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Both dark and red light germination of lettuce seeds (cv. "Maikönig") as well as their root and hypocotol elongation were inhibited when the seeds were sown in petri dishes together with a few seeds of Heracleum laciniatum Horn. This inhibition was not significantly counteracted by the presence of gibberellic acid (GA3) or/and 6-benzylaminopurine (BA). However, a large proportion of the lettuce seeds germinated abnormally (only cotyledons emerged) when treated with BA in the presence of Heracleum seeds. GA3 had alone no significant effect on abnormal germination, but it counteracted the effect of BA to some extent. The inhibitory effect of Heracleum seeds gradually disappeared during a moist incubation period of one to seven days in darkness at 25°C. When lettuce seeds were pre-incubated together with Heracleum seeds for one to five days the remaining, non-germinated lettuce seeds had lost their ability for subsequent germination in darkness in distilled water. This induced dark dormancy was to a great extent broken by red light, but not by GA3 or/and BA. H. laciniatum seeds inhibited the germination of Salix pentandra seeds and to some extent also the germination of radish but had no effect on the germination of spruce. [ABSTRACT FROM AUTHOR]

The elongation growth of the Avena first internode segments was studied in the presence of one or several of the following growth substances: indoleacetic acid (IAA), 6-furfurylamino purine (FAP, kinetin), 6-benzylamino purine (BAP), gibberellin A3 (GA3) and A4 + 7 (GA4 + 7), and abscisic acid (ABA). The cytokinins at concentrations of 10-7 to 10-6 M stimulated growth with 4 to 6 per cent but this effect was not statistically significant. Concentrations higher than 5 × 10-6 M inhibited growth. FAP and BAP (from 10-8 M to 10-6 M) had no significant interaction with any other growth substance used. The two-factor interactions of IAA × ABA, IAA × GA3, and GA3 × ABA, as well as the three-factor interaction IAA × ABA × GA3 were significant. However, the IAA × ABA interaction was significant only when high concentration (10-6 M) of ABA was used. The growth inhibition produced by 10-7 and 10-6 M ABA was overcome by about equimolar concentrations of IAA. The stimulation of growth by GA3 and GA4+7 (10-9 to 10-7 M) was prevented by simultaneous application of ABA, and it was reduced significantly by application of IAA (10-7 to 10-6 M). GA3 at 10-8 M combined with different concentrations of IAA gave slightly higher elongation than IAA alone but the observed values were significantly lower than expected assuming independent additive action. [ABSTRACT FROM AUTHOR]

Effects of controlled temperature conditions during seed development on seed and embryo germination of Syringa vulgaris were studied using vegetatively propagated mother plants. Seeds from mother plants grown at 18-24°C were partially dormant at low (15°C) but not at high (21°C) germination temperature, while seeds from outdoors or from plants grown at 12°C were not dormant at all. Seed dormancy at low temperatures was induced as well when branches from outdoor plants were kept at 18-24°C for the last two-three weeks before harvesting. The dormancy induced by 24°C during seed development was not broken by keeping branches at 12°C for the last two-three weeks. In most cases the induced seed dormancy was broken completely by gibberellic acid. Embryo germination at 24 or 15°C was not affected by mother plant temperature. Part of the embryos from plants grown at 24°C were, however, dormant at 9°C. The ability of embryos to germinate in osmoticum was only slightly affected by mother plant temperature. The mechanical resistance of the endosperm was significantly higher in the seeds from plants grown at 24°C than in seeds from 12°C. Both the embryos and the seeds of S. reflexa were dormant at the time of termination of embryo elongation. Experiments with three seed-propagated mother plants indicated that the water potential of embryos may be reduced by high mother plant temperature. [ABSTRACT FROM AUTHOR]

The mechanism of seed dormancy at low temperatures (15-9°C) was investigated in the seeds of Syringa josikaea, S. reflexa and S. vulgaris. Low temperature dormancy in Syringa species was mainly imposed by endosperm embedding the radicle. Different degrees of embryo dormancy may occur in S. reflexa seeds. In most cases the low temperature dormancy was broken completely by removing the endosperm around the radicle. The endosperm did not seem to contain significant quantities of germination inhibitors, and the results indicate that it prevents germination mainly due to its mechanical resistance., The mechanical resistance of endosperm did not change during chilling or during induction of dormancy by high temperature incubation. The strength of the endosperm decreased rapidly in non-dormant seeds before visible germination. Similar changes were not observed in dormant seeds. Generally, the strength of the endosperm was lower in the non- (or less) dormant species S. josikaea and S. vulgaris than in the more dormant S. reflexa seeds. The growth potential of the embryos, measured as their ability to germinate in osmotic solutions (mannitol or polyethylen glycol 4000), was increased by chilling and by GA3-treatment. The growth potential of untreated S. josikaea and S. vulgaris embryos was generally higher than that of S. reflexa embryos. Acid ethyl acetate fractions of methanol extracts from embryos of all three species contained substances with GA3-like activity in the lettuce hypocotyl test. The activity was found at Rf 0.9-1.0 on paper chromatograms run in distilled water. No significant changes in the activity were detected during chilling or prior to visible germination. [ABSTRACT FROM AUTHOR]

The aim of the experiments was to study the effects of gibberellic acid (GA3) on the germination of Calluna vulgaris L, Ledum palustre L. and Rhododendron lapponicum (L.,) Wahlenb. seeds under different environmental conditions. Under continuous light from white fluorescense tubes (3000 lux), untreated seeds of Calluna were partly dormant at all temperatures studied (9, 15, 21, 27, 27/9, 8/16 hours). Percentage of dormant seeds increased, however, with decreasing temperature, and it varied also from seed lot to seed lot. Untreated seeds of Ledum were dormant in light at 9° and 15° but not at higher temperatures. Untreated seeds of Rhododendron were completely dormant in light at temperatures from 13° to 24°C. Seeds of all species were completely dormant in darkness both at 15° and 27°C. GA3 stimulated greatly the germination of all species under all studied environmental conditions. The used concentrations (0.2-3.2 mM) gave nearly 100 % germination in most cases. At 9°C the dormancy in some seed lots of Calluna and Ledum was only partly broken by the used concentrations of GA3. [ABSTRACT FROM AUTHOR]

Experiments were carried out with three seed lots of Betula nana collected in 1967 from different localities in Norway. Seeds were stratified for 0-20 days in dark at +2-+3°C on filter papers moistened with distilled water, or treated with solution of GA3 for 24 h at room temperature, and then moved into special germination boxes that were placed in different temperature conditions. All the seed lots had conditional dormancy. Quantitatively, the dormancy was different in the different in the different seed lots (provenances), but there were no qualitative difference in the reaction to stratification, gibberellic acid and to germination temperature. Differences between seed lots may have been due to different stage of seed development. The dormancy was deepest at low temperatures (12 and 15°C) decreasing gradually with increasing temperature (to 24°C). The dormancy was effectively broken by a short stratification (from 5 to 15 days), and by treatment with gibberellic acid. The deeper the dormancy and the lower the germination temperature the longer the stratification that was needed for maximum germination. Similarly, the concentration of GA3 needed for maximum germination increased with decreasing temperature and with increasing dormancy. [ABSTRACT FROM AUTHOR]