Seed Research a Brief History

In the first Workshop on Seeds held in Jerusalem in 1980, the plenary speaker was the late Michael Evenari. He presented an absorbing, scholarly account of the history of seed germination, including many references to observations printed in biblical, early Greek and early Roman documents (Evenari, 1980/81). He proposed Theophrastus (372-287 bc) as being the first all-round botanist known to us, and the first seed physiologist and ecologist. Some of the writings of Theophrastus bear restatement. On seed development he wrote that 'all plant seed has in itself a certain amount of nourishment which is produced with it at the beginning just as in the case of eggs'. On germination behaviour: 'Germination begins earlier in sunny places which have an even temperature.' On after-ripening: 'Another thing which makes a difference as to the rapidity with which seeds germinate is their age; for some herbs come up quicker from fresh seeds . . . some come up quicker from old seeds.' On storage: 'No seeds [of cultivated herbs] will keep for more than four years as to be of use for sowing,' and on priming: 'Some even presoak the seed of cucumber in milk or water to stimulate germination.'

Several quotes from Pliny the Elder (ad 27-79) also appear in the article, including one that pertains to the requirement of seeds to be dried before germination: 'It is difficult for a seed contained in a pod to get dry . . . and consequently they are dried artificially to make them fertile.' This predates our own observations on the need for drying to switch seeds from a developmental mode to a germinative mode (Kermode et al., 1986) by almost two millennia. According to a quote in the publication of the writings of the American poet-naturalist, Henry D. Thoreau (1817-1862), in his book, Faith in a Seed (Thoreau, 1993), Pliny also seemed to regard plants that do not bear seed as being somewhat ominous, although his choice of species is questionable. To quote:

The only ones among the trees that bear nothing whatsoever, not so much as any seed even, are the tamarisk, which is used only for making brooms, the poplar, the Atinian elm, and the alaternus. These trees are regarded as sinister (infelices: unhappy) and are considered inauspicious.

Research, if any, on seeds seems not to be recorded until the late 17th century, although breeding of plants for improved seed traits was continuing over the centuries. The originator of modern seed physiology, and a major founding contributor to plant physiology in general (and mineral nutrition and hydroponics in particular), was Julius von Sachs (1832-1897). He made several interesting observations on the storage contents of seeds during development and following germination, and noted that tyrosine and asparagine are formed from protein reserves and transported into the young growing seedling (Evenari, 1980/81). Further biochemically related observations followed over the next 50 years, including a comprehensive account of starch breakdown in barley by Horace Brown and Harris Morris (1890).

Gregor Mendel's studies on pea plants incorporated several seed traits, including the occurrence of wrinkled (rugosus) peas with a recessive mutation in the r locus. It is now known that the primary lesion in this locus results in rr embryos lacking starch branching enzyme I (SBEI) activity; hence less amylopectin is synthesized during seed development, a build-up of sucrose and water ensues, and the embryo, which contains less than its full complement of reserves, shrinks during maturation drying (Wang and Hedley, 1991). The pioneering work of Mendel (1822-1884) also has an interesting tie-in with the pioneering work of Nobel laureate Barbara McClintock (1902-1992) almost a century later, which initially, like his own studies, was largely ignored. She discovered the transposable element, or 'jumping gene', and contended that certain autonomous elements within the maize gene are able to excise and become reincorporated into DNA elsewhere, resulting in a mutant allele (McClintock, 1948). Some of the consequent phenotypes were noted in maize seeds. In the pea seed, the loss of SBEI activity is due to the insertion of a small transposon into its gene, rendering it untranslatable (Wang and Hedley, 1991).

One of the more profound discoveries in the 20th century that was initially made on seeds, but has had wider implications in many aspects of plant growth and development, is that of phytochrome. Although not the first to note the effect of light on seed germination, Lewis Flint and E.D. McAlister (1935) were the first to assign specific wavelengths to the phenomenon of inhibition of germination, using the light-sensitive lettuce seed. Almost by default they also found that certain wavelengths -those in the red region of the spectrum - did not inhibit germination. This was followed up some 20 years later with the classical studies of the Beltsville group of Harry Borthwick, Sterling Hendricks and co-workers (Borthwick et al., 1952) showing the promotion and inhibition of germination of lettuce seed cv. Grand Rapids by exposure to red and far-red regions of the spectrum, respectively. This was the basis of their proposal for a photoreversible pigment, later called phytochrome, with an active and an inactive form.

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Growing Soilless

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