Untersuchungen zur Phytochromsteuerung der Seneszenz im Photosyntheseapparat von Hordeum vulgare L.

Abstract

Summary Caryopses of Hordeum vulgare L. were grown two days in the dark and illuminated thereafter three days with white light (Fluora, 8 W · m -2 ) . At the end of the illumination phase, the seedlings received 5 min red light (R; λ max ∽ 660 nm), or 5 min red + 10 min far red (FR; λ max ∽ 730 nm), or no additional illumination (C; dark control). Changes in composition of chloroplast prenyllipids were measured each day of the dark phase until 10 days after sowing. In the dark control the amounts of chlorophylls, carotenes, plastoquinone-9 (oxidized form), α-tocoquinone and phylloquinone K 1 decreased; the reduced prenylquinones plastohydroquinone-9 and α-tocopherol strongly increased. The continuously decreasing values of the variable fluorescence indicate a decreasing photosynthetic capacity. Similar changes of chloroplast components had been found earlier in other senescing systems. Seedlings irradiated with terminal R show that during the dark phase the values of the variable fluorescence, the amounts of chlorophylls and carotenes, the ratios chlorophyll a/b, and the amounts of total plastoquinone-9 and oxidized plastoquinone-9 were higher than those of the dark control. The ratios xanthophylls/carotenes and the amounts of phylloquinone K 1 decreased. These R induced effects can be reversed by FR. The operational criteria of phytochrome therefore seem to be fulfilled. A divergent course of the R and (R + FR)-data with time during the dark phase is seen for the ratios chlorophyll a/b and the amounts of the carotenes, total plastoquinone-9, oxidized plastoquinone-9, and phylloquinone K 1 ., It is seen from comparison to the dark control data that phytochrome action means retardation of senescence for variable fluorescence, for the amounts of chlorophylls and carotenes, and for plastoquinone-9 (oxidized form). No permanent effect of R was observed on the amounts of α-tocopherol + α-tocoquinone. The amounts of total plastoquinone-9 (R + FR), oxidized plastoquinone-9, and phylloquinone K 1 exhibit rhythmic oscillations with a period of 48 hours during the dark phase, which may reflect an endogenous rhythmicity. Until now the only known endogenous rhythmic alterations of lipid components in chloroplasts have been those of chlorophyll.