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Photoperiodic Effects on the Emanation of Volatiles from Alfalfa (Medicago sativa L.) Florets ¹

^a Plant Science Research Division, Agricultural Research Service, United States Department of Agriculture, Bee Research Laboratory, Tucson, Arizona 85719

Alfalfa (Medicago sativa L.) plants acclimated to photoperiods of 18 hours light, 6 hour dark in plant growth chambers exhibited a daily cyclic pattern of floret volatile emanation with a maximum emanation of about 6.5 nanograms of hydrocarbons/floret·30 minutes. This maximum was reached about 6 to 8 hours into the light period. After 8 hours of light, emanation of volatiles decreased rapidly to less than 0.1 ng/floret·30 min even though light and temperature remained constant. Under continuous illumination, only a small increase of volatile emanation occurred during the following 24 hours. It appeared that a dark period was necessary to promote floret volatile emanation. Floret volatile emanation was drastically affected for at least 7 days following a photoperiod change. A photoperiod change caused 6-fold concentration oscillations every 2 hours. The results are interpreted on the basis of a very active floral metabolism controlled by photoperiodically induced rhythms.