Cryopreservation of in vitro-grown apical meristems of wasabi (Wasabia japonica) by vitrification and subsequent high plant regeneration

Conservation of Green and White Ash Germplasm Using the Cryopreservation of Embryogenic Cultures

Green ash (Fraxinus pennsylvanica) and white ash (F. americana) populations are currently experiencing major declines across their native ranges in North America due to infestation by the exotic insect pest emerald ash borer (Agrilus planipennis). The development of a reliable method for the long-term storage of green and white ash germplasm in the form of embryogenic cultures using cryopreservation would be a considerable aid to ash conservation efforts. We compared recovery percentages of cryopreserved green and white ash embryogenic cultures using vitrification versus slow cooling methods. Three Plant Vitrification Solution 2 (PVS2) exposure durations (40, 60, and 80 min) for vitrification and three DMSO concentrations (5%, 10%, and 15%) for slow cooling were tested for their effects on the percentage of cultures that regrew following cryostorage. Vitrification resulted in a higher overall culture recovery percentage (91%) compared to cultures that were cryostored using the slow cooling approach (39%), and a more rapid initiation of regrowth (5 days versus 2-3 weeks) resulted. Recovery from cryostorage by cultures using the slow cooling approach varied significantly (p < 0.05) between experiments and with genotype (p < 0.05). The recovery of vitrified tissue from cryostorage did not vary with genotype, species, or PVS2 exposure duration (p > 0.05). The vitrification cryopreservation protocol provides a reliable and versatile alternative to the traditional slow cooling method, strengthening our ability to preserve valuable ash germplasm for conservation and restoration.

Insights into cryopreservation, recovery and genetic stability of medicinal plant tissues

Several plant secondary metabolites are used in the production of different pharmaceuticals based on their biological activities. The conservation and sustainable use of medicinal plants is important for the industrial production of plant-based medicines. Different cryopreservation methods are used for long-term culture preservation, which allows fast regeneration of the preserved plant material with the maintenance of its primary original traits. These methods could ensure the sustainable indefinite supply of plant tissues for theoretically unlimited periods of time, and have gained considerable attention in recent years. It is important to assess the recovery rate and the genetic stability of the recovered plant tissues after cryopreservation because cryopreservation efficiency differs among plant tissues and species. This review lays particular emphasis on the pharmaceutical applications of plant secondary metabolites that are produced through tissue culture approaches, highlighting the methods used for their cryopreservation, as well as their recovery and genetic stability.

Micropropagation of berry crops for creation of germplasm cryobanks

One of the main stages of cryopreservation of meristematic tissues in vegetative plants is a clonal micropropagation, which includes isolating the explants of the raw material in vitro and optimizing the culture medium for micropropagation. As the result of our studies, the optimal periods for in vitro micropropagation are: first - isolation of explants from initiated shoots of dormant buds (blackcurrants and raspberries) in January-March; the second - from actively growing shoots (blackcurrants and raspberries) in May-June, from the formed mustache (strawberry) in July-August. The optimal drugs for sterilization of raspberry explants are: a) 0.1% HgCl2 (6 min), then 3% H2O2 (15 min); b) chlorine-containing bleach «Domestos» in the dilution of H2O 1:9 (10 min). For blackcurrant: a) 0.1% HgCl2 (5 min) in combination with 0.1% fungicide "Topaz" (30 min); b) 0.1% HgCl2 (5 min) in combination with the treatment with KMnO4 (30 min); c) "Domestos" in the dilution of H2O 1:5 (20 min). For strawberry: a) 0.1% HgCl2 (6 min) followed by treatment with 3% H2O2 10 (min); b) 1% deochlor (7 min), 3% H2O2 (10 min); c) "Domestos" in the dilution of H2O 1:5 (8 min) with subsequent treatment 0,1% HgCl2 -7 min, then 0,20 mg/l КМnO4 - 30 min. Optimal compositions of culture media for micropropagation of blackcurrant - Murashige and Skoog (MS) medium with 0.5 mg L-1 BAP, 0.5 mg L-1 GA3, 0.1 mg L-1 IBA and 20 g L-1 glucose. For raspberry -MS medium with 0.5 mg L-1 BAP, 0.1 mg L-1 IBA, 10 mg L-1 iron chelate and 30 g L-1 sucrose. For strawberry - MS medium with 0.3 mg L-1 BAP, 0.01 mg L-1 IBA, 0.2 mg L-1 GA3, 10 mg L-1 iron chelate and 30 g L-1 sucrose. Based on these studies, the cryobank was created, which include the germplasm of in vitro meristematic tissues in 66 cultivars, hybrids and wild-growing forms of blackcurrant, raspberry and strawberry. Therefore, the aim of the research was to obtain aseptic plants, clonal micropropagation and the creation of a cryogenic collection of germplasm based on the developed technology.

In Vitro Technologies for American Chestnut (Castanea dentata (Marshall) Borkh) Conservation

American chestnut (Castanea dentata), a native species of eastern North America, is an economically important deciduous hardwood tree that has been designated as endangered in Canada. The population of American chestnut trees has dwindled significantly across Southern Ontario due to chestnut blight and many of the surviving trees continue to show blight disease symptoms. American chestnut requires efficient strategies for propagation and preservation for species recovery. The objective of this study was to develop a long-term plant conservation program using micropropagation and cryopreservation protocols. An in vitro technology using a liquid-based temporary immersion system (TIS) was developed for micropropagation of American chestnut. The highest rate of shoot multiplication was observed in cultures grown in the DKW (Driver and Kuniyuki 1984) basal medium supplemented with 2.2 µM 6-benzylaminopurine and 1.0 µM gibberellic acid. More than 95% of proliferated microshoots, about 40-50 mm in size, developed roots after 30 days of culture within bioreactor vessels containing DKW basal medium supplemented with 15 µM 3-Indolebutyric acid. Rooted plantlets transplanted to the greenhouse had a survival efficiency of 82% after one month of growth. The cryopreservation protocol for germplasm preservation was developed through droplet vitrification of shoots. Optimal regeneration of shoot tips occurred from explants precultured on stepwise concentrations of sucrose and subsequent dehydration in PVS3 for 30 min. Cryopreserved shoot tips were regenerated to whole plants using pre-optimized conditions of micropropagation. This study confirms the potential of TIS for micropropagation in ex situ conservation and reintroduction of endangered American chestnuts and possibly other woody plant species.

Vitrification Solutions for Plant Cryopreservation: Modification and Properties

Many plants cannot vitrify themselves because they lack glassy state-inducing substances and/or have high water content. Therefore, cryoprotectants are used to induce vitrification. A cryoprotectant must have at least the following primary abilities: high glass-forming property, dehydration strength on a colligative basis to dehydrate plant cells to induce the vitrification state, and must not be toxic for plants. This review introduces the compounds used for vitrification solutions (VSs), their properties indicating a modification of different plant vitrification solutions, their modifications in the compounds, and/or their concentration. An experimental comparison is listed based on the survival or regeneration rate of one particular species after using more than three different VSs or their modifications. A brief overview of various cryopreservation methods using the Plant Vitrification Solution (PVS) is also included. This review can help in alert researchers to newly introduced PVSs for plant vitrification cryoprotocols, their properties, and the choice of their modifications in the compounds and/or their concentration.

Grapevine Shoot Tip Cryopreservation and Cryotherapy: Secure Storage of Disease-Free Plants

Grapevine (Vitis spp.) is one of the most economically important temperate fruit crops. Grapevine breeding programs require access to high-quality Vitis cultivars and wild species, which may be maintained within genebanks. Shoot tip cryopreservation is a valuable technique for the safe, long-term conservation of Vitis genetic resources that complements traditional field and in vitro germplasm collections. Vitis is highly susceptible to virus infections. Virus-free plants are required as propagation material for clonally propagated germplasm, and also for the global exchange of grapevine genetic resources. Shoot tip cryotherapy, a method based on cryopreservation, has proven to be effective in eradicating viruses from infected plants, including grapevine. This comprehensive review outlines/documents the advances in Vitis shoot tip cryopreservation and cryotherapy that have resulted in healthy plants with high regrowth levels across diverse Vitis species.

Two Advanced Cryogenic Procedures for Improving Stevia rebaudiana (Bertoni) Cryopreservation

Cryopreservation is a useful tool for the long-term storage of plant genetic resources, and different cryogenic procedures have recently been developed. The present study focused on the use of the Droplet-vitrification (DV) and V cryo-plate protocol for the cryopreservation of Stevia rebaudiana in vitro-derived apical shoot tips and axillary shoot tips. A preliminary test showed that 90 and 120 min PVS2 (Plant Vitrification Solution 2) treatment significantly reduced the regrowth of the explants before immersion in liquid nitrogen (LN). For both procedures tested, the best osmoprotective condition for obtaining a higher regrowth of cryopreserved explants occurred when explants were PVS2 treated for 60 min. After direct immersion in LN, thawing and plating, the highest regrowth recorded was 80% with DV and 93% with V cryo-plate. Moreover, shoot tips proved to be a more suitable material for Stevia cryopreservation. A satisfactory vegetative regrowth was observed in the subcultures following cryopreservation by DV and V cryo-plate cryogenic procedures.

Efficient Protocol for Improving the Development of Cryopreserved Embryonic Axes of Chestnut (Castanea sativa Mill.) by Encapsulation-Vitrification

An optimized cryopreservation protocol for embryonic axes (EAs) of chestnut (Castanea sativa Mill.) has been developed based on the encapsulation–vitrification procedure. EAs of mature seeds were aseptically dissected and encapsulated in alginate beads with or without 0.3% (w/v) activated charcoal (AC). Embedded EAs were dehydrated with Plant Vitrification Solution 2 for different treatment times up to 120 min, followed by direct immersion in liquid nitrogen. Cryopreserved embryonic axes encapsulated with AC showed higher survival (70%) compared to those encapsulated without AC (50%). Sixty-four percent of embryonic axes, from synthetic seeds with AC, subsequently developed as whole plants. Plantlet regrowth was faster in AC-encapsulated EAs and showed enhanced postcryopreservation shoot and root regrowth over 2 cm after five weeks from rewarming. Results indicate that encapsulation–vitrification with activated charcoal added to the beads is an effective method for the long-term preservation of Castaneasativa embryonic axes.

Shoot Tip Cryopreservation of Lamprocapnos spectabilis (L.) Fukuhara Using Different Approaches and Evaluation of Stability on the Molecular, Biochemical, and Plant Architecture Levels

The aim of this study is to optimize and evaluate the effectiveness of vitrification, droplet-vitrification, and encapsulation-vitrification techniques in the cryopreservation of Lamprocapnos spectabilis (L.) Fukuhara ‘Gold Heart’, a popular medicinal and ornamental plant species. In vitro-derived shoot tips were used in the experiments. All three techniques were based on explant dehydration with plant vitrification solution 3 (PVS3; 50% glycerol and 50% sucrose) for 0, 30, 60, 90, 120, 150, or 180 min. The recovered microshoots were subjected to morphometric, biochemical, and molecular analyses (RAPD, ISSR, SCoT). The highest recovery level was reported with the encapsulation-vitrification protocol based on 150 min dehydration (73.1%), while the vitrification technique was the least effective (maximum 25.8% recovery). Explants cryopreserved with the encapsulation-vitrification technique produced the highest mean number of shoots (4.9); moreover, this technique was optimal in terms of rooting efficiency. The highest fresh weight of shoots, on the other hand, was found with the vitrification protocol based on a 30-min PVS3 treatment. The concentrations of chlorophyll a and b were lower in all cryopreservation-derived plants, compared to the untreated control. On the other hand, short dehydration and cryopreservation of non-encapsulated explants stimulated the synthesis of anthocyanins. A small genetic variation in 5% of all samples analyzed was detected by RAPD and ISSR marker systems. Only plants recovered from the encapsulation-vitrification protocol had no DNA sequence alternations.

Cryopreservation of shoot tips, evaluations of vegetative growth, and assessments of genetic and epigenetic changes in cryo-derived plants of Actinidia spp

A droplet-vitrification protocol was described for cryopreservation of shoot tips of kiwifruit 'Yuxiang' (Actinidia chinensis var. deliciosa). No significant differences were found in root formation and shoot growth between the in vitro-derived shoots (the control) and cryo-derived ones when cultured in vitro. No significant differences were detected in survival and vegetative growth between the in vitro-derived plants (the control) and cryo-derived ones after re-establishment in greenhouse conditions. Inter-simple sequence repeat (ISSR) and amplified fragment length polymorphism (AFLP) did not detect any polymorphic bands in the cryo-derived shoots when cultured in vitro and the cryo-derived plants after re-establishment in greenhouse conditions. These data indicate rooting ability, vegetative growth and genetic stability are maintained in the cryo-derived kiwifruit plants recovered from the droplet-vitrification cryopreservation. Methylation sensitive amplification polymorphism (MSAP) detected 12.8% and 1.6% DNA methylation in the cryo-derived shoots when cultured in vitro and the cryo-derived plants after re-established in greenhouse conditions, respectively. This droplet-vitrification was applied to five cultivars and three rootstocks belonging to A. chinensis var. deliciosa, A. chinensis var. chinensis, A. macrosperma, A. polygama and A. valvata. The highest (68.3%) and lowest (22.5%) shoot regrowth were obtained in A. macrosperma and A. chinensis var. chinensis 'Jinmi', respectively, with an average of 46.4% shoot regrowth obtained across the eight genotypes. The droplet-vitrification protocol described here can be considered the most applicable cryopreservation method so far reported for the genus Actinidia. Results reported here provide theoretical and technical supports for setting up cryo-banks of genetic resources of Actinidia spp.

A New Perspective on Cryotherapy: Pathogen Elimination Using Plant Shoot Apical Meristem via Cryogenic Techniques

Plant pathogens cause different diseases on crops and industrial plant species that result in economic losses. Pathogen-free plant material has usually been obtained by traditional procedures such as meristem culture, thermotherapy, and chemotherapy. However, there are many limitations of these procedures such as mechanical challenges of meristem excision and low regeneration rate, low resistance to high temperatures, phytotoxicity, and mutagenic effects of the chemicals used in the procedures. Cryotherapy is a newly developed biotechnological tool that has been very effective in virus elimination from economically important plant species. This tool has overcome the abovementioned limitations. This chapter aims to highlight the importance of the cryogenic procedures (vitrification, encapsulation-vitrification, droplet vitrification, two-step freezing, dehydration, encapsulation-dehydration) in order to generate virus-free germplasm.

Cryopreservation of Shoot Tips of Elite Cultivars of Cannabis sativa L. by Droplet Vitrification

Cannabis sativa L. (marijuana or hemp) is recognized worldwide for its psychoactive properties as well as for fiber production. This study focused on the evaluation of 3 droplet vitrification protocols for long-term conservation of shoot tips in liquid nitrogen (LN). Shoot tips (∼0.5 mm) were excised from 3- to 4-week-old in vitro-grown shoots of 3 cultivars (MX, VI-20, and B-5: high tetrahydrocannabinol [THC], high cannabidiol [CBD], and intermediate THC∼CBD, respectively) and pretreated on 5% dimethyl sulfoxide agar plates for 48 h. The shoot tips were then vitrified in LN using 3 separate cryoprotectant (plant vitrification solutions [PVS] #2, #3, and #4) droplets on an aluminum cryoplate. There was no significant difference between the regrowth of cryopreserved shoot tips exposed to PVS2 for 15 and 20 min, but regrowth of all 3 cultivars significantly declined after 20 min of exposure. Exposure duration of 15 min was adapted for subsequent experiments. Regrowth of cryopreserved MX was significantly higher with PVS2 (63%) than with PVS3 and PVS4 (≤5%). Regrowth of cryopreserved VI-20 was highest with PVS2 (57%) and significantly higher than with PVS3 and PVS4 (≤25%). The regrowth of cryopreserved shoot tips of B-5 was significantly different between all 3 protocols with PVS2 > PVS4 > PVS3. Both PVS2 and PVS4 produced regrowth above 55%, while regrowth with PVS3 was significantly lower (31%). These results indicate that 15–20 min of exposure to PVS2 are most suitable for cryopreservation of these varieties. This is the first report on protocol development for the cryopreservation of organized tissues of C. sativa L. for germplasm conservation.

Cryopreservation of banana's cv Grand Naine in vitro rhizomes

The preservation of banana genetic material is usually performed through seedlings. However, most banana cultivars do not produce seed and are propagated vegetatively. Therefore, cryopreservation is a feasible technique that allows the preservation of banana genotypes indefinitely. For the success of cryopreservation protocols, the selection of cryoprotectants and pre-freezing techniques are important factor. Therefore, the objective of this study was to verify the effects of different cryoprotectants with and without 1% phloroglucinol and pre-cooling periods on the development of a protocol for cryopreservation of in vitro rhizomes ofMusa accuminata(AAA) cv Grand Naine banana. The addition of 1% phloroglucinol to the cryoprotective solutions, such as PVS2 enhanced recovery of cryopreserved banana rhizomes. In addition, pre-cooling of explants in ice for 3 hours in PVS2 + 1% of phloroglucinol allowed efficient cryopreservation of banana rhizomes, followed by successful recovery and regeneration of in vitro shoots of banana cv Grand Naine.

Cryopreservation of blueberry shoot tips derived from in vitro and current shoots using D cryo-plate technique

Cryopreservation is an important tool for long-term storage of plant germplasm that is currently used for plant germplasm storage at many institutes worldwide. Recently, novel cryogenic procedures (V and D cryo-plate methods) have been developed. In this study, the most suitable conditions for preserving blueberry shoot tips derived from in vitro and current shoots using the D cryo-plate method were investigated. The D cryo-plate method has advantages such as higher regrowth after cryopreservation and a more user-friendly process compared with conventional cryogenic methods. The optimum duration of desiccation for regrowth of shoot tips from each shoot type was 1 h. To induce dehydration tolerance for the shoot tips, the effects of two cryoprotection treatments (sucrose preculture and loading solution [LS] treatment) on shoot regrowth after cryopreservation were investigated. The combined effect of both treatments significantly increased percentage regrowth (approximately 90%). No regrowth of shoot tips was attained without the two treatments. Thus, preculture and LS treatment were effective to induce dehydration tolerance for cryopreservation of blueberry shoot tips. The optimized conditions for blueberry shoot tips using the D cryo-plate technique were: preculture with 0.3 M sucrose for 1 day, LS treatment (2 M glycerol +0.4-1.0 M sucrose) for 30 min, and air dehydration for 1 h. This optimized procedure was applied to additional blueberry cultivars shoot tips derived from in vitro shoots (regrowth 46.7-100%) and current shoots (regrowth 17.2-62.7%). Furthermore, in vitro shoot tips were suitable material for the D cryo-plate method in blueberry.

Cryopreservation of Date Palm Pro-Embryonic Masses Using the D Cryo-plate Technique

In this chapter, we describe a cryopreservation (liquid nitrogen, -196 °C) protocol developed for long-term storage of date palm pro-embryonic masses (PEMs), which uses the recently established D cryo-plate technique. Clumps of PEMs (3-5 mm in size) were dissected from PEM cultures and placed on pretreatment medium containing 171 g/L sucrose for 3 days. Clumps were placed in the wells of aluminum cryo-plates in which they were made to adhere using droplets of 3% calcium alginate. PEMs were treated for 20 min with a loading solution containing 184 g/L glycerol and 136.8 g/L sucrose. They were then dehydrated for 90-120 min in the air current of a laminar airflow cabinet and immersed directly in liquid nitrogen. For rewarming, the cryo-plates holding the PEMs were immersed for 15 min in an unloading solution containing 410.4 g/L sucrose. The PEMs were then detached from the cryo-plates, placed for 3 days in the dark on posttreatment medium containing 102.6 g/L sucrose, and transferred on recovery medium under light conditions. Using this protocol, 74.6 and 95.8% recovery were achieved with the PEMs of the two cultivars tested, Sukkari and Sultany.

Ascorbate Peroxidase Activity of Aranda Broga Blue Orchid Protocorm-like Bodies (PLBs) In Response to PVS2 Cryopreservation Method

Throughout the cryopreservation process, plants were exposed to a series of abiotic stresses such as desiccation and osmotic pressure due to highly concentrated vitrification solution. Abiotic stress stimulates the production of reactive oxygen species (ROS) which include hydrogen peroxide, superoxide radicals, and singlet oxygen. Higher production of ROS may lead to oxidative stress which contributes to the major injuries in cryopreserved explants. Antioxidant enzymes in plant such as ascorbate peroxidase (APX) can protect plants from cell damage by scavenging the free radicals. This study was determined based on APX enzyme activity of Aranda Broga Blue orchid's protocorm-like bodies (PLBs) in response to PVS2 (Plant Vitrification Solution 2) cryopreservation treatments at different stages. PLBs that were precultured at 0.25 M sucrose for 3 days were subjected to vitrification cryopreservation method. Results obtained showed that the highest APX activity was achieved at PVS2 cryoprotectant treatment prior liquid nitrogen (LN) storage. This phenomenon indicating that accumulation of osmotic and dehydrating stress throughout the cryopreservation treatment resulted in oxidative burst which in turn leads to higher APX activity in order to control the excess production of ROS. To conclude, PVS2 treatment was revealed as the most detrimental step throughout cryopreservation treatment. Thus, this research also suggested that exogenous antioxidant such as ascorbic acid can be added throughout cryopreservation procedure especially at PVS2 treatment in the future experiments to aid in regrowth of cryopreserved explants by reducing oxidative stress.

Cryopreservation for preservation of potato genetic resources

Cryopreservation is becoming a very important tool for the long-term storage of plant genetic resources and efficient cryopreservation protocols have been developed for a large number of plant species. Practical procedures, developed using in vitro tissue culture, can be a simple and reliable preservation option of potato genetic resources rather than maintaining by vegetative propagation in genebanks due their allogamous nature. Cryopreserved materials insure a long-term backup of field collections against loss of plant germplasm. Occurrence of genetic variation, in tissue culture cells during prolonged subcultures, can be avoided with suitable cryopreservation protocols that provide high regrowth, leading and facilitating a systematic and strategic cryo-banking of plant genetic resources. Cryopreservation protocols for potato reviewed here, can efficiently complement field and in vitro conservation, providing for preservation of genotypes difficult to preserve by other methods, wild types and other species decided as priority collections.

Improved cryopreservation of oil palm (Elaeis guineensis Jacq.) polyembryoids using droplet vitrification approach and assessment of genetic fidelity

In the present study, polyembryoids of oil palm (Elaeis guineensis Jacq.) were cryopreserved with successful revival of 68 % for the first time using the droplet vitrification technique. Excised polyembryoids (3-5-mm diameter) from 3-month-old in vitro cultures were pre-cultured for 12 h in liquid Murashige and Skoog medium supplemented with 0.5 M sucrose. The polyembryoids were osmoprotected in loading solution [10% (w/v) dimethyl sulphoxide (DMSO) plus 0.7 M sucrose] for 30 min at room temperature and then placed on aluminium strips where they were individually drenched in chilled droplets of vitrification solution (PVS2) [30% (w/v) glycerol plus 15% (w/v) ethylene glycol (EG) plus 15% (w/v) DMSO plus 0.4 M sucrose] for 10 min. The aluminium strips were enclosed in cryovials which were then plunged quickly into liquid nitrogen and kept there for 1 h. The polyembryoids were then thawed and unloaded (using 1.2 M sucrose solution) with subsequent transfer to regeneration medium and stored in zero irradiance. Following for 10 days of storage, polyembryoids were cultured under 16 h photoperiod of 50 μmol m(-2) s(-1) photosynthetic photon flux density, at 23 ± 1 °C. Post-thaw growth recovery of 68% was recorded within 2 weeks of culture, and new shoot development was observed at 4 weeks of growth. Scanning electron microscopy revealed that successful regeneration of cryopreserved polyembryoids was related to maintenance of cellular integrity, presumably through PVS2 exposure for 10 min. The present study demonstrated that cryopreservation by droplet vitrification enhanced the regeneration percentages of oil palm in comparison with the conventional vitrification method previously reported.

Effect of the successive steps of a cryopreservation protocol on the structural integrity of Rubia akane Nakai hairy roots

In this work, we studied the impact of the successive steps of the droplet-vitrification protocol technique employed for cryopreservation of Rubia akane hairy roots on the features of cortical, pericycle and endoderm cells of apical and central root segments, using histology techniques and combining qualitative and quantitative observations. In apical segments, plasmolysis (22-71 %, depending on cell type) was observed only after the loading treatment and did not increase after the following steps of the protocol. By contrast, in central segments, plasmolysis (39-45 %) was already observed after the sucrose pretreatment; it increased to 54-68 %, depending on cell type, after the loading treatment, but no further changes were noted after treatment with the vitrification solution. After liquid nitrogen exposure and unloading treatment, deplasmolysis was more rapid in apical segments, with cortical and pericycle cells having retrieved their original features. In central segments, only cortical cells had retrieved their original features and endoderm and pericycle cells were still highly plasmolysed. Nuclei were more strongly impacted by the cryopreservation protocol in central segments, where they displayed a highly condensed nucleoplasm from the loading treatment onwards and had not retrieved their original aspect after the unloading treatment. By contrast, nuclei had a much less condensed nucleoplasm in cells of apical segments, and they had retrieved their original aspect after the unloading treatment.

Cryopreservation the seeds of a Taiwanese terrestrial orchid, Bletilla formosana (Hayata) Schltr. by vitrification

BACKGROUND

The cryopreservation of orchid seeds is an important conservation method, studies of the effects of cryopreservation on the seeds of wild orchids are scant. This investigation was to establish a method for the vitrification and cryopreservation of seeds of B. formosana that may be suitable for the long term storage of Taiwan native orchid germplasm for conservation purposes.

RESULTS

The germination rate and morphological stability of seeds from spontaneous-dehiscent capsules of Bletilla formosana (Hayata) Schltr. were evaluated after cryopreservation by vitrification. The germination rates of cryopreserved seeds varied according to immersion time and the vitrification method used. Seeds that were dehydrated by immersion in loading solution (LS; 2.0 M glycerol, 0.4 M sucrose) for 10 min to 30 min then transferred to plant vitrification solution 2 (PVS2) for 30 min prior to freezing in liquid nitrogen (LN) showed significantly higher germination rates than seeds immersed in PVS2 only. The optimal immersion times were 10 min for LS and 30 min for PVS2, resulting in an in vitro germination rate of 91%. Germination was not observed for cryopreserved seeds that were dehydrated by immersion in LS only. Seed viabilities and germination rates did not vary significantly for cryostorage times from 10 minutes to 1 year.

CONCLUSIONS

This study improve, an efficient protocol was established that maintained seed viability and enhanced the germination rates of seeds, compared with previously described cryopreservation methods, and the germinated seeds showed normal morphology of both vegetative and reproductive organs.

Cryopreservation of grapevine (Vitis vinifera L.) in vitro shoot tips

In this work, we compared the efficiency of encapsulation-dehydration and droplet-vitrification techniques for cryopreserving grapevine (Vitis vinifera L.) cv. Portan shoot tips. Recovery of cryopreserved samples was achieved with both techniques; however, droplet-vitrification, which was used for the first time with grapevine shoot tips, produced higher regrowth. With encapsulationdehydration, encapsulated shoot tips were precultured in liquid medium with progressively increasing sucrose concentrations over a 2-day period (12 h in medium with 0.25, 0.5, 0.75 and 1.0 M sucrose), then dehydrated to 22.28% moisture content (fresh weight). After liquid nitrogen exposure 37.1% regrowth was achieved using 1 mm-long shoot tips and only 16.0% with 2 mm-long shoot tips. With droplet-vitrification, 50% regrowth was obtained following treatment of shoot tips with a loading solution containing 2 M glycerol + 0.4 M sucrose for 20 min, dehydration with half-strength PVS2 vitrification solution (30% (w/v) glycerol, 15% (w/v) ethylene glycol, 15% dimethylsulfoxide and 0.4 M sucrose in basal medium) at room temperature, then with full strength PVS2 solution at 0°C for 50 min before direct immersion in liquid nitrogen. No regrowth was achieved after cryopreservation when shoot tips were dehydrated with PVS3 vitrification solution (50% (w/v) glycerol and 50% (w/v) sucrose in basal medium).

Micropropagation and cryopreservation of garlic (Allium sativum L.)

Garlic (Allium sativum L.) is a very important medicinal and spice plant. It is conventionally propagated by daughter bulbs ("cloves") and bulbils from the flower head. Micropropagation is used for speeding up the vegetative propagation mainly using the advantage to produce higher numbers of healthy plants free of viruses, which have higher yield than infected material. Using primary explants from bulbs and/or bulbils (shoot tips) or unripe inflorescence bases, in vitro cultures are initiated on MS-based media containing auxins, e.g., naphthalene acetic acid, and cytokinins, e.g., 6-γ-γ-(dimethylallylaminopurine) (2iP). Rooting is accompanying leaf formation. It does not need special culture phases. The main micropropagation methods rely on growth of already formed meristems. Long-term storage of micropropagated material, cryopreservation, is well-developed to maintain germplasm. The main method is vitrification using the cryoprotectant mixture PVS3.

Glassy state and cryopreservation of mint shoot tips

Vitrification refers to the physical process by which a liquid supercools to very low temperatures and finally solidifies into a metastable glass, without undergoing crystallization at a practical cooling rate. Thus, vitrification is an effective freeze-avoidance mechanism and living tissue cryopreservation is, in most cases, relying on it. As a glass is exceedingly viscous and stops all chemical reactions that require molecular diffusion, its formation leads to metabolic inactivity and stability over time. To investigate glassy state in cryopreserved plant material, mint shoot tips were submitted to the different stages of a frequently used cryopreservation protocol (droplet-vitrification) and evaluated for water content reduction and sucrose content, as determined by ion chromatography, frozen water fraction and glass transitions occurrence by differential scanning calorimetry, and investigated by low-temperature scanning electron microscopy, as a way to ascertain if their cellular content was vitrified. Results show how tissues at intermediate treatment steps develop ice crystals during liquid nitrogen cooling, while specimens whose treatment was completed become vitrified, with no evidence of ice formation. The agreement between calorimetric and microscopic observations was perfect. Besides finding a higher sucrose concentration in tissues at the more advanced protocol steps, this level was also higher in plants precultured at 25/-1°C than in plants cultivated at 25°C.

Review: role of carbon sources for in vitro plant growth and development

In vitro plant cells, tissues and organ cultures are not fully autotrophic establishing a need for carbohydrates in culture media to maintain the osmotic potential, as well as to serve as energy and carbon sources for developmental processes including shoot proliferation, root induction as well as emission, embryogenesis and organogenesis, which are highly energy demanding developmental processes in plant biology. A variety of carbon sources (both reducing and non-reducing) are used in culture media depending upon genotypes and specific stages of growth. However, sucrose is most widely used as a major transport-sugar in the phloem sap of many plants. In micropropagation systems, morphogenetic potential of plant tissues can greatly be manipulated by varying type and concentration of carbon sources. The present article reviews the past and current findings on carbon sources and their sustainable utilization for in vitro plant tissue culture to achieve better growth rate and development.

Cryopreservation of embryogenic cell suspensions by encapsulation-vitrification and encapsulation-dehydration

Encapsulation-vitrification and encapsulation-dehydration are two newly developed techniques for cryopreservation of embryogenic cell suspensions. Here, we describe the two protocols using grapevine (Vitis) as a model plant. Cell suspensions at the exponential growth stage cultured in a cell suspension maintenance medium are encapsulated to form beads, each being about 4 mm in diameter and containing 25% cells. In the encapsulation-vitrification procedure, the beads are stepwise precultured in increasing concentrations of sucrose medium up to 0.75 M, with 1 day for each concentration. The precultured beads are treated with a loading solution for 60 min and then dehydrated with plant vitrification solution 2 at 0°C for 270 min before a direct immersion in liquid nitrogen. Following cryostorage, the beads are rapidly rewarmed at 40°C for 3 min and then unloaded with 1 M sucrose solution for 30 min. In the encapsulation-dehydration procedure, the beads are precultured in increasing concentrations of sucrose medium up to 1 M, with 1 day for each concentration, and then maintained on 1 M sucrose medium for 3 days. The precultured beads are dehydrated for 6 h under a sterile air flow, prior to rapid freezing in liquid nitrogen. The freezing and rewarming procedures are the same as used in the encapsulation-vitrification technique. The unloaded beads from encapsulation-vitrification and rewarmed beads from encapsulation-dehydration are postcultured on a recovery medium for 3 days at 25°C in the dark for survival. Surviving cells are transferred to a regrowth medium to induce cell proliferation. Embryogenic cell suspensions are reestablished by suspending the cells in a cell suspension maintenance medium maintained on a gyratory shaker at 25°C in the dark. For plant regeneration, surviving cells are transferred from the recovery medium to an embryo maturation medium and maintained at 25°C under light conditions. Embryos at the torpedo stage are cultured on a rooting medium until whole plantlet regenerates.

Cryogenic technologies for the long-term storage of Citrus germplasm

With its beautiful trees, Citrus species have long been valued by humanity. The tasteful fruits, extensively used for nutrition, are also good for health due to the high content in vitamins, minerals, and dietary fibers. Like majority of the woody fruit plants, Citrus germplasm is conserved mainly as field collections in clonal orchards. However, such a traditional approach presents several difficulties, among which are the high cost, manual labor, and extensive land required to maintain the collections, as well as the necessity of a careful protection of plants from diseases and extreme environmental conditions. As many species in the genus have seeds recalcitrant to desiccation, conservation in seed banks is also inadequate. On the other hand, cryopreservation, i.e., the storage of specimens at ultra-low temperatures (usually in liquid nitrogen, at -196°C) where reactions within the cells are minimized, presents a unique alternative for the safe storage of such germplasm. The present contribution outlines the cryopreservation techniques applied to seeds, zygotic and somatic embryos, embryogenic callus cultures of Citrus spp. and provides sample protocols to be used for Citrus conservation.

Vitrification, a complementary cryopreservation method for Betula pendula Roth

Cryopreservation--the storage of plant germplasm in liquid nitrogen--provides a modern tool for the conservation of forest genetic resources. It is especially applicable for species in which their micropropagation can be initiated from mature tree buds, e.g., silver birch (Betula pendula Roth), thus enabling the conservation of specific genotypes: endangered elite trees and trees expressing rare, valuable or interesting characteristics. The aim of the present study was to develop a vitrification protocol applicable for the cryostorage of silver birch that avoids the use of expensive sophisticated freezers. The average recovery of vitrified axillary silver birch buds was 71% using a protocol that started with four-week cold hardening of bud-bearing in vitro donor shoots on modified medium under short day conditions. After cold hardening, the excised axillary buds were precultivated on medium containing 0.7 M sucrose for 24 h under the same conditions as during the cold hardening period. Following preculture, the buds were treated with loading solution containing 2M glycerol and 0.4 M sucrose for 20 min at room temperature. Finally, the buds were dehydrated with PVS2 cryoprotectant for 120 min followed by direct immersion in liquid nitrogen. According to the morphology and the RAPD profiles of regenerated plants in the greenhouse, the genetic fidelity of the vitrified birch material seems to have remained unchanged.

Cryopreservation of in vitro-grown shoot tips of raspberry (Rubus idaeus L.) by encapsulation-vitrification and encapsulation-dehydration

The first efficient cryopreservation procedure for in vitro-grown shoot tips of raspberry (Rubus idaeus L.) has been developed based on encapsulation-vitrification (EnVi) and encapsulation-dehydration (EnDe). EnVi resulted in higher survival (85%) and regrowth (75%) of cryopreserved shoot tips than EnDe (65 and 50%, respectively). In both cryogenic procedures, shoots regenerated from cryopreserved shoot tips without intermediary callus formation. Histological studies showed that a much larger number of meristematic cells survived following EnVi than EnDe. The EnVi procedure was applied to seven raspberry genotypes with an average survival and regrowth of 71 and 68%, respectively. Regenerated plants showed normal morphology. Results here indicate EnVi as a simple and efficient method for long-term preservation of R. idaeus germplasm.

Cryopreservation of invitro-grown shoot tips of taro (Colocasia esculenta (L.) Schott) by vitrification. 1. Investigation of basic conditions of the vitrification procedure

Invitro-grown shoot tips of taro (Colocasia esculenta (L.) Schott.) were successfully cryopreserved by vitrification. Excised shoot tips precultured on solidified MS supplemented with 0.3M sucrose and maintained under a 16 h phtoperiod at 25°C for 16 h were loaded with a mixture of 2M glycerol plus 0.4M sucrose for 20 min at 25°C. The shoot tips were then sufficiently dehydrated with a highly concentrated vitrification solution (PVS2) for 20 min at 25°C prior to immersion into liquid nitrogen. Successfully vitrified and warmed shoot tips resumed growth within 7 days and developed shoots directly without intermediate callus formation. The average rate of shoot recovery amounted to around 80%, and the vitrification protocol appeared to be very promising for the cryopreservation of taro germplasm.

Strategies for "minimal growth maintenance" of cell cultures: a perspective on management for extended duration experimentation in the microgravity environment of a Space station

How cells manage without gravity and how they change in the absence of gravity are basic questions that only prolonged life on a Space station will enable us to answer. We know from investigations carried out on various kinds of Space vehicles and stations that profound physiological effects can and often to occur. We need to know more of the basic biochemistry and biophysics both of cells and of whole organisms in conditions of reduced gravity. The unique environment of Space affords plant scientists an unusual opportunity to carry out experiments in microgravity, but some major challenges must be faced before this can be done with confidence. Various laboratory activities that are routine on Earth take on special significance and offer problems that need imaginative resolution before even a relatively simple experiment can be reliably executed on a Space station. For example, scientists might wish to investigate whether adaptive or other changes that have occurred in the environment of Space are retained after return to Earth-normal conditions. Investigators seeking to carry out experiments in the low-gravity environment of Space using cultured cells will need to solve the problem of keeping cultures quiescent for protracted periods before an experiment is initiated, after periodic sampling is carried out, and after the experiment is completed. This review gives an evaluation of a range of strategies that can enable one to manipulate cell physiology and curtail growth dramatically toward this end. These strategies include cryopreservation, chilling, reduced oxygen, gel entrapment strategies, osmotic adjustment, nutrient starvation, pH manipulation, and the use of mitotic inhibitors and growth-retarding chemicals. Cells not only need to be rendered quiescent for protracted periods but they also must be recoverable and further grown if it is so desired. Elaboration of satisfactory procedures for management of cells and tissues at "near zero or minimal growth" will have great value and practical consequences for experimentation on Earth as well as in Space. All of the parameters and conditions and procedural details needed to meet all the specific objectives will be the basis of the design and fabrication of cell culture units for use in the Space environment. It is expected that this will be an evolutionary process.