Plant regeneration from hypocotyl and petiole callus of Trifolium pratense L.

Red clover (Trifolium pratense L.) seedlings were screened for the ability to regenerate plantlets from hypocotyl-derived callus tissue. Media sequences described by Beach and Smith (1979) and Collins and Phillips (1982) and a variation using media from both sequences were tested. Plantlets were regenerated from three out of 642 genotypes. In all three cases, callus was initiated on B5C medium and regeneration was accomplished on SPL medium. Attempts to regenerate plants from petiole-derived callus tissue have so far been successful only with regenerants of clone F49. Petiole callus from epicotyl-derived F49 plants proved to be non-regenerative. Pollen viability varied significantly among individuals regenerated from callus cultures of clone F49. Root tip squashes from F49 regenerants revealed the normal diploid chromosome number (2n=14). The frequency of regeneration within progeny from reciprocal crosses between F49 regenerants and several non-regenerative genotypes was 29%.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - BAP benzylaminopurine - KN kinetin - NAA -naphthaleneacetic acid     

白三叶和红三叶对人工融冻胁迫的生理响应差异

采用人工模拟融冻胁迫方法,通过测定白三叶(Trifolium repens)和红三叶(T.prat-ense)在融冻胁迫中叶片细胞膜透性、MDA含量、抗氧化酶(SOD、POD、CAT)活力、渗透调节物(脯氨酸、可溶性糖和蛋白质)含量变化,以揭示未来气候变化对三叶草的影响。结果表明,经历融冻胁迫循环后抗冻力强的白三叶植株能恢复生长,而抗冻力弱的红三叶枯萎死亡。在融冻阶段,两三叶草叶片细胞膜透性增大、抗氧化酶活力增高、MDA和渗透调节物含量大幅增加;在冻融阶段,两三叶草叶片细胞膜透性降低、MDA含量下降、抗氧化酶活力降低。但在融冻胁迫循环中,白三叶叶片POD和CAT活力高于红三叶,脯氨酸含量较红三叶高5倍,但细胞膜透性低于红三叶。白三叶在-5℃抗逆生理指标达到最大值,而红三叶在-10℃。白三叶对环境温度变化反应敏感,在-5℃通过快速激活抗氧化酶系统和积累渗透调节物以抑制膜脂过氧化和维护细胞水分平衡在融冻适应上起重要作用。白三叶具有较强的抗融冻能力,是未来值得应用推广的优良园林绿化植物。     

Pollen--stigma Interaction in the Leguminosae: the Secretory System of the Style in Trifolium pratense L.

The canal that traverses the upper part of the style of Trifoliumpratense is derived lysigenously. The core tissue of the veryyoung style consists of elongated cells similar to those ofthe transmitting tissue of solid-style families such as theSolanaceae; as the style matures, these cells separate to formthe canal, which receives secretions both from the core tissueand the inner wall cells. The early secretion of proteins intothe intercellular spaces is associated with the presence ofparamural bodies (lomasomes) in the adjacent cells. In the cellsin the immediate vicinity of the canal, vesicles, probably derivedfrom the Golgi system enlarge during later development and accumulatea protein-carbohydrate content, which is later passed into thecytoplasm where it forms densely packed fibrillar nodules. Withthe dissolution of the cell membranes, this material is passedinto the canal, where it is progressively diluted by continuedingress of water until the cavity reaches its final volume. Leguminosae, Trifolium pratense L., pollen—stigma interaction, self-incompatibility, stylar secretion, protein secretion     

The Micro Drop Recorder; A High Resolution Monitor of the Bleeding Rate of Plant Root Systems

The micro drop recorder is an accurate automatic instrumentwhich can detect within seconds small changes in the bleedingrate of sap. It is based on the micro drop recording technique.The reliability of the micro drop recorder can be proved bycalibration using an accurate pump. We report transient changesin bleeding rate that may not be detected by measurement techniquescurrently in use. Key words: Micro drop recorder, bleeding rate, automatic measurement     

A Threshold Value for Cutting Intensity in Relation to Fusarium Root Rot of Red Clover (Trifolium pratense L.)

Although cutting the foliage is known to increase Fusarium root rot severity in red clover (Trifolium pratense L.), no quantitative relationship has so far been determined. In this study, results from a number of greenhouse experiments, where plants were artificially inoculated with Fusarium avenaceum (Corda ex Fr.) Sacc., show a linear relationship between cutting intensity and Fusarium root rot in red clover, cv. ‘Hermes II’ an increased cutting intensity giving an increased root rot severity. Theoretically, a threshold value can be calculated beyond which no increase in root rot severity, compared to an uncut plant, should be expected.     

The Influence of Root Temperature, Rhizobium Strain and Host Selection on the Structure and Nitrogen-fixing Efficiency of the Root Nodules of Trifolium subterraneum

Low root temperature greatly affected the structure and N2-fixingefficiency of root nodules. More nodule tissue was formed perplant at 11 and 15 °C than at 7 and 19 °C. Low roottemperatures either prevented or slowed bacteroid differentiation;the differentiation zone was 19 per cent of the total noduletissue at 7 °C but only 5 per cent at 19 °C. The amount of bacteroid tissue formed at the different roottemperatures by the two fully effective strains TAi and SU297reflected the environment from which they originated. Both formedthe same amount at 15 and 19 °C but only TAI, which originatedfrom a cold environment formed bacteroids at 7 °C. At 7°C a bacteroid-filled cell did not degenerate until after20 days, cf. less than 10 days at 19 °C. At 7 and 11 °Call strains formed more bacteroids in the abundantly nodulatingthan in the sparse host independently of nodule number. Strain0403 was most sensitive to both temperature and host; it formedbacteroids in nodules on the sparse host at 19 °C only,but formed bacteroids in the abundant host between 7–19°C. The amount of bacteroid tissue formed by TAI and SU297 dependeddirectly on nodule number and was approximately constant between20–40 days only at 19 °C when nodule formation hadalmost stopped. The optimum temperature for maximum fixation of nitrogen wasnot necessarily that for maximum efficiency of fixation, whichfor these experiments was 51 ug N mm-3 bacteroid tissue perday.     

The Influence of Steep Slopes on Root System Development

Mechanical forces active on steep slopes tend to overturn plants, which respond by developing a specific asymmetrical architecture in the root system. This asymmetric architecture is the consequence of preferential lateral root emergence and elongation in the up-slope and down-slope directions. Root systems show a normal symmetrical architecture when the same species is grown on plane soil. The asymmetrical root architecture on steep slopes seems to increase the plant's stability by modifying the distribution of mechanical forces into the soil. This hypothesis is supported by the observation that lateral roots developing in the up-slope or down-slope directions present considerable anatomical modifications in shape and tissue-organization compared with lateral roots from plants growing on plane soil.     

The Influence of Steep Slopes on Root System Development

Mechanical forces active on steep slopes tend to overturn plants, which respond by developing a specific asymmetrical architecture in the root system. This asymmetric architecture is the consequence of preferential lateral root emergence and elongation in the up-slope and down-slope directions. Root systems show a normal symmetrical architecture when the same species is grown on plane soil. The asymmetrical root architecture on steep slopes seems to increase the plant's stability by modifying the distribution of mechanical forces into the soil. This hypothesis is supported by the observation that lateral roots developing in the up-slope or down-slope directions present considerable anatomical modifications in shape and tissue-organization compared with lateral roots from plants growing on plane soil.     

Gibberellin-induced Changes in Protein Synthesis and Enzyme Activity in Shoot Apices of Trifolium pratense

A mutant remaining vegetative in normally inductive long-dayconditions was used. Application of exogenous gibberellin A3(GA³) produced normal flowering under inductive long-days. Isolatedapices from treated and control plants were studied with regardto changes in size and rate of protein synthesis, as measuredby leucine incorporation. Two protein synthesis peaks were detected,one during the first 4 days after CA² application and a second,larger peak with a maximum at day 15. No consistent increasesin acid-phosphatase, aminotransferase, amylase, or peroxidasespecific activities could be associated with these peaks butan almost complete repression of alanine aminotransferase occurredduring the second protein synthesis period. The physiologicalimplications are discussed.     

The Influence of Temperature on Root Hair Infection of Trifolium parviflorum and T. glomeratum by Root Nodule Bacteria: II. EFFECTS OF CHANGES IN ROOT TEMPERATURE

When seedlings grown at low (6 or 12°C) or high (36°C)root temperatures were transferred to 24°C the rates ofroot hair infection increased rapidly, generally to above thatof plants kept at 24°C. This ‘switching-on’of the infection process occurred irrespective of the time oftransfer between 6 and 14 d, but transfers from 36 to 24°C,at times later than 6 d showed a small lag period before thenumbers of infections increased. Responses to late transferat 22 d from either 6 or 36°C to 24°C were less striking.A reverse transfer from 24°C to 6 or 36°C at any timelater than 4 d caused no change in the infection rate. Whenplants at 6°C were moved at different times to temperaturesin the range of 12—36°C for 8 h and then returnedto 6°C (double transfer) rates of infection were most increasedat 30°C; 36°C was inhibitory. The greatest and the quickestresponse was with plants transferred at 2 d; transfer at 10d had no effect. When plants grown at 6°C for 6 d were exposed to 24°Cfor 0.5, 1... 24 h and then returned to 6°C rates of infectionwere enhanced compared with plants held at 6°C; responseswere directly proportional to time (>1 h) spent at 24°C.Rates of infection were greatest immediately after transferand thereafter declined.     

Pollen-Stigma Interaction in the Leguminosae: the Organization of the Stigma in Trifolium pratense L.

The intact stigma of Trifolium pratense possesses a smooth receptivesurface fringed by a few ranks of brush hairs. This surfaceis ensheathed by a thin (75–100 nm) but highly impermeablecuticle, which encloses four to five ranks of secretory cellsimmersed in their secretory products. Experimental single-grainpollinations show that pollen cannot become hydrated or germinateon the intact surface. The cuticle is ruptured when the floweris tripped; the secretion is released, and captured pollen-selfor cross-can then germinate. As in other papilionoid Leguminosae,this mechanism provides a guard against premature selling. Thesecretory cells are elongated; they remain in communicationthrough persistent pit-fields as the intercellular spaces fillwith secretion product. The secretion forms a lipid-rich emulsion,with a mucilaginous aqueous phase which reacts cytochemicallyfor protein and carbohydrate and has esterase activity. Duringthe early development of the stigma head, the cells possessa fine-structure appropriate to their secretory function, withabundant ribosomal and smooth endoplasmic reticulum, stratifiedor in the form of ramifying and anastomosing tubules, numerousmitochondria and a well developed Golgi system. Lipid globuli,partly invested in endoplasmic reticulum, are abundant in theyoung cells, but there is as yet no indication of how the lipidis transferred to the intercellular spaces during the secretoryperiod. As the stigma matures, the secretory cells become moribund. Leguminosae, Trifolium pratenseL., pollen-stigma interaction, self-incompatibility, autofertility, stigma secretory system, lipid secretion, cuticle permeability     

The Effects of Rootzone Salinity and Hypoxia on Shoot and Root Growth in Trifolium Species

The effect of concurrent salinity (0-60 mM NaCl) and rootzonehypoxia (flooding for up to 15 d) on shoot and root growth andshoot ion concentrations of six species of Trifolium (T. subterraneumL., T. fragiferum L., T. michelianum Savi., T. isthmocarpumBot., T. purpureum Lois., and T. repens L.), was studied intwo greenhouse experiments. There was a significant salinityx flooding effect for shoot yield but no significant salinityx flooding x species interaction although individual speciesdiffered significantly (P < 0·001) in their growthresponse to the saline or flooded conditions separately. Concentrationsof Na and Cl in the shoots of all species increased with increasingperiods of saline flooding and there was a significant salinityx flooding interaction. Sodium and Cl concentrations were significantlyhigher (P < 0·001) in T. purpureum, the species inwhich shoot growth was most depressed by saline flooding, thanother species. In T. michelianum, T. fragiferum and T. repens,fresh and dry weight of roots increased with flooding underboth saline and non-saline conditions while in T. subterraneumroot growth decreased. A significant proportion of the increasedroot growth in the first three species occurred as new adventitiousroots. These roots had higher percentages of internal gas spaceswithin the root tissue even in the presence of salinity comparedwith roots from non-flooded conditions. There were also significantlymore gas spaces in the total root tissue in T. fragiferum andT. repens under saline-flooding than in roots of T. subterraneum.Electron micrographs of the root cross sections illustratedthe presence of these gas spaces or aerenchyma. Trifolium fragiferum, T. repens and T. michelianum are morelikely to be suited to growth in soils prone to high salinityand to flooding than are T. subterraneum, T. purpureum and T.ishmocarpum.Copyright 1993, 1999 Academic Press Trifolium subterraneum, Trifolium fragiferum, Trifolium michelianum, Trifolium isthmocarpum, Trifolium purpureum, Trifolium repens, salinity, flooding, hypoxia, adventitious roots, aerenchyma, subterranean clover, white clover, strawberry clover, purple clover, balansa clover     

The Development of Root Nodule Xylem Transfer Cells in Trifolium repens

Stereological analysis of micrographs of developing and functioningxylem transfer cells of Trifolium repens indicates that theER and dictyosomes may be involved in wall ingrowth deposition,and the ER in intracellular solute transport.     

Physiological Studies on Nodule Formation. The Characteristics and Inheritance of Abnormal Nodulation of Trifolium pratense by Rhizobium leguminosarum

Five to 7 per cent of plants of Trifolium repens L. and T.pratenseL. and 100 per cent of plants of T. subterraneum L. were nodulatedby Rhizobium leguminosarum but none of T. hybridum L., T. glomeratumL. or T parvifirum Ehrh. The frequency of nodulation of T. pratenseby R. leguminosarum was much increased by breeding from susceptibleplants. Such plants were not nodulated by bacteria isolatedfrom any other cross-inoculation group, but remained fully susceptibleto R. trifolii. The nodules formed by R. leguminosarum are generallyassociated with lateral roots and are ineffective.     

The Influence of Growing Temperature on the Growth and Morphology of Cereal Seedling Root Systems

The root systems of cereal seedlings (wheat, rye, barley, oats),grown in a series of liquid and solid media at 5, 15 and 25?C, were measured at intervals between sowing and emergence(shoot length 4.0 cm). In all cases, the length of seminal axesincreased linearly with time, and the rate of root extensionwas increased significantly by each 10 ?C increment in growingtemperature. In general, extension rates were lower in the solidmedia than in water culture; however, there was a strong interactionbetween medium and growing temperature, indicating that highertemperatures can compensate partly for the detrimental effectsof mechanical impedance. Examination of the influence of growing temperature upon rootaxis diameter was hampered by the observation that, for allfour species, apical root diameter was inversely related toroot length. It was concluded that comparison of the diametersof roots grown at different temperatures was valid only if theroots were of the same length (but different ages). Followingthis principle, it was found that, although cereal roots grownat 5 ?C tended to be slightly thicker than those at 15 ?C or25 ?C, this effect was small and rarely exceeded 10%. Publishedreports of very large differences in root diameter at differentgrowing temperatures were examined and found to be generallyunreliable. Lateral roots did not represent a significant fractionof the root system in any of the treatments studied. Root: shoot relationships at different growing temperatureswere examined by plotting root system length against shoot lengthfor each sample. It was found that, for the same shoot length,the root systems at 5 ?C were much shorter than at 25 ?C, theresponse at 15 ?C being rather more variable. This finding,which indicates that plants grown at low temperatures have alower capacity for water and solute uptake than those grownat laboratory temperatures, has important implications for thedesign of laboratory experiments. The influence of root zonetemperature upon root growth and physiology can be determinedunequivocably only if the roots have been exposed to the experimentaltemperature throughout their growth. Key words: Barley, Oats, Rye, Wheat, Root length, Root diameter, Root, shoot ratio     

Preliminary studies on sap-transmissible viruses of red clover (Trifolium pratense L.) in England and Wales

Red clover plants, collected from nine widely separated permanent pastures in England and Wales, were tested for sap-transmissible viruses. Viruses were identified by the symptoms they caused in test plants, by electron microscopy, and by serological tests. Of the 265 plants tested 14% were infected. Only pea mosaic virus was common and widespread; it was found in 8% of the plants, and in seven of the fields. Other viruses isolated were arabis mosaic, bean yellow mosaic, red clover mottle, and red clover vein mosaic; only red clover mottle virus produced diagnostic symptoms in red clover. No viruses were detected in seedlings grown from seed from eighty-nine commercial seed crops. Attempts to transmit red clover mottle virus by the Collembolan Sminthurus viridis L., which is common on red clover, failed.     

The Influence of Plant Extracts on Phytotoxin Production and Growth Rate of Alternaria helianthi

When liquid cultures of Alternaria helianthi were supplemented with aqueous extracts of leaf tissue of its host plant (sunflower), pronounced effects on both growth and production of the toxin deoxyradicinin were apparent. Very low levels of leaf extract stimulated toxin production but did not significantly affect growth, while higher levels markedly stimulated mycelial growth and at the same time toxin production was greatly suppressed. Leaf extracts of non-host plant species were also stimulatory to phytotoxin biosynthesis.     

Correlative effects of leaf age on reproductive growth in red clover (Trifolium pratense L.)

Summary The contribution of individual leaves towards the flowering response in red clover (Trifolium pratense L.) seedlings at the three-leaf stage is described. Removal of the first (oldest) or first and second leaves resulted in large increases (up to 300%) in both the rate of stem extension and the degree of apical differentiation.Removal of the youngest leaves depressed both processes. Application of cycloheximide to specific leaves produced effects similar to defoliation, but chloramphenicol was generally inhibitory and kinetin substantially ineffective. Translocation patterns between leaves and the shoot apex were studied using [¹⁴C] sucrose and [³H] gibberellin A₁. There was appreciable movement between leaves, but exposure to long-days depressed the transport of labelled assimilate. Label arriving at the apex was increasingly derived from the younger leaves as floral induction proceeded.Abbreviations CAP D-threo-chloramphenicol - CH cycloheximide - K Kinetin - Tris Tris(hydroxymethyl) amino methane - G.S.H. Glutathione (reduced) - E.D.T.A. ethylene diamino tetra acetic acid disodium salt