ETHYLENE INHIBITORS RESTORE NODULATION TO SYM-5 MUTANTS OF PISUM-SATIVUM L CV SPARKLE

The sym 5 mutants of pea, Pisum sativum L. cv Sparkle, do not differ in growth habit from their normal parent and nodulate poorly at a root temperature of 20-degrees-C. If inhibitors of ethylene formation or action (Co2+, aminoethoxyvinylglycine, or Ag+) are added to the substrate, nodulation of the sym 5 mutants is increased. Similar treatments of four other mutant sym lines do not restore nodulation. When Ag+ is added to the substrate from 4 days before to 4 days after inoculation with rhizobia, nodulation of sym 5 mutants is increased. The roots of the mutant need only be exposed to Ag+ for 4 hours to significantly increase nodule numbers. The content of free 1-aminocyclopropane-1-carboxylic acid and the production of ethylene in the lateral roots of sym 5 mutants do not differ from Sparkle.