Light-induced changes of photosystem II activity in dark-grown Scots pine seedlings

Abstract

Virgin, !., Gustafsson. P., Andersson, B. and Oquist, G. 1992. Lightinduced changes of photosystem II activity in dark-grown Scots pine seedlings. -Physio!. Plant. 84: 6-12.Both chlorophyll a and h and polypeptides of the photosynthetic apparatus are found in gymnosperm seedlings germitiated and grown in absolute darkness. The photosystem II (PSII) activity is, however, limited, probably due to an inactive oxygen evolving system. In the present study dark-grown seedlings of Scots pine {Pimis sylveslris L.) were transferred to light and changes in antenna size and the activation process of PSII were investigated using fluorescence nieasurements and quantitative western blotting. It was found that the activation process is rapid, requires very little light and that strong light inhibits the process. It takes place without any changes in the primary reactions of PSII. Furthermore, all polypeptides except the major lightharvesting chlorophyll fl/i>-binding protein complex of PSII (LHCII) were present in dark-grown seedlings in amounts comparable to the light treated control. The darkgrown seedlings had the same LHCII polypeptide composition as light treated seedlings, and the LHCII present seemed to be fully connected to the reaction centre. The results indicate that activation of FSII in dark-grown conifer seedlings resembles the photoactivation process of angiosperms. This implies that the fundamental processes in the assembly of the photosystem II complex is the same in all plants, but that the regulation differs between different taxa.

Chlorophyll Characterization of Three Mistletoes and the Chloroplast Ultrastructure within Aerial and Endophytic Tissues of Phoradendron Juniperinum

“…This resulted in a low chlorophyll alb ratio. These results differ from that typically obtained when young gymnosperm tissue is grown in darkness, which shows chlorophyll alb ratios to be higher in dark grown seedlings (Jansson et al 1992) Fluorescence Spectrosco_py Absorbance spectra of the endophytic systems from the dark box experiments, the controls with their aerial-shoots-removed and Phoradendron villosum showed very low chlorophyll concentrations .. Accurate total chlorophyll concentrations were obtained from the 670 nm chlorophyll fluorescence peak (figure 4 ).…”

“…At decreased illumination chlorophyll b increases because it more readily absorbs low energy light. On the other hand, when gymnosperm tissue is grown in darkness (Jansson et al 1992), chlorophyll a/b ratios tend to be higher. Comparison of these three scenarios would indicate that the lower chlorophyll a/b ratio seen in the endophytic system, compared to aerial shoots of Phoradendronjuniperinum, is the result of chlorophyll synthesis in low light.…”

“…To a varying extent, gymnosperms and other non-flowering plants are able to form chlorophyll in the dark without a prior light exposure (Castelfranco and Beale 1983) and fonnnonnal chloroplasts (Michel-Wolwertzand Bronchart 1974) through a light-independent pathway. However, in gymnosperms light-independent chlorophyll biosynthesis is believed to occur predominantly within cotyledons of young seedlings, when associated with the megagametophyte (Virgin and Egn6us 1983) or, artificially, with the addition of cytoldnins to cotyledons (Jansson et al 1992). Adult plants as well have been shown to synthesize chlorophyll in the dark, however the amount fonned in light is always substantially higher (Kasemir and Mohr 1981).…”