HowStriga Parasitizes its Host: a TEM and SEM Study

The cellular contact betweenStriga hermonthica andStriga asiaticaand their hosts,Zea mays andSorghum bicolor , was investigatedby light, transmission electron and scanning electron microscopy.The xylem connections between parasites and hosts involve veryspecific, clustered intrusions into the host's water conductingelements, predominantly into the large vessel elements. A singlehaustorial cell can penetrate a host vessel element with morethan one intrusion. All intrusions become covered by an additionalelectron-opaque wall layer. During subsequent differentiation,a dissolution of specific wall parts of the cell intrusionsoccurs so that open, cup- or trunk-like structures result. Thevessel-like host contact can comprise up to five openings withina single intrusion. Concomitantly, the intrusions and the haustorialcells to which they belong lose their protoplasts and transforminto elements which take up water. The walls of the haustorialcells and both wall parts of their appendages become stronglylignified. The water and nutrient absorbing structures insertedinto the host vessel are named ‘oscula’. Withinthe whole haustorial complex of bothStriga species no phloemelements were detected. Translocation of substances from hostto parasite are briefly discussed. Striga hermonthica ; Striga asiatica ; haustorial anatomy; xylem contact; osculum     

Ecological Marginalization Facilitated Diversification in Conifers

Evolutionary Biology - Species selection occurs when species traits influence speciation or extinction. But it is often difficult to demonstrate a net effect of traits on diversification, for...     

针叶松遗传转化操作的研究进展(英文)

1986年从火炬松方面获得了首例针叶松愈伤组织以后,针叶松遗传转化研究取得了明显的进展。1991年从Larix decidua方面获得了第一个转基因再生植株。最近,通过农瘤杆菌介导的转化方式在Larix kaempferi ( L. Decidua杂交树种上获得了转基因针叶松,通过鸟枪法在Picea glauca、Picea mariana、Picea abies、Larix laricina、Pinus radiata上亦获得了转基因植株。已经有多种办法用于转化针叶松。本文就目前在针叶松上所用的遗传转化方法??诸如：T－DNA转化法、农瘤杆菌介导转法化、鸟枪法、电转化法等给以粗略的评论。     

Diversifying Coevolution between Crossbills and Conifers

Coevolution between granivorous crossbills (Loxia spp.) and conifers has been a prominent process in the diversification of crossbills. A striking example occurs in western North America where coevolution between crossbills and Rocky Mountain lodgepole pine (Pinus contorta latifolia) is ongoing in isolated ranges without the crossbill’s dominant competitor for seeds, the red squirrel (Tamiasciurus hudsonicus). Preferential foraging by crossbills on lodgepole pine cones in the South Hills and Albion Mountains, two small mountain ranges in southern Idaho where red squirrels are absent, has led to the evolution of larger, thicker-scaled cones than in nearby ranges where red squirrels are present. This in turn has favored the evolution of larger-billed crossbills that have diverged from other crossbills in the region. However, such diversifying coevolution, resulting from geographic variation in the distribution of strongly interacting species, is vulnerable to species introductions. For example, the introduction of red squirrels caused the precipitous decline and perhaps extinction of the Newfoundland crossbill and perhaps a crossbill endemic to the Cypress Hills, Canada. In general, species introductions act to reduce the geographic variation in species interactions, which may be critical for the diversification of many taxa.     

ABA促进针叶树体细胞胚胎分化

文章介绍ABA促进针叶树体细胞胚胎分化调控机制和应用的研究进展     

Value Action of Bordered Pits in Conifers

The pressure needed to displace a bordered pit membrane to seala pit aperture is compared with that needed to force an air-sapmeniscus through the largest pit membrane pore. The former issmaller for early-wood pits, which thus prevent spread of airbubbles in the transpiration stream.     

Distribution of senna seymeria (Seymeria cassioides) a root parasite on southern pines

In 1969 senna seymeria [Seymeria cassioides (J. F. Gmel.) Blake], an annual of the figwort family (Scrophulariaceae), was found to be parasitic on roots of slash pine (Pinus elliottii Engelm.). Subsequent tests showed that the plant is an obligate parasite on at least three species of southern pines and is apparently selective for pines only. A southwide survey indicated that senna seymeria is most common on moist, sandy sites of the Lower Gulf and Atlantic Coastal Plains.     

Cambium Destruction in Conifers Caused by Pinewood Nematodes

Percentage and rate of mortality in 2-4-year-old conifers depended upon the numbers of pinewood nematodes Bursaphelenchus xylophilus inoculated into their stems. In addition, percentage of conifer mortality was greater for spring inoculations when cambial activity was greater than for late summer and fall inoculations. Gross and histological examination of stems revealed destruction of the cambial layer, including fusiform and ray intitials and their derivatives. These data suggest that cambial and ray destruction causes tree death through blockage of tracheids by gas, oleoresin, or metabolites from dying ray tissues.     

Racemochrysone,a dihydroanthracenone from Senna racemosa

From the hexane extract of the bark of the stems of Senna racemosa (syn. Cassia racemosa) a new dihydroanthracenone derivative, named racemochrysone, was isolated. Its structure was established as 8,9-dihydroxy-3-methoxy-2,2,6-trimethyl-(2H)-anthracen-1-one based on spectroscopical data, mainly 1D and 2D NMR experiments. In addition beta-sitosterol, stigmasterol, chrysophanol and physcion were obtained. From the leaves extracts the piperidine alkaloid cassine and the hexitol pinitol were obtained.     

Triassic Conifers as the basis for stratigraphical correlation

Floras with abundant Conifers have been recentlydiscovered in Siberia and China. They are correlated with the floras of the Voltzia sandstones of Western Europe.