CHARACTERIZATION OF THE HARVEST-INDUCED EXPRESSION OF BETA-GALACTOSIDASE IN ASPARAGUS-OFFICINALIS

The harvest-induced senescence of asparagus spears is accompanied by b oth up-regulated and down-regulated gene expression. The expression of pTIP31, coding for asparagus P-galactosidase (EC 3.2.1.23) is tempora lly associated with removal of the asparagus spear from the main body of the plant - neither wounding or compression treatments induce up-re gulation of transcripts corresponding to pTIP31. Harvest-induced pTIP3 1 transcripts appear initially in cells below the meristems of the sid e branches, and in inner bracts and developing flowers of the spear ti p, and in the cells of the outer cortex and conjunctive tissue lower d own the spear. Transcripts are also located in vascular tissues 24 h a fter harvest. Enhanced levels of P-galactosidase activity are found in the branches and bracts of the spear tip within 12 h of harvest, whil e the rate of increase in activity in the middle zone of the spear was comparable to that of the branches and bracts after 24 h. The proport ion of galactose in spear cell walls decreases after harvest. We propo se that galactosidase activity releases galactose residues that may be used as respiratory substrate for the rapidly deteriorating asparagus spears. (C) Elsevier, Paris.