Abstract: Nodulation gene-inducing factors have been isolated and identified. A number of substituted flavones, some of which are components of exudates and extracts of leguminous plants, have been found to induce expression of certain nodulation genes in Rhizobium strains. Three components of clover extract 7,4'-dihydroxyflavone, 7,4'-dihydroxy-3'methoxyflavone, and 4'-hydroxy-7-methoxyflavone have been identified as nodulation inducers of certain Rhizobium trifolii nod genes. A number of other flavonoids including flavones, flavanones, flavanols and dihydroflavanols, not necessarily found in legume exudates, were also found to induce expression of certain nodulation genes.

Abstract: The invention concerns antigens for the production of antibodies to Platelet Activating Factor (PAF). The antigens are PAF analogues of formula (I) ##STR1## wherein X comprises a high molecular weight group, R.sup.1 is a linking group and R.sup.2 to R.sup.5 are selected from C.sub.1 to C.sub.6 alkyl.Other aspects of the invention include PAF-antibodies produced using said antigens, labelled PAF analogues, intermediates for the preparation of PAF analogues and methods and a kit for the immunoassay of PAF.