Chlorophyll accumulation in cotyledons, hypocotyls and primary needles of Pinus pinea seedlings in light and dark

Abstract

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 chlorophyll (Chl) and protochlorophyllide (Pchlide) contents of cotyledons, hypocotyls and primary needles determined spectrophotometrically alter 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 Chl concentrations achieved in darkness in these organs were approximately 60, 20 and 10% respectively, of concentrations achieved in light. The tinsel of rapid Chl 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 lag 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 Chi and Pchlide accumulation by cotyledons in darkness were similar. Pchlide did not accumulate prior to the onset of Chi accumulation and Chl slopped 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 Chl in darkness is proposed.