Nilima Kumari

Structural and functional alterations in photosynthetic apparatus of plants under cadmium stress

Cadmium is a potentially toxic heavy metal that hampers plant productivity by interfering with their photochemistry. Cd causes disturbances in a range of physiological processes of plants such as photosynthesis, water relations, ion metabolism and mineral uptake. Cd pronouncedly affects photosynthesis by alteration of its vital machinery in all aspects. Photosynthesis is a well organised and sequential process fundamental to all green plants and microorganisms which involves various components, including photosynthetic pigments and photosystems, the electron transport system and CO2 reduction pathways. Any damage at any level caused by Cd, critically affects overall photosynthetic capacity. Present review focuses on key effects of Cd on photosynthetic apparatus including chloroplast structure, photosynthetic pigments, Chl-protein complexes and photosystems resulting in overall decrease in efficiency of carbon assimilation pathway.

Two proteins homologous to PsbQ are novel subunits of the chloroplast NAD(P)H dehydrogenase.

The PsbQ-like (PQL) proteins 1 and 2, previously shown to be located in the thylakoid lumen of Arabidopsis thaliana, are homologous to PSII oxygen-evolving complex protein PsbQ. Nevertheless, pql mutants showed no defects in PSII but instead the activity of the chloroplast NAD(P)H dehydrogenease (NDH) complex was severely impaired. In line with this observation, the NDH subunits were low in abundance in pql mutants, and, conversely, ndh mutants strongly down-regulated the accumulation of the PQL proteins. In addition, the PQL2 protein was up-regulated in mutant plants deficient in the PSI complex or the thylakoid membrane-bound ferredoxin-NADP(+) oxidoreductase, whereas in pql mutants the PSI complex was slightly up-regulated. Taken together, the two PQL proteins are shown to be novel subunits of the lumenal protuberance of the NDH complex.

Drought-induced changes in chlorophyll fluorescence, photosynthetic pigments, and thylakoid membrane proteins of Vigna radiata

The effects of drought on chlorophyll fluorescence characteristics of PSII, photosynthetic pigments, thylakoid membrane protein (D1), and proline content in different varieties of mung bean plants were studied. Drought stress inhibits PSII activity and induces alterations in D1 protein. We observed a greater decline in the effective quantum yield of PSII, electron transport rate, and saturating photosynthetically active photon flux density (PPFDsat) under drought stress in var. Anand than var. K-851 and var. RMG 268. This may possibly be due to either downregulation of photosynthesis or photoinhibition process. Withholding irrigation resulted in gradual diminution in total Chl content at Day 4 of stress. HPLC analysis revealed that the quantity of β-carotene in stressed plants was always higher reaching maxima at Day 4. Photoinactivation of PSII in var. Anand includes the loss of the D1 protein, probably from greater photosynthetic damage caused by drought stress than the other two varieties.

Defense gene expression in Sorghum bicolor against Macrophomina phaseolina in leaves and roots of susceptible and resistant cultivars

The fungal disease, charcoal root rot, caused by Macrophomina phaseolina is a foremost yield restraining factor of Sorghum bicolor L. around the world. The expression analysis of genes induced in general defense response can endow with clues to reveal major defense mechanisms against pathogen infection in sorghum plant. The role of chitinase and Stilbene synthase in response to M. phaseolina in sorghum was studied under control growth conditions using a real-time polymerase chain reaction. Here, we report the expression analysis of antifungal genes in two cultivars viz. PJ-1430 (resistant) and SU-1080 (susceptible) at different hours after inoculation with M. phaseolina isolate MTCC 2165. Chitinase and stilbene synthase were induced in PJ-1430 within 0 h, 24 h and in SU-1080 in 48 h, 24 h, respectively, after inoculation. However, the expression levels of chitinase and stilbene synthase in resistant cultivar were significantly higher. The results showed that chitinase and stilbene synthase can be effective to enhance resistance to M. phaseolina.

Photosynthetic Performance of Ocimum sanctum Morphotypes in a Semiarid Region

ABSTRACT Comparative ecophysiological studies by measurements of photosystem II (PSII) chlorophyll a fluorescence, pigment composition, and proline content were used in the synecological assessments of two Ocimum sanctum (holy basil) morphotypes, viz., Sri Tulsi and Krishna Tulsi, to compare their overall “adaptiveness.” The effective quantum yield of PSII (ΔF/Fm’sat) and maximum apparent electron transport rate (ETRmax) was 30% lower in Krishna Tulsi than in Sri Tulsi plants. Chlorophyll and carotenoid content in Sri Tulsi were twofold higher than in Krishna Tulsi. Results indicated that differences in photosynthetic efficiency observed in Sri Tulsi may determine ecological dominance.

Differential gene expression in two contrasting wheat cultivars under cadmium stress

The present study investigated differences in cadmium resistance of two wheat (Triticum aestivum L.) cultivars. The cvs. RAJ 4161 (Cd resistant) and PBW 343 (Cd sensitive) were treated with 200 mg(Cd) kg−1(soil) for 3, 5, 7, and 10 d. The effect of the Cd stress was estimated by measuring growth parameters, accumulation of cadmium, sulphur, and glutathione (GSH), and by expression of some defence genes [phytochelatin synthase (PCS), glutathione reductase (GR), and ascorbate peroxidase (APX)]. The Cd treatment resulted in a significant reduction in plant growth and in an increase in the accumulation of S and GSH. Further, the expressions of PCS, GR, and APX were also mostly enhanced. The PCS was upregulated significantly in roots of RAJ 4161 (0.6-fold) and downregulated (0.9-fold) in PBW 343 on day 3 of the Cd treatment. In RAJ 4161, the expressions of APX and GR recorded a maximum increase of 2.1- and 2.4-fold in roots and leaves, respectively, after 10 d of the stress. The results show that a different ability of RAJ 4161 and PBW 343 to modulate mRNA expression after the Cd treatment was related to their Cd tolerance.

Structural insight into β-Clamp and its interaction with DNA Ligase in Helicobacter pylori

Helicobacter pylori, a gram-negative and microaerophilic bacterium, is the major cause of chronic gastritis, gastric ulcers and gastric cancer. Owing to its central role, DNA replication machinery has emerged as a prime target for the development of antimicrobial drugs. Here, we report 2Å structure of β-clamp from H. pylori (Hpβ-clamp), which is one of the critical components of DNA polymerase III. Despite of similarity in the overall fold of eubacterial β-clamp structures, some distinct features in DNA interacting loops exists that have not been reported previously. The in silico prediction identified the potential binders of β-clamp such as alpha subunit of DNA pol III and DNA ligase with identification of β-clamp binding regions in them and validated by SPR studies. Hpβ-clamp interacts with DNA ligase in micromolar binding affinity. Moreover, we have successfully determined the co-crystal structure of β-clamp with peptide from DNA ligase (not reported earlier in prokaryotes) revealing the region from ligase that interacts with β-clamp.

Phytoremediation efficiency of Brassica juncea cultivars at vegetative and reproductive growth stages under individual and combined treatment of fluoride and aluminium

ABSTRACT The objective of this study was to investigate phytoremediation ability of Brassica juncea cultivars for aluminium (Al) and fluoride (F) independently and in combination (Al + F). Out of 8 cultivars which were treated with Al, F, and (Al + F), 4 cultivars (Bio-902, Pusa-Tarak, CS-14, and Laxmi) were selected for further studies on the basis of growth parameters. These cultivars were exposed to soil (pH 5) supplemented with F (0, 25, 50, and 75 mg kg−1) and Al (0, 50, 100, and 150 mg kg−1) independently and in combination (Al + F) (0 + 0, 50 + 25, 100 + 50, and 150 + 75 mg kg−1). We found that the accumulation of F, Al, and (Al + F) was highest in the roots followed by grains, shoots, and leaves. When the plants were treated with Al or F separately, the accumulation of Al or F were less as compared to when treated in combination (Al + F). Conclusively, the results also showed that maximum tolerance index, uptake, and translocation factor for F were highest in CS-14, Al in Bio-902, and (Al+ F) in Pusa-Tarak, and were found to be the lowest in Laxmi.

Differential cadmium stress tolerance in wheat genotypes under mycorrhizal association

ABSTRACT Arbuscular mycorrhizal (AM) fungi display efficient association with the land plants and is known to protect plants against various abiotic stresses including heavy metal stress. This work reports the synergistic effects of natural genotypic variation and AM association in cadmium (Cd) stress alleviation. Two genotypes of wheat viz. RAJ 4161 (resistant) and PBW 343 (sensitive) were subjected to different concentrations of Cd (0, 100, 200 and 300 mg Cd kg−1 soil) for 30 days. Cd application resulted in increased lipid peroxidation and decreased plant growth. However, AM inoculated RAJ 4161 displayed significantly higher ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR) and superoxide dismutase (SOD) activity and calcium (Ca), iron (Fe)and zinc (Zn) concentration in plants. The coordination of increased antioxidant activity and high nutrient content in RAJ 4161 indicated better protective mechanism as compared to PBW 343.

Targeting the β‐clamp in Helicobacter pylori with FDA‐approved drugs reveals micromolar inhibition by diflunisal

The β‐clamp is the processivity‐promoting factor for most of the enzymes in prokaryotic DNA replication; hence, it is a crucial drug target. In the present study, we investigated the β‐clamp from Helicobacter pylori, aiming to seek potential drug molecules against this gastric‐cancer‐causing bacterium. An in silico screening of Food and Drug Administration (FDA) approved drugs against the H. pylori β‐clamp, followed by its in vitro inhibition using a surface competition approach, yielded the drug diflunisal as a positive initial hit. Diflunisal inhibits the growth of H. pylori in the micromolar range. We determined the structure of diflunisal in complex with the β‐clamp to show that the drug binds at subsite I, which is a protein–protein interaction site. Successful identification of FDA‐approved molecules against H. pylori may lead to better and faster drug development.