Effect of excess lead, cadmium, copper, and zinc on water relations in sunflower

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Abstract
The effect of excess concentrations of lead (Pb), cadmium (Cd), copper (Cu), and zinc (Zn) on water relations in young sunflower (Helianthus annuus L.) plants was studied in water culture under greenhouse conditions. The accumulation of the heavy metals was more intensive in the root than in the shoot. The rates of heavy metal accumulation in root were arranged in the following decreasing order: Cu, Cd, Zn, and Pb. Their transport into the above‐ground parts followed the order: Zn, Cu, Pb, and Cd. Transpiration and relative water content were significantly decreased by excess concentrations of the heavy metals. The number of stomata per unit leaf area was increased while the size of the stomata was decreased. The concentration of free proline significantly increased in the leaves of intact plants as well as in leaf discs incubated in the presence of heavy metals. The concentration of soluble proteins decreased as well, particularly when plants were exposed to high concentrations of the heavy metals. It was concluded that excess concentrations of the heavy metals significantly affected plant water status, causing water deficit and subsequent changes in the plants. The most intensive effect on the plants was exerted by Cd, less intensive by Cu and Zn and the least intensive by Pb.