Three Different Methods for Measuring Xylem Cavitation and Embolism: A Comparison

Three different methods for measuring xylem embolism due towater cavitation were compared—the acoustic method, thehydraulic method and the anatomical method. Young plants ofCeratonia siliqua L. were water stressed for 9, 16 and 23 d. Xylem cavitation was detected by counting ultrasound (100–300kHz) acoustic emissions (AE) from 1-year-old twigs (acousticmethod). Xylem embolism was detected by measuring the loss ofhydraulic conductivity of twigs of the same age (hydraulic method).The blockage of single xylem conduits was detected by perfusingSafranin into the xylem of 1-year-old twigs of stressed plantsand measuring the number and the diameters of non-conductingxylem conduits, under the microscope (anatomical method). It was noted that: (a) the number of AE and the loss of conductivityincreased with the water stress applied; (b) a linear relationseemed to exist between the number of AE and the loss of conductivity,suggesting that the AE counted could be only (or mainly) producedin the xylem conduits; (c) the vulnerability of the xylem conduitsto embolism was a direct function of their diameter; and (d)the measured loss of conductivity was of the same order of magnitudeas the theoretical one. The three methods gave fairly similar results. Nonetheless,they are not alternative to one another in that: (a) the acousticmethod allows continuous recordings to be made but does notprovide information about the actual damage suffered by plants;(b) the hydraulic method is very informative but destructive;and (c) the anatomical method is very useful both in phytogeographicaland in genetic improvement studies. Ceratonia siliqua L, Carob tree, water stress, xylem embolism, acoustic method, hydraulic method, anatomical method     

Three Different Methods for Measuring Xylem Cavitation and Embolism: A Comparison

Three different methods for measuring xylem embolism due towater cavitation were compared—the acoustic method, thehydraulic method and the anatomical method. Young plants ofCeratonia siliqua L. were water stressed for 9, 16 and 23 d. Xylem cavitation was detected by counting ultrasound (100–300kHz) acoustic emissions (AE) from 1-year-old twigs (acousticmethod). Xylem embolism was detected by measuring the loss ofhydraulic conductivity of twigs of the same age (hydraulic method).The blockage of single xylem conduits was detected by perfusingSafranin into the xylem of 1-year-old twigs of stressed plantsand measuring the number and the diameters of non-conductingxylem conduits, under the microscope (anatomical method). It was noted that: (a) the number of AE and the loss of conductivityincreased with the water stress applied; (b) a linear relationseemed to exist between the number of AE and the loss of conductivity,suggesting that the AE counted could be only (or mainly) producedin the xylem conduits; (c) the vulnerability of the xylem conduitsto embolism was a direct function of their diameter; and (d)the measured loss of conductivity was of the same order of magnitudeas the theoretical one. The three methods gave fairly similar results. Nonetheless,they are not alternative to one another in that: (a) the acousticmethod allows continuous recordings to be made but does notprovide information about the actual damage suffered by plants;(b) the hydraulic method is very informative but destructive;and (c) the anatomical method is very useful both in phytogcographicaland in genetic improvement studies. Ceratonia siliqua L., Carob tree, water stress, xylem embolism, acoustic method, hydraulic method, anatomical method     

A phi Layer in Roots of Ceratonia siliqua L

The central cylinder of the primary root of the carob tree (Ceratonia siliqua) is encircled by a layer of cells with wall thickenings, known as a phi (φ) cell layer. The development of the φ layer and the chemical composition of the cell wall thickenings have been studied in roots of C. siliqua. The results reveal the presence of condensed tannins in the mature phi thickenings and that the development of the φ layer is asynchronous: at 0–1 cm from the root tip φ thickenings appear before endodermis differentiation at the sites opposite phloem, at 1–4 cm new φ thickenings are developed at the sites opposite xylem, at 4–7 cm the φ layer consists of two layers of cells and it completely encloses the central cylinder.     

Different Aspects of Cavitation Resistance in Ceratonia siliqua, a Drought-Avoiding Mediterranean Tree

Potted plants of Ceratonia siliqua L., growing in a greenhouse,were used to detect xylem cavitation (in terms of ultrasoundacoustic emissions AE) in internodes and node-to-petiole (N-P)junctions, after different periods of drought (9, 16 and 23d). Diurnal AE were only 100 in internodes of watered (W) plantsbut 320, 1250 and 2460 in 9-, 16- and 23-d stressed ones. InN-P junctions, AE were only 15 to 20% with respect to internodes. Stem perfusion with dye allowed measurement of the percentageof xylem conduit transverse area blocked by cavitation. Thiswas 2% in internodes of W-plants and 5.2, 13.8 and 40.4% inthose of 9-, 16- and 23-d stressed ones. In N-P junctions, 18.5%of the xylem conduit transverse area was blocked in the 23-dstressed plants only. The major resistance to cavitation exhibitedby the N-P junctions is interpreted in terms of their greaternumber of narrow xylem conduits. The percentage of blocked xylemconduits within a range of diameters showed that the narrowera xylem conduit, the less likely it was that cavitation wouldoccur. After rewatering, the release of the xylem blockage causedby cavitation occurred within 2 h. Our data suggest that C.siliqua can be considered to be a cavitation avoider, especiallyin its stem-to-leaf transition zones. Ceratonia siliqua L., Carob tree, cavitation avoidance, xylem architecture, ultrasonic acoustic emissions     

Production and secretion of {alpha}-galactosidase and endo-{beta}-mannanase by carob (Ceratonia siliqua L.) endosperm protoplasts

Viable protoplasts were isolated for the first time from maturecarob (Ceratonia siliqua L.) endosperm tissue. After 5 d ofincubation 75% of the protoplasts were viable. During incubationthey underwent vacuolation and produced the carob endospermhydrolases, agalactosidase and endo-ß-mannanase, whichwere secreted in the incubation medium. The secretion of bothenzymes were under Ca²⁺ control. Many characteristics of -galactosidaseand endo-ß-mannanase production by protoplasts werethe same as those of whole endosperms: their production didnot require any hormonal signal and was inhibited in the presenceof ABA or the leachate from the carob endosperm/seed coat. Moderatewater stress (—2.0 MPa) neither affected the activityof these hydrolases nor their secretion by endosperm protoplast.However, when the osmoticum of protoplast incubation mediumwas higher, the production and secretion of both hydrolaseswere reduced. Comparison of the hydrolases activities in theincubation media of leached carob endosperms, which were incubatedunder normal and water stress (—1.5 MPa) conditions, withthe activities of the protoplast-secreted hydrolases indicatedthat (i) carob endosperm cell wall acts as a barrier for thesecreted enzymes and (ii) that water stress reduces the cellwall porosity of the carob endosperm cells, and thus the releaseof the secreted -galactosidase and endo-ß-mannanaseis inhibited. The isolation of carob endosperm protoplasts offersa potent experimental system for the study of aspects of endospermcell physiology, such as enzyme secretion Key words: Abscisic acid, carob endosperm, Ceratonia siliqua L, endo-ß-mannanase, -galactosidase, leachate, protoplasts, water stress     

Effect of Water Stress on Germination and Reserve Carbohydrate Metabolism in Germinating Seeds of Ceratonia siliqua L.

Ceratonia siliqua L. seeds were germinated in water and undera range of PEG 4000-induced moisture stresses. Germination wasretarded as water stress was stronger. Axis growth, total dryweight decrease, and starch formation in the embryo were closelycorrelated to galactomannan depletion, the latter being inhibitedwith lower external water potential. Endosperm -galactosidasewas inhibited in PEG-germinated seeds, while embryo -galactosidaseactivity was not significantly affected. Soluble sugar contentwas higher in cotyledons of seeds geminated under stress conditions,mainly due to higher sucrose accumulation. The higher sugarcontent in the endosperm was mainly due to higher galactoseand mannose content. Water stress effected a delay in the raffinose-typeoligosaccharide depletion.     

Changes in the Morphology of Roots and Leaves of Carob Seedlings Induced by Nitrogen Source and Atmospheric Carbon Dioxide

Carob seedlings were grown hydroponically for 9 weeks under360 and 800 µl l^-1CO₂. One of two nitrogen sources, nitrateor ammonium, was added to the nutrient medium at concentrationsof 3 mol m^-3. Root systems of the developing plants suppliedwith nitrate compared to those supplied with ammonium were characterizedby:(a)more biomass on the lower part of the root;(b)fewer lateralroots of first and second order;(c)longer roots;(d)higher specificroot length;(e)a smaller root diameter. The morphology of theroot systems of nitrate-fed plants changed in the presence ofelevated carbon dioxide concentrations, resembling, more closely,that of ammonium-fed plants. Total leaf area was higher in ammonium-than in nitrate-fed plants. Nitrate-fed plants had greater totalleaf area in the presence of high carbon dioxide than in normalCO₂, due to an increase in epidermal cell size that led to developmentof larger leaflets with lower stomatal frequency. The observedchanges in the morphology of roots and shoots agreed with theresults observed for total biomass production. Nitrate-fed plantsincreased their biomass production by 100% in the presence ofelevated CO₂compared to 15% in ammonium-fed plants, indicatingthat the response of carob to high CO₂concentrations is verydependent on the nitrogen source. Under elevated CO₂, nitrate-grownplants had a larger content of sucrose in both roots and shoots,while no significant difference was observed in the contentof sucrose in ammonium-grown plants, whether in ambient or enrichedcarbon dioxide. Hence, the differences in soluble carbohydratecontents can, at least partly, account for differences in rootand shoot morphology.Copyright 1997 Annals of Botany Company Ceratonia siliquaL.; carob; ammonium; carbohydrate; carbon dioxide; nitrate; morphology; sucrose     

Leaf surface characteristics and wetting in Ceratonia siliqua L.

Compound leaves of Ceratonia siliqua L. (carob tree) exhibit a long life span and are exposed to environmental stimuli for approximately twenty months. The micromorphology of the adaxial and the abaxial leaflet surfaces was studied, in comparison with treated waxless epidermises (after the removal of cuticle and epicuticular waxes) and corresponding replicas, respectively. The microstructural surface features are evaluated as possible consistent parameters related to the wetness of leaves. The abaxial leaflet surface is more hydrophobic than the adaxial leaflet surface in C. siliqua, which may be particularly important for the ecophysiological status of its hypostomatic leaves.     

Selecting matched root architecture in tree pairs to be used for assessing N2 fixation based on soil-15N-labelling

It is commonly assumed that soil-¹⁵N-labelling provides reliable estimates of N₂ fixation in trees by matching N₂-fixing and non-N₂-fixing tree pairs. As root system is a key parameter in determining suitability of the tree pairs, we compared root architecture of Acacia cyanophylla Lindl. and Casuarina glauca Sieber ex. Spreng. (two N₂-fixing trees) with Eucalyptus camaldulensis Dehn. and Ceratonia siliqua L. (two non-N₂-fixing trees) at 4-year-old in Mediterranean-semiarid zone. The rhizobium strain used appeared more motile than Frankia strain. A. cyanophylla and E. camaldulensis had extensive rooting area and volume of fine roots, and both species tended to develop marked horizontal rooting, compared to C. glauca and C. siliqua. Characteristics of fine- and horizontal-root components can be used in selecting matched root systems of N₂-fixing and reference-paired trees. Root architecture of C. glauca was more similar to C. siliqua, than to E. camaldulensis, and that of A. cyanophylla was more similar to E. camaldulensis than to C. siliqua. Accordingly, E. camaldulensis is an appropriate reference to estimate actual N₂ fixation by A. cyanophylla, and C. siliqua is an appropriate reference for C. glauca, when using soil-¹⁵N-labelling method in the prevailing site environment.     

THE DEVELOPMENTAL BASIS FOR SEXUAL EXPRESSION IN CERATONIA SILIQUA (LEGUMINOSAE: CAESALPINIOIDEAE: CASSIEAE)

The flowers of Ceratonia siliqua, an anomalous caesalpinioid legume in the tribe Cassieae, are unusual in being unisexual and in lacking petals. Inflorescence development, organogeny, and flower development are described for this species. All flowers are originally bisexual, but one sex is suppressed during late development of functionally male and female flowers. Ceratonia siliqua is highly plastic in sexuality of individuals, inflorescence branching pattern, racemose or cymose inflorescences, bracteole presence, terminal flower presence, organ number per whorl, missing floral organs, pollen grain form, and carpel cleft orientation. Order of initiation is: five sepals in helical order, then five stamens in helical order together with the carpel. Each stamen is initiated as two alternisepalous primordia that fuse to become a continuous antesepalous ridge; in some flowers, the last one or two stamens of the five may form as individual antesepalous mounds. Petal rudiments are occasional in mature flowers. Position of organs is atypical: the median sepal is on the adaxial side in Ceratonia, rather than abaxial as in most other caesalpinioids. This feature in Ceratonia may be viewed as a link to subfamily Mimosoideae, in which this character state is constant.     

The first use of morphologically isolated arbuscular mycorrhizal fungi single-species from Moroccan ecosystems to improve growth,nutrients uptake and photosynthesis in Ceratonia siliqua seedlings under nursery conditions.

The carob tree (Ceratonia siliqua L.) is an important component in semi-arid Mediterranean ecosystems, particularly in Morocco where it plays a considerable socio-economic role. This species is widely used in the reforestation programmes and in the rehabilitation of degraded soils serving both environmental and socio-economic objectives. In spite of these assets, this species is suffering the particular climatic conditions, rare and irregular rains, long hot and dry summers, generally, leading to desertification processes. To withstand these contrasting conditions, selected arbuscular mycorrhizal fungi (AMF) were tested for their contribution to the growth, nutrient uptake and photosynthesis improvement of the carob tree C. siliqua under nursery conditions.The objective of this study was, to evaluate the effects of some arbuscular mycorrhizal fungi complexes isolated in different Mediterranean ecosystems compared to single-species isolates selected using morphological tools on the growth, mineral nutrition, and chlorophyll content of C. siliqua seedlings.The results indicate that all the used AMF inocula stimulated significantly the height of C. siliqua seedlings after eight months under nursery conditions. An increase in plant height between 33% and 70% compared to a control without inoculation was recorded. Similarly, the aerial dry weight recorded an increase of 62% to 124% comparing inoculated and non-inoculated seedlings. The root dry weight has shown an increase rate of 24% to 86% compared to the control. The analysis of mineral contents in plant tissues, showed a highly significant increase in P. N. K. Ca and Mg levels of the aerial parts compared to the control. A significant increase in chlorophyll contents was noticed when inoculated seedlings were compared to non-inoculated ones. This study had confirmed the importance of AMF improving the growth of C. siliqua seedlings; the AMF complexes remain to have the important growth and mineral nutrition responses. However some single- species have shown similar magnitude to the complexes for all analysed parameters. A large biofertilizer potential of the single-species isolates in the inoculation of C. siliqua is demonstrated for the first time.     

Andamento Dell'Accrescimento Del Legno in Ceratonia Siliqua L.

Abstract

The woody tissue of Ceratonia siliqua is of the diffuse-porous type, being mainly constituted of fibres full of starch grains (sostitution fibres; fusiform cells of the wood parenchyma).

The wood formed throughout the year is uniform and the annual rings are hardly distinguishable except for the presence of apotracheal parenchyma. The cambium shows a marked activity from May to July, and a less pronounced one from July to September; it is hardly or not at all active from October to April. During these latter months the cambium is completely dormant only in January, while during the others, especially the ones prior to the late spring reawakening, it can function in localised areas for short lapses of time.

These observations have been carried out in a female plant cultivated in Apulia, a region where Ceratonia siliqua is not a normal component of the natural plant cover. It is of some interest therefore to compare them with what is known of the same species in Israel, where C. siliqua is a spontaneous element of the maquis vegetation. The behaviour of the cambium of C. siliqua is similar in both regions but in Israel the maximum of activity begins earlier in the year and last for a longer period (mid-April to mid- August), after which the cambium becomes gradually less active until its activity is reduced to a minimum during autumn and winter. A short period of dormancy precedes the spring-time reawakening. This subcontinuous activity of the cambium together with the occurrence of flowering time in autumn-winter shows C. siliqua to be a tropical type of plant, but is nevertheless in good agreement with the eastern mediterranean climate.

In Apulia on the other hand we notice that the subcontinuous activity of the cambium is more potential than real, giving rise to sporadic and localised episodes from October to May. While this and other differences can be interpreted as direct responses to local climatic conditions, the general disturbances in the vegetative cycle can not be explained in the same way. In other words while the tendency of the cambium to remain dormant from October to May is probably caused by the relatively severe winter conditions, the shorter period of functioning in the spring—summer, the full resting period occurring in January rather than in February-March, and the attempts to resume meristematic activity already in February, while the full reawakening only occurs in May, can only be ascribed to indirect climatic action. These disturbances are probably to be seen as conseguences of the fact that the climatic conditions during the Apulian summer allow the flowers, whose primordia are well evident in July, to blossom in October-November and exceptionally even in August that is at least one month earlier than in Israel, where flowering occurs in December. This alteration in the flowering time affects the rythm of cambial activity causing it to be out of phase with the climatic cycle.

C. siliqua appears therefore not to be perfectly adapted to the Apulian climate even though it can often be found where it could not possibly have been planted, as on the steep flanks of fairly deep gulleys, and can be considered to be at least sub-spontaneous.     

Combined effects of enhanced UV-B radiation and additional nutrients on growth of two Mediterranean plant species

Seedlings of two Mediterranean plants, the slow-growing, evergreen sclerophyll Ceratonia siliqua L. and the fast growing drought semi-deciduous Phlomis fruticosa L., were grown for one year in the field at ambient or ambient plus supplemental UV-B radiation (equivalent to a 15% ozone depletion) and two levels of applied fertilizers (NPK). The effects on growth, morphological, anatomical and physiological parameters were measured at final plant harvest. Additional nutrients increased leaf nitrogen, improved growth and reduced the root/shoot ratio in both plants, yet these effects were more pronounced in the fast growing P. fruticosa. A nutrient-induced increase in chlorophyll content was also observed in this plant. The growth responses to UV-B radiation were different for the two species. Growth in C. siliqua was not affected by UV-B radiation at both nutrient levels and the same was true for P. fruticosa at low nutrients. However, at the high nutrient level, supplemental UV-B radiation improved growth in P. fruticosa, indicating a strong interaction between the treatments. Photosystem II (PSII) photochemical efficiency, methanol-extractable UV-B absorbing capacity, total phenolics and tannins were not affected by either treatment in both plants. It is concluded that nutrient levels can strongly modify the UV-B radiation effects on growth of P. fruticosa. We presume that this may be correlated to the fast growing habit of this species.     

Defective Secretion of Mucilage is the Cellular Basis for Agravitropism in Primary Roots of Zea mays cv. Ageotropic

Root caps of primary, secondary, and seminal roots of Z. mayscv. Kys secrete large amounts of mucilage and are in close contactwith the root all along the root apex. These roots are stronglygraviresponsive. Secondary and seminal roots of Z. mays cv.Ageotropic are also strongly graviresponsive. Similarly, theircaps secrete mucilage and closely appress the root all alongthe root apex. However, primary roots of Z. mays cv. Ageotropicare non-responsive to gravity. Their caps secrete negligibleamounts of mucilage and contact the root only at the extremeapex of the root along the calyptrogen. These roots become graviresponsivewhen their tips are coated with mucilage or mucilage-like materials.Peripheral cells of root caps of roots of Z. mays cv. Kys containmany dictyosomes associated with vesicles that migrate to andfuse with the plasmalemma. Root-cap cells of secondary and seminal(i.e. graviresponsive) roots of Z. mays cv. Ageotropic are similarto those of primary roots of Z. mays cv. Kys. However, root-capcells of primary (i.e. non-graviresponsive) roots of Z. mayscv. Ageotropic have distended dictyosomal cisternae filled withan electron-dense, granular material. Large vesicles full ofthis material populate the cells and apparently do not fusewith the plasmalemma. Taken together, these results suggestthat non-graviresponsiveness of primary roots of Z. mays cv.Ageotropic results from the lack of apoplastic continuity betweenthe root and the periphery of the root cap. This is a resultof negligible secretion of mucilage by cells along the edgeof the root cap which, in turn, appears to be due to the malfunctioningof dictyosomes in these cells. Corn, dictyosomes, mucilage, root gravitropism, Zea mays cv. Ageotropic, Zea mays cv. Kys     

Control of Sucrose Metabolism in Polyethylene Glycol-stressed Carob (Ceratonia siliqua L.) Young Seedlings. The Role of Sucrose

Four-d-old Ceratonia siliqua L. seedlings were treated with30% PEG 4000 for several time periods, or with 26.5% and 25%PEG for 48 h. Drought stress was imposed on some seedlings inorder to compare the results of stress due to drought with thosedue to the application of PEG. The water content of the axisand cotyledons and their osmotic potentials decreased with stressfor the first 72 h and then remained constant, whilst dry weightincreased after the first 24 h of imposed stress. Results implythe existence of an osmoregulation mechanism which was morepronounced when the stress was mild. Sucrose content increasedwith stress in both axes and cotyledons, and a negative correlationwas found between osmotic potential and sucrose content in bothembryo parts, suggesting the involvement of sucrose in the osmoregulationmechanism. Upon stress recovery sucrose content decreased andfructose accumulated in the axes. Sucrose synthetase activitywas very low in cotyledons, while acid and alkaline invertaseactivity was too low to be measured. PEG-induced stress causedsucrose synthetase activity to decrease in both axes and cotyledons,while upon stress recovery sucrose synthetase activity increased.The activity of both invertases in the axes did not change significantlywith stress. Correlation of sucrose content with sucrose synthetaseactivity suggests that this enzyme is involved in the controlof osmoregulation in both parts of the embryo.     

Influence of soil drying on root development,water relations and leaf growth of Ceratonia siliqua L.

Summary Seedlings of Ceratonia siliqua L., an evergreen sclerophyll species native to the Mediterranean region, were grown in 30-cm deep tubes of John Innes II potting compost in a growth cabinet maintained at 15° C during a 12-h day where PAR was 400 mol m^–2 s^–1. After a period of acclimatisation to the conditions in the cabinet during which plants were watered every day, water was withheld from the soil in some tubes for 24 days. These conditions may be regarded as a simulation of the natural situation. Estimates of leaf and root water potential and solute potential, leaf growth and root development were made at intervals during the soil drying cycle on both watered and unwatered plants. Water potential and solute potential measurements were made both on young expanding and on fully expanded leaves. During the experimental period, root growth of C. siliqua was not much affected by soil drying, and roots in both the watered and the unwatered columns penetrated to the bottom of the soil tubes by the end of the drying treatment. Expanded leaves showed significant limitation in stomatal conductance as soil drying progressed. Leaf water potential of fully expanded leaves of unwatered plants declined substantially. In contrast, water potential of young expanding leaves on unwatered plants declined to only a limited extent and turgor was sustained. As the soil dried, stomatal conductance of young leaves was always higher than that of mature leaves; also, placticity and elasticity of young leaves slowly decreased whereas mature leaves became stiff. Changing leaf cell wall properties may determine different patterns of water use as the leaves age. A mechanism of continuous diffusion of water through the soil towards the tip and pumping towards the young leaves is proposed.     

A late Holocene pollen diagram from the Megaris,Greece, giving possible evidence for cultivation of<Emphasis Type="Italic"> Ceratonia siliqua</Emphasis> L. during the last 2000 years

A late Holocene pollen profile from the Megaris on the eastern Gulf of Corinth shows a vegetation which was strongly influenced by human impact throughout. A Pistacia-Phillyrea maquis, which is reflected in the older parts of the profile, changed later to a more degraded vegetation type. In the uppermost part Pinus dominates the pollen spectrum. A continuous record of Ceratonia siliqua pollen older than cal a.d. 100 is of special interest.     

Vulnerability to cavitation of leaf minor veins: any impact on leaf gas exchange?

Vulnerability to cavitation of leaf minor veins and stems of Laurus nobilis L. was quantified together with that of leaflets, rachides and stems of Ceratonia siliqua L. during air‐dehydration of 3‐year‐old branches. Embolism was estimated by counting ultrasound acoustic emissions (UAE) and relating them to leaf water potential (Ψ_L). The threshold Ψ_L for cavitation was less negative in L. nobilis than in C. siliqua according to the known higher drought resistance of the latter species. Leaf minor vein cavitation was also quantified by infiltrating leaves with fluorescein at different dehydration levels and observing them under microscope. Distinct decreases in the functional integrity of minor veins were observed during leaf dehydration, with high correlation between the two variables. The relationship between leaf conductance to water vapour (g_L) and Ψ_L showed that stomata of L. nobilis closed in response to stem and not to leaf cavitation. However, in C. siliqua, g_L decreased in coincidence to the leaf cavitation threshold, which was, nevertheless, very close to that of the stem. The hypothesis that stem cavitation acts as a signal for stomatal closure was confirmed, while the same role for leaf cavitation remains an open problem.     

Relationship Between Root Morphogenesis and Period of Predominant Cell Arrest in Intact and Aseptically-cultured Roots of Helianthus annuus L.

Root morphogenesis and cell cycle kinetics of intact and aseptically-grownexcised roots of Helianthus annuus L. were studied. Intact rootsshow predominant cell arrest in G1 with an absence of polyploidcells coincident with secondary vascularization. Exposure ofthe cut ends of aseptically grown excised roots to known concentrationsof indol-3-yl acetic acid, benzyladenine, and myo-inositol for8 weeks initiated the production of secondary vascular tissuesand predominant cell arrest in G2 concommitant with poiyploidization.Excised roots grown in the absence of these substances producedroots with only primary vascularization and predominant cellarrest in G1 coincident with an absence of polyploidization.These results indicate that (a) root cells of H. annuus havethe ability to undergo polyploidization that may be inducedby exogeneously applied chemicals, (b) a general relationshipbetween predominant cell arrest in G1 coincident with the absenceof secondary vascularization does not hold true and (c) althoughsecondary vascularization occurs in cultured roots exposed toall three additives similar to secondary vascularization inintact roots, the two roots should not be considered identicalin all respects. Helianthus annus L., sunflower, root, morphogenesis, cell cycle kinetics, polyploidy, cell differentiation, vascularization