Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 1, 2000
Publication Date: N/A
Interpretive Summary: Crop productivity and quality are a direct consequence of plant's ability to carry out photosynthesis in an efficient manner. High intensities of light and ultraviolet-B radiation negatively impact photosynthesis. A common target is a critical protein heterodimer consisting of two proteins called D1 and D2. In order to develop strategies to protect these critical proteins from destruction, it is a prerequisite to determine which natural plant compounds can provide protection to photosynthesis. We therefore analyzed genetic mutants altered in their content of specific phenolics. In this paper we demonstrate that phenols such as sinapic esters are important as sun screens to protect plant photosynthesis against damaging radiation. These observations can be used and implemented by plant breeders and biotechnologists to select for or produce crops that are enriched in the content of sinapic esters.
The D1-D2 proteins constituting photosystem II reaction center heterodimer are targets of UV-B radiation and can be used as an in situ sensor for UV penetration into photosynthetic tissue. Using the D1-D2 degradation assay, we characterized UV-B sensitivity of Arabidopsis mutants (tt4, tt5 and fah1) that are genetically altered in composition of phenolic compounds. We found that changes in phenol metabolism result in altered rates of PSII reaction center heterodimer degradation under environmentally relevant mixtures of photosynthetically active radiation and UV-B. Comparison of D2 degradation kinetics showed increased UV-sensitivity of the Landsberg tt5 mutant relative to the Landsberg tt4 mutant and the Landsberg wildtype. Despite lack of flavonoid accumulation, the tt4 mutant is not particularly UV-sensitive. However, the tolerance of this mutant to UV-B may reflect the increased accumulation of sinapate esters that strongly absorb in the UV-range and may thus protect the plant against environmentally relevant UV-B radiation. This protection is less obvious for the tt4 mutant in Columbia background, indicating that relative contribution of particular phenolics to total screening capacity varies with genetic background.