On the possible control of ultraviolet‐B induced response in growth and photosynthetic activities in higher plants

When Vigna sinensis L.cv. Walp seedlings were grown under control (from four 40 W white fluorescent tubes) and enhanced ultraviolet‐B (UV‐B) radiation (four 40 W white fluorescent tubes plus one Philips 20W/12 sun lamp) a large inhibition in seedling growth, particularly shoot eelongation and leaf expansion, was observed under enhanced UV‐B radiation. The UV‐B radiation also reduced the overall photosynthetic activity as measured by chlorophyll fluorescence induction. In order to check whether UV‐B causes any destruction of auxins, seedlings with either their shoot tip or primary leaves were covered with black paper and kept under both light conditions. Both the fully exposed and shoot tip‐covered seedlings showed a similar negative response on growth characteristics and physiological activities. Leaf‐covered seedlings showed well preserved photosynthetic activity under both light conditions. However, in these seedlings the pigment content decreased more than under other treatment conditions. Our experiments provide evidence for distinguishing between the UV‐B induced responses on growth and physiological activities; while the former may be controlled through auxins, the latter is probably by direct action on the organelles.