Effect of exogenous salicylic acid under changing environment: a review

Germinating seedlings of mung bean (Phaseolus vulgaris L. cv. K-16) were treated with different concentrations of cadmium acetate (10, 50 and 100 μM). Cd2+ lowered the chlorophyll and heme levels. The level of lipid peroxides were higher on day 3 than on day 6. However, Cd2+ treatment significantly enhanced the level of lipid peroxides. Similarly, a dose-dependent induction of lipoxygenase (EC 1.13.11.12) activity was observed with Cd2+ treatment. Further, the activities of antioxidant enzymes such as superoxide dismutase (EC 1.15.1.1) and catalase (EC 1.11.1.6) were decreased. Our results suggest that lipoxygenase-mediated accumulation of lipid peroxides on the one hand and inhibition of free radical scavenging enzymes like superoxide dismutase and catalase on the other caused a pronounced reduction in the chlorophyll and heme levels of the seedlings. The experiments conducted on the effect of Cd2+ on dark-grown seedlings did not conform with the result of light-grown seedlings. Though chlorophyll and heme levels decreased in a dose-dependent manner, no accumulation of lipid peroxides was observed, suggesting that the inhibition of chlorophyll synthesis by Cd2+ is achieved both by reaction with constituent biosynthetic enzymes as well as peroxide-mediated degradation.

Phytotoxicity of cadmium ions on germinating seedlings of mung bean (Phaseolus vulgaris): Involvement of lipid peroxides in chlorphyll degradation

Treatment with salicylic acid decreases the effect of cadmium on photosynthesis in maize plants.

Brassica napus L. (oilseed rape) was grown from seeds on a reconstituted soil contaminated with cadmium (100 mg Cd kg-1 dry soil), resulting in a marked chlorosis of the leaves which was investigated using a combination of biochemical, biophysical and physiological methods. Spectroscopic and chromatographic analyses of the photosynthetic pigments indicated that chlorosis was not due to a direct interaction of Cd with the chlorophyll biosynthesis pathway. In addition, mineral deficiency and oxidative stress were apparently not involved in the pigment loss. Leaf chlorosis was attributable to a marked decrease in the chloroplast density caused by a reduction in the number of chloroplasts per cell and a change in cell size, suggesting that Cd interfered with chloroplast replication and cell division. Relatively little Cd was found in the chloroplasts and the properties of the photosynthetic apparatus (electron transport, protein composition, chlorophyll antenna size, chloroplast ultrastructure) were not affected appreciably in plants grown on Cd-polluted soil. Depth profiling of photosynthetic pigments by phase-resolved photoacoustic spectroscopy revealed that the Cd-induced decrease in pigment content was very pronounced at the leaf surface (stomatal guard cells) compared to the leaf interior (mesophyll). This observation was consistent with light transmission and fluorescence microscopy analyses, which revealed that stomata density in the epidermis was noticeably reduced in Cd-exposed leaves. Concomitantly, the stomatal conductance estimated from gas-exchange measurements was strongly reduced with Cd. When plants were grown in a high-CO2 atmosphere (4,000 microliters CO2 l-1), the inhibitory effect of Cd on growth was not cancelled, suggesting that the reduced availability of CO2 at the chloroplast level associated with the low stomatal conductance was not the main component of Cd toxicity in oilseed rape.

Leaf chlorosis in oilseed rape plants (Brassica napus) grown on cadmium-polluted soil: causes and consequences for photosynthesis and growth

Effects of cadmium on antioxidant enzyme and photosynthetic activities in leaves of two maize cultivars

Inhibition of chlorophyll synthesis in Phaseolus vulgaris L. seedlings by cadmium acetate.

5-Aminolevulinic acid, porphyrin and chlorophyll contents as well the activities of 5-aminolevulinic acid dehydratase and PBG deaminase were studied in selenium treated mung bean seedlings. Selenium had no effect on 5-aminolevulinic acid synthetic ability but inhibited 5-aminolevulinic acid dehydratase and PBG deaminase activities. Further, it was observed that selenium induced accumulation of protoporphyrin-IX and Mg-protoporphyrin ester and decreased chlorophyll levels in both light and dark-grown seedlings. The results suggest the possible regulatory role of selenium on chlorophyll synthesis by interacting with sulfhydryl containing enzymes 5-aminolevulinic acid dehydratase and porphobilinogen deaminase.

A. R. K. Prasad

Papers

Inhibition of chlorophyll synthesis in Phaseolus vulgaris L. seedlings by cadmium acetate.

Selenium as a novel regulator of porphyrin biosynthesis in germinating seedlings of mung bean (Phaseolus vulgaris).