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2.
Cytokinins in the different regions of Cuscuta reflexa Roxb. vine have been extracted and assayed using the Xanthium cotyledon bioassay with N6 -benzylaminopurine as the reference cytokinin. Maximum cytokinin level was found in the haustoria-bearing region with the gradient decreasing towards the apex. The cytokinin content of the apex was less than 1% of that in the whole haustorial region. Interestingly, the concave half of the vine contained about forty times more cytokinin in the haustorial region than the corresponding convex half. The high concentration of cytokinin or cytokinin-like substances in the haustoria-bearing site in Cuscuta might be due either to a high RNase activity in the region or translocation from the host to parasite or both. 相似文献
3.
The response of the stem of a resistant host (Impatiens baslamina) to infection by the parasitic flowering plant Cuscuta japonica was studied with light and electron microscopy. The intra- and interfascicular cambial cells in the host stem first reacted to the penetrating upper haustorium by dividing, and the differentiation of the host xylem (vascular) tissues proceeded toward interfascicular areas from vascular bundles. When the host vascular tissue was invaded by the endophyte (haustorial portion in the host stem), the host xylem was displaced, and host vessels became occluded with parenchyma cells, resulting in tyloses. As the parasitism progressed, areas of the host stem penetrated by the endophyte became swollen via secondary growth and cell division in the parenchymatous cortex, pith, and interfascicular areas. During this intrusion by the endophyte, darkly stained necrotic reactions were detected at the interface between the host tissue and the invading endophyte. The results suggested that in the host tissues penetrated by the parasite, the formation of secondary tissue and swellings caused by active cell division of ground tissue and host vessel occlusion by tyloses constitute the host structural defense against the parasite. 相似文献
4.
Summary. The growth of dodders, Cuscuta reflexa and Cuscuta japonica, on the partially incompatible host poinsettia (Euphorbia pulcherrima) is studied. Poinsettia responds by bark growths to the formation of the dodder haustoria and prevents dodder from obtaining normal growth.
The growth instead becomes extremely branched, coral-like, and dodder lacks the ability to form haustoria. After a period
of coral-like growth, long shoots sprout, resembling the normal growth. These long shoots mark an ending phase for dodder,
which dies shortly after without having flowered. During the coral-like growth phase, dodder develops transfer cells in the
parenchyma cells bordering the vessels of the xylem in the shoot. The transfer cells have not been observed when dodder is
grown on the compatible host Pelargonium zonale. A coral-like growth phase has also been observed at the establishing phase when dodder is grown in vitro on agar; later
a more normal growth form takes over. In this coral phase, xylem transfer cells are also developed. The fluorochromes carboxyfluorescein
and Texas Red were loaded into the host in the phloem and xylem, respectively, and detection of these fluorochromes in the
dodder stem indicated that a functional haustorial contact developed for both vascular systems. The results show that Cuscuta spp. have the genetic ability to develop xylem transfer cells and use this in response to developmental stress.
Received June 12, 2002; accepted August 26, 2002; published online March 11, 2003 相似文献
5.
For Lolium perenne cv. Cropper, a system which resulted in 100%flowering comprised 90 short days (SD) at 4 ?C (vernalization)and 30 SD at 18 ?C followed by 8 long days (LD). The mitoticindex and G1 and G2 percentages were measured in the shoot androot apices of plants following 2, 5 or 8 LD and in SD controlssampled at the beginning and end of induction. Identical measurementswere made in plants given 48 SD at 18 ?C followed by 2, 5 or8 LD; plants remained vegetative in response to this treatmentlacking vernalization. Significant increases in both mitoticindex and meristem size occurred in the shoot apex in LD followingthe vernalizing, but not the non-vernalizing, treatment. A clusterof mitoses in the apical dome of the shoot apex was unique tothe vernalized plants given 5 or 8 LD. However, an increasein root meristem size occurred regardless of vernalization,but a significant increase in the mitotic index was limitedto vernalized plants given 5 or 8 LD. Whilst the vernalization-LDtreatment resulted in an increase in the G2 percentage in theshoot apex following 2, 5 or 8 LD, no such alteration was observedin the root meristem. Thus, the changes to the cell cycle whichcorrelated with flowering were increased mitotic indices andG2 percentages in the shoot apex at each sampling time and increasedmitotic indices in the root apex following 5 and 8 LD. Key words: Cell division, flowering, Lolium perenne L. 相似文献
6.
Observations on the origin and mature structure of the haustoriumof the Western Australian Christmas tree (Nuytsia floribunda)corroborate and extend the findings of earlier workers. We showthat the previously described sclerenchymatous hornor prong formed within the haustorium acts asa sickle-like cutting device which transversely severs the hostroot and then becomes lodged in haustorial collar tissue directlyopposite to that where it originated. The cutting process isdeduced to be rapid and the gland-like fluid filled structurein the haustorium is suggested to generate a hydrostatic forcedriving the device through the host root. The haustorial parenchymacells at the tight junction between the endophytic part of thehaustorium and the cut face of the host root develop balloon-likeoutgrowths which intrude into the lumina of severed xylem vesselsof the host. Experiments feeding 0.05% (w/v) basic fuchsin tofreshly cut ends of host root segments distal to terminally-attachedmature haustoria demonstrate an apoplastic pathway from hostxylem elements fractured at the interface into haustorial parenchyma,and thence through vascular tissue to the haustorium into thetranspiring plant of Nuytsia. Application of labelled water(D2O) to uncut basal roots of potted plants ofAcacia acuminataparasitized by Nuytsia results in labelling of leafy shootsof parasite and host, indicative of haustorial uptake of waterby Nuytsia from host root xylem in the intact association. Measurementsof xylem water potentials of pot-cultured seedling Nuytsia associatedwith a range of hosts, or of mature trees of Nuytsia and partnerwoody hosts in the native habitat, demonstrate consistentlymore negative potentials in the parasite than host, suggestingthat the parasite may regularly obtain xylem water through itshaustorial apparatus. Copyright 2000 Annals of Botany Company Root hemiparasite, Nuytsia floribunda, Loranthaceae, haustorial structure, hostparasite water relations 相似文献
7.
Dominance inhibition of shoot growth by fruit load is a major factor that regulates shoot architecture and limits yield in agriculture and horticulture crops. In annual plants, the inhibition of inflorescence growth by fruit load occurs at a late stage of inflorescence development termed the end of flowering transition. Physiological studies show this transition is mediated by production and export of auxin from developing fruits in close proximity to the inflorescence apex. In the meristem, cessation of inflorescence growth is controlled in part by the age-dependent pathway, which regulates the timing of arrest. Here, we show the end of flowering transition is a two-step process in Arabidopsis (Arabidopsis thaliana). The first stage is characterized by a cessation of inflorescence growth, while immature fruit continues to develop. At this stage, dominance inhibition of inflorescence growth by fruit load is associated with a selective dampening of auxin transport in the apical region of the stem. Subsequently, an increase in auxin response in the vascular tissues of the apical stem where developing fruits are attached marks the second stage for the end of flowering transition. Similar to the vegetative and floral transition, the end of flowering transition is associated with a change in sugar signaling and metabolism in the inflorescence apex. Taken together, our results suggest that during the end of flowering transition, dominance inhibition of inflorescence shoot growth by fruit load is mediated by auxin and sugar signaling.Dominance inhibition of inflorescence shoot growth by fruit load involves auxin and sugar signaling during the end of flowering transition. 相似文献
8.
Morphological and anatomical features of mature embryos and seedlings were observed at different growth stages in the parasitic
angiospermCuscuta japonica Choisy. The spirally coiled embryos from scarified seeds had no cotyledons but possessed blunt radicles. Seeds germinated
at 30°C in the dark. Although most embryo cells incubated for 16 h did not have starch grains, the shoot cells of three-day-old
seedlings possessed numerous starch grains. After these seedlings were transferred to a lightened growth chamber, all the
shoot apical regions of seedlings grown for 6,8, and 10 days became greenish and hooked. Most of the shoot cells, including
the green apical parts, contained abundant starch grains. The hooks opened only when one seedling made contact with another
seedling. This suggested that the green and hooked shoot apical regions played an important role in searching for and twining
about their host plants. In some two-day-old seedlings, the massive roots were circular or semi-circular. This enabled the
shoot axes to stand erect on some substratum. It would assist the shoots in making contact with the host plant. In eight-day-old
seedlings, the green apical regions also were hooked and the roots were considerably degraded. 相似文献
9.
A florigenic effect of sucrose in Fuchsia hybrida is blocked by gibberellin-induced assimilate competition 总被引:2,自引:0,他引:2
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The use of gas chromatography-mass spectrometry-selected ion monitoring along with a (13)C internal standard has allowed sensitive measurements of the sucrose (Suc) content of individual shoot apices of Fuchsia hybrida. With intact plants, as the photosynthetic irradiance increased, so did shoot apex Suc content, reaching saturation at about 500 micromol m(-2) s(-1). These same plants flowered at the higher irradiances, remaining vegetative in 10-h short days at an irradiance of 230 micromol m(-2) s(-1). The strong correlation (r = 0.93) in these studies between flowering and shoot apex Suc content indicates a role for Suc as a stimulus to flowering in this species. However, Suc is not the long-day (LD) "florigen" of F. hybrida because 2 to 4 LD given as a 14-h low-irradiance photoperiod extension (10-15 micromol m(-2) s(-1)) induced flowering but without increase in shoot apex Suc content. Flowering induced by either pathway, the LD- or the Suc-mediated one, was inhibited by applying gibberellin (GA) to the shoot tip. Such inhibition of flowering by GA, at least for the LD pathway, was associated with a reduced apex Suc content, enhanced elongation of subapical stem tissue, and a reduced import into the shoot apex of leaf-sourced assimilate. Thus, our findings show how GA inhibits flowering of F. hybrida and confirm the importance of nutrient diversion in regulating flowering. 相似文献
10.
Martin A. Piehl 《American journal of botany》1963,50(10):978-985
Piehl, Martin A. (Botanic Garden, Santa Barbara, Calif.) Mode of attachment, haustorium structure, and hosts of Pedicularis canadensis. Amer. Jour. Bot. 50(10): 978–985. Illus. 1963.—Although long known for European members of the genus, parasitism is documented for the first time for the North American Pedicularis canadensis (Scrophulariaceae) from observations made in the field. Every stand examined showed evidence for parasitism, the haustorial connections being established in the seedling stage. The haustoria, which vary somewhat morphologically, produce direct connection between the xylem of the host and that of the parasite. The great diversity of hosts, involving 80 species from 35 families, suggests that connections may be made to essentially any vascular plant with subterranean parts in proximity to those of the parasite, although some species are parasitized much more frequently than others. In addition, haustorial attachments were found to dead parts of vascular plants and, in single instances, to a fungus and small pebbles. Intraspecific parasitism has also been observed. 相似文献
11.
Stem tips of Cuscuta reflexa, cultured on modified White's medium,were subjected to different light and dark conditions. The culturesflowered when maintained either in continuous darkness or exposedto 14 hours of daily dark period. Thus Cuscuta reflexa behavesas a typically short-day plant. The presence of 5 per cent.sucrose in the medium completely obviates the requirement forhigh-intensity light exposures, otherwise essential for SDP.It appears that the bud itself is sensitive to photoinduction.In spite of the presence of natural tissue-bridge between thehost and the parasite, provided by the haustorial connexions,there is no transportation of flower-forming substance fromone plant to another. The flowering periods of host and parasiteare independent of each other. 相似文献
12.
Lee KB 《American journal of botany》2007,94(5):737-745
The anatomical and ultrastructural development of the haustorium of the Cuscuta japonica, a holoparasitic angiosperm, growing on the host plant Impatiens balsamina was studied. After the shoot tips of light-grown parasite seedlings contacted the host, the upper haustorium (external to the host organ) developed through three main successive stages of the haustorial initials, the meristem, and the endophyte primoridium (EP) within the middle layer of the cortex of the parasite stem. The haustorial initial cells were characterized by abundant starch-bearing amyloplasts and mitochondria with an expanded intermembrane space. The meristem cells had numerous large chloroplasts with well-developed thylakoids, reflecting the capability for photosynthesis. Commonly, all three stages of haustorial cells contained conspicuous, large nuclei with enlarged nucleoli and dense cytoplasm including many other organelles, indicating a very active metabolism. In the final stage of upper haustorium development, the meristem cells differentiated into the EP, a host-penetrating tissue. The primordium had smaller file cells at the proximal end and elongate digitate cells at the distal end. The file cells divided actively, while the digitate cells contained abundant chloroplasts, dictyosomes, rough endoplasmic reticulum, and other organelles, suggesting that the EP was cytohistologically well organized for penetration into the host tissue. 相似文献
13.
M. Kh. Chailakhyan V. Lozhnikova F. Seidlova J. Krekule N. Dudko V. Negretzky 《Planta》1989,178(2):143-146
Flowering of Chenopodium rubrum seedling plants was obtained in continuous light after application of fractions of a partially purified extract from leaves of flowering Maryland Mammoth tobacco (Nicotiana tabacum). The stage of flowal differentiation was dependent on the age of the Chenopodium plants used for the bioassay. Apices of plants treated with the extract at the age of four or seven days showed an advanced branching of the meristem or the beginning of formation of a terminal flower; treatment with the extract of plants 12 d old resulted in rapid formation of flower buds in all assay plants. Non-treated control plants kept in continuous light remained fully vegetative. The effects of the extract on flowering were associated with pronounced growth effects. Floral differentiation was preceeded by elongation of the shoot apex. Extension of all axial organs occurred, while growth of leaves, including leaf primordia, was inhibited. The pattern of growth after application of the flower-inducing substance(s) did not resemble the effects of the known phytohormones, but showed some similarities to growth changes resulting from photoperiodic induction of flowering. 相似文献
14.
In a study of host-parasite interrelationship and the mechanism of parasitization, ribonuclease activity was determined in Cuscuta reflexa Roxb, and in infected and control host plants of Lantana camara L. In the haustoria-bearing region of Cuscuta , the concave half of the vine bearing the haustorial site, always showed significantly higher RNase activity than the convex half, irrespective of the differing enzyme activity of the parasite tissue growing on different hosts — Brassica campestris L., Helianthus animus L., Lantana camara L., Medicago saliva L. and Solatium nigrum L. The uninfected host branch of L. camara showed the maximum specific RNase activity in the apical region which decreased toward the base, while the infected host branch showed minimum specific RNase activity in the apical region, gradually increasing towards the infected region. 相似文献
15.
Jeschke W. Dieter; Bumel Pia; Rth Nicola; Czygan Franz-C.; Proksch Peter 《Journal of experimental botany》1994,45(6):801-812
A recently developed empirically based modelling technique wasused to quantify uptake, flow and utilization of C and N inLupinus albus L., uninfected and parasitized by Cuscuta reflexaRoxb. plants over a 12 d period during flowering and early fruitsetting of the host. The modelling combined data on molar C:Nratios in host phloem and pressure-induced xylem sap, net incrementsof C and N in host and parasite plant parts and respiratorylosses of C. The modelling of the solute transfer between hostand Cuscuta was achieved by assuming non-specific intake fromthe xylem. The models predicted that Cuscuta derived 99.5% ofits carbon and 93.6% of its nitrogen demand from the host phloem.The overriding sink strength of the parasite diverted most ofthe basipetally translocated host assimilates and massivelycompeted with the host root and inhibited fruit setting. Carbonincorporation in Cuscuta consumed 56%, respiration 24% and secretionby extrafloral nectaries 1.8% of the current host photosynthate.Root respiration was inhibited by 59% and carbon was mobilizedfrom host root and leaves. Competition by the parasite for Nwas even more severe and Cuscuta incorporated nitrogen equalling223% of current fixation, but N2 fixation of the host was severelyrestricted to 37%. Withdrawal of N from host phloem led to severelosses of N from leaves and the root and marked decreases inN concentration. It required massive xylem-to-phloem transferof N, because the xylem as the major supply route for N wasnot exploited substantially by Cuscuta. The results are discussedin relation to likely causes for parasite-induced pathogeniceffects, suggesting that Cuscuta affected the host adverselyby depriving it mainly of its nitrogen, but that causal to incipientnitrogen deficiency and restricted N2 fixation was the superiorsink potential of Cuscuta, which prevented adequate supply ofassimilates to the nodulated root. The dominating sink potentialof Cuscuta is compared with the similarly strong sink competitionexerted by fruits at the stage of seed filling in annual plants. Key words: Cuscuta reflexa, Lupinus albus, parasitism, carbon, nitrogen, phloem, xylem, transport 相似文献
16.
Influence of the obligate parasite Cuscuta campestris on growth and biomass allocation of its host Mikania micrantha 总被引:3,自引:0,他引:3
As a means of biologically controlling Mikania micrantha H.B.K. in South China, the influence of the obligate parasite Cuscuta campestris Yuncker on its growth and biomass allocation was studied using pot trials. The effect of C. campestris on M. micrantha became greater with time, such that the host biomass was only 1.8% of the control after 60 d of parasitism and by day 72 almost all the aerial parts of the host plants had died. Afterwards, the hosts and the remnant parasite shoots re-grew but the total biomass of the hosts was still significantly lower than that of the controls. The infection by C. campestris greatly increased the shoot:root dry weight ratio and the allocation to stems of the infected plants from 40 to 50 d after parasitization, but decreased their relative growth rate and unit leaf rate starting from 20 d after parasitization and their leaf area ratio from 30 to 60 d after parasitization. Cuscuta campestris significantly reduced the total biomass, changed the biomass allocation patterns, and completely inhibited the flowering of the infected M. micrantha plants. These results indicate that the use of C. campestris could be a potentially effective way of controlling M. micrantha. 相似文献
17.
Impatiens balsamina L. was induced to flower by exposure to5 short days and then made to revert to vegetative growth byreturn to long days. After 9 long days reverted plants wereinduced to re-flower by returning them to short days. Petalinitiation began immediately and seven primordia already presentdeveloped into petals instead of into predominantly leaf-likeorgans. However, the arrangement of primordia at the shoot apex,their rate of initiation and size at initiation remained unchangedfrom the reverted apex, as did apical growth rate and the lengthof stem frusta at initiation. The more rapid flowering of thereverted plants than of plants when first induced, and the lackof change in apical growth pattern, imply that the revertedapices remain partially evoked, and that the apical growth patternand phyllotaxis typical of the flower, and already present inthe reverted plants, facilitate the transition to flower formation. Impatiens balsamina, flower reversion, partial evocation, shoot meristem, determination, leaf development 相似文献
18.
Leon I. Cohen 《American journal of botany》1965,52(5):455-463
In vascular plants, the apical meristem of the shoot normally represents a continuation of growth in the apical meristem of the embryo itself. This is not the case in Arceuthobium. Here the shoot apex of the embryo is rudimentary and eventually dies after infection of the host occurs. The inflorescence of Arceuthobium is, therefore, an adventitious structure originating in the endophytic system rather than from the shoot apex of the seedling. Inflorescence buds arise in either of 2 ways. In some species (A. douglasii and A. americanum), buds first appear as small meristematic protuberances on the outer surface of cortical strands. In other species (A. campylopodum), the buds arise at the ends of short branches. The former, or diffuse, type gives rise to inflorescences along the entire surface of the host branch; in the latter, or condensed, type inflorescences are formed in clusters. Early ontogeny of the inflorescence apex of both types is described. Studies of subsequent growth of the inflorescence apex show 5 well-defined plastochronic stages: (1) maximal area stage; (2) minimal area stage; (3) early post-minimal stage; (4) late post-minimal stage; and (5) pre-maximal stage. 相似文献
19.
delayed flowering1 Encodes a basic leucine zipper protein that mediates floral inductive signals at the shoot apex in maize 总被引:2,自引:0,他引:2
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Muszynski MG Dam T Li B Shirbroun DM Hou Z Bruggemann E Archibald R Ananiev EV Danilevskaya ON 《Plant physiology》2006,142(4):1523-1536
Separation of the life cycle of flowering plants into two distinct growth phases, vegetative and reproductive, is marked by the floral transition. The initial floral inductive signals are perceived in the leaves and transmitted to the shoot apex, where the vegetative shoot apical meristem is restructured into a reproductive meristem. In this study, we report cloning and characterization of the maize (Zea mays) flowering time gene delayed flowering1 (dlf1). Loss of dlf1 function results in late flowering, indicating dlf1 is required for timely promotion of the floral transition. dlf1 encodes a protein with a basic leucine zipper domain belonging to an evolutionarily conserved family. Three-dimensional protein modeling of a missense mutation within the basic domain suggests DLF1 protein functions through DNA binding. The spatial and temporal expression pattern of dlf1 indicates a threshold level of dlf1 is required in the shoot apex for proper timing of the floral transition. Double mutant analysis of dlf1 and indeterminate1 (id1), another late flowering mutation, places dlf1 downstream of id1 function and suggests dlf1 mediates floral inductive signals transmitted from leaves to the shoot apex. This study establishes an emergent framework for the genetic control of floral induction in maize and highlights the conserved topology of the floral transition network in flowering plants. 相似文献
20.
Catherine Mugnibr 《Biologia Plantarum》1977,19(1):40-47
Applications of various amounts of GA3 onto the shoot apex of biennial rosette-plantHyoscyamus niger L., exposed to long days and non vernalized, caused internodes formation and stem elongation. The stem length was proportional to the amount of GA3 applied. Number and length of developed internodes and the whole length of the shoot were maximal in plants treated with a greater amount of GA3. In the end, stem elongation stopped and plants formed perchedrosettes without flowering. Hence, gibberellic acid participates in mechanisms of flowering only by indirect effect on stem elongation and not directly on flower formation itself. 相似文献