Relationship between energy-dependent fluorescence quenching and xanthophyll-cycle-pigments in transgenic chlorophyll-deficient tobacco grown under different light intensities

Plants dissipate absorbed light energy that exceeds the photosynthetic utilization by non-radiative de-excitation, thereby protecting them selves against photodamage. The most important mechanism, which is associated with the formation of a transthylakoid pH gradient and the pigment interconversion within the xanthophyll cycle, can be measured as rapidly reversible chlorophyll fluorescence quenching referred to as energy-dependent quenching (qE). We have compared the influence of growth light on maximum qE capacity in tobacco (Nicotiana tabacum) wild type and transgenic lines with progressively reduced chlorophyll contents due to the expression of antisense RNA coding for glutamate 1-semialdehyde aminotransferase. It is found that qE does not vary among transformants and in comparison to the wild type when grown under identical light conditions. However, a higher extent of qE developed in high- than in low-light-grown plants, which correlated with the increase of the pool size of xanthophyll-cycle-pigments in the wild type only. In high-light-grown transformants, qE was apparently insensitive to the considerably larger pool size (on a chlorophyll basis) and the higher fraction of photoconvertible violaxanthin than found in the wild type. Our results suggest that the maximum attainable qE is largely independent of the extent of chlorophyll reduction in the transgenic lines; a decrease of more than 90% had virtually no influence on qE capacity. (C) 1998 Elsevier Science S.A. All rights reserved.