ETHYLENE SYNTHESIS AND GROWTH IN EMBRYOGENIC TISSUE OF NORWAY SPRUCE - EFFECTS OF OXYGEN, 1-AMINOCYCLOPROPANE-1-CARBOXYLIC ACID, BENZYLADENINE AND 2,4-DICHLOROPHENOXYACETIC ACID

Ethylene production from an embryogenic culture of Norway spruce (Pice a abies L.) was generally low, ca 2.5 nl g(-1) h(-1), whereas 1-aminoc ycloprapane-1-carboxylic acid (ACC) concentration was high, fluctuatin g between 50 and 500 nmol g(-1) during the 11-day incubation period. H ypoxia (2.5 and 5 kPa O-2) rapidly inhibited ethylene production witho ut subsequent accumulation of ACC. Exogenous ACC (1, 10 and 100 mu M) did not increase ethylene production, but the highest concentrations i nhibited tissue growth. Ethylene (7 mu l l(-1)) did not inhibit growth either when supplied as ethephon in the medium or in a continuous flo w system. Benzyladenine (BA) had little effect on ethylene production, although it was necessary for sustaining the ACC level. Omission of 2 ,4-dichloro-phenoxyacetic acid (2,4-D) from the medium caused ethylene production to increase from about 2.5 to 7 nl g(-1) h(-1) within the 11-day incubation period. Although 2,4-D did not specifically alter th e endogenous level of ACC, the lowest ACC level, 33 nmol g(-1), was ob served in tissue treated with 2,4-D (22.5 mu M) and no BA for 11 days. Data from this treatment were used to estimate the kinetic constants for ACC oxidase, the apparent K-m was 50 mu M and V-max 2.7 nl g(-1) h (-1). Growth of the tissue was strongly inhibited by 2,4-D in the abse nce of BA, but weakly in the presence of BA (4.4 mu M). The results su ggest that ethylene or ACC may be involved in the induction of embryog enic tissue and in the early stages of embryo maturation.