Effects of plant growth regulators on callus formation, growth and regeneration in axenic tissue cultures of Gracilaria tenuistipitata and Gracilaria perplexa (Gracilariales, Rhodophyta)

Abstract

The effects of auxins and cytokinin on callus formation, growth and regeneration of Gracilaria tenuistipitata Chang et Xia and G. perplexa Byrne et Zuccarello (Gracilariales, Rhodophyta) are reported. Plant growth regulators (PGR) in concentrations ranging from 0.1 to 100.0 µ mol of indole-3-acetic acid, 2,4-dichlorophenoxyacetic acid (2,4-D), and kinetin (K) were added to the ASP 12-NTA solid medium (0.7% agar), and apical and intercalary segments (5 mm long) were inoculated as initial explants. K stimulated growth rates of intercalary segments of G. tenuistipitata in a linear relation, and 2,4-D (1.0 µ mol) and K (10.0 µ mol) stimulated growth rates of apical and intercalary segments of G. perplexa , respectively. The simultaneous formation of apical, basal, and intermediate calluses is reported for the first time in axenic tissue cultures of red algae. With intercalary segments of G. tenuistipitata , basal callus induction rates were higher than those of apical and intermediate calluses in the majority of treatments, and auxins had stimulatory effects on the formation of all callus types. In apical segments of G. perplexa , intermediate callus formation was stimulated only by treatment with 1.0 µ mol of K, while apical callus formation was stimulated by indole-3-acetic acid (1.0-10.0 µ mol), 2,4-D (10.0-100.0 µ mol), or K (0.1 µ mol). Intercalary segments of G. perplexa developed only intermediate calluses, and the majority of treatments with PGR stimulated higher rates than those presented by apical segments. Potential for regeneration (development of adventitious plantlets originated from callus cells) was higher in apical calluses than in basal and intermediate calluses developed in intercalary segments of G. tenuistipitata . Moreover, auxins and cytokinin were essential to the induction of regeneration in intermediate calluses, while specific concentrations stimulated regeneration from basal and apical calluses. Plant regeneration in G. perplexa was observed only after transferring calluses from solid to liquid medium, and the majority of treatments with PGR had stimulatory effects. Regenerating plants of G. perplexa developed tetrasporangia, and released tetraspores giving rise to adult gametophytes. Our results indicate that auxins and cytokinin have a regulatory role in the growth and morphogenesis in G. tenuistipitata and G. perplexa , and diversity of responses presented by both species is related to specific developmental systems.

Auxin and cytokinin relationships in 24 microalgal strains1

“…) and improving callus growth in Gracilaria tenuistipitata and G. perplexa in culture (Yokoya et al. ). These reports provide evidence that auxin may act as a plant growth regulator in seaweeds in a similar way as in vascular plants.…”

ENDOGENOUS CYTOKININS, AUXINS, AND ABSCISIC ACID IN RED ALGAE FROM BRAZIL1

“…These extracts are used commercially as growth stimulants in agricultural crops due to the plant hormones present (Stirk and Van Staden 2006). Although the hormonal regulatory system in seaweeds has not been nearly as extensively studied as in vascular plants, there is evidence that plant growth regulators are involved in seaweed developmental processes (Bradley 1991, Evans and Trewavas 1991) including the growth and morphogenesis of red algae (Yokoya et al. 2003, 2004).…”

A laser-scanning confocal microscopy study of carrageenan in red algae from seaweed farms near the Caribbean entrance of the Panama Canal

“…e, f Phasor plot histogram that corresponds to pixels in the spectral region: 580 nm (blue) 586 nm (green), and 591 nm (red) of (c) and (d) images, respectively. g, h Pie graphs show the percentage of pixels in the three cursors for each image of enhancing strains of commercially important species (Yokoya et al 2004). Zitta et al (2013) found that the thick wall of the cells, which are composed in part of callus filaments, showed the presence of acidic polysaccharides, suggesting a large content of carrageenan and neutral polysaccharides.…”