JXB Advance Access originally published online on August 28, 2003
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Journal of Experimental Botany, Vol. 54, No. 391, pp. 2275-2284,
October 1, 2003
© 2003 Oxford University Press
Three differentially expressed basic peroxidases from wound-lignifying Asparagus officinalis
Received 4 March 2003; Accepted 25 June 2003
1 Plant Research Department, PRD-301, Risø National Laboratory, PO Box 49, DK-4000 Roskilde, Denmark
2 Department of Horticulture, Research Centre Aarslev, Danish Institute of Agricultural Sciences, Kirstinebjergvej 10, PO Box 102, DK-5792 Aarslev, Denmark
* To whom correspondence should be addressed. Fax: +45 4677 4122. E-mail: soren.rasmussen{at}risoe.dk
The activity of ionically bound peroxidases from an asparagus spear increased from 5–24 h post-harvest. Isoelectric focusing showed that the post-harvest increase of the total peroxidase activity was due to the increase of several distinct isoperoxidases. Concomitantly, a decrease in the activity of two anionic peroxidases was observed. Peroxidases with pI 5.9, 6.4 and 9.2 were detected only at 24 h post-harvest, whereas four peroxidases, with pI 8.7, 8.1, 7.4, and 6.7, detected throughout the time-course, increased in their activity. Histochemical staining demonstrated that lignin and peroxidase activity were located in the vascular bundles throughout the period of measurement. Lignin was detected in the cell walls of the protoxylem in the vascular bundles of the asparagus stem. A cDNA library of mRNA isolated from asparagus spears 24 h post-harvest was screened for peroxidases using homologous and heterologous probes. Three clones were isolated and the corresponding mature asparagus peroxidases displayed 70%, 76% and 81% amino acid sequence identity to each other. These new asparagus peroxidases are typical class III plant peroxidases in terms of conserved regions with a calculated pI >9.2, which is consistent with most basic peroxidases. One of the genes was shown to be a constitutively expressed single-copy gene, whereas the others showed an increased expression at post-harvest. The highest similarity in the amino acid sequence (71–77%) was found in peroxidases from roots of winter grown turnip TP7, to Arabidopsis AtP49, to an EST sequence from cotton fibres and to TMV-infected tobacco.
Key words: Asparagus, DNA sequence, histochemical staining, lignin, peroxidase, suberin.
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