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. The trn chloroplast gene and the intergenic spacer region (ITS) were used to create a molecular phylogeny of agave and these 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 a plethora of plant hormones on the process of root contraction. In a multitude of experiments, plants were treated with a single plant hormone or a combination of two interfering plant hormones and rates of root contraction were measured weekly. Preliminary results revealed that the plant hormone gibberellin has no affect on root contraction but ethylene may in fact stimulate root contraction. 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.