Humayra Bashir

Influence of sulfur and cadmium on antioxidants, phytochelatins and growth in Indian mustard

Sulphur(S)-deficiency is emerging as a major problem for agricultural productivity. Cadmium (Cd) exerts its phytotoxicity against defence, growth and development. S-rich compounds (glutathione, phytochelatins, etc.) limit the impacts of Cd-toxicity. We investigated what happens during S-deficiency and Cd exposure (dual stress) in mustard. Major findings were: S-deficiency increases the susceptibility of plants to Cd-generated oxidative damage and modulates the AsA-GSH antioxidant cycle; SOD is not the first line of defence against metal stress and S-rich metabolites play a prime role; S-deprived plants are more prone to Cd and oxidative stress; and great loss is incurred to defence modules and growth under dual stress, restricting the efficiency of phytoremediation.

Chloroplast and photosystems: Impact of cadmium and iron deficiency

Chloroplasts utilize photons from solar radiation to synthesize energy-rich molecules of ATPs and NADPHs, which are further used in active cellular processes. Multiprotein complexes (MPCs), including photosystems (PSII and PSI), and the cellular architecture responsible for generation of the proton motive force and the subsequent photophosphorylation, mediate the task of ATP and NADPH synthesis. Both photosystems and other multiprotein assemblies are embedded in thylakoid membranes. Advances in techniques used to study structural biology, biophysics, and comparative genomics and proteomics have enabled us to gain insights of structure, function, and localization of each individual component of the photosynthetic apparatus. An efficient coordination among MPCs is essential for normal functioning of photosynthesis, but there are various stressors that might directly or indirectly interact with photosynthetic components and processes. Cadmium is one of the toxic heavy metals that interact with photosynthetic components and damage photosystems and other MPCs in thylakoids. In plants, iron deficiency shows similar symptoms as those caused by Cd. Our article provides a general overview of chloroplast structure and a critical account of Cd-induced changes in photosystems and other MPCs in thylakoids, and suggests the possible mechanisms involved in mediating these changes. The connection between Cd-induced Fe deficiency and the elevated Cd toxicity under the Fe-deficient condition was also discussed.

Chapter 1 – Nodule Physiology and Proteomics of Stressed Legumes

Abstract Symbiotic bacteria are harboured in the nodules of the nitrogen-fixing plants. The bacteria, collectively termed rhizobia, include genera such as Rhizobium, Sinorhizobium, Bradyrhizobium, Mesorhizobium and Azorhizobium, and form specialised organs within the plant. Nitrogen fixation occurs via the conversion of N2 into NH3 by bacterial nitrogenases. Knowledge of protein profile (structural and soluble) of bacteria and host may provide information useful in understanding the bacteria–host relationship and improving N2-fixation efficiency in leguminous plants. Although the majority of nitrogen-fixing plants belong to the family Fabaceae, a few non-leguminous plants (like actinorhizal plants) can also fix nitrogen. Proteomics is an ideal tool to study the protein profile and its correlation with nodule-associated metabolic and symbiotic processes. N2-fixing symbioses are well studied but not in terms of proteomic response to abiotic stress. Data obtained in some proteomic studies on Medicago trancatula and few other leguminous plants provide useful information on root nodules, their symbiotic bacteria and the proteins produced by both partners during their constant signal exchange and growth. Mass spectrometric analysis has helped in identifying several proteins, including those associated with molecular regulation, respiration and leghaemoglobin, proteases in the nodule. Differential expression of proteins under different abiotic stresses such as temperature, drought, salinity and toxic metals that affect the profile of nodule proteome is believed to be due to the production of oxidative stress, osmotic imbalance and other direct or secondary consequences of stress. However, nutrient stress also affects proteome profile as in iron deficiency. Iron-containing proteins play a key role in symbiotic nitrogen fixation (SNF) that occurs in the nodule. Several proteins like those related to SNF, predominant components of nitrogenase complexes such as nifD, nifH, nifK, nitrogen regulatory protein II (GlnB) and PIIA (PtsN) and urease accessory protein (UreE) are known to be affected by abiotic stress. Nodules are well equipped with antioxidant enzymes (superoxide dismutase, ascorbate peroxidase and glutathione reductase, etc.) which respond to stress conditions. This review introduces nodule physiology and examines critically the recent developments in the field of nodule proteomics, emphasising, in particular, upon changes brought about by abiotic stresses to the nodule proteome, provides up-to-date information on key metabolic proteins that help to combat stress and discusses the prospects of nodule proteomics.

Drought and salinity induced changes in ecophysiology and proteomic profile of Parthenium hysterophorus

Parthenium hysterophorus is a plant that tolerates drought and salinity to an extremely high degree. Higher expression of stress-responsive proteome contributes for greater defence against abiotic stresses. Thus, P. hysterophorus could be a rich source of genes that encode stress-imparting mechanisms and systems. The present study utilizes comparative physiological and proteomic approaches for identification of key proteins involved in stress-defence of P. hysterophorus. Thirty-days-old plants were exposed to drought (10% PEG 6000) and salinity (160 mM NaCl) for 10 days duration. Both stresses induced oxidative stress estimated in terms of TBARS and H2O2. Levels of both enzymatic and non-enzymatic antioxidants were elevated, more by drought than salinity. Particularly, SOD, GR, CAT and GST proved to be assisting as very commendable defence under drought, as well as salinity. Levels of ascorbate, glutathione and proline were also increased by both stresses, more in response to drought. Comparative proteomics analysis revealed a significant change in relative abundance of 72 proteins under drought and salinity. Drought and salinity increased abundance of 45 and 41 proteins and decreased abundance of 24 and 26 proteins, respectively. Drought and salinity increased and decreased abundance of 31 and 18 proteins, respectively. The functions of identified proteins included those related to defence response (26%), signal transduction (13%), transcription and translation (10%), growth and development (8.5%), photosynthesis (8.5%), metabolism (7%), terpenoid biosynthesis (5.5%), protein modification and transport (7%), oxido-reductase (4%) and Miscellaneous (11%). Among the defence related proteins, antioxidants and HSPs constituted 26% and 21%, respectively. Present study suggests a potential role of defence proteins. Proteins involved in molecular stabilization, formation of osmolytes and wax and contributing to stress-avoiding anatomical features emerged as key and complex mechanisms for imparting stress tolerance to P. hysterophorus.

Organ-Specific Phytochemical Profiling and Antioxidant Analysis of Parthenium hysterophorus L.

Parthenium hysterophorus is a weed of global concern with high threshold of tolerance against most of biotic and abiotic stresses. Phytochemical profile and in vitro antioxidant analysis may help in understanding its tolerance to stresses. Root, stem, leaf, phyllary, and receptacle (including disc and ray florets) were chemotyped employing GC tof-MS and assessed for antioxidant activity by DPPH, FRAP, HRSA, and TAC assays. Phytochemicals identified were terpenes, fatty acids, hydrocarbons, phytosterols, and compounds of miscellaneous chemical nature. Organ-specific maximum concentration of metabolite was β-vatirenene (root), hexadecanoic acid methylester (stem), aristolene epoxide (leaf), hexadecanoic acid methylester (phyllary), and hexadecanoic acid methylester (receptacle). Identified metabolites could be associated with stress tolerance mechanisms, basic metabolism, and allelopathy, etc. Root extracts showed highest antioxidant potential followed by receptacle. It can be concluded that diverse and unique phytochemical profile and great antioxidant potential make P. hysterophorus stress-tolerant, hence a weed of global habitat.