Influence of plant growth regulators and water stress on ramet induction, rosette engrossment, and fructan accumulation in Agave tequilana Weber var. Azul

Agave tequilana Weber var. Azul plants reproduce asexually by producing ramets. Continuous production of ramets throughout the vegetative cycle of the parent delays the time of harvesting of heads for tequila production. Little is known about the factors influencing their emergence. Heads are engrossed rosettes where fructans are stored. We show here that, in plantlets grown in vitro, growth regulators such as 2,4-dichlorophenoxyacetic acid (2,4-D), a combination of 1-naphthaleneacetic acid (NAA)/6-benzyladenine (BA), or abscisic acid (ABA) increased the production of ramets, whereas BA, NAA, gibberellic acid (GA(3)), glycerol, or a combination of glycerol/ABA decreased ramet production. Plantlets that developed ramets did not form heads. Head formation was improved on solid media in the presence of BA, NAA, the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC), or the water stress inducer polyethylene glycol (PEG). Basal Murashige-Skoog (MS) liquid media also enhanced rosette engrossment, which was further increased by addition of ACC or PEG. In contrast, CoCl2, an ethylene biosynthesis inhibitor, reduced rosette engrossment. Furthermore, heads from A. tequilana plantlets grown in tissue culture in MS media, or in MS media supplemented with NAA, ACC or PEG, showed fructan concentrations 10-30 times higher than in leaves from greenhouse-grown plants. Our results indicated that BA, NAA, water stress, and ethylene are critical regulators of rosette engrossment, whereas asexual reproduction in A. tequilana seems to be controlled by a complex hormonal network.