Thin cell layer technology for induced response and control of rhizogenesis in chrysanthemum

Abstract

Chrysanthemum (Dendranthema X grandiflora Ramat. Kitamura) stem transverse thin cell layers (tTCLs) were used to obtain defined morphogenic programs with selected plant growth regulators. A rhizogenic pathway could be manipulated in vitro by the application of a single auxin (2,4-D, NAA, IBA or IAA, in increasing order of rhizogenic response), or by the addition of coconut water, with light or darkness playing a significant role. The addition of TIBA eliminated the rhizogenic capacity of all the auxins tested, but not that of coconut water, while the addition of activated charcoal was inhibitory. The absence of sucrose resulted in a limited rhizogenic response. Results clearly indicate the importance of auxins, media additives and light in the activation of a rhizogenic program in chrysanthemum tTCLs. Due to their restricted size and medium-dependant nature, the capacity to control rhizogenesis and/or organogenesis in chrysanthemum (and indeed any plant species) by TCLs has far-reaching consequences and applications in the floricultural and pharmaceutical sectors. Since all factors (exogenously-applied hormones and other growth-stimulating or growth-inhibiting substances, light, temperature, humidity and other environmental cues) may be strictly controlled in vitro, TCL technology allows for the establishment of protocols aimed at chrysanthemum flower improvement through genetic engineering, the success of which lies in its first step i.e. programmable morphogenesis and regeneration.