A full-length cDNA clone encoding microbody NAD +-dependent malate dehydrogenase (MDH) of cucumber has been isolated. The deduced amino acid sequence is 97 ~o identical to glyoxysomal MDH (gMDH) of watermelon, including the amino terminal putative transit peptide. The cucumber genome contains only a single copy of this gene. Expression of this mdh gene increases dramatically in cotyledons during the few days immediately following seed imbibition, in parallel with genes encoding isocitrate lyase (ICL) and malate synthase (MS), two glyoxylate cycle enzymes. The level of MDH, ICL and MS mRNAs then declines, but then MDH mRNA increases again together with that of peroxisomal NAD + - dependent hydroxypyruvate reductase (HPR). The mdh gene is also expressed during cotyledon senescence, together with hpr, icl and ms genes. These results indicate that a single gene encodes MDH which functions in both glyoxysomes and peroxisomes. In contrast to icI and ms genes, expression of the mdh gene is not activated by incubating detached green cotyledons in the dark, nor is it affected by exogenous sucrose in the incubation medium. The function of this microbody MDH and the regulation of its synthesis are discussed.

Item Type:	Refereed Article
Keywords:	cucumis sativus, germination, glyoxysome, NAD-malate dehydrogenase, peroxisome, senescence
Research Division:	Biological Sciences
Research Group:	Plant biology
Research Field:	Plant physiology
Objective Division:	Expanding Knowledge
Objective Group:	Expanding knowledge
Objective Field:	Expanding knowledge in the biological sciences
UTAS Author:	Smith, SM (Professor Steven Smith)
ID Code:	101588
Year Published:	1994
Web of Science® Times Cited:	41
Deposited By:	Plant Science
Deposited On:	2015-06-26
Last Modified:	2015-09-21
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