Apical callus formation and plant regeneration controlled by plant growth regulators on axenic culture of the red alga Gracilariopsis tenuifrons (Gracilariales, Rhodophyta)

Abstract

SUMMARY Axenic cultures of Gracilariopsis tenuifrons (Bird et Oliveira) Fredericq et Hommersand (Gracilariales, Rhodophyta) were established in ASP12‐NTA solid medium (0.4% agar and 1.0% sucrose) supplemented with plant growth regulators to evaluate the effects on apical callus formation and plant regeneration. Indole‐3‐acetic acid (IAA), 2,4‐dichlorophenoxyacetic acid (2,4‐D) and 6‐benzylaminopurine (BA) were added individually or in combinations (IAA : BA) over a range of concentrations from 0.5 to 5 mg L−1. Growth of apical and intercalary segments was stimulated by high concentrations of 2,4‐D (5 mg L−1) and a high IAA to BA ratio (IAA : BA = 5:1 mg L−1) respectively. Apical calluses were originated from divisions of apical and cortical cells located at apical regions of thallus segments and lateral branches. Low concentration of IAA (0.5 mg L−1) or a high IAA to BA ratio (IAA : BA = 5:1 mg L−1) were the optimal treatments for inducing apical callus formation in apical segments, while high concentration of IAA (5 mg L−1) stimulated the highest callus induction rate in intercalary segments. Conversely, equal parts IAA and BA (IAA : BA = 1:1 mg L−1) and low concentration of 2,4‐D (0.5 mg L−1) stimulated growth of apical calluses from apical and intercalary segments, respectively. Two processes of regeneration were observed: direct regeneration (upright axis originated from cells of proximal region of intercalary segments) and indirect regeneration (adventitious plantlet originated from cells of apical calluses). Direct regeneration was promoted significantly by treatment with a low IAA to BA ratio (IAA : BA= 1:5 mg L−1), and treatments with IAA (0.5 mgL−1) or 2,4‐D (0.5 or 5 mg L−1) significantly stimulated the elongation of upright axis. Plant growth regulators are essential to inducing indirect regeneration, and a high concentration of IAA (5 mg L−1) and BA (5 mg L−1) were the optimal treatments for inducing the regeneration of plantlets from apical calluses in apical and intercalary segments, respectively. Regenerating plantlets grew into plants morphologically similar to those formed from germinating spores, and became fertile after 6 weeks. The results suggest that auxins and cytokinins are involved in developmental regulatory processes in G. tenuifrons. The regeneration process from calluses in species of Gracilariales was observed for the first time in the present study. The culture system described for G. tenuifrons could be useful for micropropagation and for biotechnological applications in agarophytic algae.

Investigating the Effects of Exogenous Factors on Growth, Photosynthetic Pigments and Bud Induction in Gracilaria corticata var. cylindrica under In vitro Conditions

“…In relation to formation of lateral buds, A 2 media supplemented with K 1 regenerated the highest no of buds. Our results were not corresponding to the results of Yokoya (2000) and Hayashi et al, (2007), where direct regeneration was promoted by combinations of IAA and BAP. These effects may be due to the difference in the media or species of seaweed used in the study coupled with the combination of various PGRs synergizing with endogenous hormones in a different way.…”

Effects of temperature, salinity and irradiance on carposporeling development of Hidropuntia caudata (Gracilariales, Rhodophyta)

“…The specimens were maintained in culture medium composed by sterilized seawater enriched with 25% of Von Stosch (VSES/4) solution (Edwards, 1970) with a 50% reduction in the vitamin concentrations, according with Yokoya (2000), at 23±1 o C), with a photon flux density of 60 to 70 µmol photons m -2 s -1 , and 30 psu (practical salinity units). To reduce the growth of diatoms, 1 mg.L -1 of germanium dioxide was added to the medium (Lewin, 1966).…”

Efeitos do ágar no crescimento de explantes e na formação de calos em morfos pigmentares de Gracilaria domingensis (Kützing) Sonder ex Dickie (Gracilariales, Rhodophyta)

“…A formação dessa estrutura também pode estar relacionada à dessecação, como foi observado nos calos intermediários, e corroboram os resultados obtidos para calos apicais de Hypnea musciformis (Yokoya et al 2003, Bravin 2005 e Gracilaria tenuistipitata (Yokoya et al 2004). A formação de calos apicais foi descrita para outras espécies, em decorrência de outros fatores tais como estímulo mecânico para Solieria fi liformis (Robledo & García-Reina 1993) e a presença de fi torreguladores para Gracilariopsis tenuifrons (Yokoya 2000) e Gracilaria perplexa (Yokoya et al 2004).…”

“…Resultados similares foram observados para a indução de calos basais de Gracilaria vermiculophylla (Yokoya et al 1999) e calos apicais de Hypnea musciformis (Yokoya et al 2003). Entretanto, baixas concentrações de ágar (0,4%) induziram a formação de calos basais em Grateloupia dichotoma (Yokoya & Handro 1996), calos apicais em Gracilariopsis tenuifrons (Bird & Oliveira) Fredericq & Hommersand (Yokoya 2000) e explantes fi lamentosos em Solieria fi liformis (Yokoya & Handro 2002).…”