The regulation of plant growth and development in liquid culture

Plant liquid culture offers many benefits over solidified media. Growth and multiplication rate of shoots, roots, bulblets and somatic embryos is enhanced in liquid culture, as a consequence of better availability of water and nutrients resulting from a lower resistance to diffusion and closer contact between the explant and the medium. Morphogenic development, such as meriste- moid production and somatic embryogenesis, is influenced by the physical environment provided by the liquid culture, and benefits from reduced gradients within the medium and dilution of exuded toxins. Chemical growth regulating factors, including plant hormones, growth retardants and other bioregulators are also discussed in terms of their influence on growth and development. Automation and scaling up for bioreactor production of propagules requires optimisation before becoming commercially viable. Considerable potential exists for future research into the molecular aspects regulating developmental pathways such as somatic embryogenesis, storage organ formation and meristemoid induction.