Welcome to the National
Seed Storage Laboratory, part of the National Center for Genetic Resources
Preservation in Fort
Collins, Colorado. You've already read why we store germplasm, now
come and see how we handle and store the valuable materials when they arrive.
Take a look inside the vaults to see both conventional and liquid nitrogen
Samples are inspected and prepared for storage
in a laminar flow biological safety cabinet. Material being prepared for
increase is surface sterilized and treated with a fungicide prior to shipment.
All germplasm is increased and inspected for disease and/or insect infestations
by APHIS inspectors on the island
of St. Croix (a substation for
the Tropical Agriculture Research Station in MayagŁez) or other approved
sites prior to release into the National Plant Germplasm System.
optimal moisture content is achieved, seed analysts remove inert material,
empty seeds and contaminating seeds (i.e. weed seeds). Seed blowers such
as this one remove all light material and chaff, leaving only the heavy
seed. Seed may also be cleaned through the use of sieves and/or rubbing
Analysts select appropriate conditions and plant a subsample of the pure seed on standard germination blotters or towels. The number of seeds tested is dependent on the size of the sample. All samples scheduled for cryogenic storage in liquid nitrogen have paired tests performed to check for damage caused by the liquid nitrogen (LN2). The LN2 test exposes some of the seed for 24 hours to the vapor phase of LN2 (approximately -160° C, or -320° F). Seedling evaluation of the germinated seeds follows the "Rules of Testing Seed" of the Association of Official Seed Analysis Seedling Evaluation Handbook. Abnormalities and pathogen problems are assessed.
Seed of certain kinds of plants do not produce
a plant that is genetically identical to the parent. To preserve this plant
material, we need to store buds or meristematic tissue that will later
be grafted onto other plants or grown in a petri dish to produce small
plantlets. Fruit trees, potatoes, and sweet potatoes are examples of species
that can be stored this way. NSSL is storing apple buds cryogenically on
a routine basis. Buds are more sensitive than seeds to rapid cooling so
special protocols have been developed to bring the buds down to the low
temperature of liquid nitrogen vapor without harm to the buds.
stored by conventional methods are transferred to heat sealable, moisture-proof,
foil laminated bags. Locations are assigned and barcodes for the location
and serial numbers are placed inside and on the outside of the bags. The
bags are then heat sealed and placed in trays in the cold storage vault.
Samples stored by cryogenic methods are transferred to clear polyolefin tubes, barcoded, and closed with birchwood plugs. There is no free water in liquid nitrogen, so samples are not in danger of increasing their moisture content. Filled tubes are then placed in metal boxes, labeled with serial numbers and locations, and stored in the LN2 tanks.
CONVENTIONAL VAULT AREA:
The individual storage units have walls with six inches of insulation and are metal covered. Temperature is kept at -18° C.
This vault is 5000 square feet. The samples are stored in plastic trays on shelves which are part of a moveable rack system, which allows for a 60% greater room capacity over the old multiple aisle system. As each carriage is moved, the light from the previous aisle is turned off and the light above the newly opened aisle is turned on.
The life expectancy of a seed sample stored in this vault is from 20 to 50 years. Because of the variability of seed longevity, periodic retesting is done to identify regeneration needs.
CRYOGENIC VAULT AREA:
Two floors of the vault area are designed for cryogenic storage. One is in current use, and the other is designed for expansion. Each floor can hold 112 storage tanks, and has double-walled stainless steel piping for filling from the 13,000 gallon tanks located outside the building.
Cryotanks are like giant thermos jugs with vacuum jacketed double walled insulation. Each tank will hold 330 metal containers (metal boxes containing tubes of seed samples) on a lazy susan which holds the samples above the liquid nitrogen and allows easy access to each section. A tank holding wheat could contain 2640 samples, whereas a tank of tobacco (a very tiny seed) would contain 26,400 samples. We try to have a minimum of 3000 seeds per sample for cross pollinated crops and 1500 seeds for self pollinated crops.
Tanks are filled once a week, with about 56 liters of liquid nitrogen.
Air circulation is very important in the vault since nitrogen gas is constantly boiling from the tanks. Oxygen monitors are placed around the vault for detection of oxygen content of the air. Emergency fans are triggered by the oxygen monitors or emergency buttons. During an emergency, liquid nitrogen is shut off and fans provide 14 air exchanges per hour.
All of these elaborate precautions are to ensure that our valuable germplasm lives as long as possible, and is available for plant breeders and researchers to produce the food and fiber products we all depend upon.
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