Cryopreservation of Plant Shoot Tips of Potato, Mint, Garlic, and Shallot Using Plant Vitrification Solution 3

Cryopreservation of shoot tips facilitates long-term storage of plant genetic resources which can otherwise only be propagated vegetatively. The vitrification approach using the cryoprotectant plant vitrification solution 3 (PVS3, 50% sucrose and 50% glycerol) is easy to handle, has shown to produce high regrowth percentages in a number of potato, mint, garlic, and shallot accessions, and is, thus, highly suitable for routine cryopreservation of plant genetic resources. In the current chapter, the vitrification procedure is described for potato, mint, garlic, and shallot and includes details about modifications for the different plant species. Special emphasis is given on the preparation of the different culture media, solutions, the culture conditions prior and post-cryopreservation, and the preparation of the shoot tips from different sources. Furthermore, protocols to introduce plants into in vitro culture and methods to estimate cryopreservation success are provided.

Cytological and biophysical comparative analysis of cell structures at the microsporogenesis stage in sterile and fertile Allium species

Using a live-cell-imaging approach and autofluorescence-spectral imaging, we showed quantitative/qualitative fluctuations of chemical compounds within the meiocyte callose wall, providing insight into the molecular basis of male sterility in plants from the genus Allium. Allium sativum (garlic) is one of the plant species exhibiting male sterility, and the molecular background of this phenomenon has never been thoroughly described. This study presents comparative analyses of meiotically dividing cells, which revealed inhibition at the different microsporogenesis stages in male-sterile A. sativum plants (cultivars Harnas and Arkus) and sterile A. ampeloprasum var. ampeloprasum (GHG-L), which is phylogenetically related to garlic. Fertile species A. ampeloprasum (leek) was used as the control material, because leek is closely related to both garlic and GHG-L. To shed more light on the molecular basis of these disturbances, autofluorescence-spectral imaging of live cells was used for the assessment of the biophysical/biochemical differences in the callose wall, pollen grain sporoderm, and the tapetum in the sterile species, in comparison with the fertile leek. The use of techniques for live-cell imaging (autofluorescence-spectral imaging) allowed the observation of quantitative/qualitative fluctuations of autofluorescent chemical compounds within the meiocyte callose wall. The biophysical characterisation of the metabolic disturbances in the callose wall provides insight into the molecular basis of male sterility in A. sativum. In addition, using this method, it was possible for the first time, to determine precisely (on the basis of fluctuations of autofluorescence compounds) the meiosis stage in which normal microsporogenesis is disturbed, which was not visible using light microscopy.

'Personalisation' of droplet-vitrification protocols for plant cells: a systematic approach to optimising chemical and osmotic effects

Although an appropriate cryopreservation protocol is a prerequisite for basic studies and large-scale implementation as well as further cryopreservation studies, the process relies on trial and error. Among the vitrification-based cryopreservation techniques, droplet-vitrification produces high post-cryopreservation recovery. However, the protocol itself cannot solve the problems engaged in plant cryopreservation, prominently due to dehydration with cytotoxic vitrification solutions. This paper proposes a set of treatments to develop droplet-vitrification using a standard procedure associated with additional treatments and alternative vitrification solutions. The proposed standard protocol consists of a progressive preculture with 0.3 M sucrose for 31 h and with 0.7 M for 17 h, loading with vitrification solution C4-35% (17.5 percent glycerol + 17.5 percent sucrose, w/v) for 20 to 40 min, dehydration with vitrification solutions A3-90 percent (37.5 percent glycerol + 15% DMSO + 15 percent EG + 22.5 percent sucrose) for 10 to 30 min or B1-100 percent (PVS3) for 40 to 120 min at room temperature, cooling the samples using aluminum foil strips, rewarming by plunging into pre-heated (40 degree C) unloading solution (0.8 M sucrose) and further unloading for 20 to 60 min, depending on size and permeability of the materials. Using this systematic approach we can identify whether the material is tolerant or sensitive to chemical toxicity and to the osmotic stress of dehydration with vitrification solutions, thus revealing which is the main barrier in solution-based vitrification methods. Based on the sensitivity of samples we can design a droplet-vitrification procedure, i.e. preculture, loading, dehydration with vitrification solutions, cooling and rewarming. Using this approach, the development of appropriate droplet-vitrification protocol is facilitated.

Improved alliin yield in somatic embryos of Allium sativum L. (cv. Yamuna safed) as analyzed by HPTLC

Direct somatic embryo formation (without intervening callus) from garlic clove basal tissue was induced in which the influence of plant growth regulators (PGRs) on various explants was examined. Medium added with 2.0 mg/l 6-benzylaminopurine (BAP) and 0.5 mg/l 2,4-dichlorophenoxyacetic acid (2,4-D) were the most effective PGR combination for somatic embryo induction. It induced embryos directly in 85.5% of the basal clove explant. Callus induction was also obtained from other parts of explant and 2.0 mg/l 2,4-D induced callusing in 86.5% of the inoculated explants. Protein, amino acid and alliin content were measured in callus and in embryos. Somatic embryos had more soluble protein and free amino acid compared to callus. HPTLC analysis revealed that alliin was significantly high in somatic embryos compared to undifferentiated callus tissue; the content was even more in older embryos. The present study of Allium indicates that the event of morphogenetic development including in vitro embryogeny can effectively be analysed by monitoring the changes of biochemical profiles.

[The formation and symplastic transport function of ectodesmata-like in garlic during the parenchyma cells declining]

Using fluorescence and electron microscopy, the ultrastructure and symplastic transport function of Ectodesmata-like (ED-like) were studied in the declining parenchyma cells of garlic during germination period. The results showed that plasmodesmata (PD) were gradually stretched and broke into ED-like. The diameter of PD and the diameter of appressed endoplasmic reticulum (AER) in PD underwent a series of changes. F-actin and myosin might take part in the regulation of the symplastic transport of the ED-like.

Micronucleus frequency and lipid peroxidation in Allium sativum root tip cells treated with gibberellic acid and cadmium

Gibberellic acid (GA(3)) is a very potent hormone whose natural occurrence in plants controls their development. Cadmium is a particularly dangerous pollutant due to its high toxicity and great solubility in water. In this study, the effect of GA(3) on Allium sativum root tip cells was investigated in the presence of cadmium. A. sativum root tip cells were exposed to CdNO(3) (50, 100, 200 microM), GA(3) (10-3 M), both CdNO(3) and GA(3). Cytogenetic analyses were performed as micronucleus (MN) assay and mitotic index (MI). Lipid peroxidation analysis was also performed in A. sativum root tip cells for determination of membrane damage. MN exhibited a dose-dependent increase in Cd treatments in A. sativum. GA(3) significantly reduced the effect of Cd on the MN frequency. MN was observed in GA(3) and GA(3) + 50 mum Cd treatments at very low frequency. MI slightly decreased in GA(3) and GA(3) + Cd treatments. MI decreased more in high concentrations of Cd than combined GA(3) + Cd treatments. The high concentrations of cadmium induce MN, lipid peroxidation and lead to genotoxicity in A. sativum. Current work reveals that the effect of Cd on genotoxicity can be partially restored with GA(3) application.

Cytogenetic effects of commercial formulation of cypermethrin in root meristem cells of Allium sativum: Spectroscopic basis of chromosome damage

To validate the use of Allium sativum as a sensitive test model for genotoxicity, the cytogenetic effects of a commercial formulation of the pyrethroid insecticide, cypermethrin, were evaluated in the root meristem cells of A. sativum. Ultraviolet (UV) and Fourier transform infrared (FTIR) spectral measurements were also carried out to understand the interaction of cypermethrin with DNA. In a preliminary toxicity assay, the EC50 for Allium root growth was estimated to be 8 ppm. For the cytogenetic assay, root meristem cells were exposed to 1, 2, 4, 8 and 16 ppm of the test compound for 24 h, and either processed immediately for analysis or incubated in water for 24 h of recovery and then processed. Cells analyzed immediately after the exposure had a significant, dose-dependent inhibition of mitotic index (MI) and induction of mitotic and chromosomal aberrations (MAs and CAs). The 24 h recovery period reduced the effect of the test compound on the MI and percent aberrations; however, cells exposed to 8 and 16 ppm showed a significant frequency of aberrations despite the recovery period. One part per million cypermethrin was consistently negative in the assay. The data indicate that higher doses of cypermethrin produce toxicity, CAs and MAs in A. sativum. The present study indicates that A. sativum is a sensitive and reliable test system. A bathochromic shift observed in UV absorption spectra reveals that cypermethrin binds with DNA. Role of vibrational modes of the active site in the recognition and reaction of cypermethrin with DNA has been discussed. Based on spectroscopic data and structural properties, a possible mechanism has been proposed for the interaction of cypermethrin with DNA resulting in chromosomal aberrations.

Cryopreservation of garlic shoot tips by vitrification: effects of dehydration, rewarming, unloading and regrowth conditions

This paper investigates the effect of dehydration, rewarming, unloading and regrowth conditions and of bulb post-harvest storage duration on survival and regeneration of cryopreserved garlic shoot tips. PVS3 was the most effective of the seven vitrification solutions compared. Treating shoot tips with PVS3 for 150-180 min ensured 92 % regeneration after freezing. An air-drying treatment, performed either before or after the PVS3 treatment, was detrimental to regeneration of cryopreserved shoot tips. Rapid rewarming in a water-bath at 37 degree C gave higher regeneration than the slower rewarming procedures employed. Regeneration was similar using either sucrose or sorbitol unloading solutions. The growth regulator content of the recovery medium did not influence percentage regeneration. However, the fresh weight of explants cultured on medium containing 0.3 mg/L zeatin and 0.3 mg/L gibberellic acid was significantly higher than on other media. Post-harvest storage duration of bulbs dramatically influenced survival and regeneration of non-cryopreserved and cryopreserved shoot tips, which were nil for samples cryopreserved immediately after harvest and highest after 3 and 6 months of storage. The optimized cryopreservation protocol was applied to ten different garlic varieties, with regeneration percentages ranging between 72 and 95 %.

In situ visualization of rDNA arrangement and its relationship with subnucleolar structural regions in Allium sativum cell nucleolus

We used a DNA-specific staining technique to show the two states of DNA component distributed in the nucleolar region of Allium sativum cells. One state is the extended DNA fiber, and the other is the condensed DNA clump. In situ hybridization demonstrated that the extended DNA fiber was an rRNA gene. Anti-fibrillarin antibody immunolabeling revealed that these rRNA genes were located in the dense fibrillar component near the fibrillar center, including at the periphery of the fibrillar center. None was in the dense fibrillar component far away from the fibrillar center. The condensed DNA clump was located in the fibrillar center. Further observations showed that the rRNA genes in the nucleolus were all arranged around the fibrillar center and associated with the DNA clumps in the fibrillar center. Results of statistical analysis showed that the distribution region of rRNA genes occupied about one-third of the total dense fibrillar component region. Ag-NOR protein showed a similar distribution pattern to that of rDNA. Immunolabeling of an anti-RNA/DNA hybrid antibody demonstrated that the transcription sites of rRNA were located at the periphery of the fibrillar center and in the dense fibrillar component near the fibrillar center, and these sites were consistent with the location and arrangement of rDNA shown in situ. These results demonstrated that transcription of rRNA takes place around the fibrillar center and at the periphery, whereas the dense fibrillar component that was far away from fibrillar center was the non-transcription region. The DNA clumps within the fibrillar center were probably the anchoring sites for rDNA arrangement.

Induction of direct somatic embryogenesis in garlic (Allium sativum)

An efficient novel method of direct somatic embryogenesis from basal tissue of garlic clove was developed. The influence of plant growth regulators, basal medium and explant type on somatic embryo induction was examined. The best plant growth regulator combination was, 2,4-D and kinetin at 1.0 mg/L and 0.5 mg/L respectively, inducing direct somatic embryogenesis in 60% of explants. White's medium was used as basal medium and somatic embryos developed on explants after six weeks. The technique has potential applicability for problems associated with plant regeneration and virus elimination in garlic.

Morphological changes in garlic (Allium sativum L.) microbulblets during dormancy and sprouting as related to peroxidase activity and gibberellin A3 content

The aim of this work was to study the physiological mechanisms of dormancy and sprouting during post-harvest of garlic (Allium sativum L.) microbulblets produced by meristem culture of garlic seed cloves. The morphological changes occurring in garlic microbulblets were assessed from harvest till sprouting in relation with peroxidase activity and levels of gibberellins. Also the effect of a cold treatment (30 days at 4 degrees C) given 30 days after harvest was studied. The results showed that during the state of dormancy in garlic microbulblets formation of the leaf primordia and vascular differentiation of the storage leaf occurred, while increases of peroxidase activity and low levels of GA3 (the only active gibberellin identified) were found. At the end of dormancy the sprouting channel was formed, vascular differentiation established, and peaks of soluble peroxidase activity as well as of GA3 were observed. At day 90 post-harvest, garlic microbulblets showed physiologically mature and able to sprout. Further on, bud expansion and decrease of GA3 levels characterized sprouting of the microbulblets. The cold treatment enhanced GA3 levels and anticipated the sprouting process.

Light and electron microscopic immunocytochemical localization of two major proteins in garlic bulb

Garlic is known as a potent spice and a medicine with broad therapeutic properties ranging from antibacterial to anticancer, antidiabetic, and anticoagulant. Two major proteins of 40 KD and 14 KD constituting approximately 96% of total garlic proteins have been recently purified at our Institute. This immunocytochemical and ultrastructural study revealed that the 40 KD protein was localized in the parenchyma sheath cells (PSC) of garlic bulbs, whereas the 14 KD protein was present in the cortical cells (CC). Immunogold electron microscopy study indicated that the 40 KD protein was specifically localized in the globular granules of the cytoplasmic area of PSC. Each globular granule was amorphous and homogenous with membrane limiting its outermost layer. The yellowish color of PSC in freshly cut slices of garlic bulb suggested that PSC may have sulfur-containing compounds such as allicin, the primary contributor of the pungency and medicinal properties of garlic. Ellman's reagent test quantitatively revealed that there were 17.8 n moles sulfhydryl (SH)/ml of 40 KD garlic protein. Microtubule tubulin in mitotic figures from PHA-stimulated human short-term whole blood cultures reacted strongly with antitubulin antibody but reacted negatively with anti-40 KD garlic protein antibodies and therefore was not related to the 40 KD garlic protein immunocytochemically.

[Cell cycle phases: determination of G1, S e G2 by fluorometry (author's transl)]

The G1, S and G2 phases of the cell cycle in Allium cepa root tips were determined in Acriflavin--Feulgen--stained material. Pigeon erythrocyte nuclei were employed as standard for DNA dry mass determinations. Micro-interferometric and fluorometric measurements gave the average of 77,1. 10(-12) g for the G1 nuclei from the root tips.