Factors Affecting the Abscission of Reproductive Organs in Yellow Lupins (Lupinus luteusL.)

Abstract

Extracts of small and mature-size lupin pods yielded four substances affecting the growth of wheat-coleoptile sections: one acid promotor ( A ), two acid inhibitors( B and X ), and one neutral inhibitor( Y ). Inhibitor B was extremely active, however, coleoptile sections showed no signs of toxic effects; they resumed growth at a rapid rate after rinsing them and adding β-indolylacetic and (IAA) to the medium. 1 μg of IAA was required to counteract the effect of ‘B’ extracted from 230 mg. Of tissue. On an equal fresh weight basis the inhibiting action of ‘ B ’ in lupin pods was 500–1,500 times more potent than that of ‘inhibitor β’ in etiolated pea seedlings. Small pods of plants infected with pea-mosaic virus yielded 3 times the amount of ‘ A ’ of healthy plants (equivalent to 1 μg. IAA 0.3 μg. IAA per 25 g. of tissue respectively), and approximately ⅖ the amount of ‘B’. Mature pods of virus-infected plants again yielded more‘A’, but also 2½ times more ‘B’ than pods of healthy plants. Healthy pods yielded more ‘A’ than virus-infected pods, and there was no difference in ‘X’. A lupin abscission test was developed and the effects of proximal and distal application of α-naphthyl acetic acid (NAA) are presented, and discussed with respect to results of other abscission tests. ‘ A ’ accelerated abscission when applied proximally, and delayed or prevented it when applied distally. ‘ B ’ strongly accelerated abscission when applied in either way. A possible mechanism explaining the abscission-inducing effect of developing pods on later flowers is discussed in terms of the substances ‘ A ’ and ‘ B ’. The partly prevented abscission observed on virus-infected plants was found to agree well with the proposed mechanism.