic stresses (e.g., heavy metals, drought, cold, or combinations) induce oxidative stress with overproduction of reactive oxygen species (ROS). We have investigated the antioxidative responses of Albizia julibrissin Durazz. (silk tree, Fabaceae). Four-month-old plants grown in sand cultures were subjected to various single or sequential treatments involving exposure to cadmium (50-250 mu mol L-1 Cd), lead (1000-5000 mu mol L-1 Pb), chilling at 4 degrees C (CH), or drought (DR), for a period of 7-45 days. Leaf extracts were assayed for glutathione peroxidase (GPX), glutathione-disulfide reductase (GR), catalase (CAT), soluble proline (Pro), ascorbate peroxidase (APX), and guaiacol peroxidase (GUAPX). Cd and Pb accumulation in the leaves was also measured. CAT activity decreased strongly with increasing Pb exposure and after CH. It was also found to be reduced after Cd and DR treatments. GR activity increased highly in nearly all treatments, most strongly at high Cd or Pb, after DR ? CH, and after CH followed by Cd. GUAPX and GPX showed similar trends of increase. APX activity dropped after CH, but increased after low Cd treatment and in CH ? DR sequential stresses. Massive accumulation of soluble Pro occurred after 14-21 days in highly Cd-or Pb-stressed plants. CH or DR acclimation led to some alterations of antioxidative responses, particularly for CAT, GR, and APX. Our data indicate that GSH, GSH-linked redox systems, peroxidases, and Pro are possibly the more important antioxidants under severe stress

Study of potential impacts of using sewage sludge in the amendment of desert reclaimed soil on wheat and jews mallow plants

This investigation was conducted to study the impacts of using sewage sludge at different concentrations (0, 10, 25, 50, 75%) in amendment of desert reclaimed soil properties and some physiological aspects in wheat and jews mallow plants. Generally adding sewage sludge to desert soil improved the soil texture, raised the organic matter contents, water holding capacity and lowered pH value. The contents of NPK gradually increased as the ratio of sewage sludge increased. The fresh and dry weights and biosyntheses of pigment contents of the variously treated test plants were increased by increasing the sewage sludge levels in the soil. Also, total carbohydrate and protein contents of sewage sludge-treated test plants were positively affected. With respect to the proline content and total free amino acids, in most cases, it decreased significantly, expect at 75% sewage sludge, which was higher than that of other concentrations. Also, the accumulation of metal was generally higher, especially in the root than that in the shoot system in the test plant tissues