INFLUENCE OF UV-B RADIATION AND CD2-NAPUS( ON CHLOROPHYLL FLUORESCENCE, GROWTH AND NUTRIENT CONTENT IN BRASSICA)

The possible interaction of two stresses, UV-B radiation and cadmium, applied simultaneously, was investigated in Brassica napus L. cv. Paro ll with respect to chlorophyll fluorescence, growth and uptake of sele cted elements. plants were grown in nutrient solution containing CdCl2 , (0, 0.5, 2 or 5 mu M) and irradiated with photosynthetically active radiation (PAR, 400-700 nm, 800 mu mol m(-2) s(-1)) with or without su pplemental ultraviolet-B radiation (UV-B, 280-320 nm, 15 kJ m(-2) d(-1 ), weighted irradiance). After 14 d of treatment, the most pronounced effects were found at 2 and 5 mu M CdCl2 with and without supplemental UV-B radiation. Exposure to cadmium significantly increased the amoun t of Cd in both roots and shoots. In addition, increases occurred in t he concentration of Fe, Zn, Cu, and P in roots, while K was reduced. I n shoots the S content rose significantly both in the presence and abs ence of UV-B radiation, while significant increases in Mg, Ca, P, Cu, and K occurred only in plants exposed to Cd and UV-B radiation. Mangan ese decreased significantly under the combined exposure treatment. The rise in S content may have been due to stimulated glutathione and phy tochelatin synthesis. Cadmium exposure significantly decreased root dr y weight, leaf area, total chlorophyll content, carotenoid content, an d the photochemical quantum yield of photosynthesis. As an estimation of energy dissipation processes in photosynthesis, non-photochemical q uenching (q(NPQ)) was measured using a pulse amplitude modulated fluor ometer. the q(NPQ) increased with increasing Cd, while the combination of cadmium and UV-B reduced the q(NPQ) compared to that in plants exp osed only to cadmium or UV-B radiation. The chlorophyll a:b ratio show ed a reduction with UV-B at no or low Cd concentrations (0 mu M, 0.5 m u M CdCl2), but not at the higher Cd concentrations used (2 mu M, 5 mu M CdCl2). Thus in some instances there appeared to be a UV-B and Cd i nteraction, while in others plant response could be attributed to eith er treatment alone.