Cryopreservation of in vitro-grown shoot-tips of tropical taro (Colocasia esculenta var. esculenta) by vitrification

In vitro shoot-tips of three cultivars of tropical taro (Colocasia esculenta var. esculenta (L.) Schott) were successfully cryopreserved by vitrification. Different conditioning treatments were required for each of the cultivars, while the vitrification protocol was constant for all. For the cultivars E399 and CPUK, shoot-tips from three-month-old in vitro plants grown on solidified MS were preconditioned on MS with 0.3 M sucrose in the dark for 16 h at 25 degree C. For the cultivar TNS, donor plants were preconditioned on solid MS with 90 g per liter sucrose for seven weeks before cryopreservation. For vitrification, the shoot-tips were loaded with a solution of 2 M glycerol plus 0.4 M sucrose for 20 min at 25 degree C, dehydrated with PVS2 for 12 min at 25 degree C and plunged in liquid nitrogen. Vials were warmed by rapid shaking in a water bath at 40 degree C for 1 min 30. Shoot-tips were rehydrated in liquid MS with 1.2 M sucrose for 15 min at 25 degree C then plated on recovery medium. Shoot-tips resumed growth within a week and developed into plantlets six to eight weeks later without any callus formation. The best mean recoveries for the three cultivars were 21, 29 and 30 percent for E399, CPUK and TNS, respectively. This protocol was evaluated with five other taro cultivars with no success. However, this study has shown that vitrification has potential for cryopreserving tropical taro.     

Cryopreservation of chayote (Sechium edule JACQ. SW.) zygotic embryos and shoot-tips from in vitro plantlets

This paper presents the development of cryopreservation protocols for zygotic embryos and apices of chayote (Sechium edule Jacq. Sw.), a tropical plant species with recalcitrant seeds. Zygotic embryos of two cultivars, Ccocro negro (CN) and Claudio (Cl) could withstand cryopreservation, with survival percentages of 10 and 30 %, after desiccation to 23 and 19 % moisture content (fresh weight basis), respectively. Apices sampled on in vitro plantlets of cultivars Cl, 13 and JM were successfully cryopreserved using a vitrification technique. Optimal conditions included the culture of mother-plants for 22 days on medium containing 0.3 M sucrose, culture of excised apices on the same medium for 1 day, loading of apices for 20 min with 2M glycerol + 0.4M glycerol, treatment with a series of diluted PVS2 solution (60 % PVS2 followed by 80 % PVS2 solution for 15 min (cultivar Cocoro Blanco [CB]) or 30 min (cultivars CN and Cl) at each concentration), rapid freezing and thawing, washing of shoot-tips with a 1.2 M sucrose solution, followed by recovery on media with progressively decreasing sucrose concentrations until the standard concentration of 0.1 M was reached. The highest survival percentages achieved ranged between 17 and 38 %, depending on the cultivar.     

Importance of explant size and origin and of preconditioning treatments for cryopreservation of garlic shoot apices by vitrification

This paper investigates the effect of the origin and size of the explants employed and of the preconditioning (cold acclimation, preculture) and loading treatments on survival and regeneration of cryopreserved garlic shoot apices using vitrification with the PVS3 vitrification solution. Both the origin and size of explants had a significant effect on regeneration of cryopreserved apices. Higher regeneration was generally observed with apices excised from bulbs and bulbils, followed by cloves, and those originated from larger propagules regrew more rapidly. Smaller apices (1.5 or 3.0 mm in diameter) displayed higher regeneration than large ones (4.5 mm in diameter). Cold acclimation at 5 degree C of apices before freezing had no positive effect on regeneration after cryopreservation. Preculture of apices at 10 or 23 degree C for more than 3 days had a detrimental effect on regeneration. The optimal sucrose concentration in the preculture medium was 0.3-0.5 M. Loading apices for 30 or 60 min at 23 degree C in medium containing 2 M glycerol + 0.4 M sucrose or 1 M glycerol + 0.8 M sucrose had no effect on regeneration after cryopreservation, in comparison with apices cryopreserved without loading treatment. Under optimal conditions, regeneration of cryopreserved apices sampled from large cloves was above 90 percent.     

Cryopreservation of coconut (Cocos nucifera L.) zygotic embryos by vitrification

The present study investigates the effect of preculture conditions, vitrification and unloading solutions on survival and regeneration of coconut zygotic embryos after cryopreservation. Among the seven plant vitrification solutions tested, PVS3 was found to be the most effective for regeneration of cryopreserved embryos. The optimal protocol involved preculture of embryos for 3 days on medium with 0.6 M sucrose, PVS3 treatment for 16 h, rapid cooling and rewarming and unloading in 1.2 M sucrose liquid medium for 1.5 h. Under these conditions, 70-80 survival (corresponding to size enlargement and weight gain) was observed with cryopreserved embryos and 20-25 percent of the plants regenerated (showing normal shoot and root growth) from cryopreserved embryos were established in pots.     

Cryopreservation of in vitro grown shoots of ginger (Zingiber officinale Rosc.)

An efficient cryopreservation technique for in vitro grown shoots of ginger (Zingiber officinale Rosc) was developed based on encapsulation dehydration, encapsulation vitrification and vitrification procedures. Pregrowth and serial preculture were needed to obtain the best regrowth for all techniques. The vitrification procedure resulted in higher regrowth (80%) when compared to encapsulation vitrification (66%) and encapsulation dehydration (41%). In the vitrification procedure shoots were: precultured in liquid Murashige-Skoog medium containing 0.3 M sucrose for 3 days; cryoprotected with a mixture of 5% DMSO and 5% glycerol for 20 min at room temperature; osmoprotected with a mixture of 2 M glycerol and 0.4 m sucrose for 20 min at 25 degrees C; before being dehydrated with a highly concentrated vitrification solution (PVS2) for 40 min at 25 degrees C. The dehydrated shoots were transferred to 2 ml cryotubes, suspended in 1 ml PVS2 and plunged directly into liquid nitrogen. In all the three cryopreservation procedures tested, shoots grew from cryopreserved shoot tips without intermediary callus formation. The genetic stability of cryopreserved ginger shoot buds were confirmed using ISSR and RAPD profiling.     

Cryopreservation of garlic bulbil primordia by the droplet-vitrification procedure

The droplet-vitrification protocol, a combination of droplet-freezing and solution-based vitrification was applied for cryopreserving garlic bulbil primordia. The highest survival and regeneration percentages of cryopreserved primordia (90.1 to 95.0 percent and 82.7 to 85.0 percent, respectively) were achieved after preculture for 2-4 days at 10 degree C on solid medium with 0.1 - 0.3 M sucrose, loading for 50 minutes in liquid medium with 2 M glycerol + 0.5 M sucrose, dehydration with PVS3 vitrification solution for 90-150 min, cooling primordia in 5 microl droplets of PVS3 vitrification solution placed on aluminum foil strips by dipping these strips in liquid nitrogen, warming them by plunging the foil strips into pre-heated (40 degree C) 0.8 M sucrose solution for 30 s and further incubation in the same solution for 30 minutes. The optimized droplet-vitrification protocol was successfully applied to bulbil primordia of five garlic varieties originating from various countries and to immature bulbils of two vegetatively propagated Allium species, with regeneration percentages ranging between 77.4 - 95.4 percent.     

Improved cryopreservation of chrysanthemum (Chrysanthemum morifolium) using droplet-vitrification

A droplet-vitrification protocol has been established for cryopreserving Chrysanthemum morifolium cv. Peak using axillary shoot tips and apical shoots of in vitro plants. In the optimized procedure, explants were submitted to a step-wise preculture in liquid sucrose-enriched medium (0.3, 0.5 and 0.7 M for 31,17 and 7 h, respectively). Precultured explants were treated for 40 min with C4 loading solution comprising (w/v) 17.5 percent glycerol + 17.5 percent sucrose, then dehydrated with PVS3 vitrification solution (w/v, 50 percent glycerol + 50 percent sucrose) for 60 min (axillary shoot tips) or 90 min (apical shoots). Explants were cryopreserved by direct immersion in liquid nitrogen in minute drops of PVS3 attached to aluminum foil strips. The optimal age of donor plants was 4-5.5 weeks for apical shoots and 7 weeks for axillary shoot tips, producing post-cryopreservation regeneration percentages of 81.9 percent and 84.9 percernt, respectively. Plants regenerated from cryopreserved samples showed no phenotypical abnormalities and similar profiles of relative DNA content were recorded for control and cryopreserved plants. Our results suggest that the modified droplet-vitrification protocol described in this paper is highly effective and may prove user-friendlier than the cryopreservation protocols already published for chrysanthemum.     

Cryopreservation of sugarcane somatic embryos

In this paper, we compared three vitrification-based cryopreservation techniques, viz. vitrification, encapsulation-vitrification and droplet-vitrification for cryopreserving sugarcane somatic embryos. Viability of somatic embryos was evaluated by measuring electrolyte leakage and by regrowth on recovery medium. Droplet-vitrification was the most efficient technique. Optimal conditions included loading with a solution containing 1.5 M glycerol and 0.3 M sucrose for 30 min at 25 degree C, treatment with the PVS2 solution for 20-40 min at 0 degree C followed by rapid immersion in liquid nitrogen of clumps of somatic embryos placed in microdroplets of cryoprotectant solution. Under such conditions, viability of cryopreserved somatic embryos reached 55 percent.     

Cryopreservation of seeds of a Thai orchid (Doritis pulcherrima lindl. ) by vitrification

Seeds from selfing of a Thai orchid (Doritis pulcherrima Lindl.) were successfully cryopreserved in liquid nitrogen (LN) using the vitrification method. Seeds from 3-month-old pods were sufficiently dehydrated in 2 ml cryotubes filled with highly concentrated vitrification solution (PVS2) at 25 +/- 2 degree C for 50 min. The seeds were then rapidly plunged into LN. After rapid warming, the PVS2 solution was replaced with 0.5 ml of 1.2M sucrose in modified Vacin and Went (1949) (VW) solution and kept at 25 +/- 2 degree C for 20 min prior to transfer on VW agar medium. About 62% of cryopreserved seeds treated with PVS2 solution were able to develop into normal seedlings while without that treatment there was no survival. This vitrification protocol appears to be a promising technique for the cryopreservation of some Thai orchid germplasm     

Cryopreservation of potato cultivated varieties and wild species: critical factors in droplet vitrification

The applicability of cryopreservation protocols to a broad range of genotypes is a key issue for genebanks. We tried to identify the critical factors causing differences in survival of cryopreserved shoot tips using potato varieties coming from cultivated and wild species. The droplet-vitrification method, a combination of droplet-freezing and solution-based vitrification, was selected from several protocols. High survival after freezing was observed after dehydration with PVS2 for 20 min, cooling shoot tips placed in a droplet of PVS2 solution on aluminum foil strips by immersing the foil strips in liquid nitrogen, warming them by plunging the foil strips into a 0.8 M sucrose solution (at 40 degrees C) for 30 s and unloading in 0.8 M sucrose for 30 min. This optimized protocol was successfully applied to 12 accessions with survival ranging between 64.0 and 94.4%.     

Cryopreservation of Citrus madurensis embryonic axes by vitrification: importance of loading and treatment with vitrification solution

This paper investigates the importance of loading and treatment with a vitrification solution on the survival of Citrus madurensis embryonic axes cryopreserved using a vitrification protocol. Among the seven different loading solutions tested, the solution containing 2 M glycerol + 0.4 M sucrose was the most efficient. Of the six vitrification solutions tested, the PVS2 vitrification solution, applied for 20 min at 25 degree C or for 60 min at 0 degree C, ensured the highest survival. A three-step vitrification protocol, involving the treatment of embryonic axes at 0 degree C with half strength PVS2 solution for 20 min then with full strength PVS2 for an additional 40 min was more efficient than a two-step protocol that involved treatment of axes directly with full strength PVS2 solution for 60 min. After rapid immersion in liquid nitrogen, rapid rewarming, unloading in a 1.2 M sucrose solution for 20 min, culture on solid medium with 0.3 M sucrose for 1 day and growth recovery for 4 weeks on standard medium, survival of C. madurensis embryonic axes reached 85 % following the three-step process, compared with 70 % for the two-step process.     

Cryopreservation of in vitro shoot tips of Dioscorea deltoidea Wall., an endangered medicinal plant: effect of cryogenic procedure and storage duration

In vitro shoot tips of Dioscorea deltoidea Wall., an endangered medicinal plant, were successfully cryopreserved using the vitrification and the encapsulation-dehydration techniques with subsequent high frequency plant regeneration. Using vitrification, post-liquid nitrogen (LN) shoot regeneration up to 83% was recorded when excised shoot tips were pretreated overnight on MS medium containing 0.3 M sucrose followed by loading with MS containing 2 M glycerol plus 0.4 M sucrose for 20 min at 25 degree C, dehydration with PVS2 for 90 min at 0 degree C and quenching in LN. After 1 h of storage in LN, the shoot tips were rewarmed in a water-bath at 40 degrees C, unloaded with 1.2 M sucrose solution for 20 min and cultured on recovery growth medium. While using encapsulation-dehydration, the highest regeneration frequency recorded was 76% when sucrose-pretreated shoot tips were encapsulated with 3% calcium alginate, precultured in 0.75 M sucrose for 3 days, dehydrated to 25% moisture content (FW basis) under the laminar air flow, stored in LN for 1h and rewarmed at 40 degree C. The cryopreserved shoot tips maintained their viability and an unaltered level of regeneration capability after up to one year of storage in LN.     

Development of a vitrification-based cryopreservation protocol for the storage of saltcedar (Tamarix boveana Bunge)

We cryopreserved in vitro shoot tips of saltcedar (Tamarix boveana Bunge) using the vitrification technique. The success of the cryopreservation protocol was strongly affected by preculture, loading duration, dehydration duration in plant vitrification solution 2 (PVS2), and medium composition during post-warming regrowth. The highest explant regrowth (50 percent) occurred when the following conditions were employed: preculture in 0.4 M glycerol; treatment with a loading solution (LS) consisting of 2 M glycerol + 0.4 M sucrose in culture medium for 40 min at room temperature; and dehydration in PVS2 at 0 degree C for 45 min before rapid immersion in liquid nitrogen (LN). Rewarming was performed in a water-bath at 40 degree C for 2 min. Explants were then immersed in unloading solution for 10 min before plating on recovery medium supplemented with 0.01 mg per liter thidiazuron (TDZ). TDZ was progressively eliminated from the medium over a period of 6 weeks. Plantlets were transferred to a double-layer medium to enhance rooting. This protocol was successfully applied to three individuals of T. boveana harvested from the wild.     

Thermal analysis of garlic shoot tips during a vitrification procedure

The thermal behavior of garlic shoot tips was analyzed during the course of a vitrification protocol using the PVS3 vitrification solution. The size of shoot tips did not significantly influence the thermal behavior of garlic shoot tips. Though there was no significance, endo-thermal enthalpy from melting of crystalline ice increased as preculture duration increased to 6 days. Preculture on medium with 0.5 M sucrose significantly lowered exo- and endothermal enthalpies of dehydration-control shoot tips. By contrast, after dehydration with PVS3 solution, the concentration of sucrose in preculture medium had no significant effect on the value of enthalpies. A big thermal event was observed in garlic shoot tips air-dried for 1-3 h before dehydration. Both vitrification solution and dehydration duration significantly (P < 0.0001) influenced exo- and endothermal enthalpies. After dehydration with PVS1, PVS2, Fahy or Steponkus solutions for 120 min, only a small peak was detected in some shoot tips, but recovery of cryopreserved shoot tips was low. Dehydration duration with PVS3 solution significantly (P < 0.0001) influenced exo- and endothermal enthalpies and onset temperatures during cooling and warming. After dehydration for 150 and 180 min with PVS3 vitrification solution, no crystallization was observed during cooling and warming in most replicates, and recovery of cryopreserved shoot tips was highest (> 80%). There was a significant (P < 0.001) negative correlation between moisture content of shoot tips and concentration of sucrose and glycerol, and regeneration of cryopreserved shoot tips. By contrast, there was a significant (P < 0.001) positive correlation between MC and enthalpy of ice melting, and onset temperature of crystallization. Overall, the results of the analysis of the thermal behavior of garlic shoot tips coincide very well with their recovery after cryopreservation and provide a very useful tool for the establishment and optimization of cryopreservation protocols.     

Cryopreservation of hairy roots of Rubia akane (Nakai) using a droplet-vitrification procedure

An efficient protocol for the cryopreservation of madder (Rubia akane Nakai) hairy root cultures was developed using droplet-vitrification and alternative loading and vitrification solutions formulated previously in our laboratory. Among eight preculture treatments tested, the highest post-cryopreservation regeneration was obtained for explants incubated in liquid half-strength MS medium with progressively increased sucrose concentration (0.3 M for 54 h, then 0.5 M for 16 h). Loading of precultured explants improved their post-cryopreservation regeneration by 50-75% compared with non-loaded control. Combining loading solution C4 (35% PVS3) and vitrification solution B5 (80% PVS3) was the most effective, while applying six PVS2-based solutions at room temperature resulted in low post-cryo regeneration. Treatment duration was optimized to 30 min for loading and to 10-20 min for vitrification solution. Apices of primary and secondary hairy roots showed similar post-cryo regeneration (88 and 95%, respectively), which was significantly higher than regeneration of root sections without apices (65%). Droplet-vitrification produced higher post-cryo regeneration than 'classical' vitrification in cryovials. Our results suggest that droplet-vitrification using alternative loading and vitrification solutions is an efficient method for cryopreservation of R. akane hairy root cultures.     

Cryopreservation of carrot (Daucus carota l.) cell suspensions and protoplasts by vitrification

Carrot cell suspensions and protoplasts were successfully cryopreserved by vitrification. Cells were precultured in liquid Murashige and Skoog medium containing 0.175 M sucrose for 3 d and then in liquid MS medium containing 0.4 M sorbitol for 1 d. After loading of the precultured carrot cells in 25 % PVS2 at room temperature for 5 min and treatment with 100 % PVS2 at 0 degrees C for 7.5 min, they were quenched in liquid nitrogen. Optimal survival was 83.3 % (based on the triphenyl tetrazolium chloride reduction assay) following warming and unloading. Recovered cells retained the ability to regenerate plantlets in vitro. In the case of vitrification of protoplasts isolated from carrot cell suspensions, the optimal loading and dehydration durations were 5 min in 25% PVS2 and 3 min 100 % PVS2 respectively. Survival of 47 % of the untreated control (based on the FDA-PI (fluorescein diacetate-propidium iodide) staining) was achieved after cryopreservation.     

Effect of preculture, pvs2 and vitamin C on survival of recalcitrant Nephelium ramboutan-ake shoot tips after cryopreservation by vitrification

This paper reports the cryopreservation of Nephelium ramboutan-ake shoot tips derived from in vitro shoot multiplication and in vitro seed germination using vitrification. Preculture with either 0.5 M sucrose for 2 days or a combination of 0.3 M sucrose and 0.5 M glycerol for 3 days enhanced dehydration tolerance and resulted in the highest survival of shoot tips; however, none of the shoot tips withstood liquid nitrogen (LN) exposure. The use of a lower temperature (0 degree C) during exposure to plant vitrification solution (PVS2) led to higher survival of shoot tips, compared to exposure at 25 degree C. The survival percentage of shoot tips exposed to PVS2 for up to 20 min at 0°C was 83.3 percent. It was only 53.3 percent when shoot tips were exposed to PVS2 at 25 degree C for 5 min. The importance of vitamin C for reducing oxidative stress in shoots tips was demonstrated. The addition of 0.28 mM vitamin C during critical steps of the vitrification process resulted in a high survival (96.7 percent) without LN exposure, compared to 73.3 percent for shoot tips not treated with vitamin C. Moreover, 3.3 percent shoot tips withstood LN exposure when vitamin C was added during the loading step. This result suggests that cryopreservation is possible for this tropical, recalcitrant seeded tree species.     

Cryopreservation of in vitro shoot apices of Oxalis tuberosa Mol

Oca (Oxalis tuberosa Mol.) is an under-utilized tuber crop from the Andean region. Cryopreservation would allow the safe and long-term preservation of the genetic resources of this crop. A protocol for the cryopreservation of in vitro grown shoots has been developed using the vitrification solution PVS2. Two genotypes were studied (G1 and G27). Nodal segments were cultured on MS medium and incubated at 10 degree C with 16 h photoperiod and 10 mol per square meter per second irradiance, for two weeks. Apices were then excised and cultured on MS+0.15 M sucrose for 3 days at 5 degree C in darkness. Subsequently, apices were immersed in a loading solution (liquid MS medium+2 M glycerol+0.4 M sucrose), and then treated with the vitrification solution PVS2 for 0 to 40 minutes. Cryovials were then immersed in liquid nitrogen. Four weeks after rewarming and culture on recovery medium, genotype G1 showed approximately 60 percent recovery (normal growth) with 20 min PVS2 treatment. Genotype G27 showed lower recovery (30 percent). Differential scanning calorimetry yielded a Tg midpoint for PSV2 solution of ca. -120 degree C. Calorimetric studies on apices at different stages of the cryopreservation protocol showed a change in calorimetric parameters consistent with a decrease in the amount of frozen water as the protocol advanced.     

Cryopreservation of shoot tips of Picrorhiza kurroa Royle ex Benth,an indigenous endangered medicinal plant,through vitrification

The cryopreservation of shoot tips of Picrorhiza kurroa Royle ex Benth (IC 266698), an endangered medicinal plant of India was investigated. Shoot tips (about 1 mm in length) excised from four-week-old proliferating shoot cultures were precultured on MS medium supplemented with various osmotica before dehydrating with PVS2 solution at 0 degrees C. The dehydrated shoot tips were directly immersed in LN2. Following cryopreservation, and after rapid rewarming at 45 degrees C, shoot tips were quickly washed with 1.2 M sucrose solution and then plated on solidified shoot culture medium. Shoot tips were successfully cryopreserved by vitrification, when they were precultured on medium supplemented with 5% DMSO at 4 degrees C for two days before dehydrating in PVS2 for 10-20 minutes at 0 degrees C. Average survival in terms of normal shoot formation after 4 wks of plating was about 20% without callus formation. Cold hardening of shoot cultures for four weeks at 4 degrees C significantly improved the survival and shoot regeneration of cryopreserved shoot tips to 70% and 35%, respectively.     

Cryopreservation of basal stem buds of in vitro-grown mat rush (Juncus spp.) by vitrification

An optimal protocol for the cryopreservation of in vitro-grown mat rush (igusa) buds by vitrification has been successfully developed. Established multiple stemmed cultures, which were induced in liquid MS medium containing 8.9 microM BA by roller culture, were cut into small clumps, plated on solid MS medium and cultured for three weeks at 25 degree C. Clumps that grew many buds were cold-hardened at 5 degrees C, with an 8 h photoperiod, for more than 30 d. The basal stem bud (1 to 2 mm long) was dissected from the clumps and precultured at 5 degrees C for 2 d on solid MS medium containing 0.3 M sucrose. The precultured buds were placed in 2 ml plastic cryotubes and osmoprotected with 1 ml loading solution containing 2 M glycerol and 0.6 M sucrose for 30 min at 25 degree C. Then they were dehydrated in 1 ml PVS2 solution at 25 degree C for 30 min and immersed in liquid nitrogen. Using this protocol, the survival level of cryopreserved igusa 'NZ219' buds reached 87 percent. This protocol was successfully applied to 42 different lines from three Juncus species, which had relatively high survival levels ranging from 30 to 90 percent and an average of 63 percent.