Tapetal Organization During Sporogenesis in Psilotum nudum

Stages in the differentiation of the tapetum of Psilotum nudumare described. Two concurrently occurring components of thetapetum can be recognized. A plasmodial tapetum with associatedfunctional nuclei develops within the sporangial loculus duringthe early stages of differentiation, appears to remain viablefor several months, that is during the entire period of sporogenesis,and undergoes reorganization on three occasions. During MeiosisI groups of spore mother cells are enclosed in clear areas withinthe plasmodium: by the end of Meiosis II each tetrad is isolatedin a plasmodial chamber; and, finally, mature spores are enclosedwithin individual tapetal chambers. Typically enlarged cellsare present during the development of a cellular, parietal tapetum.A sporopollenin-containing layer or tapetal membrane characteristicof a secretory tapetum develops on the inner tangential walland lines the surface of the loculus. This tapetal membranepersists even after dehiscence of the sporangium. These observationsare discussed in relation to previously published conflictingdata and may be relevant to the arguments concerning the relationshipof the Psilotaceae to the Filicales. Psilotum nudum, light microscopy, parietal tapetum, plasmodial tapetum, tapetal membrane, tapetal reorganization, sporogenesis, sporopollenin     

The dynamics of the actin cytoskeleton during sporogenesis in Psilotum nudum L.

The actin cytoskeleton (microfilaments, MFs) accompanies the tubulin cytoskeleton (microtubules) during the meiotic division of the cell, but knowledge about the scope of their physiological competence and cooperation is insufficient. To cast more light on this issue, we analysed the F-actin distribution during the meiotic division of the Psilotum nudum sporocytes. Unfixed sporangia of P. nudum were stained with rhodamine-phalloidin and 4′,6-diamidino-2-phenylindole dihydrochloride, and we monitored the changes in the actin cytoskeleton and nuclear chromatin throughout sporogenesis. We observed that the actin cytoskeleton in meiotically dividing cells is not only part of the kariokinetic spindle and phragmoplast but it also forms a well-developed network in the cytoplasm present in all phases of meiosis. Moreover, in telophase I F-actin filaments formed short-lived phragmoplast, which was adjacent to the plasma membrane, exactly at the site of future cell wall formation. Additionally, the meiocytes were pre-treated with cytochalasin-B at a concentration that causes damage to the MFs. This facilitated observation of the effect of selective MFs damage on the course of meiosis and sporogenesis of P. nudum. Changes were observed that occurred in the cytochalasin-treated cells: the daughter nuclei were located abnormally close to each other, there was no formation of the equatorial plate of organelles and, consequently, meiosis did not occur normally. It seems possible that, if the actin cytoskeleton only is damaged, regular cytokinesis will not occur and, hence, no viable spores will be produced.     

Anaesthetic Enhancement of Echinochloa crus-galli (L.) Beauv. Seed Germination: Possible Membrane Involvement

Taylorson, R. B. 1988. Anaesthetic enhancement of Echinochloacrus-galli (L.) Beauv. seed germination: possible membrane involvement.—J.exp. Bot 39: 50–58. Dormant E. crus-galli seeds can be stimulated to germinate bycontact with solutions of several anaesthetic-like substances.The order of activity was n-pentanol > benzyl alcohol >n-butanol > n-propanol > ethanol. 2-propanol is nearlyinactive. The relative activity of the substances as germinationstimulants is closely related to their membrane-buffer partitioncoefficients in a manner similar to their effectiveness as anaestheticsin animals. Thus, n-pentanol is a more active stimulant of germinationthan ethanol and its increased effectiveness is correlated witha higher membrane-buffer partition coefficient Similarly, ananaesthetic that stimulated germination (n-propanol) causedgreater leakage of electrolytes, U.V. absorbing substances andamino acids from E. crus-galli seeds than a substance that wasnot active as a germination stimulant (2-propanol). In animals,action of anaesthetics can be prevented by application of externalpressure, an argument for membrane action. Action of n-propanolin stimulating germination can be similarly prevented by pressurein E. crus-galli seeds. The several lines of evidence supporta membrane action for anaesthetic-like substances in seeds and,accordingly, a membrane site as the locus of seed dormancy. Key words: Anaesthetics, germination, membranes     

Nodules associated with axial cores and synaptonemal complexes during zygotene in Psilotum nudum

Two-dimensional spreads of synaptonemal complexes (SCs) from the lower vascular plant Psilotum nudum were examined after staining with uranyl acetate-lead citrate (UP). Staining with UP allows visualization of lateral elements/axial cores (ACs), central elements, kinetochores, and nodules. Numerous darkly stained nodules were associated with forming SCs. In addition to nodules found on the central element of SC segments, other nodules were found at points of convergence between two adjacent ACs. Of these latter nodules, some were obviously associated with a fiber that connected adjacent ACs. No central element material was visible between the ACs, and the nodule complex appeared to be the only structure holding the ACs together. Although the function(s) of nodules during zygotene is unknown, the presence of a nodule-fiber complex that connects adjacent ACs before central element formation suggests that at least some of the nodules may be involved in synaptic initiation.     

新模式禾草植物短柄草的研究现状

随着短柄草基因组测序基本完成,短柄草其因生长周期短、植株矮小、基因组较小及在进化上比水稻与小麦的亲缘关系更为接近等特点,成为继水稻之后,加速获取遗传信息相对缺少的小麦等相关物种遗传信息的新兴起的禾草类模式植物。对近年来有关短柄草的生理生化、组织培养、实验室条件下各生态型的生长状况,分子及细胞遗传学等方面的研究加以综述,希望对这一新的禾草类模式植物有进一步的了解。     

Correlative Inhibition in the Shoot of Agropyron repens ( L.) Beauv

Correlative inhibition was investigated in plants of Agropyronrepens at two temperatures. Reciprocal inhibition ocrurred betweenthe main shoot apex and the outgrowing axillary shoots, withthe balance of inhibition varying with temperature. Apical dominancewas stronger at 10 °C than at 20 °C , but even at 10°C release of apical dominance by decapitation had onlyminor effects on the timing of outgrowth, growth pattern andrate of dry weight aocumulation of the axillary shoots. Dominanceof the main shoot apex by the axillary shoots was stronger at20 °C than at 10 °C. Removal of axillary buds preventeddecline in size and activity of the main shoot apex ard resultedin increased rates of primordium initiation, leaf emergenceand dry weight accumulation in the main shoot. It is suggestedthat a system of reciprocal dominance provides a mechanism formaintaining the characteristic habit of the grass plant andlimits growth in height of vegetative shoots. Agropyron repens (L.) Beauv, couch grass, correlative inhibition, apical dominance, shoot, apex     

Some competition experiments with alang-alang (Imperata cylindrica (L.) Beauv.) in replacement series

Summary The interaction between alang-alang (Imperata cylindrica) and maize or sorghum was studied in competition experiments according to the replacement principle. Dry matter yield of alang-alang in these experiments appeared hardly affected by the presence of maize or sorghum, while this yield of the latter two was strongly reduced by the presence of alang-alang. The relative yield total (RYT) reached unity except in one experiment in which a value of 0.6 was obtained.The results suggest that the allelopathic activity of alang-alang will find expression in an RYT deviating from one only if alang-alang is not able to utilize all available space.Part of the research supported by the Netherlands Foundation for Advancement of Tropical Research (WOTRO) grant W86-34     

Growth of the Stem of Agropyron repens (L.) Beauv

The growth rate of the stem of Agropyron repens (L.) Beauv.begins to decline when the sixth foliage leaf has expanded butthe relative growth rate declines throughout the period betweenthe production of one and ten mature leaves. On an absolutetime scale there is a progressive decline in growth rate ofsuccessively formed stem (node-internode) units. On a plastochronscale the relative growth rate of successive stem units declineswithin the apical region but increases behind the apex. Thedecline in the apical region is related to a decrease in therate of cell division and in the later formed stem units thereis no significant increase in cell number from the time of theirformation by the apex until the internode is initiated duringtheir fourth plastochron. These changes are related to concurrentchanges in the size of the shoot apex and in rates of leaf growth.     

Seed defensins of barnyard grass Echinochloa crusgalli (L.) Beauv

From the annual weed barnyard grass Echinochloa crusgalli (L.) Beauv., two novel defensins Ec-AMP-D1 and Ec-AMP-D2 that differ by a single amino acid substitution were isolated by a combination of different chromatographic procedures. Both defensins were active against several phytopathogenic fungi and the oomycete Phytophthora infestans at micromolar concentrations. The Ec-AMP-D1 showed higher activity against the oomycete than Ec-AMP-D2. The comparison of the amino acid sequences of the antifungal E. crusgalli defensins with those of earlier characterized T. kiharae defensins [T.I. Odintsova, Ts.A. Egorov, A.Kh. Musolyamov, M.S. Odintsova, V.A. Pukhalsky, E.V. Grishin, Seed defensins from T. kiharae and related species: genome localization of defensin-encoding genes, Biochimie, 89 (2007) 605-612.] that were devoid of substantial antifungal activity point to the C-terminal region of the molecule as the main determinant of the antifungal activity of E. crusgalli defensins.     

The evaluation of Murray's law in Psilotum nudum (Psilotaceae), an analogue of ancestral vascular plants

Previous work has shown that the xylem of seed plants follows Murray's law when conduits do not provide structural support to the plant. Here, compliance with Murray's law was tested in the stem photosynthesizer Psilotum nudum, a seedless vascular plant. Psilotum nudum was chosen because the central stele does not provide structural support, which means that Murray's law is applicable, and because its simple shoot structure resembles the earliest vascular plants. Murray's law predicts that the sum of the conduit radii cubed (Σr(3)) should decrease in direct proportion with the volume flow rate (Q) to maximize the hydraulic conductance per unit vascular investment. Agreement with Murray's law was assessed by estimating the transpiration rate distal to a cross-section, which should determine Q under steady state conditions, and comparing that with the Σr(3) of that cross-section. As predicted, regressions between the Σr(3) of the cross-section and Q resulted in a linear relationship with a y-intercept that was not different from zero. Two more rigorous statistical tests were also unable to reject Murray's law. Psilotum nudum plants also increased their conductance per investment by having more conduits distally than proximally, which is more efficient hydraulically than equal or declining conduit numbers distally.     

A Study of the Nitrogen and Water Factors in Competition with Agropyron repens (L.) Beauv.

From a consideration of the possible relationships between thelevel of a nutrient in the soil, the depletion due to a competitor,and the response of a test plant, it is argued that a validcriterion for the implication of a nutrient factor in root competitionis that some growth response of the test plant to competitionshould be less at higher levels of supply of that nutrient thanat lower levels. Young test plants of Impatiens parviflora were transplantedinto pans of soil in which stands of Agropyron repens were growing.Two levels of nitgrogen and gtwo rates of watering were appliedin a multifactorial design, and from half of the test plantsroot competition was excluded, so that their responses to rootcompetition could be measured under the various nitrogen andwatering treatments. A preliminary experiment hadf shown, and the competition experimentconfirmed, that the optimum nitrogen level for root growth andNet Assimilation Rate was less than the higher level employed,whereas this level was not sufficient for maximum leaf-growth.In agreement with this, the depressions of relative root growth-rateand Net Assimilation Rate caused by competition at the lowernitrogen level were significantly reduced at the higher level,but for relative leaf-growth this reduction did not reach significance.The effects of competition were reduced by the higher rate ofwstering, and for relative leaf growth-rate this interactionwas highly significant. It is deduced that competition from A. repensfinvolves bothnitrogen and water, and that water is probably the more importantfactor under normal conditions. There is no need to postulkateany toxic root product to account for the experimentalo results.Compared with competition above ground, it appeared that rootcompetition could have an effect on the relative growth-rateof I. parviflora about as great as a reduction of light intensityfrom full to 5–10 per cent. of summer daylight.     

Rates of Leaf Initiation and Leaf Growth in Agropyron repens (L.) Beauv.

Rates of leaf initiation, emergence, and growth have been measuredduring the period between the production of one and of ten matureleaves on the primary shoot of Agropyron repens. There is aprogressive decline in the growth rate of successively formedleaves so that at the time of formation of the next leaf primordiumeach primordium is smaller than its predecessor at a comparablestage of development. There is also a trend towards a diauxicpattern of growth with a lag phase apparently coinciding withthe transition from apical to intercalary growth of the youngleaf. Up to the six-leaf stage the rate of leaf formation exceedsthe rate of emergence and leaf primordia accumulate on the shootapex. Thereafter the rate of emergence exceeds the rate of formation.These changes in rates of leaf formation and growth are interpretedin terms of competition for assimilates between expanding leavesand leaf primordia, and between the primary and axillary shootapices.     

The Development of the Shoot Apex of Agropyron repens (L.)Beauv.

During the phase of growth between the production of one and10 mature leaves the primary shoot apex of Agropyron repensundergoes first an increase and then a decrease in size. Theapical dome was found to attain a maximum size at the six leafstage. The changes are attributable to changes in cell number,mean cell size remaining constant after an initial decrease.The zonation pattern, and particularly the number of tunicalayers, varies with the size of the dome. The apex as a wholeundergoes a greater increase in height than in diameter, withcommensurate changes in the number of leaf primordia presentupon it. Similar changes occur in the tiller but no such obvioustrends were found in the rhizome. In an experiment in whichall axillary buds were excised from the primary shoot it wasfound that the apex continued to increase in size well beyondthe maximum attained by that of an intact plant. On this evidenceit is suggested that the eventual decline of the primary shootand tiller apices is due to an inhibitory effect on the mainshoot by the developing axillary shoots.     

Tapetal Cell Changes and Sporoderm Development in Rhigozum trichotomum (Burch.)

Rhigozum trichotomum is a perrenial woody shrub which is indigenousto the arid regions of southern Africa. Primexine developmentis initiated while the microspores are still enclosed by callose.This is followed by the appearance of probacula which give riseto the tectum, bacula and nexine. At the time of callose dissolution,the exine pattern is well established and intine developmenthas been initiated. During the tetrad stage, the protoplastsof the tapetal cells exhibit shrinkage while conspicuous stacksof rough endoplasmic reticulum become evident in their cytoplasm.These stacks produce numerous vesicles which are associatedwith lipid globules and which migrate to the tapetal/locularwall where, it is suggested, they give rise to the pro-orbicules.The pro-orbicules become coated with an osmiophilic substance,probably sporopollenin, and are released into the thecal fluidto become intimately bound to the exine, Here they are strippedof the osmiophilic layers which appear to be incorporated intothe sporoderm. Rhigozum trichotomum (Burch.), sporoderm, pollen wall, exine, orbicules, pro-orbicules, sporopollenin, tapetum     

Development and utilization of novel intron length polymorphic markers in foxtail millet (Setaria italica (L.) P. Beauv.)

Introns are noncoding sequences in a gene that are transcribed to precursor mRNA but spliced out during mRNA maturation and are abundant in eukaryotic genomes. The availability of codominant molecular markers and saturated genetic linkage maps have been limited in foxtail millet (Setaria italica (L.) P. Beauv.). Here, we describe the development of 98 novel intron length polymorphic (ILP) markers in foxtail millet using sequence information of the model plant rice. A total of 575 nonredundant expressed sequence tag (EST) sequences were obtained, of which 327 and 248 unique sequences were from dehydration- and salinity-stressed suppression subtractive hybridization libraries, respectively. The BLAST analysis of 98 EST sequences suggests a nearly defined function for about 64% of them, and they were grouped into 11 different functional categories. All 98 ILP primer pairs showed a high level of cross-species amplification in two millets and two nonmillets species ranging from 90% to 100%, with a mean of ～97%. The mean observed heterozygosity and Nei's average gene diversity 0.016 and 0.171, respectively, established the efficiency of the ILP markers for distinguishing the foxtail millet accessions. Based on 26 ILP markers, a reasonable dendrogram of 45 foxtail millet accessions was constructed, demonstrating the utility of ILP markers in germplasm characterizations and genomic relationships in millets and nonmillets species.     

Induced mutations in foxtail millet (Setaria italica Beauv.)

Summary Viable mutations for ear characters in two cultures of foxtail millet (Setaria italica Beauv.) were induced by individual and combined treatments of gamma rays, EMS (ethyl methanesulphonate), and dES (diethylsulphate). Four doses of gamma rays (10Kr to 40Kr), and four durations (6hrs to 24hrs) each of EMS (0.1 %) and dES (0.1 %) were used. In the combined treatments, only two durations (6hrs, 12hrs) of the chemical mutagens were used following each of the four doses of gamma rays.The mutation frequencies were recorded as mutants per 100 M₂ plants and these were found to be higher in MU-1 than in MU-2 in all the treatments except dES. The frequencies also increased with increase in dose or duration of treatments and were found to be much higher in the combined treatments than in the individual treatments. In several combined treatments, a synergistic effect was observed in culture MU-1, the degree of synergism ranging from 1.01 to 1.62. Thus there was a differential response by the two cultures to the mutagenic treatments. The mutation spectrum was also found to be wider in culture MU-1, where 11 different kinds of mutants were recorded compared with only eight kinds of mutants recorded in MU-2.     

Thermotropic Properties of Cellular Membranes in Dormant and Non-Dormant Echinochloa crus-galli(L.) Beauv. Seeds

Steady-state fluorescence polarization measurements with l,6-diphenyl-l,3,5-hexatriene(DPH) were used to monitor thermotropic transitions in microsomalfractions and plasma membrane vesicles isolated from barnyardgrass[Echinochloa crus-galli (L.) Beauv.] seeds during the transititionfrom dormancy to germination. The effect of dormancy-relievingor inactive alcohols on the thermotropic properties of the cellularmembranes was determined both in vivo and in vitro. Membranefractions isolated from dormant seeds showed some discontinuitiesin the Arrhenius plots. In non-dormant or germinating seedscellular membranes showed linear Arrhenius plots over the entirerange of temperature examined. Membrane preparations from imbibedseeds showed a similar pattern in their Arrhenius plots upontreatment with the various alcohols in vitro. The results suggestthat the release from dormancy in seeds is associated with somechanges in their cellular membranes. Key words: Germination, alcohols, thermotropic transition