Novel screening methods for plant micropropagation

Abstract

The techniques of plant micropropagation have not been successfully applied to all species. This study was carried out with the objectives of developing new techniques for rapidly assessing the relative merits of cultural treatments and identifying fundamental and genotype-specific problems associated with micropropagation. Anatomical characteristics of mlcropropagated Hosta spp. and Paeonia lactiflora were investigated. A root exodermis was present and apoplastic tracer studies indicated it was functionally and anatomically the same as ex vitro root exodermes in the literature. Specialised cells rather than simple wound tissue were present at the plantlet /medium interface An endodermls was present in the shoot base of Hosta plantlets. It is suggested that the basal zone of the shoot is functionally a specialised "root". It is hypothesised that carbohydrate status (or solute potential) of vascular cambla and/or root initial cell Is Important in the induction of adventitious root formation. Growth medium GA, and possibly raised inorganic phosphate, resulted in Increased shoot "health" but inhibited rooting in P. lactiflora cultures, possibly through changes in assimilate partitioning and sucrose uptake. A low mobility esterase isoenzyme was specific to these changes. Water relations are identified as a critical factor in the micropropagation of P. lactiflora. Cold storage of Hosta spp. led to sequential leaf senescence, abscission and changes in isoenzyme patterns. No true dormancy was identified in culture, although it was demonstrated after weaning if a requirement for cold storage was not met. In vitro, "dormancy" was expressed as a reduction in the rate of new leaf production. Removal of this growth inhibition was correlated with the appearance of a highly mobile esterase isoenzyme. The possibility of using this isoenzyme to predict subsequent in vitro growth inhibition and ex vitro dormancy is discussed. The objectives of this study were fulfilled, and the direction of future research is discussed.