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 cucum ber (Cucumis sativus L.) were grown in growth chambers at 600 mumol m- 2 s-1 of photosynthetically active radiation provided by metal halide (MH) or high pressure sodium/deluxe (HPS/DX) lamps. Plants were irradi ated 15 days from seeding for 6 h per day under 18.2 kJ m-2 day-1 of b iologically effective UV-B (UV-B(BE)) radiation. One of the most prono unced effects of UV-B was a 27 to 78% increase in phenylalanine ammoni a-lyase (PAL) activity. UV-B also increased total polyamines. Catalase and superoxide dismutase varied greatly in their response to UV-B. Th ere were no interactive effects on PAL or catalase activity, or total polyamines. There was a UV x PAR source interaction for superoxide dis mutase activity. UV-B increased chlorosis and decreased height, dry we ight and leaf area. Stem elongation, biomass production, leaf enlargem ent 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 e ffects of UV-B, PAR source or cultivar on any of the growth parameters measured, suggesting that the growth response of cucumber seedlings t o 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.