The Effect of Light Intensity on the Release of Ethylene from Leaves

Abstract

When leaf discs of Xanthium strumarium L. a C3 plant, or Zea mays L. a C4 plant, are incubated in 1-aminocyclopropane-l-carboxylic acid (ACC) in closed flasks, ethylene is released. The rate of ethylene release appears to be dependent on the levels of light and C02 available for photosynthesis in the tissues. In Xanthium the rate of ethylene release is lower in the light than in the dark regardless of the presence or absence of added bicarbonate as a source of C02. The inhibition of ethylene release is most apparent in the absence of added bicarbonate (i.e. at the C02 compensation point), and at light intensities sufficient to saturate photosynthesis (had the C02 level in the test flask been maintained). In contrast, light dramatically promotes the rate of ethylene release from Zea leaf tissue when the C02 level is maintained above the C02 compensation point. The rate of ethylene release from either Xanthium or Zea, incubated with or without added bicarbonate, does not appear to be altered by further increasing the light intensity above the minimal levels sufficient to saturate photosynthesis. In the closed system used in these studies and at a light intensity sufficient to saturate photosynthesis, Xanthium and Zea leaf tissue both appear to release comparable amounts of ethylene from ACC when the data is expressed on a chlorophyll basis. However, in Xanthium the rate of ethylene release is similar in light and dark, while in Zea the rate in the light is much greater than in the dark when the data is expressed either on a leaf area or on a chlorophyll basis. It is suggested that the different responses of these tissues to light/dark transients may reflect differences in their ability to metabolize ACC and/or differences in their ability to retain and metabolize ethylene itself.