The involvement of ethylene in root architectural responses
to phosphorus availability was investigated in common
bean (Phaseolus vulgaris L.) plants grown with sufficient
and deficient phosphorus. Although phosphorus deficiency
reduced root mass and lateral root number, main root
length was unchanged by phosphorus treatment. This
resulted in decreased lateral root density in phosphorusdeficient
plants. The possible involvement of ethylene in
growth responses to phosphorus deficiency was investigated
by inhibiting endogenous ethylene production with aminoethoxyvinylglycine
(AVG) and aerating the root system with
various concentrations of ethylene. Phosphorus deficiency
doubled the root-to-shoot ratio, an effect which was suppressed
by AVG and partially restored by exogenous ethylene.
AVG increased lateral root density in phosphorusdeficient
plants but reduced it in phosphorus-sufficient
plants. These responses could be reversed by exogenous
ethylene, suggesting ethylene involvement in the regulation
of main root extension and lateral root spacing.
Phosphorus-deficient roots produced twice as much ethylene
per g dry matter as phosphorus-sufficient roots.
Enhanced ethylene production and altered ethylene sensitivity
in phosphorus-deficient plants may be responsible for
root responses to phosphorus deficiency.