Some aspects of lead in plant nutrition

Accretion of lead by abscised barley roots from a lead nitrate solution was metabolically obtained, complemented by a fraction acquired physico-chemically. Added calcium supply did not significantly modify lead accretion. A ten-fold increase in supply concentration produced approximately a two-fold increase in lead accretion. During growth of bean, barley, and tomato plants in solution cultures, a substantial part of the lead supplied became associated with the roots; correspondingly little was present in the tops. A very large fraction of the lead associated with the roots of barley was readily extracted by various solvents, probably resident on the root surface or from free spaces therein; the remainder of the lead acquired may have been that sorbed within the root cells. A possible relationship of lead to phosphate accretion was not evident. There was no apparent effect of applied lead on the sorption of the other elements supplied. Plant dry weights, their top to root ratios and dry-weight percentages were constant under various lead supply concentrations in solution. Where lead supplies were advertently withheld, lead contents in plants were 5 to 25 times that which could have been expected under the solution culture conditions in a greenhouse with carbon filtered ambient air supply. Restriction of advertent lead supply caused no limitation of growth. If lead is essential to growth of these plant species, the critical concentration will probably be less than 2 to 6 ng atoms/g dry weight in plant tops.