Induction and release of secondary seed dormancy in genetically pure lines of Avena fatua

Induction and release of secondary dormancy in genetically pure dormant (AN-51, Mont 73) and non-dormant (CS-40, SH-430) lines of wild oat ( Avena fatua L.) were studied. These lines differed with regard to the optimal period of anaerobiosis necessary for induction of dormancy, and/or the degree (% of seeds acquiring dormancy) and duration of the dormancy induced. Secondary dormancy could be induced more effectively in the after-ripened seeds of dormant lines than in the non-dormant lines, where only a short-term dormancy could be induced (in 5–7 week-old-seeds). Higher anaerobiosis temperatures were more effective in inducing dormancy in all lines studied. Thus, as with primary dormancy, wild oat biotypes exhibit genetic variability in their secondary dormancy behaviour and factors like temperature can modify the expression of this trait.
The germination stimulants kinetin, isopentenyl adenine, sodium azide, potassium nitrate, ethanol and substituted phthalimides, which break primary dormancy in wild oats, stimulated germination of secondarily dormant seeds (line AN-51). Since these chemicals are structurally diverse, primary and secondary dormancies appear to be similar in part in their regulation.
Salicylhydroxamic acid, an inhibitor of cyanide-insensitive (alternative) respiration, did not inhibit: 1, spontaneous release of secondary dormancy in the line SH-430; and 2, stimulation of germination of secondarily dormant AN-51 seeds by various chemicals (except azide), suggesting that this respiratory pathway is not necessary for the release of induced dormancy.     

Studies on the mechanism of light-dependent germination of akinetes of blue-green algae

This paper deals with the role of light in the germination of akinetes of Anabaena azollae. The two maxima action spectra are situated at 385 and 615 nm and the stimulation of the germination process by photosynthate was confirmed. The photoreceptor absorbing at 385 nm was identified as a flavin and that at 615 nm as a phytochrome. A model is suggested for the mode of action of light in the germination of akinetes of blue-green algae.C. Tsui     

Seed germination in Chenopodium album L.: further evidence for the dependence of the effects of growth regulators on nitrate availability

Abstract Chenopodium album L. plants, grown under controlled environmental conditions on different levels of soil nitrate, produced seeds with proportionately different NO^?₃ contents. Regardless of the endogenous NO^?₃ content, few seeds germinated in water or upon treatment with KNO₃. Ethylene promoted germination, and the extent of germination was positively correlated with the endogenous seed NO^?₃ content. Combined application of ethylene and KNO₃ in the dark had a synergistic effect on NO^?₃ -deficient seed. The synergism between ethylene and KNO₃ was attributable to the NO^?₃ moiety of the nitrate salt. Ethylene and light showed moderate synergism in seeds with low or high endogenous nitrate. Addition of nitrate, however, masked the interaction between ethylene and light. Gibberellic acid₄₊₇ (GA₄₊₇) or red light, each alone or combined with KNO₃, had little effect on germination. When applied together in the dark, ethylene and GA₄₊₇ synergistically enhanced the germination of NO^?₃-deficient seed. The combined effects of the two hormones on this seed were further enhanced by the addition of KNO₃. There was no synergism between ethylene and GA₄₊₇ in NO^?₃-rich seed. These interactions among GA₄₊₇, ethylene and KNO₃ were not affected by light. The results confirm and further elaborate our earlier finding that the sensitivity of C. album seeds to ethylene may depend on nitrate availability.     

Triadimefon reduces transpiration and increases yield in water stressed plants

The total free amino acid pools in radicles of watermelon seeds, investigated during imbibition of water at 25°C, were higher under the most (darkness) than under the least (continuous broad spectrum far-red light) favourable light regime for germination. When seeds were imbibed in an appropriate osmotic solution of PEG-6000 (fully suppressing germination), in darkness or under continuous red or far-red light, the biochemical analyses of the radicles after 1,2,3 and 4 days from the onset of imbibition show that while the total soluble sugar content remains rather constant in all treatments, significant changes are observed in the total free amino acid pools. After the first day, a considerable increase characterizes the "darkness" pool in contrast to a moderate one under red, while the "far-red" pool remains constant. Ultimately, at 4 days, the three pools are 190,142 and 123% of the 0 day radicle one. The qualitative free amino acid determination of the 4 day darkness and far-red pools shows a considerably increased percentage contribution of glutamic acid, arginine and citrulline in the "darkness" pool. The free amino acid increase in non-illuminated radicles may be correlated to germinability; moreover, it is evidently a phytochrome-mediated, pre-germinatory event, probably due to the hydrolysis of proteins (known to be rich in glutamic acid and arginine), stored in the radicle.     

Patterns of protein synthesis during the germination of pea axes,and the effects of an interrupting desiccation period

As germination of axes of Pisum sativum L. seeds progressed, profound quantitative and qualitative changes occurred in the patterns of protein synthesis. This was shown by fluorography of gels following two-dimensional polyacrylamide gel electrophoresis separation of [³⁵S]methioninelabelled proteins. The effects of desiccation during germination on these in-vivo protein-synthesis patterns were followed. Desiccation differentially affected the synthesis of proteins. Usually, however, upon rehydration following desiccation the types of proteins being synthesized were recognizable as those synthesized earlier during imbibition of control, once-imbibed axes: seeds imbibed for 8 h, and then dried, did not recommence synthesis of proteins typical of 8-h-imbibed control seeds, but rather of 4-h-imbibed control seeds. Seeds imbibed for 12 h, and then dried and rehydrated, synthesized proteins typical of 4-h-and 8-h-control seeds. Thus drying of germinating pea axes caused the proteinsynthesizing mechanism to revert to producing proteins typical of earlier stages of imbibition. Drying during germination never caused the seed to revert to the metabolic status of the initial mature dry state, however.Abbreviation DR dried and rehydrated     

The use of embryo culture for the recovery of plants from cassava (Manihot esculenta Crantz) seeds

Cassava fertility and seed viability are frequently low, which can be a disadvantage in a breeding programme. An embryo culture method is described whereby embryonic axes are excised from mature seeds and placed on a culture medium containing 1.23 M indolebutyric acid (IBA) at 30°C under continuous light. The number of plants recovered by embryo culture was much greater than the number recovered from conventional seed germination procedures.     

Differential effects of camptothecin and interactions with plant hormones on seed germination and seedling growth

Effects of camptothecin, a naturally occurring alkaloid, on seed germination varied from promotive to inhibitory, depending on the species used. It markedly inhibited seedling root growth but its inhibition of hypocotyl growth varied among species. Camptothecin inhibited GA₃-induced dark germination of lettuce (Lactuca sativa L.) seeds and hypocotyl elongation of seedlings. In contrast to ABA, the camptothecin inhibition of GA₃-induced germination could not be overcome by cytokinin. When seeds were germinated at 29C with a 0.5 h light treatment, little or no germination occurred in the camptothecin treatment, but addition of cytokinin overcame this inhibition.     

Dormancy inDioscorea: Different temperature adaptation of seeds,bulbils and subterranean organs in relation to north-south distribution

Temperature dependencies of sprouting and germination were compared for subterranean perennating organs and seeds of ten closely related species of the genusDioscorea (Dioscoreaceae), a group of monocotyledonous summer perennials which are distributed from the tropics to the subarctic. The species used wereD. nipponica Makino,D. tokoro Makino,D. japonica Thunb.,D. tenuipes Franch. et Savat.,D. septemloba Thunb.,D. quinqueloba Thunb.,D. izuensis Akahori,D. bulbifera L. f.spontanea (Makino) Makino et Nemoto,D. pentaphylla. L. andD. alata L.; they are distributed from cold northern areas to warmer southern areas approximately in this order in and around Japan. Bulbil sprouting was also studied in those forming bulbils. Subterranean organs of the tropical species sprouted faster without any prior temperature treatment, whereas those of species from the more northern areas sprouted after prechilling. Northern species required longer, periods of prechilling for sprouting. On the other hand, with seeds or bulbils, the southern species required longer periods of prior temperature treatment for dormancy breaking. This difference in the length of dormant periods between seeds or bulbils and subterranean organs among the ten species may be related to their size and position of shedding; seeds or bulbils are small and are shed on the ground surface, whereas subterranean organs are large and are located below the surface. It is important to determine in other perennials whether the above relation between dormant features of seeds or bulbils and subterranean organs are common properties or not.