Far-red induced changes of the protochlorophyllide components in wheat leaves

Biosynthesis of chlorophyll is partly controlled by the phytochrome system. In order to study the effects of an activated phytochrome system on the protochlorophyllide (PChlide) biosynthesis without accompanying phototransformation to chlorophyll, wheat seedlings (Triticum aestivum L. cv. Starke II Weibull) were irradiated with long wavelength far-red light of low intensity. Absorption spectra were measured in vivo after different times in the far-red light or in darkness. The relationship between the different PChlide forms, the absorbance ratio _{650nm636 nm} changed with age in darkness, and the change was more pronounced when the leaves were grown in far-red light. Absorption spectra of dark-grown leaves always showed a maximum in the red region at 650 nm. For leaves grown in far-red light the absorption at 636 nm was high, with a maximum at the 5 day stage where it exceeded the absorption at 650 nm. At the same time there was a maximum in the total amount of PChlide accumulated in the leaves, about 30% more than in leaves grown in darkness. But the amount of the directly phototransformable PChlide, mainly PChlide_650–657, was not increased. The amount of PChlide_628–632, or more probably the amount of (PChlide_628–632, + PChlide _636–657) was thus higher in young wheat leaves grown in far-red light than in those grown in darkness. After the 5 day stage the absorption at 636 nm relative to 650 nm decreased with age, and at the 8 day stage the spectra were almost the same in both types of leaves. Low temperature fluorescence spectra of the leaves also showed a change in the ratio between the different PChlide forms. The height of the fluorescence peak at 632 nm relative to the peak at 657 nm was higher in leaves grown in far-red light than in dark-grown leaves. – After exposure of the leaves to a light flash, the half time for the Shibata shift was measured. It increased with age both for leaves grown in darkness and in far-red light; but in older leaves grown in far-red light (7–8 days) the half time was slightly longer than in dark-grown leaves. – The chlorophyll accumulation in white light as well as the leaf unrolling were faster for leaves pre-irradiated with far-red light. The total length of the seedlings was equal or somewhat shorter in far-red light, but the length of the coleoptile was markedly reduced from 8.1 ± 0.1 cm for dark-grown seedlings to 5.2 ± 0.1 cm for seedlings grown in far-red light.