Practice question

Phenotype of transformed roots reflects activity of rol genes integrated into nuclear genome. rolA, rolB, rolC alter auxin perception and secondary metabolism. Roots exhibit lack of strong positive geotropism, grow plagiotropically or ageotropically on agar, and display prolific lateral branching due to diminished apical dominance and enhanced pericycle activation. Branch tips are covered with dense root hairs, increasing surface area. Growth occurs without exogenous auxin on hormone-free medium, showing hormone autotrophy, and biomass accumulation is rapid, doubling every 2 to 3 days in liquid. Neoplasticity and genetic stability maintained over long term distinguish them from normal roots that require auxin for initiation. Recognition of high lateral branching as diagnostic marker helps differentiate hairy root cultures during selection and explains industrial interest for continuous secondary metabolite extraction in immersed bioreactors. Microscopic analysis reveals increased pericycle cell divisions and early lateral initiation, attributed to rolB mediated increase in auxin sensitivity and reduced expression of AUX/IAA repressors. Root hairs dense and elongated, increasing absorptive surface. Biomass productivity high because growth not dependent on external auxin supply. This highly branched phenotype exploited for rhizosphere interaction studies and secondary metabolite exudation.