白沙蒿种子萌发特性的研究Ⅱ.环境因素的影响

白沙蒿（Artemisia sphaerocephala Krasch.）是中国西北部沙漠的流动及固定沙丘上广泛分布的优势种藻木。白沙蒿种子为需光种子,种子在光下萌发而在黑暗中受到抑制,种子萌发的适宜温度为25℃,在10℃和30℃萌发速率和萌发率都很低,萌发在℃受到抑制。种子在沙中被旱越深,其萌发速率和萌发率就越低。在沙平面下2cm或更深层沙土下出苗率为零。但是,当将种子上层沙土移走,只保留0.5cm沙土覆盖种子,这些种子的萌发率达到原先就位于沙土下0.5cm的种子的萌发率,但是后者的萌发速率较高,土壤水分含量越高,从1.7％至14.7％,其萌发就越快。土壤水分含量从19.4％起,种子的萌发受到了延迟,苗的发育受到了抑制。     

CHANGES IN SENSITIVITY OF MAIZE CHROMOSOMES TO X RAYS DURING SEED GERMINATION

Latterell , Richard L., and Dale M. Steffensen . (Brookhaven Natl. Lab., Upton, L. I.. N. Y.) Changes in sensitivity of maize chromosomes to X rays during seed germination. Amer. Jour. Bot. 49(5): 472–478. Illus. 1962.—Changes in the radiosensitivity of maize seeds during early stages of germination were studied by means of somatic-mutation techniques. Seeds heterozygous for the yg₂ (yellow-green) locus were irradiated with 800 r of X rays after soaking in running tap water up to 42 hr. Yellow-green sectors, representing mutations affecting the dominant yg₂ locuss in leaves 4 and 5 of seedling plants were used as a criterion of radiosensitivity. The frequency of somatic sectors was virtually nil for dry seed and for seeds soaked up to 16 hr. Sector frequencies underwent a marked (9- to 15-fold) rise from 16 to 28 hr, reached a plateau of sensitivity and subsequently declined. Manometric studies were conducted on seeds soaked under the same conditions as those irradiated. The rate of oxygen consumption rose rapidly from 0 to 7 hr, remained essentially constant from 7 to 16 hr, then underwent an approximately 2-fold increase from 16 to 24 hr, after which the rate of progressive increase was retarded. The fact that the marked rise in frequency of X-ray-induced somatic sectors coincided with the major increase in oxygen consumption suggests that radiosensitivity of soaked seeds is conditioned by metabolic changes during seed development. Changes in radiosensitivity that followed attainment of peak sector frequencies were apparently governed by factors that influenced the rate of seed development.     

GERMINATION-REGULATING MECHANISMS IN SOME DESERT SEEDS VIII. ARTEMISIA MONOSPERMA

Germination of achenes of Artemisia monosperma is absolutelydependent on light, irrespective of temperature. Full saturationby light was obtained with 24 meter-candle seconds and morethan half with 0.1 meter-candle second. Nevertheless, even withsaturating irradiation, action of light was cumulative, requiringrepeated short irradiation, the number depending on temperature,separated by a minimal interval. Responsiveness to light increasedwith progress of incubation. The cumula-tiveness and the increasein responsiveness are discussed. A gradual achievement of anequilibrium between an inactive precursor and a substance whichparticipates in the light-induced reactions, is postulated.The stage of equilibrium, as well as the rate at which it isreached are temperature-dependent. Light-independent reactionswhich are triggered by irradiation may be reversed by incubationat supra-optimal temperatures, or by desiccation, and full promotionmay be restored after re-imbibition or after return to optimaltemperatures, by an additional irradiation. The ecological significanceof the germination responses is also discussed. ¹ This study was supported by grant FG-Is-115 from the UnitedStates Department of Agriculture.     

GERMINATION OF LIGHT-INHIBITED SEED OF NEMOPHILA INSIGNIS

Germination of Nemophila insignis seed is inhibited by light over a wide range of temperatures. At low temperatures the light intensity required for inhibition is higher. At 25 C there is little germination (in darkness as well as in light); at 27.5 C germination is inhibited altogether. Virtually complete germination in light is obtained when the endosperm directly covering the radicle is removed. This operation also improves germination in darkness at 25 C. Mechanical scarification performed elsewhere in the seed is without effect. As with Phacelia tanacetifolia, Nemophila seed apparently fails to germinate in light because the endosperm restrains the expansive growth of the embryo. The embryo of dark-imbibed seed develops a force which enables it to overcome the physical resistance of the endosperm. Light inhibits the process which leads to generation of “expansive force.” Gibberellic acid at 5 × 10^–4 m stimulates germination in light and in the dark. Abscisic acid at 10^-4 m inhibits germination; at 10^-6 m it inhibits only root growth. The inhibition of germination or root growth caused by abscisic acid cannot be reversed by gibberellic acid. Eighty per cent oxygen under certain conditions promotes germination. The rate of O₂ uptake is enhanced in oxygen-enriched atmosphere; however, there is no corresponding increase in the rate of CO₂ output. Thus high oxygen tension enhances an oxidative process other than respiration. This reaction is favorable to seed germination.     

SEED DORMANCY AND GERMINATION IN MELAMPYRUM LINEARE

Immature seeds of Melampyrum lineare Desr. have very high germination percentages and dormancy is induced in a variable fraction of the seed crop during ripening. Correlated with this is the endogenous gibberellin-like activity which is found in considerable amounts in immature seeds, less in batches of ripe seeds, and is not detectable in batches containing only dormant seeds. For germination dormant seeds require activation followed by cold storage. In the laboratory activation is produced by allowing moist, dormant seeds to respire freely for several weeks at 20 C, or by treatment with exogenous GA₃. Dormancy appears to be most directly related to inability of the embryo to hydrolyze the thickened, mannan-containing endosperm cell walls. Embryos excised from dormant seed can be grown on agar enriched with whole macerated dormant seeds or with the ethanol-extractable materials from these (mostly sucrose and a glycoside). However, dormant seed material does not support growth when extracted to remove benzene- and ethanol-soluble materials.     

蒿属和千里光属植物中桉烷型倍半萜的光谱特征

本文就菊科中的两个大属蒿属和千里光属植物中一类典型倍半萜成分——桉烷型倍半萜的光谱特征进行综述.     

花生种子萌发过程中胚轴多胺氧化酶的活性变化

研究花生（Ａｒａｃｈｉｓｈｙｐｏｇａｅａ）种子萌发过程中胚轴多胺氧化酶（ＰＡＯ）的活性变化及其与种子萌发的关系表明：胚轴中的ＰＡＯ活性是在种子萌发过程中逐渐形成的,而黑暗条件更有利于该酶的活性形成;放线菌素Ｄ（１０ｍｇ／Ｌ）、环己酰亚胺（１０ｍｇ／Ｌ）处理对种子萌发的抑制率分别为２６．３％和８７．３％,对胚轴ＰＡＯ活性的抑制率分别为４１．１％和９４．０％,显示胚轴中的ＰＡＯ很可能参与花生种子的萌发过程,且其ｍＲＮＡ在种子发育过程中已合成并贮存于种子中,萌发时ＰＡＯ活性的出现主要是由于这些ｍＲＮＡ转译合成了ＰＡＯ。     

AFTER-RIPENING AS A FACTOR IN LETTUCE SEED GERMINATION RESPONSE

The physiological state of lettuce seeds could be divided into three distinct stages. The first is the dormant stage, the second is the nondormant one and the third is the deteriorating one. The dormant and the deteriorating stages can be classified further into three phases, respectively, by the actions of germination temperature, red light, and chemical substances. The effects of an exposure to red light and of the application of gibberellic acid A₃ and thiourea on germination can be divided into two functions: 1) dormancy-releasing effect on dormant seeds, and 2) stimulating effect on aged seeds which have reduced their germinability.     

INTERACTION OF GIBBERELLIN A3, AND INORGANIC PHOSPHATE IN TOBACCO SEED GERMINATION

1. Investigation was made on the influence of inorganic phosphateupon the germination of positively photoblastic tobacco seed(Nicotiana tabacum L. var. uirginica (AGDH.) COM. "Bright Yellow")induced by GA₃, GA₃M, kinetin, red light, and ammonium saltsof various organic acids.
2. Inorganic phosphate increases theGAs-induced germination, andinhibits the germination causedby ammonium citrate, while itdoes not influence the germinationbrought about by GA₃M, kinetin,and red light.
3. The optimumpH for the GA₃-induced germination lies in the acidicpH range,indicating that the undissociated form of GA₃ is operative.The stimulatory effect of phosphate is, however, not ascribedmerely to the pH control in the mediurr. Phosphate exerts somespecific influence for which the presence of the free carboxylgroup of GAs is required.
4. The observed contrasting effectsof phosphate on the GA₃-inducedgermination (i.e., acceleration),on the one hand, and on theammonium citrate-induced germination(i.e., inhibition), onthe other, were explained by assumingthat the phosphate effectsultimately consist in acceleratingthe uptake of the carboxylicacid into the seeds.
5. GA₃M alsohas an activity of inducing the germination of tobaccoseedwithout light.

¹Present address: Department of Vegetable Crops, Universityof California, Davis, California, U.S.A. (Received March 12, 1962; )