Comparative study of plant defense response in volicitin treated and mechanically wounded Zea mays plants under the action of the calcium channel blocker Gadolinium(III)

Dalvi, Chinmay Vilas
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Zea mays plants were treated with varying concentrations of Gd3+ and further subjected to insect elicitor (IE) and mechanical wounding (MW) treatment. Transcript accumulation of genes involved in plant defense and calcium signaling studied by semi-quantitative PCR are differentially regulated. The AOC (allene oxide cyclase) gene playing an important role in Jasmonic acid (JA) synthesis is down-regulated with higher Gd3+ concentration in volicitin treated plants whereas the mechanically wounded plants show a rise in AOC expression till 1mM of Gd3+ but goes down when subjected to 10mM Gd. These results suggest that the JA synthesis and plant defense response could be primarily regulated by apoplastic Ca2+ reserves for insect elicitor (IE) induced defense response whereas the mechanical wounding induced defense response might be using the intracellular Ca2+ reserves as its primary source of Ca2+. A stronger possibility exists that Ca2+ signaling is not involved in MW induced defense response. Further expression of AOC and important Ca2+ regulatory protein calmodulin (gene CAM) suggest that, in plant cells the calcium channels on the plasma membranes are saturated by 1mM Gd3+ treatment. A sudden variation in expression of genes at 10mM Gd3+ concentration suggests that Gd3+ ions might show membrane permeability. Due permeability of plasma membrane to Gd3+, the Gd3+ ions can enter the cells and block the Ca2+ channels on the intracellular organelle. The gene expression data for calcium binding protein CCD1 and calcium dependent protein kinase isoform AK1 shows that they do have a regulatory function in IE mediated plant defense response. Rise in transcript accumulation of CCD1 and AK1 genes under high Gd3+ stress (10mM) gives rise to a possibility of high protein synthesis in order to maximize Ca2+ utilization in Ca2+ starved conditions. Though a lot of variations were observed, the average expression data for the CAM gene suggests a down-regulated expression of the calmodulin transcribing gene at 10mM suggesting a lowered cytosolic calcium concentration. Surprisingly the gene expression data from Inositol (1, 3, 4) - Triphosphate kinase (gene IPK3) which plays an important role in JA signaling does not show any noticeable changes in transcript accumulation.

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Integrative Biology