ACTION SPECTRA FOR ENHANCEMENT OF ULTRAWEAK LUMINESCENCE BY UV-RADIATION (270-340 NM) IN LEAVES OF BRASSICA-NAPUS

Fluence-response relationships for the enhancement of ultraweak lumine scence by UV radiation were determined in leaves of Brassica napus L. (cv. Ceres) when either the adaxial or abaxial leaf surface was expose d to monochromatic radiation (270-340 nm). Action spectra for both lea f surfaces were constructed from the fluence-response curves at the fl uence required to obtain a doubling of the ultraweak luminescence leve l over the unirradiated controls. The action spectrum for the abaxial leaf surface showed a steeper slope than that for the adaxial leaf sur face at wavelengths below 280 nm. Both action spectra were flatter tha n the generalized plant action spectrum of Caldwell (M.M. Caldwell, in A.C. Giese (ed.), Photophysiology, Vol. 6, Academic Press, New York, 1971, pp. 131-177) at wavelengths above 280 nm. Under a depleted ozone layer, the action spectra yielded a radiation amplification factor ap proximately 50% of that obtained with Caldwell's generalized plant act ion spectrum. The shape of the action spectrum for the induction of ul traweak luminescence was approximately the same for both surfaces abov e 290 nm.