Synergistic action of red and blue light and action spectra for malate formation in guard cells of Vicia faba L.

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Abstract
Malate formation in guard cells of Vicia faba leaves is enhanced by light. The action spectrum for this effect was determined for epidermal strips of Vicia faba, and two different spectra were obtained under different light conditions and with and without background irradiation with high-irradiance red light (>600 nm, 3.0 mW cm−2) superimposed on monochromatic light of other wavelengths. The spectrum obtained at quantum fluxes of 1.7–2.2 nE cm−2 s−1 of monochromatic light without background red light showed a sharp peak at 433 nm with a shoulder around 475 nm and a lower peak at 670–680 nm; the spectrum obtained at much lower quantum fluxes of 0.05–0.07 nE cm−2 s−1 of monochromatic light with red-light background had two peaks of comoparable heights at 380 and 460 nm. The formation of malate with 430-nm blue light was saturated at a quantum flux of 3 nE cm−2 s−1 without the background red light but at a much lower quantum flux of 0.2 nE cm−2 s−1 with the background red light. At this low intensity, blue light was practically ineffective without background red light. A synergistic action of red light presumably absorbed by the chlorophylls, and blue light absorbed by a yellow pigment is thus demonstrated by these experiments. The action maxima at 380 and 460 nm for the blue-light effect in the presence of background red light agree with the absorption maxima of flavins.