Doi:10.3906/bot-1302-49 Shortcut to long-distance developing of a tissue culture medium: micropropagation of mature almond cultivars as a case stud

Maturation imposes several changes in plants, which are particularly drastic in the case of trees. In recalcitrant woody species, such as chestnut (Castanea sativa Mill.), one of the major maturation-related shifts is the loss of the ability to form adventitious roots in response to auxin treatment as the plant ages. To analyze the molecular mechanisms underlying this phenomenon, an in vitro model system of two different lines of microshoots derived from the same field-grown tree was established. While juvenile-like shoots root readily when treated with exogenous auxin, microshoots established from the crown of the tree rarely form roots. In the present study, a transcriptomic analysis was developed to compare the gene expression patterns in both types of shoots 24 h after hormone and wounding treatment, matching the induction phase of the process. Our results support the hypothesis that the inability of adult chestnut tissues to respond to the inductive treatment relies in a deep change of gene expression imposed by maturation that results in a significant transcriptome modification. Differences in phytohormone signaling seem to be the main cause for the recalcitrant behavior of mature shoots, with abscisic acid and ethylene negatively influencing the rooting ability of the chestnut plants. We have identified a set of related MADS-box genes whose expression is modified but not suppressed by the inductive treatment in mature shoots, suggesting a putative link of their activity with the rooting-recalcitrant behavior of this material. Overall, distinct maturation-derived auxin sensibility and homeostasis, and the related modifications in the balance with other phytohormones, seem to govern the outcome of the process in each type of shoots.

This study aims to develop a suitable micropropagation protocol for black mulberry, which cannot be easily clonally propagated like other mulberry species. Clonal propagation of this species is gaining importance due to its health benefits and utilization in pharmacology. The effects of culture media and cytokinin types on micropropagation of Morus nigra L. were investigated. Single-axillary bud explants grown on MS, DKW, and NRM containing 0.25 mg/l benzyl adenine (BA) plus 0.01 mg/l indole-3-butyric acid (IBA) were compared to cultures grown on NRM with thidiazuron, metaTopolin (mT) or BA at 1.25, 2.5, 5.0 or 7.5 mg/l plus 0.01 mg/l IBA. The culture medium had a significant effect on shoot length. Shoot length was greater on NRM (3.3 shoots per explant) compared to the other medium types. Shoot multiplication was similar in all tested media types. Thidiazuron negatively affected shoot formation and triggered rosette shoots and/or large callus formation. Benzyl adenine and mT promoted both shoot proliferation and elongation. Around 84% of the micro shoots rooted and rooted shoots were successfully acclimatized to ex vitro conditions.