CHLOROPHYLL ACCUMULATION IN COTYLEDONS, HYPOCOTYLS AND PRIMARY NEEDLES OF PINUS-PINEA SEEDLINGS IN LIGHT AND DARK

Seeds of Pinus pinea L. were germinated and grown in darkness or under natural photoperiodic (day/night) conditions for 8 weeks. Samples were taken for analysis at frequent intervals and chlorophyl (Chi) and protochlorophyllide (Pchlide) contents of cotyledons, hypocotyls and primary needles determined spectrophorometrically after separating the esterified from unesterified pigments by partitioning between ammoniacal acetone and petroleum ether. Chlorophyll accumulated in cotyledons, hypocotyls and primary needles of dark as well as light grown seedlings. The maximum Chi concentrations achieved in darkness in these organs were approximately 60, 20 and 10% respectively, of concentrations achieved in light. The onset of rapid Chi accumulation by cotyledons in darkness coincided with the emergence of the radicle from the seed. Light had no effect on the timing of this process or on the duration of the fag period. However, it extended the exponential growth phase of cotyledons by at least a week and, once the seedlings were about 2 weeks old, enabled Chl to accumulate at a faster rate. Time courses of Chl and Pchlide accumulation by cotyledons in darkness were similar. Pchlide did not accumulate prior to the onset of Chi accumulation and Chi stopped accumulating once the Pchlide pool reached maximum size. The implications of these findings are discussed and a hypothesis to account for the inability of primary needles of smaller seeded pines to accumulate Chi in darkness is proposed.