Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: THURSDAY, January 27, 1994 TAG: 9401260126
SECTION: CURRENT PAGE: NRV5 EDITION: NEW RIVER VALLEY
SOURCE: Joe Hunnings
DATELINE: LENGTH: Medium
Considering the odds, it amazes me regularly that any seeds manage to sprout.
Horticultural researchers are seeking ways to surmount these problems. In the process, they're also finding out just what goes on when a seed germinates.
One of the most promising methods of improving germination is a process known as osmotic priming.
This technique has produced faster, more uniform germination in crops including lettuce, sweet corn, carrots and tomatoes.
Osmotic priming consists of soaking seeds in an aerated solution for a period of time - usually for a week or so - then either immediately planting the seeds or drying them for later planting.
Osmosis (you may remember from science class) is water movement from a region of low-solute concentration into a region of high-solute concentration.
The priming solution concentration is adjusted to control the rate of osmosis into the seed.
Afterward, the treated seeds are "primed for action," hence the name, osmotic priming.
Horticulturists are pleased with the results. For example, lettuce - primed for 14 days in a polyethylene glycol solution - showed accelerated germination at low temperature. Priming for as little as one day allowed germination at high temperatures, where untreated seed failed to germinate.
Botanists also are pleased, for by figuring out why osmotic priming improves germination, they are figuring out germination itself.
One theory is that there are two stages to germination: imbibition and radicle - or root-tip - emergence.
During imbibition, water swells the seed and its metabolism fires up. The seed begins to accumulate various solutes as a result of that initial metabolism.
Through osmosis, the solutes cause more water to enter the seed. When enough water has entered the seed, radicle emergence begins.
Osmotic priming may result in faster germination by taking the seed through the first step at germination while keeping the second step on hold.
Since the priming solution has a relatively high concentration of solutes, sufficient water from the priming solution is not drawn into the seed, and radicle emergence is not triggered.
But when the seed is dried, the solutes generated in early germination remain in the seed. When it is planted these solutes quickly draw water from the soil into the seed and start the root tip growing.
Osmotic priming probably affects germination at adverse temperatures because the initial germination processes are more temperature-sensitive than radicle emergence.
Again, priming takes the seed partly through the early stages and holds it ready to start growth in the next phase of germination.
Osmotically primed seeds maintain their enhanced germination even after storage for several months.
Whether they will germinate after longer periods - allowing seeds to be primed for sale to gardeners and farmers - remains to be seen.
I wouldn't be surprised, though, to see specially prepared seeds on the market someday.
In the meantime, I'm even more amazed by the growing process than I was before.
\ Joe Hunnings is the Virginia Cooperative Extension Service agent for agriculture in Christiansburg. If you have questions call the Montgomery County extension office at 382-5790.
by CNB