Modulation of cadmium uptake and toxicity in Spirodela polyrrhiza (L.) schleiden due to malathion

Time Course of Age-Linked Changes in Photosynthetic Efficiency of Spirodela polyrhiza Exposed to Cadmium

Short-term assessment of adverse effects is essential for populations exposed to higher risk of environmental pollution. This study presents the time course of physiological and morphological changes attributed to cadmium, emphasizing age-linked differences in the susceptibility of photosynthetic apparatus of Spirodela polyrhiza fronds exposed to different cadmium concentrations. A four-frond colony represented by mother, daughter, and granddaughter plants was exposed to cadmium concentrations for 6, 24, and 72 h to establish its effect on different generations of the great duckweed. The duration of cadmium exposure accounted for the most variation in chlorophyll content as the most influential variable, and after 72 h, frond responsiveness was a function of cadmium concentration. Carotenoid contents behaved slightly differently in fronds of different ages, with the oldest mother frond exhibiting accelerated senescence. Chlorophyll fluorescence measurements showed that cadmium affects different photosynthetic electron transport segments relative to the frond's chloroplast structure level. Photosynthesis of mother fronds exposed to low cadmium and daughter fronds exposed to high cadmium was determined by the functionality of primary electron acceptance at the PSII level. Mother plants exposed to higher cadmium concentrations were characterized by closed and inactive reaction centers, dissipated energy outflux, and inhibited photosynthesis. Young fronds exposed to low and high cadmium concentrations were characterized by increased non-reducing reaction centers and thermal phase reduction, with activated dissipative mechanisms at high cadmium concentrations. Cadmium-induced changes in the ultrastructure of chloroplasts were visible after 6 h of exposure to lowest concentrations, with gradual degradation of the thylakoid system as the fronds aged. Younger fronds responded to cadmium more dynamically through molecular, physiological, and anatomical changes and tolerated a more reduced electron transport chain under given conditions than older fronds.

Oxidative stress induced by HCH in Hydrilla verticillata (l.f.) Royle: modulation in uptake and toxicity due to Fe

The effect of hexachlorocyclohexane (HCH) singly and in combination with iron was studied on chlorophyll, malondialdehyde, cysteine, total -SH contents and potassium ion leakage in the plants of Hydrilla verticillata. The effect of HCH was also studied on glutathione (reduced and oxidised) content and superoxide dismutase activity. The results showed an increase in malondialdehyde content and potassium ion leakage with increase in HCH concentrations, however, the presence of Fe played a protective role. The chlorophyll content was decreased with increase in HCH concentrations and exposure period. However, the chlorophyll content at 2 and 5 microg ml(-1) was significantly higher in HCH-treated plants as compared to HCH + Fe after 168 h, showing protective role of Fe. The results showed significant increase up to 1 microg ml(-1) in cysteine content with increase in concentrations in both the treatments. The total -SH content was increased with increase in concentrations in both the treatments. In HCH-treated plants, non-significant change was noticed in reduced glutathione (GSH) content however, oxidised glutathione (GSSG) content was increased significantly after 168 h, indicative of oxidative stress. In addition, superoxide dismutase activity was increased non-significantly with increase in HCH concentrations. The accumulation of HCH singly and in presence of Fe was concentration- and duration-dependent. The accumulation of HCH was decreased in presence of Fe at higher concentrations. In contrast, the accumulation of Fe was increased in presence of HCH at higher concentrations. The results showed that malondialdehyde content and potassium ions leakage are the primary responses of toxicity.

Phytoaccumulation and phytotoxicity of cadmium and chromium in duckweed Wolffia globosa

The phytoaccumulation and phytotoxicity of heavy metals, cadmium (Cd), and chromium (Cr) on a common duckweed, Wolffia globosa, were studied. W. globosa were cultured in 3% Hoagland's nutrient medium, which was supplemented with 1, 2, 4, and 8 mg/L of Cd and Cr and were separately harvested after 3, 6, 9, and 12 days. The accumulation of Cd and Cr in W. globosa showed significant increases when the exposure time and metal concentration were increased. The effects of Cd and Cr on the biomass productivity and total chlorophyll content in W. globosa indicated that there were significant decreases in the biomass productivity and total chlorophyll content when the exposure time and metal concentration were increased.