In vitro culture of a root parasite,Aeginetia indica L.

Seed germination and further growth of seedlings of an obligate root parasiteAeginetia indica L. are described. (1) Germination: dormancy of fresh seeds can be broken by sodium hypochlorite treatment, but seeds stored for 1–5 years at 5 C did not necessarily require halogen treatment for good germination. (2) Formation of the tendril, which facilitated the organic connection with the host, was stimulated greatly byMiscanthus root extract. (3) Septation (cell division) of tendril was promoted by addition of sucrose to the basal medium. (4) Rhizogenesis of the seedlingin vitro was stimulated by deproteinized coconut milk.     

Some Observations on Infection of Arachis hypogaea L. by Rhizobium

The infection process in Arachis hypogaea by rhizobia differsfrom that normally found in Trifolium spp. in that no infectionthreads are formed. The root hairs, which are long (up to 4mm), septate, and often with large basal cells, occur only atthe sites of emerging lateral roots. Infection occurs only wherethe root hairs have large basal cells. Rhizobia cause curlingand deformation of the root hairs (as in Trifolium spp.) butenter the root at the junction of the root hair and the epidermaland cortical cells. The bacteria are distributed intercellularlyvia the middle lamellae and enter the cortical cells throughthe structurally altered cell wall, often close to the hostcell nucleus. The root hairs and large basal cells become infectedin the same way. Within the cortical cells of the emerging lateralroot the rhizobia multiply rapidly and the invaded cells dividerepeatedly to form the nodule tissue. Bacteriod formation occursonly when the host cell ceases to divide.     

Effect of Post-anthesis Drought on Cell Division and Starch Accumulation in Developing Wheat Grains

Wheat plants (Triticum aestivum L., cv. Warigal) were subjectedto 20 d of water deficit during the period of endosperm celldivision. Drought accentuated the differences in final grainweight between spikelets and between grains within spikelets.The distal grains of top spikelets were most affected by drought.The maximum number of endosperm cells was, respectively, 30and 40 per cent lower in basal grains and distal grains of draughtedplants. In basal grains of middle spikelets, the number of largestarch granules per cell was unaffected but the number of smallstarch granules per cell was 45 per cent lower in grains ofdraughted plants. The initiation of small starch granules wasmore affected than cell division because severe water deficitoccurred earlier during the former process than the latter.Final dry weight appeared to correlate well with the maximumnumber of endosperm cells, but depended also on the number ofstarch granules per cell. Consequently, the amount of dry matterper cell was not constant in both treatments. The concentration of sucrose per endosperm cell was lower onlyin the droughted distal grains of top spikelets. The supplyof sucrose to endosperm cells did not regulate the initiationof small starch granules. Triticum aestivum L., wheat, drought, grain growth, cell division, starch     

The Effects of Gibberellins on the Growth of Excised Tomato Roots

1. At appropriate concentrations both gibberellic acid (GA) and1-naphthalene-acetic acid (NAA) enhance the main axis growthof excised tomato roots grown in culture media containing sucroseat concentrations below 1 per cent. Lateral root extension growthis enhanced by GA at all sucrose concentrations tested; onlyat the lower sucrose concentrations is this effect observedwith NAA. Both GA and NAA increase the number of emergent lateralroots and this effect is most marked in media of low sucrosecontent. Both GA and NAA at higher concentrations inhibit rootgrowth but NAA exhibits its full range of growth effects overa much narrower concentration range than GA.
2. GA, like NAA,speeds up the loss of meristematic activity whichoccurs whenindividual meristems are repeatedly subculturedin media containing1 per cent, or higher concentrations ofsucrose.
3. The promotionof main axis growth by both GA and NAA involvesenhanced cellelongation and cell division. At a moderatelyinhibitory concentrationGA reduces both cell elongation andcell division; this is notthe case with NAA.
4. Gibberellins A₁, A₂, and A₄ resemble GA(gibberellin A₃) intheir growth effects. Allogibberic acidlike G A promotes lateralroot extension growth but causes markedinhibition of root growthat a much lower concentration thanGA.

     

Infection and Root-Nodule Development in Stylosanthes Species by Rhizobium

Root nodules of the tropical forage legume Stylosanthes occurredonly at lateral root junctions and resulted from direct invasionby rhizobia through spaces between epidermal cells. No infectionthreads were present in either the root hairs or nodules. Invasionof the host cortical cells was through structurally alteredcell walls. The bacteria reached the site of nodule initiationin the lateral root cortex by progressive collapse of the initiallyinvaded cells which were compressed by neighbouring cells toform intercellular thread-like infection zones. The bacteriamultiplied in the invaded cells of the nodule initial whichdivided repeatedly to form the nodule. Bacteroids formed onlywhen the host cells ceased to divide. Some abnormal associations occurred in S. capltata and S. hamata40264A. Division of invaded cells was restricted in S. capitataand the bacteria became enlarged and grossly deformed. In S.hamata restricted cell division was immediastely followed bythe brcakdown of the host cells and, although the bacteria multiplied,no bacteroids were formed. Bacteria isolated from these nodulesformed both effective and abnormal nodules when inoculated ontothe same host.     

Deterministic Patterns of Cellular Growth and Division Within a Meristem

The primary root meristem of maize (Zea mays L.) is composedof longitudinal files of cells arranged in groups of familialdescent (sisters, cousins, etc.). In the proximal portion ofthe meristem, the cells in these groups, or packets, show orderedsequences of division that are transverse with respect to theapico-basal axis of the root. The division sequences fall intoa relatively small number of pathways which can be describedusing deterministic 'bootstrap' L-systems. Although these systemscan operate through the assignment of determinate lifespansto sister cells which thus specify their subsequent interdivisionalperiod, because of their exponential growth kinetics the systemscan also operate with determinate units of cell extension. Thisdeterministic type of system allows simulation not only of thedivision sequences, but also of the lengths of the cells thatare present within the packets which participate in the differentdivision pathways. The types of L-systems used to describe thesepathways also predict the distributions and ranges of cell andpacket lengths found after varying numbers of cell generations.These distributions compare favourably with those actually foundin the maize root meristem. Theoretical aspects of bootstrapL-systems, essential for their application to the one-dimensionalcellular arrays of the meristematic cell-files of the maizeroot apex, are also presented.Copyright 1994, 1999 AcademicPress Cell division, cell elongation, cell polarity, L-system, root meristem, Zea mays     

Effects and Absorption of Sethoxydim in Cell Cycle Progression of Corn (Zea mays) and Pea (Pisum sativum)

The mechanisms of selective herbicidal action of sethoxydim were investigated by using cultured root tips of corn (Zea mays L. cv Goldencrossbantam) and pea (Pisum sativum L. cv Alaska). Meristematic cells in the cultured roots were arrested in G₁ and G₂ of the cell division cycle by sucrose starvation and resumed growth and cell division (proliferation) when sucrose was provided. Corn root growth after sucrose addition was inhibited by sethoxydim at concentrations of 0.01 micromolar and greater when roots were treated in the presence of sucrose but was not inhibited at 10 micromolar sethoxydim when they were treated during sucrose starvation. Greater absorption of [¹⁴C]sethoxydim into the meristematic region of corn roots was observed when cells were in proliferative condition but not when they were arrested by sucrose starvation, whereas no greater absorption of the herbicide into pea meristems was observed in either growth condition. In the cell cycle study, greater absorption of [¹⁴C]sethoxydim into the corn root meristem was observed at a certain limited time before S (DNA synthesis) stage. The physiological effects and the greater absorption of sethoxydim clearly depended on cell cycle progression of corn root meristem, whereas fatty acid synthesis, as well as its inhibition by sethoxydim, was not associated with either cell cycle progression or greater absorption of the herbicide.     

An Automata-theoretical Model of Meristem Development as Applied to the Primary Root of Zea mays L.

Observations were made of the sequence of division within thecellular packets (groups of cells of common descent) which comprisethe cell files that run the length of the central cortex ofthe primary root meristem ofZea mays. These sequences, and alsothe relative lengths of the cells within the packets recordedat various times during root growth, indicate that cell-filedevelopment can be expressed using one, or a limited number,of deterministic ‘bootstrap’ L-systems which assigndifferent lifespans to sister cells of successive cell generations.The outcome is a regular pattern of divisions from which daughtercells emerge usually with unequal, but definite, lengths. Inthe immediately post-germination stage of root growth, one divisionpathway is especially common in the cortex and generates sequencesof unequal daughters having a particular basi-apical orientation.Later in root growth, the cellular pattern in the cortex indicatesthat this pathway is replaced by another where unequal divisionsare not so marked, but which nevertheless continues to maintaina regular arrangement of differently sized cells. This latterpathway is characteristic of a zone close to the initial cellsof the cortex. It is present at all stages of root growth andspreads along the length of the cortex as the descendants ofthese initials proliferate. The development of the whole corticalcell file can be simulated from knowledge of the growth functionsof the bootstrap systems. The files so generated contain allthe observed cell patterns. The growth functions also predictthe sequence in which cells cease dividing near the proximalmargin of the meristem, but for this it is necessary to incorporatea counter for the number of divisions that will be accomplishedin the cell file. Cytological requirements for the propagationof unequal divisions, together with a consideration of the natureof the division counter, as well as the significance of theswitch in division pathways encountered during early root growth,are discussed in the context of this deterministic model ofcell division. Cell division; root meristem; L-systems; Zea mays     

Biosynthesis of furano-terpenes by sweet potato cell culture

Callus was induced from sweet potato root tissue on an agarmedium containing Heller's minerals, vitamins, 2,4-D, yeastextract and sucrose. Furano-terpenes were scarcely detectedin the callus. However, when the callus was transferred to aliquid culture medium and incubated with reciprocal shaking,furano-terpenes were rapidly produced mainly in the culturemedium. Furano-terpene production by the cell culture was suppressedby addition of Ceratocystis fimbriata spores or HgCl₂ to theculture medium. Yeast extract and sucrose in the culture mediumwere important for furano-terpene production. 3-Hydroxy-3-methylglutarylcoenzyme A (HMG-CoA) reductase activity increased in the cells,followed by the production of furano-terpenes. The TLC patternof furano-terpenes produced by the cell culture was essentiallythe same as that produced by sweet potato root tissue infectedby C. fimbriata or treated with HgCl₂, but the quantitativeproportion of the individual furano-terpenes in the former differedmarkedly from that in the latter. (Received January 11, 1979; )     

Relationship Between Photosynthate Supply and Endosperm Development in Maize

Maize (Zea mays L., cultivar Pioneer 3925) plants were givenshaded, thinned and control light treatments during 10 d or20 d periods surrounding pollination. Glucose, sucrose, starch,and dry matter (DM) contents were measured at intervals in compositesamples of pericarp/nucellus (PN), and in endosperms taken fromdeveloping kernels. Total kernel DM per ear at maturity washigher in the thinned treatment than control and shaded treatmentsdue to higher kernel set in apical regions of ears. In PNs at11 d after pollination (DAP), DM and sucrose contents were slightlygreater in thinned than control and shaded plants. Glucose contentswere substantially greater than controls in PNs of thinned plantsand were less than controls in shaded plants. In endospermsfrom apical kernels at 8 to 12 DAP (during cell division), DM,glucose and sucrose contents were substantially less in shadedthan control and thinned plants. Sucrose contents were greaterin endosperms of thinned than control plants. Sugar contentsin endosperms from basal kernels were nearly the same in thethree light treatments. At 12 DAP, apical and basal endospermsin shaded plants had fewer nuclei than those of the other lighttreatments. The light treatments appeared to effect apical kernelgrowth by influencing the extent of cell division. Zea mays L, maize, light treatment, endosperm, cell division, glucose, sucrose, starch     

The Structure and Development of Trifolium subterraneum L. Root Nodules: I. IN PLANTS GROWN AT OPTIMAL ROOT TEMPERATURES

The structure of effective nodules on Trifolium subterraneumL. grown at a root temperature favourable for nitrogen fixationwas examined by light microscopy. Rhizobium were released intohost cells from vesicles on infection threads which were closelyassociated with the host cell nucleus. Enlargement into bacteroidforms was rapid and synchronous in similarly-aged host cells,but groups of rhizobia close to the nucleus sometimes did notdevelop into bacteroids. Rhizobium changed in shape from smallrods to more elongate and then to irregularly swollen formsbefore finally becoming coccoid. On degeneration clusters ofbacteroids became un evenly stained before coalescing at thecentre of the host cell and finally disintegrating. Small vegetativerods multiplied amongst the degenerating bacteroids and in thegreatly enlarged intercellular spaces; host cell walls becamefolded and distorted and sometimes broke before collapsing ontoeach other.     

Embryology ofCymbidium sinense:the Microtubule Organization of Early Embryos

InCymbidium sinense, the pattern of embryo development is unusualin that oblique cell divisions result in the formation of severalsuspensor cells prior to the development of the embryo proper.Characteristic changes in microtubular distribution can be foundwithin the zygote and the proembryo during their development.After fertilization, the ellipsoid-shaped zygote has randomlydistributed microtubules within its cytoplasm. As the zygotetakes on a more rounded appearance, microtubules organize intoa dense meshwork. Furthermore, microtubule bundles appear atthe chalazal region of the cell prior to the first mitotic divisionof the zygote. At the preprophase stage of mitosis, a preprophaseband of microtubules appears in the cytoplasm of the zygote.The zygote divides obliquely and unequally and gives rise toan apical cell and a slightly larger basal cell. Many randomly-alignedmicrotubules can be found in the cortex of the basal cell. Theincrease in the abundance of microtubules coincides with theisotropic expansion of the basal cell. The early division ofthe basal cell and subsequent division of the apical cell resultsin the formation of a four-celled embryo, of which three cellsnear the micropylar pole develop as suspensor cells. In thesuspensor cells, the microtubules tend to orient in the samedirection as the long axis of the cell. In addition, prominentmicrotubules can also be found near the adjoining cell wallsof the four-celled embryo. The terminal cell is highly cytoplasmicwith abundant microtubules within the cell. Subsequent divisionsof the terminal cell give rise to additional suspensor cellsand the embryo proper. In the mature embryo, five suspensorcells are usually present; one eventually grows through themicropyle of the inner integument and four grow towards thechalazal pole. The cortical microtubules of suspensor cellsredistribute from a longitudinal to a transverse direction asthey grow towards their respective poles.Copyright 1998 Annalsof Botany Company Embryogenesis, endosperm, microtubules, preprophase band, suspensor cells,Cymbidium sinense(Andr.) Willd.     

Effects of Root Excision on Swelling of Leaf Sheath Cells and on the Arrangement of Cortical Microtubules in Onion Seedlings

Unlike abundantly-leafed mature plants, 2- to 3-leafed youngonion seedlings (Allium cepa L. cv. Senshu-Chuko) showed noswelling of leaf sheaths even when they were kept under long-dayconditions. When their roots were excised, however, the seedlingsshowed sign of swelling. Before swelling became evident, changesin the arrangement of cortical microtubules occurred in leafsheath cells. The microtubules, which were oriented transverselyto the cell axis in unexcised seedlings, were oriented longitudinallyor obliquely in excised seedlings. Such effects of root excisionwere observed only in seedlings grown under long-day conditions,but not under short-day conditions. (Received July 14, 1984; Accepted September 26, 1984)     

Response to Phosphate Deficiency in Bean (Phaseolus vulgarisL.) Roots. Respiratory Metabolism, Sugar Localization and Changes in Ultrastructure of Bean Root Cells

Bean plants (Phaseolus vulgarisL. ‘Zlota Saxa’)were cultured on complete (+P) or phosphate-deficient (-P) nutrientmedium. A large increase in glucose concentration was foundin the meristematic zone of -P roots compared to control roots.The increased glucose concentration in the meristematic zonedid not influence total respiration rate. Glucose or uncoupler(carbonyl cyanide m-chlorophenylhydrazone) failed to increasethe respiration rate in -P root segments, but stimulated respirationin +P roots. The ultrastructure of cortical cells from the meristematicroot zone showed marked differences between +P and -P plants.Large vacuoles, invaginations of the plasmalemma and condensedforms of mitochondria were dominating features in cortical cellsof -P roots. Analysis of extracts after treating roots withdimethylsulfoxide (DMSO) indicated different localization ofsugars in the cell compartments. In roots of -P plants, mostof the reducing sugars were detected in the cytoplasm fractionwhile most sucrose was in the vacuole. Observations of the effectof 10% DMSO on cell ultrastructure indicated partial destructionof the plasmalemma but not the tonoplast. The localization ofreducing sugars in secondary vacuoles or plasmalemma invaginationsin the cells from the meristematic region of -P roots is discussed.Copyright1998 Annals of Botany Company. Bean (Phaseolus vulgarisL.), roots, Pi deficiency, respiration, meristematic zone, ultrastructure, sugar efflux, reducing sugars and sucrose localization.     

Anatomical Changes Which Occur in Cuttings of Agathis australis (D. Don) Lindl 1. Wounding Responses

The basal and sub-basal regions in cuttings of Agathis australisundergo a complex series of anatomical changes. Many of theseare categorized as wound responses and include cell divisionsassociated with the cut base and the proliferation of tracheidsand phloem which arise in the interfascicular region about 4mm above the cut base. The vascular tissue arcs outwards anddownwards through the cortex. It may develop as isolated strandsonly a few cells wide or as sheets involving a number of cells.The precise pattern of vascular development appears to be determinedby its extent at the point of origin and by the presence ofobstacles such as primary and secondary resin canals which arelocated to the outside of the vascular bundles in the stem.Secondary resin canals are produced only in the rooting zonein cuttings that show extensive cell division. They arise schizogenouslyand do not form an interlinking network. Root primordia arise in the cortex at the end of isolated strandsof newly developed vascular tissue. Primordia never form inassociation with sheets of tracheids or after the convergenceof strands. In some cases virtually the entire sub-base is filledwith vascular tissue as a result of cell division and the differentiationof parenchymatous tissue. Root primordia never appear in thissituation. Agathis australis (D. Don) Lindl, kauri, cuttings, wound responses, vascular development, resin canals, root primordia, cellular differentiation     

Sugar concentrations along and across the Ricinus communis L. hypocotyl measured by single cell sampling analysis

Single cell sap sampling and analysis were used to measure the longitudinal and radial distribution of sucrose, glucose and fructose in the apical cell division zone and in the basal, elongated zone of the Ricinus hypocotyl. Sucrose and hexose increased in concentration from the apex to the base of the seedling axis. In the cell division zone low hexose and sucrose concentrations prevailed in cortex and pith, with a slightly higher hexose concentration in pith cells. The sucrose concentrations in sieve tubes and in phloem were much higher than in the cortex and pith cells. In the basal zone of the hypocotyl high levels of sucrose in phloem, cortex and pith were found, therefore radial, diffusional sucrose flow away from the phloem was considered unlikely. It is proposed that radial flow of growth-water to the hypocotyl periphery together with the down-regulation of a sucrose transporter at the phloem leads to a preferential sucrose flow to the expanding cortex. The pith cells, which do not experience flow of growth-water, are probably insufficiently supplied with sucrose from the phloem resulting eventually in cell death as the plant grows. Shortage of sucrose supply, experimentally achieved by removal of the endosperm, led to sucrose hydrolysis in the pith. The sucrose levels in the other tissues decreased less. It appears that the hydrolysis to hexose was initiated to maintain the osmotic value in the pith cell sap. It is speculated that high hexose levels in the cells are indicative of insufficient sucrose supply via the phloem and that the pith cells are confronted with that situation during early seedling development.     

Cell Cycle Duration in the Root Meristem of Sonoran Desert Cactaceae as Estimated by Cell-flow and Rate-of-cell-production Methods

Slow rates of cactus growth in the Sonoran Desert and high productivityof some Cactaceae under cultivation suggest that relativelylow growth rates are not the consequence of a long cell divisioncycle but of short optimal periods for growth and adverse environmentalfactors. To verify this hypothesis, the duration of the celldivision cycle (T)in the root apical meristem of seedlings ofthree sympatric species from the Sonoran Desert [Ferocactuspeninsulae(F. A. C. Weber) Britton & Rose ‘Townsendianus’(Britton & Rose) N. P. Taylor, stat. nov.,Stenocereus gummosus(Engelm.)Gibson & Horak andPachycereus pringlei(S. Watson) Britton& Rose] was estimated with the rate-of-cell-production (RCP)and the cell-flow (colchicine) methods. Both methods were appliedduring the steady-state growth phase, which was relatively shortin the first two species because of the determinate patternof root growth. The RCP method permitted estimation ofTin eachroot individually. Durations of the cell division cycle wereinversely proportional to the rate of root growth (r²rangedfrom 0.42 to 0.88,P<0.05).T,determined by the cell-flow method,ranged from 14.4 to 19.3 h in these species and was within thesame range asTdetermined by the RCP method. The averageTdeterminedby the RCP method was 67 to 75% of that determined by the cell-flowmethod. Results obtained with both methods are compared andanalysed. The proposed hypothesis appears to be correct, indicatingthat these species can be more productive under cultivationthan in the wild due to the relatively short duration of thecell division cycle. Adaptive features of these findings arealso considered.Copyright 1998 Annals of Botany Company Cactaceae, cell division cycle, root growth, root meristem, Sonoran Desert     

Endosymbiosis in Hydra and the Evolution of Internal Defense System

Certain species of Chlorella have exploited an intracellularhabitat and occur naturally as cytobionts in Hydra viridissima.The algae evoke phagocytosis by Hydra digestive cells and aresequestered in individual phagosomes that migrate to the baseof the host cells and resist fusion with lysosomes. The abilityto resist digestion is closely correlated with release of extracellularcarbohydrate (maltose) by the algae. The established populationof algae grows at an average rate equal to or greater than thatof the host and a constant population density is maintained.The host regulates algal population density by expelling ordigesting excess algae, or by controlling algal cell division.The control mechanism is unknown but can be breached by additionof inorganic ions to the Hydra culture medium with the resultthat the algae overgrow the Hydra. The Hydra-Chlorella symbiosis is probably mutually beneficial,but conditions such as prolonged darkness (with or without feeding)can reduce the competitive fitness of the host since this conditionresults in heterotrophy by the algae at the expense of selectedhost substrates. The evolution of selective permeability toorganic substrates is a major feature of the successful colonizationof the intracellular habitat by symbiotic Chlorella.     

Some Observations on Invertase Activity in Roots of Vicia faba L.

Invertase activity has been determined at intervals along primaryroots of Vicia faba as they elongated from 0·5 to 8 cm.Little activity was evident in 0·5–1·0 cmlong primaries but in those 2–8 cm in length the mainpeak of enzyme activity was associated with the region of cellelongation. Changes took place in the pattern of invertase activityalong the primary roots as they lengthened and these changeshave been correlated with fluctuations in both the rate of rootelongation and the supply of sucrose to the root from the cotyledons.The presence of a root cap did not increase the activity ofthis enzyme in the apical 1 mm of these roots. Invertase activity was higher in lateral root primordia thanin most parts of the primary root basal to the meristem, presumablybecause of the presence of sucrose in the adjacent cavity inthe cortex of the primary root. The peaks of invertase activityfound basal to the region of cell elongation in 3–8 cmlong primary roots probably resulted from the development ofroot pnmordia in these parts of the root.     

Morpho-histogenic studies on tendrils of Passiflora

The ontogenetic development of the tendril and its associatedorgans is investigated in 17 species of Passiflora. The shootapex shows a single tunica layer though the second layer simulatestunica. The cytohistological zonation is not a constant feature.In P. caerulea Linn., it is distinct at leaf initiation butin P. pruinosa Mast., P. vespertilio Linn., and P. watsonianaMast., it is indistinct. The main axillary bud differentiatesfrom the peripheral meristem of the shoot apex. The differentiationof this bud into floral and tendril menstems occurs at a nodeimmediately below the shoot apex in P. minima Blanco. and Pracemosa Brot. In other species this differentiation generallyoccurs at the lower nodes. The floral meristem is initiatedas an accessory bud from this bud, thus forming a bud complex.The residuum of the bud complex develops as a tendril. The thirdaccessory bud which does not originate from this bud complex,develops into a vegetative branch. The fundamental nature ofthe vascular relationship between the flower, tendril, accessorybud, subtending leaf, and the axis is similar in most of theinvestigated species.