Anatomy of Ricciocarpus natans, with emphasis on fine structure

The amphibious liverwort Ricciocarpus natans has been investigated with regard to structure and differentiation of cells and tissues.
The differentiation of the tissues was determined starting with their origin from the meristem situated in the median furrow. From this zone there is dorsally a differentiation of epidermis and aerenchyma, and ventrally a differentiation of epidermis and scales. Air–chambers arise schizogenously. They become divided by cells, which grow out from lateral walls and form an internal pore.
Parenchyma (aerenchyma and euparenchyma) cells and epidermis cells (including thallus margin and main scale cells) appear similar in ultrastructure. A characteristic localization of heteropycnotic chromatin close to the nucleolus is recognized. Mic–robodies have an extraordinary cap–shape. Vacuoles often contain electron dense bodies. Lipid droplets occur frequently in the cytoplasm. Storage products are not restricted to a certain tissue. Young scales have an apical papilla cell with many dictyosomes. Chloroplasts of the oilbody idioblast are much smaller than those of unspecialized cells. The rhizoids are smooth–walled.     

Thallus Differentiation in the Marchantialean Liverwort Asterella wilmsii (Steph.) with Particular Reference to Longitudinal Arrays of Endoplasmic Microtubules in the Inner Cells

This light and electron microscope study of the liverwort Asterellareveals that, as in other Marchantiales, the cells lining thedorsal air chambers are highly vacuolate with numerous amylochloroplastsin the peripheral cytoplasm. The ventral parenchyma in the midribof the thallus contains aseptate fungal hyphae surrounded byan interfacial matrix and host cytoplasm forming transvacuolarstrands. These are lined with microtubules, rarely seen in otherfungal-hepatic associations or in mycorrhizas. Numerous lipidbodies found in all the thallus cells are thought to be associatedwith perennation during the winter dry season. Elongated, thick walled inner thallus cells, between the dorsalair chambers and the fungus-containing tissue, have a cytologicalorganization not previously recorded in land plants. Initiallyhighly vacuolate, with numerous microtubules of random orientationlining the tonoplast, these cells subsequently show interdigitationof vacuoles and cytoplasm producing a labyrinth of sphericaland elongate tonoplast profiles lined by longitudinal arraysof microtubules. At the same time the cytoplasm becomes increasinglyelectron-lucent and the ribosomes, progressively lost from theER, clump together. At maturity the inner thallus cells arehighly polarized with most of the vacuoles lying nearer thethallus apex. In pits in the end walls, numerous plasmodesmata,with expanded cytoplasmic annuli recall the plamodesmatal fieldsin the mesophyll and phloem of the leaves in vascular plants. Far from being supporting parenchyma or sclerenchyma as assumedhitherto, the inner thallus cells of Asterella are clearly highlydifferentiated. Their vacuole microtubule associations are highlysuggestive of a microtubule-based translocation system akinto that seen in many animal cells and perhaps fungal hyphae,but very different from bulk flow in sieve elements and actin-basedcytoplasmic streaming.Copyright 1994, 1999 Academic Press Cytoskeleton, liverwort, microtubules, plasmodesmata, solute transport     

An Examination of some Symbiotic Systems for Fixation of Nitrogen

By the use of ¹⁵N the occurrence of fixation of elemental nitrogenhas been demonstrated in the lichens Collema granosum and Leptogiumlichenoides (both of which contain Nostoc as a symbiont), andalso in the liverwort Blasia pusilla (which has Nostoc-containingcavities in the thallus). The circumstances indicate that thefixation in these instances should be attributed to the Nostoc. No evidence of fixation was obtained in similar isotopic testson the mycorrhizal roots of intact plants of Calluna vulgarisand of Pinus sylvestris, although these, more especially inthe case of Calluna, have been held by some previous authorsto be nitrogen-fixing.     

Variation in the Structure and Response to Flooding of Root Aerenchyma in some Wetland Plants

The structure and response to flooding of root cortical aerenchyma(air space tissue) in a variety of wetland (flood-tolerant)species was investigated and compared with some flood-intolerantspecies. In some species aerenchyma consisted of enlarged schizogenousintercellular spaces and in others aerenchyma formation involvedlysigeny. Two types of lysigenous aerenchyma were distinguished.In the first the diaphragms between lacunae were arranged radiallyand consisted of both collapsed and intact cells. In the secondtype, which was confined to the Cyperaceae, the radial diaphragmscontained intact cells, and stretched between them were tangentially-arrangeddiaphragms of collapsed cells. Flooding in sand culture generally increased root porosity (airspace content) although there were exceptions. The flood-intolerantspecies Senecio jacobaea produced aerenchyma but did not survivelong-term flooding. Among the flood-tolerant species, Filipendulaulmaria did not produce extensive aerenchyma even when flooded.Eriophorum angustifolium and E. vaginatum produced extensiveaerenchyma under drained conditions which was not increasedby flooding. In Nardus stricta root porosity was increased bylow nutrient levels as well as by flooding. Aerenchyma, root cortex, wetland plants, waterlogging, flooding-tolerance, Ammophila arenaria, Brachypodium sylvalicum, Caltha palustris, Carex curia, Eriophorum vaginatum, Filipendula ulmaria, Glyceria maxima, Hieracium pilosella, Juncus effusus, Myosotis scorpioides, Nardus stricta, Narthecium ossifragum, Phalaris arundinacea, Senecio jacobaea, Trichophorum cespitosum     

Water Distribution in Foliose Lichen Species: Interactions between Method of Hydration, Lichen Substances and Thallus Anatomy

Three lichens (Neofuscelia pokornyi, N. pulla and Xanthoriaparietina) from a semi-arid habitat were examined using low-temperaturescanning electron microscopy to evaluate the effects of hydrationmethod, lichen substances and thallus anatomy on the water distributionof hydrated thalli. In theNeofuscelia species, extracellularwater within the thallus was observed in association with cracksin its otherwise impervious upper cortex, while X. parietinashowed abundant extracellular water between medullary hyphae.Spraying the thalli followed by maintenance for 14–20h in a water-saturated atmosphere led to the disappearance ofthe external water film in X. parietina but not in the Neofusceliaspecies. Surface water was abundant in specimens of all speciesimmediately after spraying for 15 min. No extracellular waterwas observed inside the thallus 14–20 h after spraying,but after rinsing with acetone its presence was detected inall three species. Hydric strategy correlated with cortex hygroscopicity:X. parietina, an aero-hygrophytic species, had a more hygroscopicupper cortex than theNeofuscelia species, which are substrate-hygrophytic.The hygroscopicity of the upper cortex was linked with the amountof extracellular water in the thalline interior. Differencesbetween X. parietina and Neofuscelia in the polarity and distributionof their lichen substances agreed with species differences inthe presence and distribution of free water both as a film overthe surface and inside the thallus. Lichen substances appearto play a role in the maintenance of air-filled intrathallinespaces in species whose anatomy, habitat, or both, favour water-loggedconditions. Copyright 2000 Annals of Botany Company Lichen, water relations, semi-arid, lichen substances, LTSEM, thallus anatomy, extracellular water, Neofuscelia pokornyi(Körb.) Essl., Neofuscelia pulla(Ach.) Essl., Xanthoria parietina(L.) Th. Fr     

Studies in the Physiological Action of 2,2-Dichloropropionic Acid: II. THE EFFECTS OF LIGHT AND TEMPERATURE ON THE FACTORS RESPONSIBLE FOR THE INHIBITION OF GROWTH

When Lemna minor and Salvinia natans, grown in a constant environment,are subjected to sub-lethal concentrations of 2,2-dichioropropionicacid (DCPA), the relative growth-rates are progressively reduced.These cumulative reductions, which are greater for S. natans,are correlated with decreases in (1) the rate of leaf or frondformation, (2) the mean area per leaf or frond, and (3) thenet assimilation rate. Of these components, the first is themost important and the third is the least. The effects of light intensity (300, 600, 900 f.c.), temperature(20, 25, and 30°C), and concentration of DCPA on both therelative growth-rate and rate of leaf or frond multiplicationhave been examined in multi-factorial experiments. Over theconcentration range selected (100, 200, and 400 mg/l for S.natans and 100, 300, and 6oo mg/l for L. minor) there are positiveeffects of light intensity, temperature, and concentration.For each concentration the order of the depression is maximalunder a combination of the highest temperature and the greatestintensity. Using radioactive DCPA it has been established that uptake isalso a cumulative process, and that S. natans has a greatercapacity to absorb DCPA. The rate of uptake is independent ofthe light intensity but increases with temperature and concentration. DCPA brings about morphological and structural changes. In S.natans, many of the leaves become submerged and the proportionis positively dependent on light, temperature, and concentration.This failure to float is associated with a reduction in thedensity of epiderrnal hairs. It is concluded that the inhibitory effects of DCPA are maximalunder conditions which are optimal for both meristematic activityand accumulation.     

A frxC Homolog Exists in the Chloroplast DNAs from Various Pteridophytes and in Gymnosperms

Chloroplast DNAs (ctDNAs) from several pteridophytes were analysedby cross-hybridization with the liverwort frxC gene as probe.Hybridization signals were observed without exception, suggestingthe presence of the frxC gene in ctDNAs of non-flowering vascularplants as in liverwort. A frxC homolog was also identified intwo gymnosperms. (Received November 7, 1991; Accepted January 13, 1992)     

The Effect of Oxygen Radicals on Proteolysis in Isolated Oat Chloroplasts

Chloroplast DNAs (ctDNAs) from several pteridophytes were analysedby cross-hybridization with the liverwort frxC gene as probe.Hybridization signals were observed without exception, suggestingthe presence of the frxC gene in ctDNAs of non-flowering vascularplants as in liverwort. A frxC homolog was also identified intwo gymnosperms. (Received July 5, 1991; Accepted January 28, 1992)     

Effect of Some Auxins and Cytokinins on Growth and Gametangial Formation in the Liverwort Riccia gangetica Ahmad

The present work deals with the effect of some auxins [2,4-D,IAA, NAA and ß-naphthoxyacetic acid (NOA)] and cytokinins[6-benzylaminopurine (BAP), 6-(,-dimethylallylamino)purinc (2iP),KN and 6-(4-hydroxy-3-methylbut-2-enylaimno)purine (zeatin)]on growth and gametangial formation in the liverwort Ricciagangetica. Of these, 2,4-D and IAA stimulate vegetative growth,induce the formation of rhizoids on dorsal surface of thallusand shorten the time required for gametangial initiation. NAAand NOA inhibit growth, and do not affect the time of gametangialproduction. The auxins increase archegonial number without affectingantheridial induction and, among those tested, IAA is the mosteffective. Archegonial number is enhanced by the cytokinins,but antheridial production decreases. The maximum number ofarchegonia is initiated in response to 2iP, and this effectappears to be specific. On the other hand, thallus growth, stimulatedby the other cytokinins, is inhibited by 2iP. Riccia gangetica Ahmad, liverwort, auxins, cytokinins, growth, gametangial, formation     

Free-living culturable bacteria and protozoa from the rhizoplanes of three floating aquatic plant species

Terrestrial plant roots exude compounds that promote the proliferation of microorganisms, a phenomenon called the rhizosphere effect. However, little is known about the influence of roots of aquatic plants on microbial populations. We compared cultivable bacteria and protozoa from the rhizoplanes of Azolla filiculoides Lam., Lemna gibba L., and Ricciocarpus natans L., collected at the Tecocomulco Lagoon (Hidalgo, Mexico). The functional bacterial groups isolated from A. filiculoides, L. gibba and R. natans, were macro- and microscopically characterized, and phylogenetically identified using the 16S rDNA gen. About 96% of isolates corresponded to Gram-negative bacteria, and potential N-fixing free-living bacteria (diazotrophic bacteria) were the most abundant. Molecular analysis detected 15 bacterial genera in the rhizoplane of R. natans, whereas A. filiculoides and L. gibba only yielded five genera, among which Aeromonas was predominant. Twenty-five genera of flagellated and 20 genera of ciliated protozoa were identified. Bodo was the more abundant flagellated, whereas Halteria was the most frequent ciliate. All three aquatic plants showed the rhizospheric effects. The most abundant and diverse community of protozoa was found in A. filiculoides, which also had the most abundant bacterial community, but the highest bacterial diversity was found in R. natans.     

Polyamine Content and Action in Roots of Zea mays L. in Relation to Aerenchyma Development

Roots of Zea mays L. developed more aerenchyma (cortical gas-filledspace) when partially deficient in oxygen (3 kPa) than whensupplied with air (20·8 kPa oxygen) in association withfaster production of ethylene (ethene). The possibility wastested that the additional ethylene production resulted fromdecreases in spermidine (spd) and spermine (spm) which share,with ethylene, a common precursor, S-adenosylmethionine. However,no decreases in spd and spm were seen in root tissue up to 4d-old. Removing oxygen completely also had little effect onspd and spm, but strongly suppressed both ethylene productionand aerenchyma formation. Partial oxygen shortage (3 kPa) increased the concentrationof putrescine (put), the precursor of spd and spm. This increasewas not a response to the extra ethylene formed by such rootssince ethylene treatment did no reproduce the effect. Applicationof inhibitors of put biosynthesis, difluoromethylarginine anddifluoromethylornithine, led to increased aerenchyma formation.Exogenous put inhibited the development of aerenchyma whilestimulating rather than inhibiting ethylene production, whentested in either air or 3 kPa oxygen. Thus, put appears to limitaerenchyma formation by suppressing ethylene action rather thanits production.Copyright 1993, 1999 Academic Press Ethylene, ethene, roots, aerenchyma, polyamines, oxygen shortage, anaerobiosis, environmental stress, Zea mays     

The Comparative Biology of Closely Related Species Living in the Same Area: V. INTER- AND INTRASPECIFIC INTERFERENCE WITHIN CULTURES OF LEMNA spp. AND SALVINIA NATANS

Studies were made of the growth of populations of Lemna minor,L. polyrrhiza, L. gibba, and Salvinia natans under controlledlaboratory conditions. The intrinsic exponential growth-ratesof the clones were determined in un-crowded cultures, and thechanges in growth-rate of self-crowding cultures were measuredand interpreted in terms of an initial exponential growth-ratefollowed by a phase of arithmetic increase in weight and followedin turn by a phase in which the death of submerged and shadedfronds caused a decline from the arithmetic rate of growth.Mean frond weight declined in self-crowding cultures (exceptof L. gibba). Mixed cultures of two species were examined under self-crowdingconditions and changes in the proportions of the species werefollowed. Whereas the total weight of mixed cultures remainedvery constant between replicates, there was wide variation inthe proportions of components. The variation in the two componentswas most closely correlated (negatively) when the struggle forexistence was most evenly balanced. The mean frond weight ofthe losing component declined during the experiments. The order of decreasing vigour of species measured by variousparameters was as follows: Relative (intrinsic) growth-rate: L. minor > S. natans > L. gibba > L. polyrrhiza Arithmetic growth-rate when crowded: S. natans > L. polyrrhiza > L. gibba > L. minor Asymptotic yield per culture: L. polyrrhiza > L. minor > S. natans > L. gibba Success in mixed cultures: The success of a species in mixture could not be predicted fromthe parameters of growth in pure culture. Morphologic featuressuch as the gibbosity of L. gibba     

Light-Dependent Expression of Protochlorophyllide Oxidoreductase Gene in the Liverwort, Marchantia paleacea var. diptera

A cDNA encoding the NADPH:protochlorophyllide oxidoreductase(EC 1.6.99.1 [EC] ) was isolated from suspension-cultured cells ofthe liverwort, Marchantia paleacea var. diptera. In contrastto the situation in most higher plants, the liverwort gene wasexpressed in a light-dependent manner. ²Present address: Department of Biological Science, Facultyof Science, Kumamoto University, Kurokami, Kumamoto, 860-8555Japan.     

Aerenchyma (Gas-space) Formation in Adventitious Roots of Rice (Oryza sativa L.) is not Controlled by Ethylene or Small Partial Pressures of Oxygen

Jackson, M. B., Fenning, T. M., and Jenkins, W. 1985 Aerenchyma(gas-space) formation in adventitious roots of rice (Oryza sativaL.) is not controlled by ethylene or small partial pressuresof oxygen.—J. exp. Bot. 36: 1566–1572. The extent of gas-filled voids (aerenchyma) within the cortexof adventitious roots of vegetative rice plants (Oryza sativaL. cv. RB3) was estimated microscopically from transverse sectionswith the aid of a computer-linked digitizer drawing board. Gas-spacewas detectable in 1-d-old tissue and increased in extent withage. After 7 d, approximately 70% of the cortex had degeneratedto form aerenchyma. The extent of the voids in 1-4-d-old tissuewas not increased by stagnant, poorly-aerated external environmentscharacterized by sub-ambient oxygen partial pressures and accumulationsof carbon dioxide and ethylene. Treatment with small oxygenpartial pressures, or with carbon dioxide or ethylene appliedin vigorously stirred nutrient solution also failed to promotethe formation of cortical gas-space. Furthermore, ethylene productionby rice roots was slowed by small oxygen partial pressures typicalof stagnant conditions. Silver nitrate, an inhibitor of ethylene action, did not retardgas-space formation; similarly when endogenous ethylene productionwas inhibited by the application of aminoethoxyvinylglycine(A VG), aerenchyma development continued unabated. Cobalt chloride,another presumed inhibitor of ethylene biosynthesis, did notimpair formation of the gas in rice roots nor did it decreasethe extent of aerenchyma even if A VG was supplied simultaneously.These results contrast with those obtained earlier using rootsof Zea mays L. We conclude that in rice, aerenchyma forms speedily even inwell-aerated environments as an integral part of ordinary rootdevelopment There seems to be little or no requirement for ethyleneas a stimulus in stagnant root-environments where aerenchymais likely to increase the probability of survival. Key words: Rice (Oryza sativa L.), ethylene, flooding, aeration, aerenchyma, environmental stress     

Development and Structure of the Root Cortex in Caltha palustris L. and Nymphaea odorata Ait.

Structural features of the mature root cortex and its apoplasticpermeability to dyes have been determined for two dicotyledonouswetland plants of differing habitats: Nymphaea odorata, growingrooted in water and mud, and Caltha palustris, growing in temporalwetlands among cattails. In mature roots, movement of the apoplasticdyes, berberine and safranin, into the roots was blocked atthe hypodermis, indicating the presence of an exodermis. A hypodermiswith an exodermis, i.e. Casparian bands in the outermost uniseriatelayer plus suberin lamellae, is present in both species. InN. odorata, hypodermal walls are further modified with cellulosicsecondary walls. Roots of N. odorata and C. palustris have anendodermis with Casparian bands only. A honeycomb aerenchymais produced by differential expansion in N. odorata and includesastrosclereids and diaphragms, while roots of C. palustris haveno aerenchyma, but some irregular lacunae are found in old roots.These aspects of cortex structure are related to an open meristemorganization, with unusual patterns of cell divisions in certainground meristem cells (called semi-regular hexagon cells) ofN. odorata. The correlation between aerenchyma pattern and hypodermalstructure appears to be related to habitat differences.Copyright2000 Annals of Botany Company Caltha palustris, Nymphaea odorata, root development, cortex, endodermis, aerenchyma, exodermis, hypodermis, permeability, wetland plants     

A Transmission and Cryo-Scanning Electron Microscopy Study of the Formation of Aerenchyma (Cortical Gas-Filled Space) in Adventitious Roots of Rice (Oryza sativa)

The initiation and development ofaerenchyma in adventitiousroots of rice (Oryza sativa) was studied in tissuc up to approximately36-h-old using transmission electron microscopy (TEM) and cryoscanningelectron microscopy (cryo-SEM). Aerenchyma resulting from selective cortical cell collapse isa naturally occurring feature of rice roots. Evidence of somecortical cell disruption was noticeable by TEM in cells thatwere approximately 6-h-old; it became more advanced as the cellsaged. At 12 h, early stages of cell wall breakdown and lossof cell turgidity were seen. Complete collapse of columns ofcells had occurred by 24 h. In tissue that was 36-h-old, thesenescent cytoplasm of many remaining cells began to disperse.The visual evidence suggests that cell collapse was the resultof autolysis. This pattern of cortical degeneration in ricewas dissimilar to that reported elsewhere for Zea roots grownin an oxygen depleted environment. Cryo-SEM revealed the occurrence of small structures withinthe cortex with the external appearance of miniature, intactcells which are not preserved during conventional SEM preparativeprocedures. Key words: Rice (Oryza sativa L.), roots, aerenchyma, ultrastructure     

Anatomical study of an aquatic mustard: Subularia aquatica (Brassicaceae)

Subularia aquatica is a small annual aquatic plant in the family Brassicaceae with unique leaf morphology. Its anatomical features were studied using light microscopy. We show that the leaves of S. aquatica are bifacial dorsiventral phyllodes, having adaxial-abaxial polarity, rather than the alternative unifacial type. This morphology is also manifested in the collaterally arranged vascular bundles, which are clearly bifacial. The roots exhibit typical anatomical features of an aquatic plant, including prominent aerenchyma. Although unique within the Brassicaceae, S. aquatica displays many of the same morphological characteristics as other Isoetid life-forms.     

Seasonal Trends in Nitrogen Status of Antarctic Lichens

The thallus nitrogen (N) concentration of two dominant macrolichensof continental Antarctica (Usnea sphacelata and Umbilicariadecussata) was estimated each month for 1 year on a low roundedknoll on Clark Peninsula, Windmill Islands, Wilkes Land, Antarctica.Thallus N was significantly higher in Umbilicaria decussatathan in Usnea sphacelata and varied according to site. Duringthe winter months, when the lichens were metabolically inactive,thalli gradually accumulated N. At the onset of warmer conditions,thallus N content fell dramatically in both species, with thetiming of the decline being related to microclimatic conditions.The strongly seasonal pattern of metabolic activity in thesespecies is reflected in their nitrogen relations. Copyright2000 Annals of Botany Company Lichen, nitrogen, Antarctica, season, Usnea sphacelata, Umbilicaria decussata     

Evidence of biosynthetic simplicity in the flavonoid chemistry of the ricciaceae

The major flavonoids in Riccia crystallina are naringenin and its 7-O-glucoside, apigenin 7-O-glucoside and apigenin 7-O-glucuronide and derivatives. Ricciocarpus natans is a rich source of luteolin 7,3′-di-O-glucuronide and also contains the 7-O-glucuronides of apigenin and luteolin and the 3′-O-glucuronide of luteolin. A parallel between the production of biosynthetically simple flavonoids and reduced morphology is evident among these liverworts.