Influence of Temperature and Ageing of Ovules and Pollen on Reproductive Success in Trifolium repens L.

Four clones of Trifolium repens L., originating from Iceland,Denmark and Israel, were cultivated in controlled environmentchambers at 10, 14, 18 and 22°C. Seed set at 10°C was,on average, 45% lower than at 18°C. Generally, seed frequencieswere higher in the stylar ovule positions than in the basal.This polarization became more pronounced at low temperatures.At least 30% of the decrease in seed set was caused by inadequatepollen tube growth. This was further supported by in vitro studieswhich showed that pollen developed significantly shorter pollentubes at low temperatures and a strong positive correlationbetween the capacity of male parents to induce seed set in basalovule positions and the length of pollen tubes in vitro. Femaleage, determined by days relative to anthesis, was also foundto have a significant influence on seed set, i.e. when pollinationwas delayed until the fifth day of flowering, seed set decreasedby an average of 60% when compared to florets pollinated onthe first day of anthesis. Pollen age did not influence seedset. Ageing of pollen decreased in vitro germinability, tubeelongation and the percentage of pollen tubes with sperm cells.Seed set, pollen germinability, pollen tube lengths, and abilityto form sperm cells in vitro varied significantly among clones.Copyright1994, 1999 Academic Press Trifolium repens, white clover, temperature, pollen tube, sperm cells, ovule fertility, seed set     

温度胁迫对白车轴草水浸提液化感作用的影响

采用蚕豆根尖细胞微核试验和染色体畸变试验,研究了温度胁迫下白车轴草水浸提液对蚕豆根尖细胞的化感作用。结果表明:不同温度(5℃、25℃和35℃)处理后的白车轴草的水浸提液对蚕豆根尖细胞有丝分裂指数的影响为低浓度促进,高浓度抑制。在白车轴草水浸提液的作用下,蚕豆根尖细胞内出现了多种染色体畸变,如微核、染色体断片、染色体桥、落后染色体等,对微核率和染色体畸变率的诱导效应表现为随水浸提液浓度的增大而增大。温度胁迫后的化感作用明显大于胁迫前,其化感效应表现为低温(5℃)下白车轴草水浸提液高温(35℃)常温(25℃)白车轴草水浸提液。推测原因可能是温度胁迫改变和增加了化感物质的释放。     

Phosphate and Membrane Electropotentials in Trifolium repens L.

In Trifolium repens L. there were immediate transient depolarizationsof the membrane electropotential (E_vo) when KH₂PO₄ was addedto phosphate-free media, but these were of the same magnitudeas the controls (K²SO⁴ and KCI). Furthermore, the extents ofdepolarization were the same as the expected effect of the addedK⁺ calculated using the Goldman equation. There was no significantdepolarization on adding H₃PO₄ to buffered media. Consequently,there was no evidence for a depolarization caused by phosphate.This result provides evidence that the H⁺–H₂PO₄ symportin roots of T. repens operates with a stoichiometry of 1: 1. In a group of control plants ( + P plants) and a group whichwere stressed by reducing the supply of phosphate (– Pplants), the – P plants had lower values for E_vo than+P plants (– 118 mV and – 130 mV, respectively).The absence of phosphate from the measurement media also reducedE_vo (mean effect = 9 mV). A significant difference in E_vo between– P and + P plants persisted when phosphate was addedto – P plants. The electropotential difference acrossthe tonoplast (E_vo) in – P plants became more positivewith time. Key words: White clover, membrane transport, roots, tonoplast, symport     

The inheritance of cyanoglucoside content in Trifolium repens L.

A four generation backcross breeding program was undertaken. Analysis of the levels of cyanoglucoside in Acac progeny shows that the level of cyanoglucoside (linamarin and lotaustralin) is inherited and that part of the inherited variation in cyanoglucoside levels is attributable to the existence of different Ac alleles in the parent plant. In vitro microsomal cyanoglucoside biosynthetic activity was measured in a high-level and a low-level parent plant. There was no evidence for the presence of microsomes with different qualitative properties in the two plants. The Ac locus was shown to segregate independently of the S incompatibility locus.This research was supported in part by SERC Grant GRA 95550.     

Accumulation of Metabolites during Seed Development in Trifolium repens L.

Metabolite deposition during seed development was examined histochemicallyin Trifolium repens by light- and fluorescence microscopy. Allendosperm haustorium at the chalazal pole of the embryo sacand wall protrusions in cell walls of the suspensor and theembryo sac suggest that transfer of metabolites from maternalto offspring tissue takes place primarily at these sites. Thisis further supported by prominent cutinization of the interpolarregion of the embryo sac wall, accumulation of starch in integumentaltissue at the embryo sac poles, and breakdown of interpolarendothelial cells. Decomposition of osteosclereid starch isfollowed by accumulation in the cellular endosperm and subsequentlyin the embryo parallel to endosperm degradation. The starchaccumulates gradually inward from the subepidermal cells ofthe embryo to the stele. Protein bodies are formed in the vacuolesalong the tonoplast, later to be cut off in vesicles releasedinto the cytoplasm. At maturity the embryo is packed with proteinand starch, but without lipid reserves. Phytin is observed inthe protein bodies. The mature embryo is surrounded by a proteinand starch containing aleurone layer which originates from theendosperm.Copyright 1994, 1999 Academic Press White clover, protein, starch, cuticle, embryo sac wall     

Genetic analysis of shikimate dehydrogenase allozymes in Trifolium repens L.

 A genetic analysis was carried out on progeny families from pair crosses among plants polymorphic for shikimate dehydrogenase (SDH) isozymes in white clover (Trifolium repens L.). SDH was controlled by two independently assorting disomic loci. This result is consistent with the presence of a single gene (Sdh) represented in this putative allotetraploid by one locus in each of the genomes. One of the Sdh loci is linked (6.0±2.0 cM) to the linamarase (Li) locus. There was no evidence for differentiation of the duplicate Sdh loci (both carry common alleles). White clover behaves genetically as a diploidised allotetraploid but the possibility of a low frequency of multivalent formation and homoeologous pairing has not been ruled out. The SDH locus is likely to be useful for the marker-assisted selection of agronomic traits. Received: 5 June 1997 / Accepted: 19 November 1997     

Physiological integration in the clonal perennial herb Trifolium repens L.

Summary Translocation of ¹⁴C-labelled carbohydrates between the parent stolon and branches, and among branches, of Trifolium repens plants was investigated in two glasshouse experiments to determine patterns of physiological organisation in this clonal species. Differential defoliation treatments were applied to the parent stolon and/or branches to test the sensitivity of translocation to the short-term carbon needs of defoliated sinks. Strong reciprocal exchange of carbohydrate between the parent stolon and branches was observed, with 18 41% of the ¹⁴C exported from leaves on the parent stolon moving to branches, while branches simulta-neously exported 25% (for old source branches) to 54% (for young source branches) of the ¹⁴C they assimilated to the parent plant, including translocation to other branches. Branch-to-branch translocation occurred both acropetally and basipetally. Parent-to-branch, branch-to-parent and branch-to-branch carbon fluxes all increased in response to defoliation of the sink, at the expense of carbon supply to stolon tissue or roots of the source module. Reduced export to stolon tissue of the parent axis played a major role in facilitating C reallocation from leaves on the parent stolon to defoliated branches. The observed patterns of C allocation and translocation could be adequately explained by accepted source-sink theory, and are consistent with a high degree of intra-plant physiological integration in resource supply and utilisation. This information provides mechanistic explanations for aspects of the growth dynamics and ecological interactions of T. repens in the patchy environment of a grazed pasture.     

Floral Initiation of White Clover (Trifolium repens L.) in Response to Daylength and Temperature

The response to different combinations of daylength (14, 15and 16 h) and day/night temperature (20/10°C, 30/15°C)of four white clover (Trifolium repens) varieties in terms offloral initiation and development was studied. More plants flowered under long days (16 h) at 30°C thanin any other combination. Varietal differences in response todaylength were large but temperature was the factor controllinginitiation. Daylength was more important in regulating peduncle length,floret and ovule numbers than was temperature. The amount ofnectar produced was lowest at the higher temperature althoughnectar concentration was unaffected by temperature. Nectar concentrationwas lowest in the shortest daylength (14 h). White clover, floral initiation, temperature, daylength     

The Carbon Economy of Clonal Plants of Trifolium repens L.

Fluxes of carbon between sources and sinks were quantified forclonal plants of Trifolium repens L. (cv. Blanca) in two glasshouseexperiments. Carbon sources were (a) leaves on the parent (=main)stolon apex, or (b) leaves on either young or old branches,and the major sinks of interest were the parent stolon apex,branches, and the adventitious root arising at the same parentstolon node as a young source branch. Defoliation treatmentswere applied to the parent stolon and/or branches (excludingsource branches). Carbon moved freely from the parent stolon to branches and vice-versa;these bidirectional exchanges of C provided important supplementarysources of carbohydrate for the sinks and buffered them againstthe effects of defoliation. Young branches exported more C tothe parent plant (mean=6.3µmol d^–1) than they importedfrom leaves on the parent stolon (5·2µmol d^–1)which, in turn, exceeded the amount fixed by leaves on the branchand utilized within the branch itself (2·7µmold^–1). In contrast, the C economy of old branches was largelyself-contained with, on average, 25·4µmol d^–1exported to the parent plant, 1·8µmol d^–1imported from the parent, and 63·0µmol d^–1fixed and utilized by the branch itself. Thus the growth ofyoung branches was immediately reduced by removal of parentstolon leaves, but old branches were unaffected. An estimated 42% of the C utilized by the main stolon apex originatedfrom branches, while by far the largest proportion (84%) ofthe C used for growth of young nodal roots originated from theassociated branch and not from leaves on the parent stolon towhich the root was directly attached. Key words: Trifolium repens, clonal growth, carbon economy, physiological integration, defoliation     

On the origin of the cyanogenic polymorphism in Trifolium repens L.

Trifolium repens L. and Trifolium nigrescens Viv. are two of the approximately six cyanogenic species known in the genus Trifolium. The two species are closely related: T. nigrescens is considered to be one of the diploid ancestors of the amphidiploid T. repens . We studied morphology, meiosis and the cyanogenic system in T. repens (amphidiploid), T. nigrescens (diploid) and their reciprocal hybrids. A comparison of the enzyme linamarase in the species and hybrids shows that there is a general resemblance between their linamarases. Immunological studies indicate that the linamarases must have a somewhat different three-dimensional structure. These facts are consistent with the view that T. nigrescens (or an ancestral form of this species) has donated the Li gene of T. repens . The other putative parent, T. occidentale has probably not donated an active Li gene. The hypothesis of the origin of the Li gene does not explain its polymorphism in European populations of T. repens , as T. nigrescens is monomorphic for cyanogenesis and amphidiploids do not segregate for genes which are homozygous dominant in one of the parents. Segregation for Li could be caused by a gene mutation or a small exchange between homeologous chromosomes. The latter event is more probable. A nigrescens-repens exchange would give rise to a chromosomal region with reduced homology to both parental chromosomes. The genes in the region of exchange will be tightly linked due to diminished cross-over frequency. It has been known for years that Li has effects on the vegetative and reproductive characters in T. repens and we have recently shown that these effects must be the result of genes linked to Li . As the associated characters influence the fitness of the cyanotypes, not only the origin but also the maintenance of the cyanogenic polymorphism is closely related to the evolutionary history of T. repens .     

Studies on the {beta}-glucosidase System of Trifolium repens L.

Using DEAE-cellulose two distinct ß-glucosidase enzymeshave been identified in white clover; one form is primarilyassociated with the seed, the other with young leaves. Evidenceis presented for the separate nature of ß-glucosidaseand ß-galactosidase activity in dry seed flour andin young leaf tissue. These results are considered in relationto the function of the Li locus in white clover, which is shownto control both ß-glucosidase and ß-galactosidaseactivity in expanding leaves.     

铜胁迫下链格孢菌对白车轴草生理生态的影响

通过盆栽实验研究了Cu胁迫下接种病原菌链格孢菌(Alternaria tenuis Nees)对白车轴草(Trifolium repens L.)生理生态指标的影响.结果表明:在未接种的对照组中,随着Cu浓度的增大(0~3000mg.kg-1),植株叶片失绿,生物量下降,叶绿素a、b、a b和类胡萝卜素及叶片可溶性蛋白质含量下降;植物体内丙二醛(MDA)高度积累,细胞膜结构遭到损坏,电导率增大;植株活性氧清除系统受损,不能保持原有平衡,超氧化物歧化酶(SOD)和过氧化氢酶(CAT)活性显著降低,过氧化物酶(POD)活性升高.接种链格孢菌后,植株叶片色素、膜系统及保护酶系统的损伤均加重,与不接种对照组相比,相同浓度Cu处理的叶绿素a、b、a b和类胡萝卜素、可溶性蛋白质含量、SOD和CAT活性均呈不同程度的下降,而电导率、MDA含量和POD活性则有所上升.     

白车轴草病原菌链格孢菌及其症状研究

通过对不同白车轴草无性系病叶样本的病原菌分离、接种、鉴定及致病力测定,并结合野外观察,研究了安徽铜陵铜尾矿区白车轴草叶斑病病原菌链格孢菌(Alternaria tenuisNees)的致病、发病状况和寄主植物的抗病性、研究表明,不同白车轴草无性系抗病性有明显差异,根据寄主植物发病情况,以及病斑大小、形状、颜色等,将白车轴草无性系分为抗病型(R)和感病型(S)。     

Influence of boron on the reproductive growth of white clover (Trifolium repens L.) cultivars

The effect of boron on the reproductive growth of four contrasting white clover cultivars was examined in a controlled environment and glasshouse experiment. Plants grown under a nutrient regime excluding boron and those receiving 0.5 mg/litre boron had fewer stolons, reproductive stolons and inflorescences than those receiving 1, 2 or 3 mg/litre. Inflorescences were also smaller and had fewer seeds per floret. A boron concentration of 1 mg/litre gave optimum reproductive growth, higher levels of boron giving no further increase. Peduncle length and nectar quantity, but not nectar quality, were also influenced by boron indicating a possible beneficial effect of this element on pollinator activity. Cultivars differed in both vegetative and reproductive growth. Cv. Gwenda, a small leaved cultivar, had more stolons but fewer inflorescences than cv. Menna and smaller inflorescences than cv. Olwen, a large leaved cultivar. Generally, these cultivars responded similarly to boron. The implications of these results for the reproductive growth of white clover are discussed.     

Functional plasticity of Trifolium repens L. in response to sulphur and nitrogen availability

Recent control of atmospheric SO₂ pollution is leading to important soil sulphur impoverishment. Plasticity could be a mechanism allowing species to adapt to this rapid global change. Trifolium repens L. is a key grassland species whose performances in community are strongly linked to nitrogen availability. Plasticity of three white clover lines contrasting in their ability to use atmospheric N₂ or soil N was assessed by analysing a set of functional traits along a gradient of nitrogen and sulphur fertilisation applied on a poor soil. White clover traits showed high morphological and physiological plasticity. Nitrogen appeared to be the most limiting factor for the VLF (Very Low Fixation) line. S was the element that modulated the most traits for the nitrogen fixing lines NNU (Normal Nitrate Uptake) and LNU (Low Nitrate Uptake). As expected, N fertilisation inhibited white clover fixation, but we also observed that N₂ fixation was enhanced when S was added. S fertilisation increased nodule length as well as the proportion of nodules containing leghaemoglobin. S fertilisation, with a direct effect and an indirect effect through N₂ fixation, increases white clover performances particularly with regards to photosynthesis and potential vegetative reproduction. The important plasticity in response to S availability should allow it to adapt to a large range of abiotic conditions, but its sensitivity to S nutrition would be a disadvantage for competition in a situation of soil sulphur impoverishment. In contrast, S fertilisation could help maintain this species when nitrogen status is against it.     

Effects of VA mycorrhizal colonization on photosynthesis and biomass production of Trifolium repens L.

The influence of vesicular–arbuscular mycorrhizal (M) colonization on biomass production and photosynthesis of Trifolium repens L. was investigated in two experiments in which the foliar nitrogen and phosphorus contents of non-mycorrhizal (NM) plants were manipulated to be no lower than that of M plants. Throughout both experiments there was a stimulation in the rate of CO₂ assimilation of the youngest, fully expanded leaf of M compared with NM plants. In addition, M plants exhibited a higher specific leaf area compared with NM plants, a response that maximized the area available for CO₂ assimilation per unit of carbon (C) invested. Despite the increased rate of photosynthesis in M plants there was no evidence that the additional C gained was converted to biomass production of M plants. It is suggested that this additional C gained by colonized plants was allocated to the mycorrhizal fungus and that it is the fungus, by acting as a sink for assimilates, that facilitated the stimulation in the rate of photosynthesis of the plant partner.     

Ovule abortion in white clover (Trifolium repens L.)

Plants of white clover ( Trifolium repens L.) cv. Olwen were grown in an open glasshouse maintained at a mean temperature of 20^oC and ovule growth and seed production measured. Differences in the rate of growth of ovules within ovaries were observed as early as 2 days after pollination. Ovules reached a maximum size after 8 days with the smallest only half the size of the largest. After 8 days, the smallest ovules became flaccid and shrivelled. Ovule position within the ovary had little effect on the frequency of seed set and although there was an apparently higher probability that central ovules produced a seed than those nearer the peduncle or style this was not statistically significant. Inflorescence position and floret position on the inflorescence had a significant effect on the number of seeds per floret and seed weight; the first formed inflorescences and the first florets to be pollinated on each inflorescence had more seeds per floret and heavier seeds and fewer florets with no seed than later pollinated florets. There were also differences between florets within the same whorl. The role of a number of factors which may influence floret site utilisation are discussed.     

Studies on {beta}-Glucosidase Production in Cultured Tissue of Trifolium repens L.

Variation observed in the growth and cytology of white clovercells is considered in relation to enzyme production in culturedtissue. Variation also occurred in the production of ß-glucosidaseby groups of cultured cells derived from the same plant andwith identical cultural histories. This variability betweencultures grown in a completely defined medium, provided an approachto the investigation of the factors affecting ß-glucosidaseproduction in cultured cells. Evidence was obtained from Michaelisconstants that two distinct ß-glucosidases were producedby cultured tissue.     

Floral Nectaries of Rosmarinus officinalis L. Structure, Ultrastructure and Nectar Secretion

The nectary of Rosmarinus officinalis L. has the form of a four-lobed,asymmetrical disc situated around the base of the ovary. Thenectary lobe facing the lower flower lip is enlarged and isthe only one to have modified stomata. Vascular strands consistingof phloem only occur in the nectariferous tissue. It is suggestedthat the pre-nectar originating in the phloem accumulates primarilyas starch grains in plastids of the nectariferous cells. Thenumber of grains is very large before anthesis and decreasesconsiderably at anthesis. The transport of the pre-nectar tothe various nectariferous cells appears to be mainly via thesymplast. It could not be determined whether the process ofelimination of the nectar is solely eccrine or partly granulocrine. Rosmarinus officinalis, nectary, nectar secretion, starch grains, phloem