ALTERNATIVE AND CYTOCHROME PATHWAY RESPIRATION DURING SHOOT BUD FORMATION IN CULTURED PINUS-RADIATA COTYLEDONS

Respiration rates for excised cotyledons of Pinus radiata cultured in the presence (shoot-forming) and absence (non-shoot-forming) of N6-benzyladenine (BA) over a 21-day period were measured using a Clark-type oxygen electrode. The capacities and activities of cytochrome and alternative pathways of respiration were determined from titrations with KCN (1-10 mM) and salicylhydroxamic acid (2-20 mM) individually and in combination. Respiration accounted for by alternative (AP) and cytochrome (CP) pathways varied with both culture treatment and age in culture. Rates of total respiration, CP respiration and AP activity rose concurrent with key developmental events of shoot bud formation. The greatest AP capacity was measured at day 3 in shoot-forming tissue. In contrast, for cotyledons cultured under non-shoot-forming conditions, no AP activity was observed after day 3 despite relatively constant AP capacity throughout the culture period. Although initial increases in cotyledon respiration during the culture period may be related to wounding and introduction to a tissue culture environment. later differences in respiratory patterns between shoot-forming and non-shoot-forming cotyledons appear to be associated with the cytokinin-induced developmental changes which give rise to shoot primordia in cultured radiata pine cotyledons.