Elongation rates and endogenous indoleacetic acid levels in roots of pea mutants differing in internode length

Abstract

Growth of the primary root of 12 genotypes of peas (Pisum sativum) differing in their stem height was recorded for 14 days. The growth rate of roots of wild‐type tall, gibberellin (GA)‐deficient le dwarf or slender mutants (with la crys) was similar (3 cm day−1); that of severely GA‐deficient nana (na‐1) plants was 50% of wild‐type but elongation ceased after 8 days; moderately severe dwarf GA‐deficient lines ls‐1 and lh‐1 had a 15% reduction in elongation rate but displayed no time‐dependent slowing of the growth rate and brassinosteroid‐insensitive and ‐deficient dwarfs lka and lkb showed slightly decreased root elongation. GA (levels reported in Yaxley et al. 2001) is not substantially limiting to root growth until it is severely deficient. The terminal 3 cm of roots of tall plants contained about 25 or 35 ng g−1 fresh weight indole‐3‐acetic acid (IAA), depending on the genetic background, and le‐1 dwarfs were similar. Nana (na‐1) had less than 50% the level of IAA of tall, all the moderately severe dwarfs had reductions of about 30% and the slender plants had about 40% more IAA than the corresponding wild‐type. With the exception of slender plants, IAA level in the root tips correlated with root elongation. Root growth seems to be promoted by IAA within the range of the internal concentrations detected. Nana plants had a reduced amount of IAA and a lower root‐growth rate. Whereas external application of IAA always inhibits root growth, even at very low concentrations, root growth is not similarly inhibited by internal IAA as slender plants had the highest IAA level and growth rate similar to wild‐type, regardless of the shoot GA content.