Hormone growth responses of roots of shoot height mutants of pea

Abstract

Growth of the roots vertical roots of 12 genotypes of peas (Pisum sativum), which differed in stem height because of differing gibberellin (GA) or brassinosteroid content or signal transduction, was recorded during continuous exogenous applications of differing concentrations of indoleacetic acid (IAA) and GA3, over a period of 12 h with a sensitivity of 2 μm. IAA was inhibitory to all genotypes tested at concentrations of 0.5 nM and above. The response was rapid, reaching a maximum within 20 min. There was no response to 0.1 nM IAA, and no concentration tested promoted growth. At 0.5 nM the growth rate dropped to the same extent as with higher concentrations but then recovered slowly over about 12 h. Roots of nana (na) plants, which have reduced levels of IAA, partially recovered slowly from the inhibition of even 1 μM IAA, to about 20% of the non‐IAA growth rate after 10 h. When IAA (even 1 μM) was removed the growth rate of all lines slowly recovered over about 9 h after a lag of 1 h. IAA application to horizontal roots prevented bending in response to gravity. Roots of 3‐day‐old pea plants of all genotypes were unresponsive to exogenous GA but 5‐day‐old nana plants showed a gradual increase in elongation rate in response to GA, after a lag of a few hours, possibly because of a depletion of GAs provided from the cotyledons of the young plants. Roots in liquid culture did not branch and gradually became thinner. The growth of cultured roots was about 25% of that of intact plants of the same genotype. GA produced no effect on cultured roots, except in nana where it enhanced elongation. IAA was always inhibitory to growth in culture but stimulated branching. Some shoot‐provided factor is necessary for the normal growth and development of the roots.