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Title: The regulation of calmodulin gene expression by nuclear calcium in plants
Author: Van der Luit, Arnold H.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1998
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DNA constructs of Agrobacterium-mediated transformation into Nicotiana plumbaginifolia were prepared. The Ca2+-sensitive luminescent protein, aequorin was placed in frame with the nuclear localisation signal (NLS) peptide of the simian virus SV40 Large T-antigen, Xenopus leavis' nucleoplasmin, and high mobility group protein, HMG1 from Pisum sativum. After analysing individual transformants, nucleoplasmin was shown to successfully target aequorin to nuclei. These plants, together with plants transgenic for cytosolic aequorin, were used to study Ca2+ dynamics when exposed to the environmental stimuli, wind and cold shock. Wind induced immediate Ca2+ transients in the cytoplasm and nucleus, while cold shock induced a Ca2+ transient in the cytoplasm that was followed by a delayed Ca2+ transient in the cytoplasm that was followed by a delayed transient in the nucleus. Wind and cold shock induced calmodulin gene expression that followed distinct kinetics. Rapid Amplification of cDNA Ends (3' RACE) identified the presence of two calmodulin transcripts in tobacco seedlings; NpCaM-1 and NpCaM-2 of which only NpCaM-1 was induced by both stimuli. The transcripts comprise two different nucleotide sequences but encode identical polypeptides. The expression kinetics of NpCaM-1 was related to wind and cold shock-induced nuclear and cytosolic Ca2+ changes by using Ca2+ agonists/antagonists. Wind-induced nuclear Ca2+ changes correlated closely to the subsequent expression of and accumulation of NpCaM-1 while changes in cytoplasmic Ca2+ levels did not. Cold shock, on the other hand, did not reveal this correlation, and a role for intracellular Ca2+ levels during subsequent expression of NpCaM-1 remains therefore speculative. Heat shock induced a prolonged increase in nuclear Ca2+ level. Seedlings pretreated with Ca2+ or EGTA showed respectively enhanced or diminished subsequent thermotolerance, therefore it was suggested that these increases in Ca2+ levels were required for the acquisition of heat-induce thermotolerance.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available