METABOLISM OF C-14 ASPARTATE DURING SHOOT BUD FORMATION IN CULTURED COTYLEDON EXPLANTS OF RADIATA PINE

Aspartate metabolism was investigated in excised cotyledons of radiata pine (Pinus radiata D. Don). These cotyledons were cultured under sho ot-forming (plus N-6-benzyladenine, SF), non-shoot-forming (minus N-6- benzyladenine, NSF) and unresponsive (plus N-6-benzyladenine, OLD) con ditions, then incubated with [C-14]-aspartate for 3-h pulse treatments followed by 3-h chase treatments with cold aspartate. The majority of label was recovered in the CO2, amino acid, organic acid and pellet f ractions. Uptake was greatest in all tissue types early in culture. Mo st (over 80%) of the [C-14]-aspartate taken up by the tissues was conv erted to CO2 at day 0 in SF and NSF tissues. CO2 accounted for less th an 50% of the total radioactivity in other tissues. Greater incorporat ion into fractions was observed in SF tissues during promeristemoid fo rmation, while in NSF tissues the greatest incorporation was observed during a period of rapid elongation. Generally, less incorporation was observed in OLD cotyledons than in SF and NSF cotyledons, Analysis of the amino acid fraction showed that labelled aspartate was converted to other amino acids, mainly glutamate, glutamine, asparagine and 4-am inobutyric acid.