REGULATION BY LIGHT OF CHLOROPHYLL SYNTHESIS IN THE COTYLEDONS OF SCOTS PINE (PINUS-SYLVESTRIS) SEEDLINGS

Seedlings of gymnosperms, unlike angiosperms, synthesize chlorophyll(i de) (Chi) in darkness (D). In Scots pine cotyledons (Pinus sylvestris L.) Chi accumulation ceases in D at a low level but Chi accumulation i s strongly increased by light, red light (R) being more effective than blue light (B), whereas in Pinus maritima Chi synthesis is almost lig ht-independent, In Scots pine the capacity to form Chi can be increase d by R pulses, fully reversible by far-red light, demonstrating the in volvement of phytochrome. However, when B- or R-grown seedlings were t ransferred to D, Chi accumulation stopped immediately irrespective of the level of P-fr (far-red light absorbing form of phytochrome), indic ating that the conversion of protochlorophyllide (PChl) is light-depen dent. Dose response curves in R and B and simultaneous irradiation wit h R and B show that R and B are perceived by separate photoreceptors. The immunodetected NADPH-dependent protochlorophyllide oxidoreductase (FOR, EC 1.6.99.1), assumed to regulate light-dependent Chi synthesis in angiosperms, is not correlated with the capacity of gymnosperm Chi accumulation in darkness. While two FOR bands could be separated in ex tracts from dark grown material (38 and 36 kDa) of Pinus sylvestris an d P. maritima, only the 38 kDa band disappeared consistently in the li ght. However, the significance of the more light resistant 36 kDa band for chlorophyll synthesis remains unclear as well.