Detailed Quantitative Analysis of Architectural Traits of Basal Roots of Young Seedlings of Bean in Response to Auxin and Ethylene  

Abstract

Vertical placement of roots within the soil determines their efficiency of acquisition of heterogeneous belowground resources. This study quantifies the architectural traits of seedling basal roots of bean (Phaseolus vulgaris), and shows that the distribution of root tips at different depths results from a combined effect of both basal root growth angle (BRGA) and root length. Based on emergence locations, the basal roots are classified in three zones, upper, middle, and lower, with each zone having distinct architectural traits. The genotypes characterized as shallow on BRGA alone produced basal roots with higher BRGA, greater length, and more vertically distributed roots than deep genotypes, thereby establishing root depth as a robust measure of root architecture. Although endogenous indole-3-acetic acid (IAA) levels were similar in all genotypes, IAA and 1-N-naphthylphthalamic acid treatments showed different root growth responses to auxin because shallow and deep genotypes tended to have optimal and supraoptimal auxin levels, respectively, for root growth in controls. While IAA increased ethylene production, ethylene also increased IAA content. Although differences in acropetal IAA transport to roots of different zones can account for some of the differences in auxin responsiveness among roots of different emergence positions, this study shows that mutually dependent ethylene-auxin interplay regulates BRGA and root growth differently in different genotypes. Root length inhibition by auxin was reversed by an ethylene synthesis inhibitor. However, IAA caused smaller BRGA in deep genotypes, but not in shallow genotypes, which only responded to IAA in the presence of an ethylene inhibitor.

Spatio-temporal analysis of development of basal roots of common bean (Phaseolus vulgarisL.)

“…10 Sequential emergence of seminal and adventitious roots have also been reported in grass. 11 But our results show that the emergence of basal roots in common bean is almost simultaneous and therefore the heterogeneity of lengths of basal roots due to genotypic differences and position of origin reported in Basu et al 7 is primarily dependent on variations in growth rate. Initially the growth rate was slower and after 12-18 h the growth rate accelerated as indicated by the change in slope of the root length vs. time lines.…”

“…We have recently demonstrated important differences in architectural traits of the basal roots of common bean in the early seedling stage between two contrasting class of genotypes and how auxin-ethylene interplay regulates these traits. 7 While this study of basal roots at a fixed time allows assessment and comparison of root development up to that point of time, investigation of the temporal events of emergence and growth of the basal roots is important and complementary to the understanding of their architectural traits. Therefore in the present study, we examined the detailed developmental patterns of basal roots through time lapse imaging in two genotypes.…”

“…8 The germinated seedling with 2-3 cm radical was transferred to the blue germination paper (Anchor Paper Co., St. Paul, MN), which was suspended in nutrient solution 7 inside a growth chamber (ACMAS Technocracy Limited, Delhi, India) maintained at 25 ± 1°C. Time artIcLe addendum angle between gravity and the line connecting the root tip to the base is BRGA.…”

“…Time artIcLe addendum angle between gravity and the line connecting the root tip to the base is BRGA. 7 The vertical distance of the root tip from the base of the lowest emerging root along the gravity vector is tip depth. From the midline, root curvature was also determined using the equation (1) where [x(x), y(s)] is coordinate of any point along the root midline, s is normalized distance along the midline, and the primes denote derivatives with respect to s. Here positive curvature signifies bending upward and vice versa.…”

Plasticidade Fenotípica E Frações Fosfatadas Em Espécies Florestais Como Resposta À Aplicação De Fósforo

“…O que está de acordo com outros estudos, posto ser o comportamento diferencial das espécies quanto à nutrição geneticamente controlado (BASU et al, 2011).…”