The effects of lead on photosynthesis, 14C distribution among photoassimilates and transpiration of maize seedlings

Abstract

Roots of whole 3 week-old seedlings of maize were exposed for 24 h to a solution of PbCl₂. The concentrations of Pb were: 0, 200, 400, 800, 1200, 2400 mg dm^-3. The amount of Pb taken up by roots was independent of the concentration of this element in the medium. The Pb taken up by shoots increased linearly with increasing treatment concentration. Pb caused: concentration-dependent inhibition of photosynthesis (PS), transpiration (T), ¹⁴CO₂ uptake and incorporation of label into photosynthetic products. The largest limitation by Pb of the flow of photoassimilated carbon occurred into starch and sugar phosphates. Among the water-soluble photoassimilates, the largest limitation of carbon flow occurred into organic acids and sugars and the smallest into amino acids.