Identification of chitinase mRNA in abscission zones from bean (Phaseolus vulgaris Red Kidney) during ethylene-induced abscission

Abstract. Total RNA was extracted from bean leaf abscission zones at different times after the induction of abscission by ethylene. The RNA was translated in the wheat germ system and the products analysed by SDS-PAGE. Products of molecular weight (raw) 42, 32 and 17 kD were seen to accumulate substantially during the induction. An attempt was made to establish that the mRNA species which produced the 32 kD product, which was coded for the ethylene-regulated enzyme chitinase. Mature chitinase (30 kD) was purifed from ethylene-treated abscission zones and used to raise monospecific antibodies in rabbits. These antibodies recognized the 32 kD product and mature chitinase. The 2 kD difference in molecular weight was due to the presence of the signal sequence which could be removed by microsomal membranes. Chitinase was also detected by enzymatic assay and immunoblotting of crude homogenates from ethylene-treated abscission zones. Chitinase appears to be ubiquitous in bean plants and probably does not have a direct role in abscission.