The Molecular Analysis of the Light Adaptation Reactions in the Yellow-green Alga Pleurochloris meiringensis (Xanthophyceae)

The xanthophycean alga Pleurochloris meiringensis was homocontinuously cultured under high light (16 W/m²) and low light (2 W/m²) conditions. In low light cells, the chlorophyll a content and the dry weight on per cell basis is increased, the maximal photosynthetic capacity per chlorophyll is decreased. The content of chlorophyll c, vaucheriaxanthin-ester and heteroxanthin is similar in both cultures, whereas the content of diadinoxanthin and ß-carotene is twice as high in high light cultures. High light cells contain more photosystem I and cytochrome f per chlorophyll than low light cells, whereas the Q_B content is found to be unchanged. Therefore, the ratio reaction center II/reaction center I is twofold higher in low light cells than in high light ones. The regulation of energy distribution between the photosystems is examined by fluorescence emission spectra at 77 K scanned after different preillumination of the cells. No wavelength dependent state I/state II transition can be detected. However, P. meiringensis regulates the energy distribution in response to light intensity: The higher the irradiance of preillumination, the higher the energy transfer to photosystem I. The sensitivity of the regulation to light intensity is increased in low light cells.