Species of Avena differ markedly in their levels of pre-and post-harvest dormancy. These species offer the opportunity of determining if dormancy is related to the endogenous level of growth inhibitor. Germinability in two species of differing levels of dormancy, common oat Avena sadva L., and wild oat Avena fatus L. was assessed as were the contents of abscisic acid and volatile fatty acids of chain length C6-ClO. In A. sativa which did not possess postharvest dormancy there was no correlation between germination and inhibitor levels but in A. fatua the relationship between the content of fatty acid and dormancy was good. The loss of these fatty acids in dry storage by evaporation could explain after ripening.In oats (A vena spp.) there is a considerable range of degrees of dormancy from the almost nondormant common oat (A. sativa L.) which at most shows a brief postharvest dormancy, through the appreciable dormancy of the wild oat (A.fatua L.) to the profound dormancy of the winter wild oat (A. ludoviciana Dur.), especially with respect to the upper grain of the dissemule. The level of dormancy in this last species during maturation is less than when fully ripe (17,21). However, Morgan and Berrie (17) showed that if immature grains were dried before testing these dried grains showed a degree of dormancy equivalent to the mature grain.Wright (25) showed that water-stressed plants had elevated levels of an ABA-containing complex, possibly produced to control stomatal aperture (12). It might be concluded that ABA would accumulate in plant tissues in which the water contents were reduced compared to average normal tissues. Inasmuch as ABA is a well known germination inhibitor, such accumulation could explain the pattern of emergence found in maturing A vena spp.With the possible exception of ABA, naturally occurring plant growth inhibitors are considered to be nonspecific (15). This includes the coumarins which can impose light sensitivity on lettuce seed (4). Fatty acids of chain length C6-C12 occur in many plants and influence seed germination and hydrolase production in a manner contrary to known promotive plant hormones (3,9 Ripe grains were stored at a constant temperature of 20 C in darkness until required for analysis.Single large batches of grain were collected. Prior to beginning the routine extractions, a model system employing replication at all levels was carried out for each acid. Isotope dilution was employed to estimate efficiency of extraction and recoveries were also estimated by "seeding" samples with known amounts of acid. From these experiments the coefficient of variation for each acid was determined. In the working analyses the final analysis was carried out in triplicate and the average of these was employed, using the appropriate coefficient of variation to estimate the standard deviation. It is this value which is reported in the tables.Extraction

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Straight-chain saturated fatty acids (C6-C11) and abscisic acid (ABA) accumulate in the leaves of Phaseolus vulgaris L. and Hordeum vulgare L. under water stress. ABA and certain of the fatty acids, particularly decanoic and undecanoic acid, can inhibit stomatal opening and cause stomatal closure in epidermal strips of Commelina communis L. depending on the incubating medium used. 10(-4) M (±)-ABA inhibits opening in media containing either high or relatively low concentrations of KCl but causes closure only in the latter medium. The fatty acids (at 10(-4) M) prevent opening in both media while significant closure of open stomata was caused only by undecanoic acid in both media and, additionally, by decanoic acid in the low-KCl medium. 10(-4) M formic acid also caused stomatal closure and prevented opening to significant extents in the low-KCl medium (it was not tested in the high-KCl medium). The efficacy of undecanoic acid in causing 50% inhibition of opening is about three orders of magnitude lower than that of ABA. At a concentration of 10(-3) M, nonanoic, decanoic and particularly undecanoic acid and all-trans-farnesol cause increased cell leakage in Beta vulgaris L. root tissue. Undecanoic acid (10(-4) M) also causes some loss of guard cell integrity in C. communis within 1.5 h of treatment. ABA (10(-4) M) reduces transpiration rates in barley and C. communis leaves when applied via the transpiration stream but decanoic and undecanoic acids did not have this effect. Transpiration was not affected when ABA or the fatty acids were applied to the leaf surfaces.