Institutional Publications

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Author: search.filters.author.Sinha, Alok KrishnaSubject: search.filters.subject.Stress

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    Role of α-tocopherol in cellular signaling: α-tocopherol inhibits stress-induced mitogen activated protein kinase activation
    (Springer Science, 2011) Hyun, Tae Kyung; Kumar, Kundan; Rao, Kudupudi Prabhakara; Sinha, Alok Krishna; Roitsch, Thomas
    Tocopherols belong to the plant-derived poly phenolic compounds known for antioxidant functions in plants and animals. Activation of mitogen-activated protein kinases (MAPK) is a common reaction of plant cells in defense-related signal transduction pathways. We report a novel non-antioxidant function of α-tocopherol in higher plants linking the physiological role of tocopherol with stress signalling pathways. Pre-incubation of a low concentration of 50 μM α-tocopherol negatively interferes with MAPK activation in elicitor-treated tobacco BY2 suspension culture cells and wounded tobacco leaves, whereas pre-incubated BY2 cells with α-tocopherol phosphate did not show the inhibitory effect on stimuli-induced MAPK activation. The decreased MAPK activity was neither due to a direct inhibitory effect of α-tocopherol nor due to the induction of an inhibitory or inactivating activity directly affecting MAPK activity. The data support that the target of α-tocopherol negatively regulates an upstream component of the signaling pathways that leads to stress dependent MAPK activation.
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    Differential responses of arsenic stress in two varieties of Brassica juncea
    (Elsevier B.V., 2009) Gupta, Meetu; Sharma, Pallavi; Sarin, Neera Bhalla; Sinha, Alok Krishna
    Present study showed the toxicity caused by Arsenite (As(III)) and its detoxification responses in two varieties (Varuna and Pusa Bold) of Brassica juncea. Comparisons were made in leaves and roots of both the varieties, which showed that the accumulation pattern in both the varieties were dose and duration dependent, being more in roots for two days and in leaves for four days. Increase/decrease of antioxidant enzymes activities (SOD, CAT, GPX) showed not much changes at the given concentrations except that the enzyme activities showed significant increase at the lower concentrations. Semi quantitative RT-PCR analysis of PCS showed more expression of its transcript in P. Bold as compared to Varuna variety due to As(III) stress. The analysis of isoenzyme pattern in leaves of P. Bold showed five and two major bands of SOD and GPX, respectively. As(III) treatment leads to the activation of MAPK activity indicating role of this important cascade in transducing As(III) mediated signals. The data presented indicates the differential responses in both the varieties and also that the increased tolerance in P. Bold may be due to the defensive role of antioxidant enzymes, induction of MAPK and up regulation of PCS transcript which is responsible for the production of metal binding peptides.
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    Cloning and characterization of a novel LpWRKY1 transcription factor in tomato
    (Elsevier B.V., 2008) Hofmann, Markus Georg; Sinha, Alok Krishna; Proels, Reinhard Korbinian; Roitsch, Thomas
    The initiation of defence responses in plants is accompanied by fundamental changes in gene expression: the expression of pathogenesis- related genes is co-ordinately regulated with metabolic changes such as down regulation of photosynthesis and induction of sink metabolism. To identify candidate regulators of this co-ordinated regulatory mechanism, the role of WRKY transcription factors in the initiation of defence response was analysed in tomato. A WRKY-type transcription factor (LpWRKY1) from tomato was cloned by a reverse Northern approach. The corresponding mRNA is rapidly and transiently induced after challenging the cells with an elicitor-preparation derived from the wilt inducing fungus Fusarium oxysporum lycopersici (E-FOL) and the fungal elicitor chitosan, whereas the endogenous signals systemin and salicylic acid are inactive. Inhibition of protein biosynthesis by cycloheximide results in sustained induction of mRNA for LpWRKY1. In contrast, the transient induction of the gene encoding LpWRKY1 in response to elicitation by E-FOL is inhibited by the protein-kinase inhibitor staurosporine and may be mimicked by the phosphatase inhibitors endothall and cantharidine indicating the involvement of protein phosphorylation in the regulation of WRKY-type transcription factors. Direct proof of this postranslational modification of LpWRKY1 was obtained by demonstrating in-gel kinase assays using recombinant LpWRKY1 as substrate. A 44 kDa and a 67 kDa protein kinase were shown to be transiently activated to phosphorylate LpWRKY1 protein in response to elicitation with E-FOL.