Effect of Pre-Illumination on the Response of Split Pea Stems to Growth Substances

Abstract

1. Light has a marked effect on the response of the seedlings in the pea test for detecting growth-regulating activity of chemicals. Split stems from seedlings grown in complete darkness give little or no response to solutions of growth substances, while pre-illumination is effective in securing a response. The time of exposure and amount and quality of the light are all critical in obtaining maximal response. 2. Red light is most effective; single exposures should be started 32 hours prior to harvesting the pea stems. At an intensity of 10 foot-candles, a 4-hour exposure to red light was found to result in the greatest curvature in the pea test. 3. A preharvest exposure of the seedlings to red light greatly increases the curvature in the pea test and eliminates occasional batches which otherwise would not respond to growth substances. Although the reproducibility of the pea test still leaves something to be desired in assigning a numerical rating of activity to test compounds, the present study does indicate the importance of the factor of light in controlling response.