Comparative study of silicon and selenium to modulate chloroplast pigments levels, Hill activity, photosynthetic parameters and carbohydrate metabolism under arsenic stress in rice seedlings

Arsenic (As) in groundwater severely harms global economic development by affecting growth and productivity of agricultural crops that causes human health risk. The comparative influence of silicon (Si) and selenium (Se) to modulate pigments levels, photosynthetic parameters using LI-6400XT Portable Photosynthesis System and carbohydrate metabolism under arsenate (As-V) stress in rice cv. MTU-1010 were evaluated. As(V) stress significantly decreased chlorophyll-a (32% on an average), chlorophyll-b (58% on an average), total chlorophyll (46% on an average), fluorescence intensity (31% on an average),, carotene (39% on an average), xanthophyll (33% on an average), Hill activity (47% on an average) and the photosynthetic parameters viz., intercellular-CO2-concentration (52% on an average), net photosynthesis (54% on an average), transpiration rate (36% on an average) and stomatal conductance (38% on an average) in the test seedlings. As(V) + Si treatments enhanced the said parameters more than As(V) + Se treatments in rice seedlings. Sugar contents viz., reducing (85% on an average) and non-reducing sugar (61% on an average) were increased but starch content (57% on an average) was decreased in As(V) treated seedlings. The activities of carbohydrate metabolizing enzymes were increased, while sucrose synthase activity was decreased due to As(V) toxicity in the test seedlings. Co-application of Si and As(V) as well as Se and As(V) showed ameliorative effects on the said parameters but more potential effect was observed under combined application of Si and As(V) in rice seedlings. Thus, the present study is focused to highlight the comparative capability of Si and Se to ameliorate the As induced toxic effects on chloroplast pigments, photosynthetic activities and sugar metabolism in rice seedlings which will be an effective approach to develop possible strategies in As contaminated agricultural soil to improve normal growth and productivity of rice plants.

Salt induced inhibition in photosynthetic parameters and polyamine accumulation in two legume cultivars and its amelioration by pretreatment of seeds with NaCl

Enhancement of salt tolerance by pretreatment with sublethal dose of NaCl (50mM) has been investigated in arhar (Cajanas cajan L.) and maskalai (Vigna mungo L.) seedlings. Degradation of photosynthetic pigments in both the NaCl stressed legume cultivars resulted in less photosynthetic activity to occur. This was evident from reduced Hill activity recorded. NaCl stress hampered stomatal conductance that subsequently affected internal CO2 concentration, net photosynthetic rate and also transpiration rate. Both the tested cultivars accumulated polyamines to limit cellular damage under such stressed conditions. Increased level of (Spermine+Spermidine)/Putrescine ratio and decreased level of cadavarine were observed in the nonpretreated seedlings grown under NaCl stress. However, seed pretreatment with 50mM NaCl for two hours helped the cultivars to overcome adverse effects caused by NaCl stress on stomatal activity, gas exchange parameters and polyamine contents that resulted the cultivars to acclimate such that it improved their metabolism under saline conditions.

Cyanoacrylate Inhibitors as Probes for the Nature of the Photosystem II Herbicide Binding Site

Three series of phenyl-substituted 2-cyanoacrylates were evaluated using simple quantitative structure activity relationships (QSAR) in an attempt to elucidate the nature of the regions of the binding site occupied by different parts of the molecules. Inhibition of the Hill reaction by substituted 3-phenylamino-2-cyanoacrylates correlated well with the lipophilicity of the substituent. The hydrophobic effect was also dominant when the Hill activity of a series of 3-benzylamino-2-cyanoacrylates was analyzed, although potency was considerably higher in the latter series. Lipophilicity and the electronic nature of the substituents were not major determinants in the Hill inhibitory activity of a series of substituted phcnoxycthyl 2-cyanoacrylic esters. In this case, a significant correlation was found with the molar rcfractivity (MR) of meta substituents, a parameter reflecting substituent size. The results indicate that the phenyl moiety of substituted 3-phenylamino- and 3-bcnzyl- amino-2-cyanoacrylates interacts with an essentially lipophilic binding domain, though it is likely that the two series are oriented differently with the 3-bcnzylamino series able to bind with greater affinity. In the phcnoxycthyl ester series, the substituted phenyl group interacts with a different environment, wherein ortho- and we7tf-substitution is tolerated, dependent on the bulk of the substituent, but /wra-substitution is detrimental to affinity for this region of the site.

Studies of Uptake and Toxic Effects of Cr(VI) on Pistia stratiotes

The uptake of Cr(VI) and toxic effects of the metal on some biochemical parameters in Pistiastratiotes L. were studied. The uptake of Cr(VI) by the plants gradually increased with increase in concentration of Cr(VI) in the culture medium. Maximum accumulation of Cr(VI) was noted within 5 days. Maximum removal (about 90%) of Cr(VI) was recorded below 5 ppm. Accumulation of Cr(VI) occurred mainly in roots. At 5 and 10 ppm, Cr(VI) promoted senescence of Pistia plants by decreasing chlorophylls, protein, RNA, Hill activity and activities of catalase, protease as well as increasing dry weight, free amino acid content, peroxidase activity and ratio of acid to alkaline pyrophosphatase activity over control values. At Cr(VI) concentrations below 5 ppm, these constituents were least affected. So, Pistia plants can be utilised as the scavenger of Cr(VI) from waste water.