ETHYLENE EVOLUTION, RADIAL GROWTH AND CARBOHYDRATE CONCENTRATIONS IN ABIES-BALSAMEA SHOOTS RINGED WITH ETHREL

The terminal (1-year-old) shoot of quiescent, 2-year-old Abies balsame a CL.) Mill. seedlings was either left untreated or ringed with 0, 1 o r 10 mg Ethrel g(-1) lanolin. After 5 weeks of culture under environme ntal conditions favorable for growth, the shoots were harvested to mea sure ethylene evolution and carbohydrate concentrations by gas chromat ography, and tracheid number and bark radial width by microscopy. In u ntreated shoots, the basal rate of ethylene evolution followed the ord er: cambial region > cortex + periderm = xylem + pith = needles. Wound -induced ethylene production was not detected until at least 4 h after excision, but was evident in all fractions 24 h after excision; the i ncrease in wound-induced ethylene evolution followed the order: cambia l region > cortex + periderm > xylem + pith > needles. Compared with u ntreated controls, the application of plain lanolin, which involved th e removal of needles and periderm, increased bark radial width and wou nd-induced ethylene production by the cambial region and the cortex periderm, but decreased cambial region concentrations of fructose, glu cose and starch at the application point. At the application point, Et hrel concomitantly increased ethylene evolution from the cambial regio n and the cortex + periderm, tracheid number, bark radial width, and t he cambial region concentrations of fructose, glucose, sucrose and sta rch. No effects of Ethrel treatment were detected above or below the a pplication point, with the exception that the 10 mg g(-1) Ethrel treat ment stimulated ethylene evolution and decreased starch concentration of the cambial region. The results indicate that: (1) the cambial regi on is the major source of endogenous ethylene in the 1-year-old shoot; (2) the magnitude of the difference in ethylene evolution between par ticular shoot fractions is different before and after the start of wou nd-induced ethylene production; (3) the Ethrel-induced increase in tra cheid number and bark radial width at the application point is positiv ely related to ethylene evolution from the cambial region and the cort ex + periderm, respectively; and (4) ethylene derived from Ethrel appl ied laterally to a woody stem can mobilize carbohydrates to the applic ation point.