Synergistic effect of ethylene inhibitors and putrescine on shoot regeneration from hypocotyl explants of Chinese radish (Raphanus sativus L. var. longipinnatus Bailey) in vitro

The role of ethylene and putrescine on shoot regeneration from hypocotyl explants of Chinese radish (Raphanus sativus L. var. longipinnatus Bailey cv. Red Coat) was investigated. Explants were recalcitrant in culture, but exogenous application of ethylene inhibitor [20-30 μM aminoethoxyvinylglycine (AVG) or AgNO3] enhanced shoot regeneration of explants grown on medium supplemented with 2 mg/l N(6)-benzyladenine and 1 mg/l 1-naphthaleneacetic acid. The best regeneration occurred in the medium containing AgNO3 in combination with AVG. Culture medium solidified with agarose in the presence of AgNO3 but not AVG was also beneficial to shoot regeneration. Exogenous putrescine, 2-chloroethylphosphonic acid and 1-aminocyclopropane-1-carboxylate had no effect on shoot regeneration. However, regeneration was greatly promoted by 10-25 mM putrescine in combination with 30 μM AgNO3 or AVG. Explants with high regenerability grown in the presence of AgNO3 or in combination with putrescine emanated high levels of ethylene throughout the 21-d culture period. By contrast, AVG or putrescine alone resulted in a decrease in ethylene production. For rooting of shoot cuttings, IAA and IBA at 1-5 mg/l were more effective than NAA.

Effect of AgNO3 and aminoethoxyvinylglycine on in vitro shoot and root organogenesis from seedling explants of recalcitrant Brassica genotypes

The presence of 1-10 μM aminoethoxyvinylglycine (AVG) or 5-30 μM AgNO3 markedly enhanced shoot regeneration from cotyledon and hypocotyl cultures of eight recalcitrant Brassica campestris and B. juncea genotypes tested. Expiants of B. campestris ssp. chinensis and ssp. parachinensis grown with a high AVG concentration (20 μM), regenerated poorly. All cytokinins tested were equally effective in promoting shoot formation, except that kinetin was inhibitory to shoot regeneration from hypocotyls of B. campestris ssp. pekinensis (cv. Wong Bok). Both AgNO3 and AVG had no effect on percent rooting and number of roots per rooted cutting of Wong Bok, White Sun and Leaf Heading, but AgNO3 was inhibitory to rooting of India Mustard. However, root elongation of all cuttings was markedly inhibited by AVG at concentrations of 5 and 10 μM.

Direct somatic embryogenesis from protoplasts of Citrus mitis Blanco

Protoplasts isolated from embryogenic suspension cultures of Citrus mitis were cultured in a medium without any plant growth substances. Somatic embryos developed directly from protoplasts without an obvious intervening callus phase. As many as 1,800 somatic embryos developed from 4 ml of protoplast suspension (density 2×10(6)/ml) cultured for 35 days. Upon transferring the embryoids to medium with 1 mgl(-1) GA3, they developed into plant-lets. Rooted plantlets were obtained in 3 months after protoplast isolation.