Leigh E. Towill

Pollen-handling protocol and hydration/dehydration characteristics of pollen for application to long-term storage

SummaryThe National Seed Storage Laboratory in Fort Collins, Colorado, is investigating pollen storage as a practical means for storing germplasm of clonally-held species. Careful regulation of pollen moisture content is necessary to safely store pollens and perform accurate in vitro germination tests. A series of dehydration and hydration curves were generated for Pinus ponderosa Dough. ex P. Laws., Picea pungens Engelm., and Carya illinoensis (Wangenh.) K. Koch pollens using five saturated salt solutions and water. Equilibrium moisture contents (EMCs) were also determined for Typha latifolia L., Phoenix dactylifera L., Corylus avellana L., and Zea mays L. Although rates of dehydration and hydration, and EMC varied with salt, pollen, and temperature, the pollens tested did survive the drying procedures and could successfully be stored in liquid nitrogen.

Cryopreservation and long-term storage of pear germplasm

SummaryGermplasm collections of vegetatively propagated crops are usually maintained as plants in fields or potted in greenhouses or screened enclosures. Safety duplication of these collections, as duplicate plants or separate collections, is costly and requires large amounts of space. Cryopreservation techniques which were recently developed for long-term storage of pear germalasm may offer an efficient alternative to conventional germplasm collection maintenance. Pear (Pyrus L.) germplasm may now be stored as seeds (species), dormant buds or pollen from field-grown trees, or shoot tips fromin vitro-grown plants (cultivars). Pear germplasm may now be cryopreserved and stored for long periods (> 100 yr) utilizing slow-freezing or vitrification ofin vitro-grown shoot-tips. Dormant bud freezing, pollen, and seed cryopreservation of other lines are being developed to complete the base collection forPyrus. This cryopreserved collection provides base (long-term) storage for the field-grown pear germplasm collection at the National Clonal Germplasm Repository, Corvallis, Oregon.

Temperature changes in lipid and protein structure measured by fourier transform infrared spectrophotometry in intact pollen grains

Abstract Fourier Transform infrared (FTIR) spectroscopy was used to monitor structural changes in lipids and proteins in four species of pollen grains at different temperatures. Spectral data were used to determine membrane phase transition temperature (Tm) in pollen at two hydration levels. Imbibition was conducted at temperatures above and below the determined Tm values to correlate damage to the presence of gel phase. For three species of pollen, hydration overcame imbibitional damage at low temperature. However, dry pecan pollen, which had a high lipid content, was injured during imbibition at temperatures above and below the Tm. Changes in protein structure were not related to imbibitional damage. FTIR spectroscopy is a useful tool in examining biochemical properties of intact pollen grains and has potential for evaluating cryopreservation protocols.

Cryopreservation of Plant Germplasm: Introduction and Some Observations

It has been amply stated that preservation of germplasm is important not only for plant improvement and utilization for food, fiber, medicinal and forest crops, but also for conservation of rare and endangered species (Knutson and Stoner 1989; Falk and Holsinger 1991; Reaka-Kudla et al. 1997). As documented in contributed chapters in this volume and in comprehensive compendia, reasons for species or landrace loss are diverse but usually related to pressures from increasing human populations and the attendant habitat loss, land use changes and desire for productive crops. Whatever the root causes, the final effect is certainly the loss of genotypes. In efforts to stave off further loss, preservation systems have been devised to retain as much genetic diversity for the species as possible. Broadly classed, both in situ and ex situ preservation systems have been proposed and have been implemented in varying degrees for different species. In situ preservation allows for evolutionary forces to continue and can be argued to be important, for example, for disease-resistance development. However, in situ preservation still requires management and is not suitable for more domesticated lines. Preservation ex situ (within genebanks) is, therefore, used as a system around the world for many species, both commercially important and endangered.

Cryopreservation of Mentha (Mint)

The genus Mentha is in the Lamiaceae and is divided taxonomically into five sections (Chambers and Hummer 1994a). The 19 species are all herbaceous perennials, except for the annual M. micrantha (Table 1), and have origins in Europe, Asia, Australia, Japan and Morocco. A discussion of the taxonomy of mint and some of the difficulties involved therein can be found in Harley and Brighton (1977) and Tucker et al. (1980). Chromosome numbers range from 18 to 96 among species. A base number of 12 is common, but within the section Pulegium base numbers of 10 and 12 are described (Murray et al. 1971; Chambers and Hummer 1994a). Hybridization among species within the section Mentha has been widely recognized and several hybrids are named, the most important one being peppermint (Mentha × piperita) arising from crosses between M. aquatica and M. spicata.

Refrigeration can save seeds economically

Seed genebanks around the world are seeking economical ways to store seeds as a means of conserving plant biodiversity. Zheng et al. suggest that the use of ‘ultra-dry’ technology,, in which the seeds are dried to a water content of less than 5%, can extend the longevity of some seed species sufficiently to reduce or eliminate the need for refrigeration. This would benefit in particular some developing countries, such as China, for which they say the cost of cold storage is prohibitive.

Seed set with potato pollen stored at low temperatures

Pollen from several tuber-bearingSolarium species was exposed to liquid nitrogen (LN2) and tested forin vitro germination and seed set capabilities. Pollen placed in LN2 or in the vapor phase above LN2 retained high levels ofin vitro germination after 11 to 24 months of storage. This pollen also set significant numbers of seed. Brief drying of the pollen over anhydrous CaCl2 prior to freezing increased survival in most samples. Rehydration of dried, LN2 treated pollen prior toin vitro germination testing was necessary to obtain maximum germination percentages. Rehydration, however, was not necessary for seed set, and in several samples decreased seed set compared to pollen that was not rehydrated. Storage of pollen from tuber-bearingSolanum species in LN2 appears to be practical for maintaining pollen for crossing and for germplasm preservation.ResumenPolen de varias especies tuberíferas deSolanum fue expuesto a nitró-geno liquido (LN2) y evaluado luego para germinaciónin vitro y capacidad para producir semillas en cruzamientos. El polen colocado en LN2 o en la fase de vapor sobre LN2, retuvo niveles altos de germinaciónin vitro, luego de 11 a 24 meses de almacenamiento. Este polen también fue capaz de producir semilla en forma significativa. La desecación breve del polen sobre CaCl2 anhidro antes del congelamiento incrementó su sobrevivencia en la mayoría de las muestras. La rehidratación del polen deshidratado al tratarse con LN2 fue necesaria antes de someterlo a la prueba de germinaciónin vitro, para asegurar el máximo porcentaje de germinación. La rehidratación, sin embargo, no fue necesaria para su uso en la producción de semilla, más aún en algunas muestras que se rehidrataron, la producción de semilla fue menor que aquella no rehidratada. El almacenamiento de polen en nitró-geno líquido de especies tuberíferas deSolanum parece práctico para mantener polen viable para cruzamientos y preservar germoplasma.