EFFECT OF JUVENILITY STATUS ON GROWTH AND ENDOGENOUS IAA AND ABA IN PRUNUS-AVIUM CALLUS OF INTERNODAL ORIGIN

Callus was initiated from internodal explants from Prunus avium cv. St ella selfed seedlings or rooted mature cuttings growing rapidly in ear ly May, or growing slowly in June, when callus was also initiated from rooted mature cuttings of the clonal rootstock F12/1. After culture p eriods of 12-19 weeks, replicate callus lines were transferred to fres h medium, and weighed at weekly intervals for five weeks. Cv. Stella c allus of juvenile origin initiated in early May grew faster during the exponential growth phase than the equivalent mature callus, but growt h rates of the juvenile and mature callus lines initiated in June were similar. Callus of juvenile, but not that of mature origin, initiated in May also grew faster than that initiated in June. At the end of th e period of growth measurement, juvenile callus initiated in May, but not that initiated in June, contained 7-4 times greater IAA concentrat ions and eight times larger IAA/ABA ratios than equivalent mature call us. Mature F12/1 callus initiated in June was as vigorous as juvenile callus initiated in May, but maintained similar IAA concentrations and IAA/ABA ratios to cv. Stella mature callus initiated in May. These re sults indicate that there are differences, including in endogenous IAA status, between Prunus avium juvenile and mature cell lines whose exp ression is continued through successive cell divisions, and which are only manifested when juvenile callus is initiated during a period of r apid growth.