Effect of Cryopreservation on the Ex Vitro Establishment of Olive Plants Regenerated via Somatic Embryogenesis

Cryopreservation is considered the best technique for the safe, long-term conservation of embryogenic cultures. However, before integrating it into a somatic embryogenesis system, the influence of cryopreservation on the final production of plants should be investigated. The objective of this investigation was to evaluate the effect of cryopreservation on the regeneration performance of olive embryogenic cultures as well as on the quality of the plants obtained and their response to ex vitro establishment. In order to analyze the influence of the genotype, all the investigations were carried out in two genetically distinct embryogenic lines. The results obtained revealed no variation in the regeneration potential or the quality of the regenerated plants due to cryopreservation. The subsequent multiplication, rooting, and acclimatization steps were not influenced by cryopreservation either, although a significant genotype × cryopreservation interaction was found for shoot length during the multiplication step. The genotype played an important role, determining the quality of the regenerated plants and some aspects of the multiplication and rooting phases. This investigation revealed that the droplet-vitrification procedure optimized for the cryopreservation of olive somatic embryos can be efficiently used for the long-term conservation of olive embryogenic lines.

Effect of Cryopreservation on Olive (Olea europaea L.) Plant Regeneration via Somatic Embryogenesis

Olive somatic embryos have been successfully cryopreserved using the droplet-vitrification method on aluminum foil strips. Although acceptable recovery rates have been obtained after rewarming, the influence of this cryopreservation protocol on the somatic embryogenesis process is unknown. To evaluate the effect of cryopreservation on olive somatic embryogenesis, the behavior of cultures established from cryopreserved somatic embryos was compared with that of control, non-cryopreserved cultures in the different phases of the somatic embryogenesis process. In order to analyze the influence of the genotype, this investigation was carried out in two independent lines. During the proliferation step, only the line T1 was affected by cryopreservation, with higher fresh weight increases. Although similar total embryos were produced per culture, freezing in liquid nitrogen significantly improved the maturation pattern in the line P5. Better germination results were also found in this embryogenic line. The genotype plays a key role, largely determining the effect of cryopreservation on olive somatic embryogenesis. A specific genotype-dependent response was found depending on the culture step. Variations observed could not be associated to differences in the embryogenic lines’ instability to maintain their morphogenic competence after cryopreservation. Embryogenic cultures established after rewarming retained their regeneration capacity, with no evident negative effects affecting their regeneration capacity.

Key Techniques for Somatic Embryogenesis and Plant Regeneration of Pinus koraiensis

Korean pine is the dominant species of Korean pine forests. It is an economically valuable species that yields oil, high-quality timber and nuts, and it offers great prospects for further development. Complete regenerated plants of Korean pine were obtained via somatic embryogenesis using megagametophytes as the explant. The seeds of 27 families of Korean pine were collected to induce embryogenic lines. We compared the effects of explant collection time, family and medium components (concentrations of sucrose, plant growth regulators and acid-hydrolyzed casein) on embryogenic lines induction. The effects of plant growth regulators and L-glutamine contents on the proliferation and maturation of embryogenic cell lines were studied, and the germinating ability of different cell lines was evaluated. The embryogenic lines induction percentage of Korean pine reached 33.33%. When 4.52 μmol·L−1 2,4-D and 2.2 μmol·L−1 6-BA were added to the medium of embryogenic lines proliferation, the ability of embryo maturation was the best (cell line 001#-100 was 135.71·g−1 fresh weight). Adding 1–1.5g L−1 L-glutamine to the proliferation medium can improve the ability of embryo maturation (cell line 001#-100 was 165.63·g−1 fresh weight). The germination percentage of the three cell lines tested was significant, and the highest was 66%. We report on successful regeneration and cryopreservation methods for somatic embryos of Korean pine. This technology could be used to propagate the excellent germplasm resources of Korean pine and to establish multi-varietal forestry.

Morpho-histological development of the somatic embryos of Typha domingensis

Background Sustainable methods of propagation of Typha domingensis through somatic embryogenesis can help mitigate its current condition of ecological marginalization and overexploitation. This study examined whether differentiation up to coleoptilar embryos could be obtained in an embryogenic line proliferated with light and high auxin concentration. Methods Murashige and Skoog medium at half ionic strength and containing 3% sucrose and 0.1% ascorbic acid was used for the three embryogenic phases. Induction started with aseptic 9-day-old germinated seeds cultured in 0.5 mg L−1 2,4-dichlorophenoxyacetic (2,4-D). Proliferation of the embryogenic callus was evaluated at 2,4-D concentrations ranging from 0 to 2 mg L−1 in cultures maintained in the dark. The dominant embryogenic products obtained in each treatment were used as embryogenic lines in the third phase. Thus, maturation of the somatic embryos (SEs) was analyzed using four embryogenic lines and under light vs. dark conditions. Embryogenic differentiation was also monitored histologically. Results Proliferation of the nine morphogenetic products was greater in the presence of 2,4-D, regardless of the concentration, than in the absence of auxin. Among the products, a yellow callus was invariably associated with the presence of an oblong SE and suspended cells in the 2,4-D treatments, and a brown callus with scutellar somatic embryos (scSEs) in the treatment without 2,4-D. During the maturation phase, especially the embryogenic line but also the light condition resulted in significant differences, with the highest averages of the nine morphogenetic products obtained under light conditions and the maximum concentration of auxin (YC3 embryogenic line). Only this line achieved scSE growth, under both light and dark conditions. Structurally complete coleoptilar somatic embryos (colSEs) could be anatomically confirmed only during the maturation phase. Discussion In the embryogenic line cultured with the highest auxin concentration, light exposure favored the transdifferentiation from embryogenic callus to scSE or colSE, although growth was asynchronous with respect to the three embryogenic phases. The differentiation and cellular organization of the embryos were compatible with all stages of embryogenic development in other monocotyledons. The growth of colSEs under light conditions in the YC3 embryogenic line and the structurally complete anatomic description of colSEs demonstrated that differentiation up to coleoptilar embryos could be obtained. The diversity of embryogenic products obtained in the YC3 embryogenic line opens up the opportunity to synchronize histological descriptions with the molecules associated with the somatic embryogenesis of Typha spp.

Somaclonal Variation During Picea abies and P. omorika Somatic Embryogenesis and Cryopreservation

Embryogenic cultures of plants are exposed to various stress factors bothin vitroand during cryostorage. In order to safely include the plant material obtained by somatic embryogenesis in combination with cryopreservation for breeding programs, it is necessary to monitor its genetic stability. The aim of the present study was the assessment of somaclonal variation in plant material obtained from embryogenic cultures ofPicea abies(L.) Karst. andP. omorika(Pančić) Purk. maintainedin vitroor stored in liquid nitrogen by the pregrowth-dehydration method. The analysis of genetic conformity with using microsatellite markers was performed on cotyledonary somatic embryos (CSE), germinating somatic embryos (GSE) and somatic seedlings (SS), obtained from tissues maintainedin vitroor from recovered embryogenic tissues (ETc) and CSE obtained after cryopreservation. The analysis revealed changes in the DNA of somatic embryogenesis-derived plant material of bothPiceaspp. They were found in plant material from 8 out of 10 tested embryogenic lines ofP. abiesand in 10 out of 19 embryogenic lines ofP. omorikaafterin vitroculture. Changes were also detected in plant material obtained after cryopreservation. Somaclonal variation was observed in ETc and CSE ofP. omorikaand at ETv stage ofP. abies. However, most of the changes were induced at the stage of somatic embryogenesis initiation. These results confirm the need for monitoring the genetic stability of plants obtained by somatic embryogenesis and after cryopreservation for both spruce species.