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-ben zyladenine (BA) over a 21-day period were measured using a Clark-type oxygen electrode. The capacities and activities of cytochrome and alte rnative pathways of respiration were determined from titrations with K CN (1-10 mM) and salicylhydroxamic acid (2-20 mM) individually and in combination. Respiration accounted for by alternative (AP) and cytochr ome (CP) pathways varied with both culture treatment and age in cultur e. Rates of total respiration, CP respiration and AP activity rose con current with key developmental events of shoot bud formation. The grea test AP capacity was measured at day 3 in shoot-forming tissue. In con trast, for cotyledons cultured under non-shoot-forming conditions, no AP activity was observed after day 3 despite relatively constant AP ca pacity throughout the culture period. Although initial increases in co tyledon respiration during the culture period may be related to woundi ng and introduction to a tissue culture environment. later differences in respiratory patterns between shoot-forming and non-shoot-forming c otyledons appear to be associated with the cytokinin-induced developme ntal changes which give rise to shoot primordia in cultured radiata pi ne cotyledons.