White Light Enhances Adhesive Strength Between Epidermal and Inner Tissues of Pea Epicotyls via Accumulation of Cell Wall-Bound p-Coumaric Acid

The epidermal and inner tissues of stem organs adhere via the cell wall, and the adhesion of both tissues is involved in the structural integrity of the stem. We have developed a method to quantitatively measure adhesive strength between these tissues. In this study we examined the effects of white light on adhesive strength between epidermal and inner tissues of pea epicotyls, as well as the chemical properties of cell walls in both tissues. The irradiation of white light to etiolated seedlings resulted in significantly higher adhesive strength between epidermal and inner tissues, as well as inhibition of elongation growth of the epicotyls. Further observation of epicotyl cross-sections revealed that white light substantially increased the intensity of autofluorescence emitted from the cell wall in epidermal tissue and the outermost layer of inner tissue, accompanied by color alteration. Overall, the spectrum of the autofluorescence emitted from light-irradiated epicotyl sections matched that of reference standard p-coumaric acid, a phenolic acid. Further chemical analysis of cell wall constituents revealed that cell wall-bound p-coumaric acid was predominantly accumulated in epidermal tissue in response to light irradiation. Taken together, these results suggest that light-induced accumulation of cell wall-bound p-coumaric acid in epidermal tissue may enhance the adhesive strength between epidermal and inner tissues. Moreover, increased adhesive strength between these tissues may contribute to light-induced inhibition of pea epicotyl elongation.