Effect of low Zn supply on growth, leaf pigments and photosynthesis in red cabbage (Brassica oleracea L. var. capitata f. rubra) plants grown under different light conditions

The effect Zn deficiency on growth, leaf pigments and photosynthesis was studied in red cabbage (Brassica oleracea L. var. capitata f. rubra) plants under three different light conditions including 100, 200 and 400 µmol m-2 s-1 in hydroponic medium either with adequate (725 pM free Zn activity) or low (30 pM free Zn activity) Zn supply. Dry matter production of shoot and root was reduced by low Zn supply up to 95% and 63% respectively, but increased with increasing light intensity. Low Zn supply caused reduction of shoot growth up to 80% under low light intensity (100 µmol m-2 s-1), while this reduction was only 24% for plants grown under higher (400 µmol m-2 s-1) light conditions. Significantly lower Zn was allocated to shoot than roots in Zn deficient compared with Zn sufficient plants. Leaf chlorophyll and carotenoids content decreased in Zn deficient plants but anthocyanins and phenolics accumulated under these conditions. Zn deficiency did not cause any damage to PSII reaction centers but caused inhibition of both photochemical and non-photochemical quenching demonstrating reduction of electron use in dark reactions and lower heat dissipation in low Zn plants. Stomatal resistance was elevated in Zn deficient leaves that led to reduction of CO2 assimilation rate and transpiration.