A genotype-independent system of regeneration from cotyledons of sunflower ( Helianthus annuus L.) The role of ethylene

Abstract

A system of regeneration which allows shoot organogenesis, at high frequencies, from mature cotyledon tissues of 30 genotypes of sunflower ( Helianthus annuus L.) is described. This new two-step protocol included an incubation period of 3 days for cotyledon explants, for 3 days, in liquid Murashige and Skoog's modified medium supplemented by 5.4 μM naphthaleneacetic acid (NAA) and 4.4 μM benzylaminopurine (BAP); then, they were subcultured on the same medium solidified by agar. After 4 weeks of culture, the shoots were transferred to rooting medium, then the rooted plantlets were successfully acclimatized and gave fertile plants. This process of regeneration allowed the triggering of shoot formation in 19 genotypes which had previously been found recalcitrant to regeneration and enhanced the regeneration potential in other poorly regenerative genotypes. The variation of ethylene production by explants directly cultured on solid medium or incubated in liquid medium was studied. The production of this hormone reached a maximum value after 3 days of culture on solid medium while incubation in liquid medium greatly reduced it. The addition of Ethephon to the liquid medium during the incubation period increased ethylene concentration and caused inhibition of shoot formation. On the basis of these findings, it is suggested that the induction of shoot regeneration is controlled by ethylene, so the reduction of ethylene production caused by the period of explant incubation in liquid medium allows regeneration in all genotypes tested. These data suggest that the process of regeneration might be general for sunflower genotypes.