The effect of Zn deficiency was studied in red cabbage (Brassica oleracea l. var. capitata f. rubra) plants grown in nutrient solution under controlled environmental conditions. Zinc starvation affected the number (61%), surface area (72%) and biomass (62%) of leaves more than root biomass (42%). although chlorophyll fluorescence parameters revealed occurrence of photoinhibition following declined stomatal conductance and reduction of Co 2 available at carboxylation sites, photosynthesis apparatus was not damaged seriously under Zn deficiency conditions. Chlorophyll a, chlorophyll a/b ratio, soluble carbohydrates and starch declined but anthocyanins and free phenolics were accumulated under Zn deficiency conditions. activity of ascorbate peroxidase, catalase and peroxidase enhanced under Zn deficiency conditions, whereas activity of superoxide dismutase declined in leaves but not in roots of Zn-deficient plants. Maintenance of superoxide dismutase activity and malondialdehyde content in roots demonstrated that roots were more protected against reactive oxygen species imbalance under Zn deficiency conditions compared with leaves that was correlated well with the lower sensitivity of roots to low Zn supply.

The responses of red cabbage (Brassica oleracea L. var. capitata f. rubra) plants to a low Zn supply and cold conditions (10°/7°C day/night temperature) were investigated in a hydroponic growing medium. A low Zn supply caused a significant reduction of shoot and root dry weight -up to 55% and 45% for the control and 62% and 52% for cold-treated plants, respectively. The total soluble carbohydrates and starch declined in Zn-deficient plants. Exposure to low temperatures, however, led to a decline in starch but an increase in soluble sugars. In Zn-sufficient plants, low temperatures increased the excitation capture efficiency of open photosystem II (PS II) reaction centres (RCs) (F′ v /F′ m ), the quantum yield of PS II (Ф PSII ), the electron transport rate (ETR) and the proportion of active chlorophyll associated with the RCs of PS II (F v /F 0 ). Low temperatures did not affect net CO 2 uptake in Zn-sufficient plants, though a reduction of stomatal conductance occurred. The results demonstrated that although cold-treated plants were slightly more susceptible to Zn deficiency, cold treatment caused greater shoot biomass (up to 32%) in plants supplied with adequate Zn. The adaptation of red cabbage plants to cold conditions is attributable to improved photochemical events in the leaves, a maintenance of the net CO 2 assimilation rate, lower water loss and the accumulation of anthocyanins as antioxidants. Abbreviations:Chl -chlorophyll, Φ PSII -effective quantum yield of PS II, ETR -electron transport rate, F' v /F' m -excitation capture of open PS II, F 0 -initial fluorescence of dark adapted leaves, F m -maximum fluorescence of dark adapted leaves, F v /F m -maximum quantum yield of PS II, A -net assimilation rate, E -net transpiration rate, qN -non-photochemical quenching, qP -photochemical quenching, PAR -photosynthetically active radiation, RCs -reaction centres, ROS -reactive oxygen species, g s -stomatal conductance, F v -variable fluorescence of dark adapted leaves, F v /F 0 -proportion of active chlorophyll associated with the RCs of PS II Photochemistry and gas exchange in cold conditions in Zn-deficient red cabbage (Brassica oleracea L. var. capitata f. rubra) plants