Evolutionary Relationships and Physiological Traits of Agaves and Yuccas with Contractile Roots

Abstract

Root contraction, found among a variety of agave and yucca species, is not only of physiological importance but may also provide evidence of evolutionary linkages between species. To better resolve evolutionary relationships within the genus Agave , we performed extraction, amplification, and sequencing of DNA for several species of agave known to have contractile roots. Molecular findings were then compared to a phylogenetic tree previously created using only plant morphology. To better understand the physiology of contractile roots, we investigated the effects of the plant hormones gibberellin and ethylene on the process of root contraction. In two separate experiments, plants of agave and yucca were subjected to regular treatments of either gibberellin or ethylene. Wires inserted at the base of the plants just above the roots were measured weekly to determine the amount of root contraction that occurred. Preliminary results reveal that root contraction occurred over time; however, there was no significant difference between the contraction that occurred in plants treated with hormones as opposed to those that were not. Data collected from these two lines of research offer further understanding into the phenomenon of contractile roots including their phylogenetic distribution within the genus Agave as well as a better understanding of the role hormones may play in stimulating or inhibiting root contraction.