Physiological and ecological studies on the oestrogenic isoflavones in subterranean clover (T. subterraneum L.). VI. Effects of defoliation including grazing

Abstract

The effects of defoliating plants of different ages in different ways on the isoflavone content of the remaining leaves were investigated. When the fully expanded leaves were removed from 3-month-old plants, formononetin and genistein were reduced and brochanin A was unaffected in leaves which expanded during the subsequent 10 days. In seedlings, all three isoflavones were reduced in concentration following defoliation. But when young leaves were removed from seedlings, the isoflavones in the older remaining leaves were increased. It is suggested that severe defoliation affects soluble carbohydrate levels which in turn affect the synthesis of the isoflavones. Continuous grazing with 3–7 breeding ewes per acre had little wffect on isoflavone levels in fully expanded clover leaves.