Cryopreservation of Duckweed Genetic Diversity as Model for Long-Term Preservation of Aquatic Flowering Plants

Vegetatively propagating aquatic angiosperms, the Lemnaceae family (duckweeds) represents valuable genetic resources for circular bioeconomics and other sustainable applications. Due to extremely fast growth and laborious cultivation of in vitro collections, duckweeds are an urgent subject for cryopreservation. We developed a robust and fast DMSO-free protocol for duckweed cryopreservation by vitrification. A single-use device was designed for sampling of duckweed fronds from donor culture, further spin-drying, and subsequent transferring to cryo-tubes with plant vitrification solution 3 (PVS3). Following cultivation in darkness and applying elevated temperatures during early regrowth stage, a specific pulsed illumination instead of a diurnal regime enabled successful regrowth after the cryopreservation of 21 accessions of Spirodela, Landoltia, Lemna, and Wolffia genera, including interspecific hybrids, auto- and allopolyploids. Genome size measurements revealed no quantitative genomic changes potentially caused by cryopreservation. The expression of CBF/DREB1 genes, considered as key factors in the development of freezing tolerance, was studied prior to cooling but was not linked with duckweed regrowth after rewarming. Despite preserving chlorophyll fluorescence after rewarming, the rewarmed fronds demonstrated nearly zero photosynthetic activity, which did not recover. The novel protocol provides the basis for future routine application of cryostorage to duckweed germplasm collections, saving labor for in vitro cultivation and maintaining characterized reference and mutant samples.

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.

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.