Structural and Histochemical Changes in Palisade Cells of Prosopis juliflora Seed Coat in Relation to its Water Permeability

Histochemical investigations on the Prosopis juliflora seedcoat indicate the occurrence of a hydrophobic ‘strip’as the primary water barrier. Its position and the structureand histochemistry of the palisade cells of the seed coat differaccording to their location on the seed. These differences maybe responsible for differences in the water permeability ofvarious parts of the seed coat. In particular, parts of theseed coat in which the hydrophobic ‘strip’ is locatedmore superficially tend to be more water impermeable than partslike the chalaza, in which the ‘strip’ is more deeplylocated within the palisade cells. Prosopis juliflora, seed coat impermeability, palisade cells, hydrophobic ‘strip’     

The Role of the Lens in Seed Imbibition and Seedling Vigour of Sesbania punicea (Cav.) Benth. (Leguminosae: Papilionoideae)

Seeds of Sesbania punicea (Cav.) Benth. are largely impermeable,and the natural, low, percentage which germinate are permeableat the lens. Scarifying seed in acid stimulates germinationand causes various types of damage to the testa, including thelens. Placing seeds in boiling water stimulates germinationby rendering the seeds permeable at the lens. Seeds were mechanicallyscarified at precise sites on the testa to assess influenceof the site and degree of damage on germination. Results indicatethat both the site of initial water entry and the rate of waterentry are important in determining seed and seedling vigour.Damaging the lens is more effective in stimulating germinationand reducing seedling abnormalities than complete excision ofthe lens. This effect can be reversed if seeds from which thelens was excised are allowed to imbibe gradually in inert osmotica.The leguminous lens thus acts as the site of initial water entryand regulates the rate of water uptake, thereby increasing seedand seedling vigour. Sesbania punicea (Cav.) Benth., hardseededness, lens, seed germination, imbibition damage, seedling vigour     

Seed Coat Structure and Histochemistry of Abelmoschus esculentus. Chalazal Region and Water Entry

The seed coat structure and histochemistry of Abelmoschus esculentuswere studied by bright-field, fluorescence and scanning electronmicroscopy. The seed coat was typical of species of the Malvaceae.The endotesta cells had inner tangential walls which were verythick and autofluorescent. The occurrence of phenolic substancesat this level has been related to seed coat imposed dormancy.The palisade cells were composed of three differently shapedparts: an upper ‘prismatic part’, a medium ‘transitionpart’ and a lower ‘twisted part’. The formerwas rich in hydrophilic substances, the latter was lignified.The swelling of the ‘prismatic parts’ was relatedto seed coat cracks. The region controlling onset of water entrywas thought to be the chalazal area. Thanks to the presenceof a large amount of highly acidic polysaccharide, water wasable to penetrate from the permeable maternal tissue, throughthe chalazal cap and plug as far as the boundary between thepalisade and underlying mesophyll. During imbibition of watera kidney-shaped ‘blister’ was seen to rise, formedby separation of the palisade cells from an underlying singlelayer of subpalisade cells. The palisade layer forming the blisterroof showed the same histochemical characteristic of other seedregions. The single layer of the blister floor showed an affinitywith Toluidine Blue O and Alcian blue. Both blister roof andfloor were strongly autofluorescent. Abelmoschus esculentus (L.) Moench, okra, seed coat, chalazal region, water entry, structure, histochemistry     

Changes in Levels of Naturally Occurring Gibberellin-like Substances during Germination of Seed of Lycopersicon esculentum Mill.

Naturally occurring gibberellin-like substances possessing acidic,basic, and neutral properties were detected, by paper partitionchromatography, in ethanolic extracts of tomato seed and ofetiolated seedlings after 72 and 116 hours' growth. Dwarf maizemutants of the d-1 and d-5 types, ‘Meteor’ pea seedlingsand young ‘Potentate’ tomato plants were used asbioassay material. Hydrolysis of seed and seedling proteinsby ficin in phosphate buffer, pH 6.2, after removal of ethanol-solublesubstances, liberated more and different ‘bound’gibberellin-like substances. It is suggested that protein hydrolysisduring germination is an important means of liberating thesesubstances at different stages of seedling development. Acidic substances were present in all the extracts prepared,but in general two with Rfs 0.25 and 0.55 in iso-propanol: ammonia:water : : 10:1:1 v/v were differentiated on d-2 and d-5 maizerespectively. Neutral substances in dry seed extracts chromatographedin the same solvent, had Rfs of 0.05, 0.35, and 0.95 and thesewere found only in the ethanolic (‘free’) extracts.They were active on d-1 and d-2 maize and ‘Meteor’pea. Basic gibberellin-like substances with Rfs of 0.05 and0.35 were found in ‘free’ extracts of both dry seedand etiolated seedlings after 116 hours' growth which were activeon d-2 maize only. Two others with Rfs 0.45 and 0.95 were extractedfrom seedlings after 72 hours' growth and these were activeon young ‘Potentate’ tomato plants. It is suggested that certain gibberellin-like substances, capableof reversing dwarfism in test plants, may be responsible formorphogenetic or other responses not involving stem extensionin the parent species. Changes were found in the levels of gibberellin-likesubstances but there was no evidence of changes in levels ofseed inhibitors relative to seed growth substances.     

ERRATA

WARBURG, M. R., 1965. On the water economy of some Australianland snails. Proc. malac. Soc. Lond. 36, 297–305. Page 298: second line from bottom, should read ‘within± 1 µg for Themapupa’. Page 300: Fig. 2 legend, should read ‘Evaporative waterloss from Sinumelon remissum (a), Pleuroxia sp. (b) and Themapupaadelaidae (c)’. Page 300: section 4 heading, should read ‘Continuous curvesfor water loss’. Page 301: second line, for ‘Fig. 9’ read ‘Fig.3’. Page 301: Table 1, last line, for ‘0.120024’ read‘0.12024’. Present address: Israel Institute for Biological Research, Ness-Ziona,Israel.     

The Reproduction and Germination of Limosella aquatica

Quantitative data are furnished respecting the seed productionand germination of Limosella aquatica, which is shown to havea large reproduction potential like other species of intermittentlyavailable habitats, despite its small assimila-tory surface.A tentative estimate of the seed output of the rarer diploidspecies L. subtdata suggests that this may be only about one-sixththat of the tetraploid L. aquatica. Features described indicatespecialization primarily to dispersal by water, and submergedcapsules readily dehisce. Germination, which may occur within3 days, is shown to be quasi-simultaneous in bright light underwhich over 90 per cent may be attained but a very small percentagewere found able to germinate in dim light. Experimental evidenceis provided that indicates the presence of an inhibitor in theseeds the amount of which may, it is suggested, vary from seedto seed in a normal manner. As with other ‘mud species’the seedling develops a zone of supporting ‘prop hairs’around the base of the radicle. The markedly intermittent occurrence of the species is attributablemainly to the irregular incidence of the requisite environmentalconditions.     

Mutant genes at the r and rb loci affect the structure and physico-chemical properties of pea seed starches

Mutant genes at two loci, r and rb, known to encode genes affectingthe starch biosynthetic pathway, were studied for their effecton the structure and gelatinization of pea seed starches. Comparisonswere made using starches from four lines {RRRbRb, rrRbRb, RRrbrb,and rrrbrb), near-isogenic except for genes at these two loci.All the starches had C-type X-ray diffraction patterns, butdifferent contents of ‘A’ and ‘B’ polymorphs.The presence of a mutation at either locus increased the ‘B’polymorph content in the starches, although the influence ofthe r mutation was much greater than that of rb. Differenceswere discovered in the crystalline stucture of the rrRbRb starchwhich correlated with a high content of amorphous phase as wellas with the changes in amylopectin structure. In addition, changesin the crystalline structure of this sample correlated witha lack of co-operative transition during starch gelatinizationin excess water. The RRrbrb starch had a greatly increased enthalpyof gelatinization in excess water compared with the wild-typestarch. It is proposed that this effect is connected with specificcharge interactions between the molecules in the starch granule.The rrrbrb starch had parameters of crystalline structure andgelatinization which reflected the different influences of thetwo genes. With regard to gelatinization, this starch had relativelywide co-operative transition and low enthalpy and a very highpeak temperature of transition. Key words: Pisum sativum, starch structure, genetic effects, rugosus mutants     

Developmental Genetics and Morphological Evolution of Flowering Plants, Especially Bladderworts (Utricularia): Fuzzy Arberian Morphology Complements Classical Morphology

This review compares new developmental models on flowering andother vascular plants with evolutionary hypotheses formulatedby Agnes Arber (1879–1960) and like-minded botanists.Special emphasis is laid on philosophical basics such as perspectivism,pluralism about evolutionary modelling, continuum way of thinking,and fuzzy logic. Arber's perspective is best labelled as F uzzyA rberian M orphology (FAM Approach). Its proponents (‘FAMmers’)treat structural categories (e.g. ‘roots’, ‘shoots’,‘stems’, ‘leaves’, ‘stipules’)in vascular plants as concepts with fuzzy borderlines allowingintermediates (including transitional forms, developmental mosaics).The FAM Approach complements Cla ssical Plant M orphology (ClaMApproach), which is the traditional approach in botany. ClaMproponents (‘ClaMmers’) postulate that the structuralcategories of vascular plants are regarded as concepts withclear-cut borderlines and without intermediates. However, duringthe evolution of vascular plants, the root-shoot distinctionand the stem-leaf distinction have become blurred several timesdue to developmental changes, resulting in organs with uniquecombinations of features. This happened, for example, in thebladderworts (Utricularia, Lentibulariaceae). When focusingon the ‘leaf’, the FAM Approach is identical toArber's ‘partial-shoot theory of the leaf’ and Sinha's‘leaf shoot continuum model’. A compound leaf canrepeat the developmental pathway of the whole shoot, at leastto some degree. For example, compound leaves of Chisocheton(Meliaceae)with indeterminate apical growth and three-dimensional branchingmay be seen as developmental mosaics sharing some growth processeswith whole shoots! We focus here on the FAM Approach becausethis perspective is especially promising for developmental geneticistsstudying flowering and other vascular plants. Copyright 2001Annals of Botany Company Review, body plan, developmental mosaics, leaf development, history of botany, homeosis, homeotic genes, Lentibulariaceae, morphological evolution, process morphology, stipules, Utricularia, flowering plants     

Studies on Mature Seeds of Cuscuta pedicellata and C. campestris by Electron Microscopy

The seeds of Cuscuta pedicellata have been investigated by transmissionand scanning electron microscopy. Additional observations havebeen made on seeds of C. campestris by SEM only. The seed coatconsists of an outer single epidermis, two different palisadelayers, and an inner multiparenchyma layer. The outer epidermalwall in C. pedicellata has a thick cuticle and zones rich inpectic substances. The thicker ‘U-shaped’ cell wallsin the outer palisade layer are strengthened by a wall layerof hemicellulose. The inner palisade layer has thick walledcells with a ‘light line’. The inner cell wall ofthe compressed multiparenchyma layer has a thin cuticle. A fairlythick cuticle is positioned directly on the endosperm surface.The aleurone cell walls are different from the remaining endospermwalls. The latter are thick and believed to be of galactomannans.There is a ‘clear’ zone between the plasmalemmaand the cell wall in the aleurone cells. The embryo cells arepacked with lipids and proteins. In Cuscuta campestris mostendosperm has been absorbed during the seed development. Theembryo apex has two minute leaf primordia. The features of theCuscuta seeds are discussed in relation to functional and environmentalconditions. Cuscuta pedicellata, Cuscuta campestris, seed, seed coat, cuticle, cell walls, endosperm, aleurone cells, galactomannan, embryo, TEM, SEM     

Relative Sensitivity and Tolerance of some Gladiolus Cultivars to Sulphur Dioxide

Five Gladiolus cultivars, namely ‘Aldebaran’, ‘BrightEye’, ‘Illusion’, ‘Manisha’ and‘Manmohan’, were exposed to 1 and 2 µg l^–1sulphur dioxide to test their relative-sensitivity toleranceto the pollutant Plants were fumigated experimentally for 2h daily Foliar injury symptoms were observed first in ‘Manisha’followed by ‘Aldebaran’ and ‘Illusion’at the higher dose Photosynthetic pigments and leaf extractpH were significantly decreased, particularly in ‘Manisha’and ‘Illusion’ Overall disturbances in the plantmetabolism due to SO₂ treatment led to retarded growth of plants,as evident from decreased shoot length and phytomass valuesThe order of sensitivity of the five Gladiolus cultivars toSO₂ was as follows, with the greatest first Manisha, Illusion,Aldebaran, Bright Eye, Manmohan Cultivars, Gladiolus, sensitivity, sulphur dioxide, tolerance     

Effects of the 'Stay Green' Genotype GGd1d1d2d2 on Leaf Gas Exchange, Dry Matter Accumulation and Seed Yield in Soybean (Glycine max L. Merr.)

The homozygous combination of the recessive mutations d1 andd2, i.e.d1d1d2d2 , causes retention of chlorophyll, chlorophyll-bindingproteins and Rubisco in senescing leaves of soybean (Glycinemax L. Merr.). Together with G(a gene that preserves only chlorophyllin the mature seed coat), d1d1d2d2 prolonged photosyntheticactivity and increased seed yield in growth chamber experiments.The objective of this work was to test the effects of GGd1d1d2d2(abbreviatedto Gd1d2) on leaf gas exchange, growth and seed yield in soybeanplants cultured outdoors during the normal growing season. Despitepreservation of the photosynthetic machinery in Gd1d2, photosynthesisduring the seed filling period was similar in Gd1d2 and itsnear-isogenic wild type line ‘Clark’. The main factorlimiting photosynthesis in the mutant appeared to be stomatalconductance, which was substantially lower in Gd1d2 than in‘Clark’. In Gd1d2 the rate of dry matter accumulationduring the seed filling period was similar or lower than inthe wild type. At maturity, Gd1d2 had fewer nodes, fruitingnodes, fruits and seeds per plant, and therefore its seed yieldwas reduced by 10–20% compared to ‘Clark’.Thus, pleiotropic effects of G, d1 and/or d2 affecting stomatalconductance and seed number appear to be major limitations tothe yield potential of Gd1d2. These pleiotropic effects suggestthatG , d1 and/or d2 have regulatory functions in addition tothe control of chloroplast disassembly during senescence. Copyright2001 Annals of Botany Company Glycine max L. Merr., photosynthesis, seed yield, senescence, soybean, stay green, stomatal conductance     

Diurnal Phototropism in Leaves of Lavatera cretica L. under Conditions of Simulated Solar-Tracking

Diurnal laminar reorientation was followed in solar-trackingleaves of Lavatera cretica L. under simulated conditions. Asimulated ‘sun’ was moved over the lamina in a 180?arc in the vertical plane of the mid-vein, at an angular velocityof 15? h^–1 in a regime of 12-h photoperiods. In one groupof plants the petioles of the experimental leaves were arrangedto face ‘sunrise’, while in the other they werearranged to face ‘sunset’. At ‘sunrise’,the laminae in both groups, which were inclined towards theanticipated direction of ‘sunrise’, changed theirelevation towards the rising ‘sun’, resulting inprogressive reduction in the angle of incidence (AI) of lighton the laminar surface (AI= differential between laminar and‘solar’ elevation). As a result, laminar and ‘solar’elevation converged, and laminar reorientation gradually ceased,until the ‘solar’ elevation had passed the normalto the laminar surface (AI=0?). laminar reorientation was thenresumed, but its direction was reversed to follow the directionof ‘solar’ reorientation. During most of the remaining‘day’, laminar elevation (LE) trailed that of the‘sun’ by an average of 11?-14?. Laminar reorientationthen anticipated ‘sunset’ by starting to slow down60 to 90min in advance. During the 12-h dark period, the laminareoriented towards the anticipated direction of the subsequent‘sunrise’. The time-course of nocturnal reorientationwas qualitatively different in the two groups of experimentalplants. The time-course of diurnal phototropism under naturaland simulated conditions is analysed and compared and differencesand similarities between them are discussed. Key words: Diurnal phototropism, solar-tracking, vectorial excitation     

Anther Culture of Lolium temulentum, Festuca pratensis and Lolium x Festuca Hybrids. I. Influence of Pretreatment, Culture Medium and Culture Incubation Conditions on Callus Production and Differentiation

This study was conducted with Lolium temulentum, Festuca pratensis,and the two hybrids L. multiflorum x F. pratensis ‘Elmet’and L. perenne x F. pratensis ‘Prior’. In a comparisonof various durations (7–42 d) of pretreatment at 4 or7 °C the highest yield of microspore-derived callus of L.temulentum was obtained after pretreatment of spikes at 7 °Cfor 28 d, conditions which also proved optimal for panicle pretreatmentwith F. pratensis. For ‘Elmet’, durations of 21–42d were optimal, and for ‘Prior’ the responses tendedto decline with increasing duration. In L. temulentum addition of charcoal (1–2 g l^–1)to medium containing 2, 4-D and KN wa     

Seasonal patterns of growth, dehydrins and water-soluble carbohydrates in genotypes of Dactylis glomerata varying in summer dormancy

• Background and Aims Summer dormancy in perennial grasseshas been studied inadequately, despite its potential to enhanceplant survival and persistence in Mediterranean areas. The aimof the present work was to characterize summer dormancy anddehydration tolerance in two cultivars of Dactylis glomerata(dormant ‘Kasbah’, non-dormant ‘Oasis’)and their hybrid using physiological indicators associated withthese traits. • Methods Dehydration tolerance was assessed in a glasshouseexperiment, while seasonal metabolic changes which produce putativeprotectants for drought, such as carbohydrates and dehydrinsthat might be associated with summer dormancy, were analysedin the field. • Key Results The genotypes differed in their ability tosurvive increasing soil water deficit: lethal soil water potential(_s) was –3·4 MPa for ‘Kasbah’ (althoughnon-dormant), –1·3 MPa for ‘Oasis’,and –1·6 MPa for their hybrid. In contrast, lethalwater content of apices was similar for all genotypes (approx.0·45 g H₂O g d. wt^–1), and hence the greater survivalof ‘Kasbah’ can be ascribed to better drought avoidancerather than dehydration tolerance. In autumn-sown plants, ‘Kasbah’had greatest dormancy, the hybrid was intermediate and ‘Oasis’had none. The more dormant the genotype, the lower the metabolicactivity during summer, and the earlier the activity declinedin spring. Decreased monosaccharide content was an early indicatorof dormancy induction. Accumulation of dehydrins did not correlatewith stress tolerance, but dehydrin content was a function ofthe water status of the tissues, irrespective of the soil moisture.A protein of approx. 55 kDa occurred in leaf bases of the mostdormant cultivar even in winter. • Conclusions Drought avoidance and summer dormancy arecorrelated but can be independently expressed. These traitsare heritable, allowing selection in breeding programmes.     

A Seed Treatment for Eliminating Non-hybrid Plants when using Atrazine Resistance as a Genetic Marker for Hybrid Seed Production

Brassica plants, with a combination of chloroplasts encodingtriazine resistance and mitochondria encoding cytoplasmic malesterility, offer new opportunities for hybrid seed production.Such plants can be grown as a random mixture with a male parent,thereby allowing more effective pollen transfer for greaterefficiency of hybrid seed production. Harvested seed consistsof hybrid seed from the ‘female’ parent, which istriazine-resistant, and non-hybrid, triazine-sensitive seedresulting from self pollination of the ‘male’ parent. This study demonstrates that triazine-sensitive broccoli (BrassicaoleraceaL. var.italica) progeny can easily be eliminated byallowing the seed to imbibe a solution of 10 g l^-1atrazine overnightthen drying-back the seed for subsequent germination. Such atreatment prevents triazine-sensitive broccoli from developingbeyond the cotyledon stage following germination, and remainseffective for at least 3.5 years after seed treatment. The growthof triazine-resistant broccoli plants is unaffected by thisseed treatment. Atrazine; Brassica oleracea; broccoli; hybrid seed; triazine resistance; seed treatment     

The relationship between 'dehydrin-like' proteins and seed longevity in Ranunculus sceleratus L.

The relationship between the abundance of proteins homologousto the dehydrin/RAB group of LEAs and seed longevity has beenstudied in Ranunculus sceleratus L. The presence of these ‘dehydrin-like’proteins was not related to increases in seed longevity associatedwith seed development or priming treatments. Similarly, a drying-inducedincrease in the amount of ‘dehydrin-like’ proteinswas not accompanied by an improvement in longevity. Key words: Dehyclrin, LEA, longevity, R. sceleratus, seed     

Influence of Irradiated Pollen on Embryo and Endosperm Development in Kiwifruit

Development of seeds following pollination with irradiated pollenwas studied inActinidia deliciosa(kiwifruit) ‘Hayward’.Pollinations were carried out using two different sources ofpollen (‘Tomuri’ and ‘Matua’) irradiatedwith gamma rays at doses of 700 and 900 Gy. Non-irradiated crosseswere used as controls. Pollen irradiation had little effectonin vitropollen germination. Irradiated pollen affected seedset and seed content, and induced the formation of parthenogeneticembryos. In comparison to the control, the embryo growth ratewas slower and the endosperm contained very low amounts of storageproducts. Seed set was significantly reduced following bothdoses of irradiation. Two types of seeds were observed: (1)seeds with endosperm only; and (2) seeds with both embryo andendosperm. The proportion of seeds containing endosperm onlywas almost ten-fold higher than those containing both embryoand endosperm. Embryo production by gamma-irradiated pollenwas genotype- and dose-dependent. The induction of parthenogenesiswas higher following gamma ray doses of 900 Gy than 700 Gy,which suggests the ‘Hertwig Effect’; the best efficiencywas obtained with ‘Tomuri’ pollen. Ploidy levelof parthenogenetic embryos was evaluated by nuclear size (area)with the use of image analysis. There was a large differencein embryo nuclei size between control and parthenogenetic embryos(mean size 90.8 and 49.1 µm², respectively). It is concludedthat parthenogenetic embryos represent trihaploids.Copyright1998 Annals of Botany Company. Actinidia deliciosa, kiwifruit, pollen irradiation, induced parthenogenesis.     

Pyrimidine Nucleotide Biosynthesis in Vinca rosea Cells: Changes in the Activity of the de novo and Salvage Pathways during Growth in a Suspension Culture

Marked changes in the activity of the ‘de novo’and ‘salvage’ pathways of pyrimidine biosynthesisduring growth of Vinca rosea cells in a batch suspension culturewere observed. The activity of these pathways was investigated by determiningthe contribution of ¹⁴C of [2-¹⁴Cluracil, 12-¹⁴Cluridine. and[6-¹⁴Clorotate to the cell constituents and by measuring theactivity of the several enzymes of these pathways. During the lag phase of the culture, ‘uracil-’ and‘uridine-salvage’ pathways made the predominantcontribution to nucleotide biosynthesis, but, following theinitiation of cell division, the ‘de novo’ pathwayfor nucleotide biosynthesis operated appreciably. These results suggest that nucleotide synthesis during cellgrowth in a suspension culture can be divided into two stages:a ‘turnover stage’, during the lag phase of cellgrowth, and a ‘true biosynthetic stage’, which isinitiated in the cell division phase.     

Source-sink Relationships, Seed Sucrose Levels and Seed Growth Rates in Soybean

Field experiments using two soybean (Glycine max L. Merrill)cultivars (‘Elgin 87’ and ‘Essex’) wereconducted for 2 years near Lexington, KY, USA to evaluate theeffect of source-sink alterations on seed carbohydrate statusand growth. Sucrose concentrations in developing cotyledonsof control plants were consistently low (<50 m M) early inseed development, but they increased to 100–150 m M byphysiological maturity. The concentrations increased in bothyears by 47 to 59% when 90% of the pods were removed from ‘Elgin87’, but the increase had no effect on individual seedgrowth rate (SGR). Shading (80%) reduced cotyledon sucrose levelsand SGR in both years. The critical cotyledon sucrose concentration(the concentration providing 80% of the maximum cotyledon growthrate) was estimated fromin vitro cotyledon growth at sucroseconcentrations of 0–200 m M. These critical concentrationsvaried from 72–124 m M;in planta control cotyledon sucroseconcentrations were below this critical level during the firsthalf of seed growth but exceeded it in the later stages of growthin all experiments. The estimated critical concentration wasconsistent with the failure of in planta SGR to respond to anincrease in assimilate supply and with the reduction in SGRassociated with a decrease in assimilate supply. The resultssuggest that soybean SGR is generally sink limited if photosynthesisincreases during seed filling, but source limited if photosynthesisis reduced. Copyright 2001 Annals of Botany Company Glycine max(L.) Merrill, soybean, source-sink ratios, sucrose, starch, depodding, shade, in vitro culture     

Influence of Flooding on Net CO2Assimilation, Growth and Stem Anatomy of Annona Species

A series of experiments was conducted to assess net CO₂assimilationand growth responses to waterlogging of grafted and seedlingtrees in the genus Annona. Seedlings of A. glabra, A. muricataandA. squamosa L., and scions of ‘Gefner’ atemoya(A. squamosaxA. cherimola Mill.), ‘49-11’ (‘Gefner’atemoyaxA. reticulata L.), ‘4-5’ (‘Priestley’atemoyaxA. reticulata), A. reticulata grafted onto either A.glabra, A. reticulata orA. squamosa rootstocks were floodedfor up to 60 d. Soil anaerobiosis occurred on the third dayof flooding. Seedlings ofA. glabra and A. muricata, and thescions ‘49-11’, ‘Gefner’ atemoya, andA. reticulata grafted onto A. glabra rootstock were consideredflood tolerant based on their ability to survive and grow inflooded conditions. Scions of the normally flood-sensitive A.reticulata, ‘Gefner’ atemoya, and ‘49-11’tolerated root waterlogging when grafted onto the flood-tolerantspecies, A. glabra. In contrast, flooding of A. squamosa seedlingsand rootstocks, and A. reticulata rootstocks greatly reducedgrowth and net CO₂assimilation rates, and resulted in 20–80%tree mortality. Stem anatomical responses to long-term flooding(12 continuous months) were assessed in seedlings of A. glabraand A. muricata, and trees of ‘49-11’ grafted ontoA. glabra. Flooded trees developed hypertrophied stem lenticels,particularly in A. glabra, and enlarged xylem cells resultingin thicker stems with reduced xylem density. Flooding did notincrease air spaces in pre-existing xylem near the pith or inxylem tissue that was formed during flooding. Thus, flood tolerancedid not involve aerenchyma formation in the stem. Copyright1999 Annals of Botany Company Flood tolerance, net CO₂assimilation, photosynthesis, stem anatomy, shoot growth, anaerobiosis, Annonaceae.