Action of ultraviolet radiation (UV-B) upon cuticular waxes in some crop plants

The surface structure and composition of surface lipids were examined in leaves of barley, bean, and cucumber seedlings grown in a growth chamber under white light and low levels of ultraviolet (UV-B; 280-320 nm) radiation. The cuticular wax of cucumber cotyledons and bean leaves appeared as a thin homogeneous layer, whereas on barley leaves crystal-like structures could be observed under these irradiation conditions. Principally, the amount of cuticular wax found in barley leaves was five times greater than in bean or cucumber leaves. The prediominant wax components were primary alcohols in barley, primary alcohols and monoesters in bean, and alkanes in cucumber cotyledons. Irradiation with enhanced UV-B levels caused an increase of total wax by about 25% in all plant species investigated. Aldehydes, detected as a minor constituent of cucumber and barley wax, increased twofold. Distribution patterns of the homologs within some wax classes were different at low and enhanced UV-B levels. In general, the distribution of the homologs was shifted to shorter acyl chain lengths in wax of leaves exposed to enhanced UV-B levels. This was most apparent in cucumber wax, less in bean or barley wax. The UV-B-caused effects upon cucumber wax were mainly due to a response by the adaxial surface of the leaf.