Effects of auxins and cytokinins on tissue culture of Grateloupia dichotoma (Gigartinales, Rhodophyta)

The role played by plant growth regulators in algae is poorly known. In order to increase the knowledge about the function of auxins and cytokinins in seaweeds, explants such as apical and intercalary segments and calluslike structures (CLS) of Grateloupia dichotoma were cultured in semi-solid or liquid artificial media ASP 12NTA. Two auxins, indole-3-acetic acid (IAA) and 2,4-dichlorophenoxyacetic acid (2,4-D), and one cytokinin, 6- benzylaminopurine (BA), at concentrations of 0.5 and 5.0 mg l were tested. Moreover, IAA and BA were tested together at concentrations of 1:5 and 5:1 mg l. All treatments promoted the growth of CLS in intercalary segments; CLS from apical segments were significantly higher in treatments with 2,4-D or IAA:BA (1:5 mg l). The morphogenetic responses for auxins and BA were opposite, auxins inhibited while BA promoted the formation of lateral branches; however, auxins promoted the elongation of such branches. The process of plant regeneration observed on CLS was stimulated significantly by treatment with high concentration of BA or IAA:BA (1:5 mg l) in semi-solid and liquid media. The growth of upright axes was stimulated significantly by treatment with 2,4-D in semi-solid medium, and IAA:BA (1:5 mg l) in liquid medium. These results show the importance that plant growth regulators could have in the control of growth, morphogenetic processes and micropropagation in red algae.