UV‐B response of cucumber seedlings grown under metal halide and high pressure sodium/deluxe lamps

UV‐B‐sensitive (Poinsett) and ‐insensitive (Ashley) cultivars of cucumber ( Cucumis sativus L.) were grown in growth chambers at 600 μmol m −2 s −1 of photosynthetically active radiation provided by metal halide (MH) or high pressure sodium/deluxe (HPS/DX) lamps. Plants were irradiated 15 days from seeding for 6 h per day under 18. 2 kJ m −2 day −1 of biologically effective UV‐B (UV‐B BE ) radiation. One of the most pronounced effects of UV‐B was a 27 to 78% increase in phenylalanine ammonialyase (PAL) activity. UV‐B also increased total polyamines. Catalase and superoxide dismutase varied greatly in their response to UV‐B. There were no interactive effects on PAL or catalase activity, or total polyamines. There was a UV × PAR source interaction for superoxide dismutase activity. UV‐B increased chlorosis and decreased height, dry weight and leaf area. Stem elongation, biomass production, leaf enlargement and chlorosis were greater under HPS/DX lamps than under MH lamps. Chlorosis was greater in Poinsett than in Ashley and in lower leaves than in upper ones. Aside from chlorosis, there were no interactive effects of UV‐B, PAR source or cultivar on any of the growth parameters measured, suggesting that the growth response of cucumber seedlings to UV‐B is unaffected by PAR source or cultivar. Similarly, except for SOD activity, the biochemical response to UV‐B was also not influenced by PAR source or cultivar.