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121.
云南热带种子植物区系 总被引:27,自引:2,他引:25
云南热带是指云南东南,南极西南的沿边热带地区,其地理范围在现今热带雨林及热带季雨林分布的区域。其种子植物区系有4915种,隶属于1447属和248科,基本上是热带北缘性质但同时明显表现出向亚热带过渡的特点。经分析,云南热带东西两侧的地理联系,替代现象、特有现象和区系起源和演化上有很大差异。其原因可能有不同地史背景。因此,将云南热带东西两侧划分古热带植物区中两个不同的植物区系地区是合理的,但其范围和 相似文献
122.
粤北大东山种子植物区系研究 总被引:1,自引:0,他引:1
大东山位于广东北部,地理位置约为24°50′~25°00′N,112°37′~112°47′E。大东山有种子植物161科,560属,1124种。其中裸子植物6科,10属,14种;被子植物155科,550属,1110种。大东山区系的表征科是蔷薇科、樟科、茶科、壳斗科、山矾科、冬青科、木兰科、安息香科和金缕梅科。属的地理成分组成为热带分布属占54.34%,温带分布属占45.66%。本区系与江西九连山及福建武夷山区系有密切的联系,与黑石顶、大瑶山和花坪区系的联系也较紧密。大东山区系属华南地区的一部分。 相似文献
123.
沙坡头人工固沙区的种子库动态 总被引:77,自引:0,他引:77
沙坡头人工固沙区的土壤种子库中共有46种植物的种子,属于17个科。其中菊科植物最多,达11种;其次为藜科,7种;禾本科7种;豆科4种。既是现有植被组分种,其种子又存在于种子库中的,占总种数的33.3% 。油蒿(Artem isia ordosica)、花棒(Hedysarum scoparium )和柠条(Caragana korshinskii)的种子产量为545±676.73粒/m 2、6.67±13.74粒/m 2、0.032±2.43×10- 3粒/m 2。油蒿在植株上成熟时不受虫害,而花棒、柠条的种子受害比例分别为31.92% 和83.29% 。在最适埋藏深度下,油蒿、柠条、花棒种子的累积发芽率分别可达78.3% 、85.0% 和66.7% ;萌发速度:油蒿> 柠条> 花棒。根据种子库动态分析和植被调查结果可初步预测:沙坡头人工固沙植被的演替趋向将是灌木以油蒿为主,草本以雾冰藜(Bassia dasyphylla)、小画眉草(Eragrostispoaeoides)为主的群落 相似文献
124.
An examination was made of the structure of the coats of Scots pine (Pinus sylvestris L.) seeds of different provenance and the contribution of this factor to differences in imbibition. The seed coat layers
derived from the integument, the sarcotesta, sclerotesta and endotesta did little to restrict imbibition, even though the
sclerotesta of the northern provenance seeds was composed of a double multicellular layer and the sarcotesta contained large
numbers of pigmented, phenol-bearing cells. In addition to the micropyle, the sclerotesta was found to possess structural
openings at the chalazal end and at the ridge joining the two halves of the seed, but being covered by the pigmented cells
of the sarcotesta, these did not allow water to enter any more than did the micropyle itself. Imbibition was chiefly regulated
by the lipophilic covers surrounding the endosperm, which are mainly of nucellar origin, especially by the megaspore membranes
nearest to the endosperm, the outer and inner exine. The nucellar cap covering the micropylar end of the endosperm proved
to be impermeable to water, and its edge extended between the exine layers, which further enhanced the importance of the endosperm
covers as regulators of imbibition. 相似文献
125.
Evidence presented elsewhere (G.B. Williams, E.M. Elder, and M. Sussman 1984, Dev. Biol. 105, 377-388) indicates that NH3 and certain carboxylic acids including propionate, succinate, and acetate modulate the cAMP relay in Dictyostelium discoideum. The former appears to act as a cAMP accumulation inhibitor, the latter as cAMP release inhibitors. The cohesive properties of aggregation competent cells have been assayed quantitatively in the presence of these modulators. The following results were obtained: (1) At pH 7.5, EDTA-resistant cohesivity was greatly inhibited by NH4C within the concentration range tested (30-3.8 mM). Even at the higher concentrations the effect was not immediate but required ca. 10 min for full expression. At the lower concentrations, the inhibitory level was only slightly reduced but the time for full expression progressively increased. At pH 6.5, the level of inhibition was marginal, indicating that NH3 is the active molecular species. By themselves, neither ambient pH nor ionic strength appeared to affect cohesive performance within the ranges employed. The inhibition was immediately and completely reversed upon removal of NH4Cl or a shift of ambient pH from 7.5 to 6.5. The presence of cycloheximide did not affect the recovery of cohesivity after NH4Cl removal. (2) The presence of 15 mM succinate, propionate, or acetate also reduced cell cohesivity. The timing and extent of the inhibition were identical at pH 7.5 and 6.5. The inhibition was expressed immediately and was reversible. Each of the acids acted synergistically with NH4Cl. The relative potencies of these metabolites acting singly or in combination as inhibitors of cohesivity corresponded roughly to their potencies as modulators of the cAMP relay (Williams et al., 1984). (3) The sensitivity to the metabolites was stage specific, being maximal during and shortly after aggregation and disappearing abruptly at 11-12 hr. This corresponds to the time at which this cohesive system, responsible for the end-to-end cell associations evident during aggregation (H. Beug, G. Gerisch, S. Kempff, V. Riedel, and G. Cremer, 1970, Exp. Cell. Res. 63, 147-158) is supplanted by a newly arisen, serologically and genetically distinct system which thereafter maintains the integrity of the aggregate (C. Steinemann and R.W. Parish, 1980, Nature (London) 286, 721-724; D.K. Wilcox and M. Sussman, 1981, Dev. Biol. 82, 102-112, and Proc. Natl. Acad. Sci. USA 78, 358-362; C.L. Saxe III and M. Sussman, 1982, Cell 29, 755-759). The activities of the metabolites, detailed above, are discussed in relation to their previously demonstrated activities as morphogens. 相似文献
126.
A short period (15–30 min) at 30° C promotes germination of seeds of Lactuca sativa L. cv. Repolhuda in darkness. Far-red light reverses this stimulation, and the escape curves for phytochrome and high-temperature action are quite similar, indicating that the two factors act at a common point in the chain of events leading to germination. It is suggested that high temperature acts by decreasing the threshold of the active, far-red absorbing, form of phytochrome (Pfr) needed to promote germination.Abbreviations FR
far-red light
- Pfr
far-red-absorbing form of phytochrome
- R
red light 相似文献
127.
The seed coat morphology, investigated in taxa representative of the main European groups ofAconitum, are in good agreement with the current taxonomy of the genus. The seed coat microcharacteristics (warty epidermal cells) are very constant. There is a trend for the reduction of longitudinal wings on the edges concomitant with the development of ridges and transverse wings on the faces. Another morphological progression leads from smooth to rugulose and eventually to transverse wing-bearing seed faces. A working hypothesis suggests an ecological adaptative significance to these changes. 相似文献
128.
M. H. Soliman 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1980,56(4):175-182
Summary Seeds from 27 wild strains (18 tetraploids and 9 diploids) of Glycine weightii were germinated at a pH range of 5 to 8. The differences in germination (%) between all the strains were highly significant but between pH levels they were only nearly significant (P=0.067) with no interaction between pH levels and strains. Mean germination (%) for all tetraploids seems to be slightly higher ( 2%) than that for all diploids, especially at pH's 5, 7 and 8 but this may be due to the significantly longer time ( one day) it took tetraploids to complete germination. The apparent inverse relationship between seed weight and germination (%) was not significant.Mean germination time was highly significant for strains, pH's and their interaction. Increasing mean germination (%) resulted in decreasing mean germination time among strains. Large seeds took less time to germinate especially those from some of the tetraploid strains. This indicates that it is possible to produce a variety with high germination (%), fast germination rate and possibly large seeds. If the marked difference in pH tolerance among strains will prove to be mainly hereditary, then it will be also possible to select for either specific pH tolerance or tolerance at a wide range of pH. 相似文献
129.
Miss S. Dobrofsky Dr. W. F. Grant 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1980,58(2):157-160
Summary A study of seed position in the pod ofLotus corniculatus L. cv. Mirabel (Fabaceae) suggested that reduced seed set after self-pollination is not due to an inability of the self-pollen tube to reach the end of the ovary. As in other cultivars, it has been demonstrated that cultivar Mirabel produced less seed per pod and shorter pods after self- than after cross-pollination. No differences were noted for percent germination of seeds produced by both types of pollination indicating that the number of seeds per pod is a reliable index of the ultimate productive potential of the pollination. 相似文献
130.
The development of glyoxysomal malate dehydrogenase (gMDH, EC 1.1.1.37) during early germination of watermelon seedlings (Citrullus vulgaris Schrad.) was determined in the cotyledons by means of radial immunodiffusion. The active isoenzyme was found to be absent in dry seeds. By density labelling with deuterium oxide and incorporation of [14C] amino acids it was shown that the marked increase of gMDH activity in the cotyledons during the first 4 days of germination was due to de novo synthesis of the isoenzyme. The effects of protein synthesis inhibitors (cycloheximide and chloramphenicol) on the synthesis of gMDH indicated that the glyoxysomal isoenzyme was synthesized on cytoplasmic ribosomes. Possible mechanisms by which the glyoxysomal malate dehydrogenase isoenzyme reaches its final location in the cell are discussed.Abbreviations mMDH
mitochondrial malate dehydrogenase
- gMDH
glyoxysomal malate dehydrogenase
- D2O
deuterium oxide
- EDTA
ethylenediaminetetraacetic acid, disodium salt 相似文献