MINERAL STATUS OF DICOTYLEDONOUS CROP PLANTS IN RELATION TO THEIR CONSTITUTIONAL TOLERANCE TO LEAD

Four crop species-mustard, flax, tomato and sunflower used in experime nts, were grown in the growth chamber in solution culture. The plants were used in the following studies: (i) constitutional tolerance to Pb (index of tolerance was estimated using Wilkin's root test with 0, 5, 10 and 20 mg dm-3 Pb concentrations in Knop's medium deficient in PO4 -3 ions); (ii) tolerance to deficit of P. Ca and Mg and to general nut rient stress (50 x diluted Knop's medium) as determined by dry matter yield; and (iii) effect of Pb and used nutrient regimes on mineral sta tus of the plants, by estimation of internal ion concentration. The sp ecies most tolerant to Pb was tomato. Tomato was also the least tolera nt to P deficit (although the test for Pb tolerance was conducted in m edium without PO4-3 ions). The least Pb-tolerant species, mustard and sunflower, were moderately tolerant or non-tolerant to the mineral def iciencies used in the study. High constitutional tolerance to Pb in to mato was associated with the highest tissue level of Ca during adminis tration of Pb, and with the highest tolerance to Ca deficit. The magni tude of the Pb concentration in the media and its absolute amounts in the roots and shoots were not proportional to the degree of Pb toleran ce. Two of the least Pb-tolerant species had the highest (mustard) and lowest (sunflower) root Pb concentrations. The absolute amount of Pb in the roots was highest in mustard. However, the amount of Pb which w as transported to the shoot in relation to the total amount of Pb take n up by the plant was the highest for the least tolerant species, sunf lower (43.4%).