FUENTES DE SACAROSA Y NITROGENO ORGANICO INFLUYEN EN LA EMBRIOGENESIS SOMATICA DE AGAVE ANGUSTIFOLIA

The somatic embryogenesis protocol in Agave angustifolia involves the induction of embryogenic calluses, the development and maturation of embryos and their conversion or germination to form a complete plant. In this sense, a judicious selection of the nutrients present in the culture medium is required. In this work, the effect of sucrose concentrations and sources of organic nitrogen on the somatic embryogenesis of A. angustifolia was studied. Our results showed that the induction of embryogenic callus and the production of somatic embryos can be controlled positively by changes in the sucrose concentration and are affected by the addition of amino acid sources. The frequency of conversion to seedlings ranged from 90 to 95% with a 100% survival in ex vitro conditions.Rev. Mex. Cienc. Agríc. vol. 9 num. 7 September 28 -November 11, 20181509A. angustifoliais one of most important raw materials for production of high quality mescal, this economic value results in tremendous national and international demand makingthe speciean important target forin vitromass propagation and genetic improvement.Somatic embryogenesis is a desirable mode of plant regeneration. However, for particular genotypes, in vitroculture conditions and the stages of somatic embryogenesis (acquisition of embryogenic competence, induction and maturation of somatic embryos and conversion to seedlings) must be experimentally optimised especially the compounds of the culture medium.In this sense, carbohydrates play vital role in plants life, they are substrate of respiration, perform function in synthetic pathway of many compounds and build blocks of macromolecules that may control several developmental processes in the cells (Smeekens, 2000). Sucrose is the most common carbohydrate source used in plant tissue culture and present dominantly in the phloem affected the formation of somatic embryos in culture medium (Nakagawa et al., 2001).On the other hand, in the somatic embryogenesis the growth of cells hashigh energy demands and synthesize large amounts of proteins and nucleic acids. It is an alternative energy source for rapidly dividing cells and cells that use glucose inefficiently. Cells require nitrogen atoms to build molecules such as nucleotides, amino acids, amino-sugars and vitamins. When glucose levels are low and energy demands are high, cells can metabolize amino acids from organic nitrogen sources for energy. In this sense, glutamine is one of the most readily available amino acids for use as an energy source and it is a major source of energy for many rapidly dividing cell typesin vitro because it plays an important role in nitrogen assimilation as it is an intermediate in the transfer of ammonia into amino acids. Likewise,casein hydrolysatescan be a source of calcium, phosphate, several microelements, vitamins and most importantly, a mixture of up to 18 amino acids.Sucrose (6%) only has been used as a carbon source for the induction of somatic embryos in A. angustifolia(Arzate-Fernándezand Mejía-Franco, 2011), but the effect of differentsugar concentrations or the influence of sources of amino acids (glutamine and casein hydrolysate) on somatic embryogenesis of Agavehas not yet been investigated. In the present work, the effect of different sucrose concentrations and its interaction with organic nitrogen on somatic embryogenesis of A. angustifoliahas been studied.To carry out our research,aseptic mature zygotic embryoswere dissected from Agave angustifoliaHaw seeds and used as initial explants for callus induction. This were placedin callus induction mediumconsisting of quarter-strength MS salt basal medium (Murashige and Skoog,1992) with 3 mg 2,4-D L-1and 1 mg BA L-1supplemented with L2 vitamins(Phillips and Collins, 1979),inthis stagefive levels of sucrose (40, 50, 60, 70 and 80 g L-1) and organic nitrogen (500 mg L-glutamine or Casein hydrolysate) on the induction of somatic embryogenesis from callus of Agave angustifoliaHaw. were evaluated. Medium pH was adjusted to 5.6-5.8 before adding the gelling agent (8 g agar L-1) (Sigma-Aldrich®) and autoclavingat 121°C for 20 min. Thus, ten random treatments were assayed. Each treatment consisted of 12 replicates of ten explants each. The cultures were maintained in darkness at 25 ±2°C for 60 days.CONACy