Interactive role of ethylene and polyamines on shoot regenerability of Chinese kale (Brassica alboglabra Bailey) in vitro

Abstract

The regulatory role of ethylene and polyamines (PAs) on shoot regeneration of Chinese kale (Brassica alboglabra Bailey) grown on medium solidified with different gelling agents was investigated. Among the 4 gelling agents tested, medium solidified with 0.4% agarose was the most effective in shoot regeneration. Shoot regenerability was further enhanced by incorporation of inhibitors of ethylene biosynthesis and action (25 μmol · L-1 aminoethoxyvinylglycine (AVG) or 10 μmol · L-1 AgNO3) in the medium. AVG decreased ethylene production during the first week of culture, whereas AgNO3 markedly stimulated ethylene synthesis. The promotive effect of AVG on shoot regeneration was overcome in the presence of 100 μmol · L-1 exogenous 1-aminocyclopropane-1-carboxylate or 2- chloroethylphosphonic acid, while AgNO3-enhanced regeneration was only slightly affected by these chemicals. Application of difluoromethylarginine at ≤ 0.1 mmol · L-1 also suppressed ethylene inhibitor-enhanced regeneration, however growth could be restored by application of 10 mmol · L-1 putrescine. Difluoromethylornithine had no effect on shoot regenerability of the explant. Apart from ethylene inhibitors, regenerability was also enhanced by exogenous application of 5-20 mmol · L-1 putrescine, 0.75 mmol · L-1 spermidine or 0.075 mmol · L-1 spermine, but ethylene synthesis of the explant was not affected by exogenous PAs. The level of α- naphthaleneacetic acid (NAA) in the medium was important to shoot regeneration, which occurred at a high frequency at 1 mg · L-1 NAA in combination with 2 mg · L-1 benzyladenine, despite the absence or presence of ethylene inhibitor. NAA at concentrations lower than 1 mg · L-1 was inhibitory to regeneration, although it stimulated ethylene production.