CHLOROPHYLL ORGANIZATION IN DARK-GROWN AND LIGHT-GROWN PINE (PINUS-BRUTIA) AND BARLEY (HORDEUM-VULGARE)

A study was conducted comparing the organization of chlorophyll during development of the photosynthetic apparatus in dark-grown and light-g rown pine and barley. The rationale was that gymnosperms, but not angi osperms, have a capacity to synthesize chlorophyll in darkness. Seedli ngs of Pinus brutia were germinated and grown in darkness or under pho toperiodic (day/night) conditions. The low-temperature (77 K) fluoresc ence spectra of newly-emerging dark-grown seedlings exhibited a single fluorescence band peaking at 678-679 nm, which decayed primarily with a similar to 5.5 ns lifetime. Over the first few days of growth, the emission shifted to longer wavelengths and a subnanosecond lifetime co mponent became prevalent. After several days of dark growth the emissi on spectrum and lifetime profile of the low temperature fluorescence c ame to resemble those of light-grown pine and barley. At room temperat ure, dark-grown pine showed little variable fluorescence, though addit ion of DCMU caused a substantial fluorescence rise. Illumination with moderate light for a few hours was sufficient to 'photoinduce' the app earance of normal variable fluorescence. At 77 K, DCMU-treated samples clearly showed a very long-lived (similar to 40 ns) fluorescence life time component in light-grown pine and barley, This component was unde tectable in dark-grown pine. If, however, dark-grown samples were illu minated either before or after DCMU addition and then frozen to 77 K, the similar to 40 ns lifetime component appeared at a fluorescence int ensity similar to that in light-grown samples. These results are expla ined primarily in terms of photoactivation of the photosystem II (PSII ) donor side. The temporary maintenance of PSII in an inactive, highly -quenched state is suggested to provide an available, yet protected pr ecursor for active PSII.