Effects of environmental factors and plant growth regulators on growth of the red alga Gracilaria vermiculophylla from Shikoku Island, Japan

Abstract

Growth and tolerance of Gracilaria vermiculophylla (Ohmi) Papenfuss from Shikoku Island were investigated under a variation of temperature (5–30 °C), salinity (5–60‰), and photon irradiance (20–100 μmol photons m−2 s−1) in unialgal culture. G. vermiculophylla showed wide tolerances for all factors tested, characterizing a euryhaline and eurythermal species. Two clones, one of a tetrasporophyte and the other of a female gametophyte, showed different growth rates, attributable to the difference either in phase or in genotype. The optimum temperature for the growth of the tetrasporophyte clone was 15–25 °C while that of the gametophyte clone was 20–30 °C. Maximum growth of both phases was observed at 80–100 μmol m−2 s−1. G. vermiculophylla presented higher growth rates in low salinities (15–30‰). Tissue cultures were established in solid ASP 12-NTA medi um supplemented with plant growth regulators (PGR), 0.5% agar, 1.0% sucrose and 0.5% inositol. Effects of two auxins (indole-3-acetic acid (IAA), and 2,4-dichlorophenoxyacetic acid (2,4-D)), and one cytokinin (6-benzylaminopurine (BA)) were tested in concentrations ranging from 0.1 to 10.0 mg l−1. Growth of apical segments was significantly stimulated by the majority of treatments supplemented with PGR, while maximum growth of calluses was observed in treatments with low concentration of auxins or BA (1.0 mg l−1). All treatments supplemented with PGR significantly promoted the growth of intercalary segments, except for IAA (1.0 mg l−1) in combination with BA (1.0 mg l−1). Growth of calluses originating from intercalary segments was observed in treatments with IAA (0.1 mg l−1), 2,4-D (10.0 mg l−1) or IAA (1.0 mg l−1) in combination with BA (0.1 mg l−1). Tr eatments with high concentration of IAA and BA (10.0 mg l−1) were lethal for apical and intercalary segments. These results show that auxin and cytokinin play a regulatory role on the growth of G. vermiculophylla in tissue culture. Furthermore, results on the effects of temperature, salinity and irradiance indicate that G. vermiculophylla could be cultivated in brackish temperate environments with potential for economic purposes and for pollution management.