Light-controlled Leaf Expansion in Peas Grown under Different Light Conditions

Several photosystems control leaf expansion in Alaska peas (Pisum sativum). Phytochrome is known to control expansion in dark-grown peas. But plants exposed briefly to red light are insensitive to phytochrome, an insensitivity that is itself phytochrome-produced. Leaf expansion in these plants is promoted by 440 or 630 nm of light (probably mediated by protochlorophyll). Plants grown in white fluorescent light required simultaneous exposure to high intensity blue and yellow light for promotion of leaf expansion. Since these results parallel studies on light-controlled inhibition of stem elongation, shoot growth as a whole is coordinated by these photosystems. Such coordination might be a mechanism of plant competition for light.