Light‐cytokinin interaction in shoot formation in cultured cotyledon explants of radiata pine

Abstract

Previous studies utilizing cotyledon explants of radiata pine (Pinus radiata D. Don) revealed that cytokinin was required for shoot formation. This was confirmed and extended in the present study, which also showed that light was required. As little as three days of exposure to 16 h photoperiod light at a photon fluence rate of ca 80 μmol m−2 s−1 was sufficient to give some meristematic tissue formation. Longer exposure to light increased this formation. While cytokinin must be present during the first three days in culture for shoot formation, the exposure of the cotyledons to light could be delayed at least until day 10, but after 21 days in darkness, transfer to light did not permit shoot formation. Anatomical examination of the cotyledons confirmed the morphogenetic interactions of light and cytokinin in shoot formation. The data suggest that cytokinin is directly involved in the induction of shoot initiation and both light and cytokinin are required for the development of meristematic tissue and subsequent shoot formation.

In vitro propagation of Pithecellobium saman (Raintree)

“…saman hypocotyl explants required only 7 d of exposure to a culture medium containing BA for adventitious bud induction. These results agree with the findings of other authors, e.g., Villalobos et al (1984), who observed that in Pinus radiata, 3 d of exposure to BA was enough to start the morphogenetic process. Also, Martinez Pulido et al (1991) observed that BA exposure period affected bud number, quality, and growth rate in Pinus canariensis cotyledonary explants, with the optimum exposure ranging between 2 and 3 wk.…”

“…Explants taken between 5 and 15 d after germination were more organogenic than those taken after 20 d. In other studies, explant age has been found to be a very important factor for regulation of organogenesis, because juvenile tissues have shown a higher regeneration rate aptitude (Villalobos et al, 1984;Webb et al, 1988;Goldfarb et al, 1991;Martfnez Pulido et al, 1991). Regarding the section and explant's orientation, polarity was observed within the explant since the distal part of the hypocotyl was less responsive for adventitious bud development, and horizontal placement on the medium favored both the speed of production and number of adventitious buds.…”

Factors affecting shoot regeneration from zygotic embryo and seedling explants of Cycas revoluta thunb

“…Therefore, adventitious shoot induction appears to be influenced by light and by relative amounts of ammonium and nitrate. It has to be noticed that light has been repeatedly reported to promote shoot bud organogenesis, as in cotyledon explants of Pinus radiata, in which continuous cytokinin treatments and light exposure were required for shoot development beyond the promeristemoid stage (Villalobos et al, 1984).…”

Environmental and Hormonal Effects in Micropropagation

“…The influence of light intensity seems to be related to species, with some benefitting from high intensities, others responding to intermediate levels, while still others are best cultured under low light or darkness (papachatzi et al, 1981;Miller and Murashige, 1976;Thorpe and Murashige, 1970). Reports for a wide range of species generally place the optimum light intensities for tissue culture of woody plants at about 70 to 80I'M/(m2·sec) Hutchinson, 1984;Villalobos et al, 1984;Read, 1989). However, both high and low light levels have been reported to depress shoot proliferation for species such as black currant and azaleas (Wainwright and Flegman, 1984;Economou and Read, 1987).…”

“…Blue light has been implicated in both stimulation (Ward and Vance, 1967) and inhibition (Seibert et al, 1975). Furthermore there have been numerous other conflicting reports regarding the relative value and role of light of various wave lengths on in vitro responses (Kadkade and Jopson, 1978; and their interaction with cytokinins in the medium (Villalobos et al, 1984;Husemann and Reinert, 1976;Badilla et al, 1985). Although these and most reports relate to a response by the tissue to specific light qualities, a recent report by Hangarter and Stasinopoulos (1991) suggests that evidence exists that light of differing qualities can cause changes in the constituents of the medium.…”