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. I n order to increase the knowledge about the function of auxins and cyt okinins in seaweeds, explants such as apical and intercalary segments and callus-like structures (CLS) of Grateloupia dichotoma were culture d in semi-solid or liquid artificial media ASP 12-NTA. Two auxins, ind ole-3-acetic acid (IAA) and 2,4-dichlorophenoxyacetic acid (2,4-D), an d one cytokinin, 6-benzylaminopurine (BA), at concentrations of 0.5 an d 5.0 mg l(-1) were tested. Moreover, IAA and BA were tested together at concentrations of 1:5 and 5:1 mg l(-1). 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(-1)) . 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 plan t regeneration observed on CLS was stimulated significantly by treatme nt with high concentration of BA or IAA:BA (1:5 mg l(-1)) in semi-soli d and liquid media. The growth of upright axes was stimulated signific antly by treatment with 2,4-D in semi-solid medium, and IAA:BA (1:5 mg l(-1)) 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.