Pith Autolysis in Herbaceous, Dicotyledonous Plants: Experimental Manipulation of Pith Autolysis in Several Cultivated Species

Pith autolysis, a condition in which dicotyledonous herbaceousplants have a hollow stem, results from the autolysis of a plant'sstorage pith. Our central hypothesis concerning the aetiologyof pith autolysis states that the carbon from the pith is transportedto the growth regions of the plant and used at times when theplant cannot meet its carbon needs by photosynthesis alone.According to this hypothesis, accelerated growth should increasepith autolysis. We here provide supporting evidence for thecentral hypothesis. More pith autolysis was found in fastergrowing tomato varieties than in dwarf varieties. More pithautolysis was found in both beans and tomatoes treated withGA₃ than in controls. More pith autolysis was found in leggybean plants grown in low light than in normal plants grown undernormal light conditions. Pith autolysis decreased in both beansand tomatoes when mechanically perturbed or sprayed with paclobutrazol,both treatments that reduced growth. The stems of buckwheatplants that were flowering showed greater pith autolysis andtherefore were more hollow than plants which were not floweringor which had the incipient flowers pinched off. This indicatedthat carbon from the storage pith may also be used in the formationof reproductive structures which require extra carbon. Alsoin support of the central hypothesis is the prevention of pithautolysis by the addition of extra carbon to the plant, in theform of an increased CO₂ concentration of the surrounding air.Copyright1995, 1999 Academic Press Bean, tomato, buckwheat, pith autolysis, CO₂, GA, thigmomorphogenesis, packobutrazol     

PITH DEVELOPMENT IN NORMAL AND SHORT INTERNODE SEEDLINGS OF PRUNUS PERSICA VAR. LOVELL

Holmsen , Theodore W. (U. Florida, Gainesville.) Pith development in normal and short internode seedlings of Prunus persica var. Lovell. Amer. Jour. Bot. 47 (3): 173—175. Illus. 1960.–Investigation of pith cells of mature (no longer elongating) internodes of normal- and short-internode seedlings of Prunus persica var. ‘Lovell’ indicates that the short internode condition results largely from a suppression of cell division. The pith cells of normal seedlings were found to occur in an irregular fashion. The pith cells of short-internode seedlings were found to retain the linear order characteristic of the rib meristem. The relationship of these findings to the accepted long- and short-shoot conditions are discussed.     

Pith Autolysis in Plants: IV. The Activity of Polygalacturonase and Cellulase during Drought Stress Induced Pith Autolysis

The water potential, amount of pith autolysis and activitiesof apoplastic cellulase and polygalacturonase of tomato stemswere measured during 24 h of drought stress (DS) and for 24h following reirrigation. During DS the water potential droppedfrom —5.5 to —10.4 bars and rose to —8.3 barssoon after reirrigation. Drought stress induced considerablepith autolysis, more of which occurred after reirrigation. Pretreatmentwith mechanical perturbation (MP) of the stems or applicationof exogenous ethephon on the buds hardened the tomato plantsagainst DS-induced pith autolysis. Drought stress caused anincrease in apoplastic polygalacturonase and an even greaterincrease in apoplastic cellulase. Reirrigation caused a largetransient increase in the former and a decrease in the latter.The apoplastic reducing sugar content (as galacturonic acid)of the stem rose in parallel with the activity of the enzymes.Both DS and MP caused an increase in ethylene evolution, althoughthe former was significantly greater than the latter. However,when MP preceded DS, the amount of ethylene produced was significantlyless than DS alone induced. Pretreatment with either MP or exogenousethephon inhibited the increase in apoplastic cellulytic enzymes. It is concluded that DS induces ethylene evolution from thetomato stem, causing an increase in the stem apoplastic cellulyticenzymes, which in turn start the autolysis of the pith cellwalls. Pretreatment with MP or ethephon, each of which inducesethylene evolution, hardens the stem so that it does not producemore ethylene during DS, and thus becomes resistant to DS-inducedpith autolysis. ¹Supported by Bi-national Agricultural Research and Developmentgrant I-127, NASA grant NAGW 96 and NSF grant 8003689to MJJ. ²Permanent address: Horticulture Department, Faculty of Agriculture,The Hebrew University Rehovot, Israel ³Permanent address: Vegetable Crops Department, AgriculturalResearch Organization, the Volcani Center Bet Dagan, Israel     

Invertase Activity, Carbohydrate Metabolism and Cell Expansion in the Stem of Phaseolus vulgaris L.

In the stem of Phaseolus vulgaris L. the specific activity ofacid invertase was highest in the most rapidly elongating internode.Activity of the enzyme was very low in internodes which hadcompleted their elongation, in young internodes before the onsetof rapid elongation, and in the apical bud. From shortly afterits emergence from the apical bud the elongation of internode3 was attributable mainly to cell expansion. Total and specificactivities of acid invertase in this internode rose to a maximumat the time of most rapid elongation and then declined. Transferof plants to complete darkness, or treatment of plants withgibberellic acid (GA₃), increased the rate of internode elongationand final internode length by stimulating cell expansion. Bothtreatments rapidly increased the total and specific activitiesof acid invertase in the responding internodes; peak activitiesof the enzyme occurred at the time of most rapid cell expansion. In light-grown plants, including those treated with GA₃, rapidcell and internode elongation and high specific activities ofacid invertase were associated with high concentrations of hexosesugar and low concentrations of sucrose. As cell growth ratesand invertase activities declined, the concentration of hexosefell and that of sucrose rose. In plants transferred to darkness,stimulated cell elongation was accompanied by a rapid decreasein hexose concentration and the disappearance of sucrose, indicatingrapid utilization of hexose. No sucrose was detected in theapical tissues of light-grown plants. The results are discussed in relation to the role of acid invertasein the provision of carbon substrates for cell growth. Key words: Cell expansion, Acid invertase, Hexose, Sucrose, Phaseolus     

Tracheary Element Differentiation Induced in Isolated Cylinders of Lettuce Pith: a Bipolar Gradient Technique

To study the influence of morphogenetic gradients on vasculardifferentiation patterns, a new technique was developed whichallows different substances to be applied at opposite ends ofa tissue block. It yielded information on the mobility of particularmorphogens and on the dependence of callus formation and trachearyelement differentiation on their presence. Application of indol-3ylacetic acid (1AA) (10 mg l^–1), zeatin (0.1 mg l^–1)and sucrose (3 per cent, w/v) in various combinations to theends of cylindrical explants of lettuce pith (Lactuca sativaL.) showed that (a) callus formation was stimulated by IAA,whereas induction of tracheary elements required both IAA andzeatin; (b) callus was confined to a few millimetres at theends of the explants, and tracheary elements occurred mainlywithin the callus; (c) sucrose or its metabolic products diffusedthe 10 mm length of the explants, while IAA and zeatin wereeffective only close to the application site; and (d) some callusand tracheary elements formed when no sucrose was applied, butboth increased with sucrose application, though inhibition oftracheary elements formation occurred with high sucrose concentrations. differentiation, pith explant, tissue culture, xylogenesis, indol-3yl acetic acid, sucrose, zeatin, lettuce, Lactuca sativa     

Thigmomorphogenesis: Changes in Cell Division and Elongation in the Internodes of Mechanically-perturbed or Ethrel-treated Bean Plants

Examination of first internodes of young Phaseolus vulgarisL. plants which have been subjected to mechanical perturbationshows decreased elongation and increased radial growth. Thedecreased elongation can be attributed to both reduced cellelongation of epidermal and cortical cells and a reduced numberof cells in the vascular and pith tissues. The increased radialenlargement is due to increased cortical cell expansion andincreased secondary xylem production resulting from increasedcambial activity. All of these responses are observable withina few hours of a single mechanical perturbation. Treatment ofplants with ethrel mimics all of these effects of mechanicalperturbation. Phaseolus vulgarisL, Kidney bean, thigmomorphogenesis, mechanical perturbation, ethrel, (2-chloroethyl phosphonic acid), cell division, internode elongation     

Mobility of Impatiens capensis flowers: effect on pollen deposition and hummingbird foraging

Flexible pedicels are characteristic of birdpollinated plants, yet have received little attention in studies of hummingbird-flower interactions. A major implication of flexible pedicels is that flowers may move during pollination. We examined whether such motion affected interactions between ruby-throated hummingbirds (Archilochus colubris) and jewelweed (Impatiens capensis) by increasing pollen deposition and by altering the effectiveness of nectar removal. For I. capensis, flower mobility enhanced pollen deposition: birds had significantly longer contact with anthers and more pollen deposited on their bills and crowns when foraging at mobile flowers than at flowers that had been experimentally immobilized. In contrast, flower mobility imposed a cost on hummingbirds by significantly increasing their handling times and reducing their extraction rates relative to their interactions with immobile flowers. Field observations indicated that the motion observed during hummingbird visits did not occur when bees (Bombus spp., Apis mellifera) visited I. capensis flowers, which suggests that the mobility of I. capensis flowers is an adaptation for hummingbird pollination.     

Cytokinin Habituation in Juvenile and Flowering Tobacco

The possible link between cytokinin and flowering was examine in tobacco. The degree of cytokinin autotrophy and the competence for cytokinin habitution were measured in callus derived from pith tissue of Nicotiana tabacum cvs. H425 an W38.Explants were taken from internodes at all positions up the stem in juvenile and mature plants. To test whether the competence of cells to form flowers was linked with crtokinin habituation, thin cell layer explants from comparable internodes were tested for their ability to form floral buds. Callus derived from the upper parts of plants showed cytokinin autotrophy whether or not the plants were flowering. Flower buds were formed only on thin cell layer explants from the upper part of plants which were already flowering. Cytokinin habituation and competence to flower are therefore not directly linked although cytokinin habituation could be a prerequisite for meristematic activity and for flowering. Pith from internodes in the lower half of mature pants formed callus which was cytokinin-dependent, although these same internodes in juvenile plants were cytokinin-autotrophic. The ability to form cytokinin-autotrophic callus was therefore greatest in the meristematic regions and was lost as the pith cells aged. Competence to habituate after 35 °C treatment was also shown by pith callus from a few internodes in the middle of the plant below those already forming cytokinin-autotropic callus.     

ASSOCIATION OF α-AMYLASE WITH CELLULAR AUTOLYSIS IN PEA STEM TISSUES

Increased activity of α-amylase in bean stems occurred during cellular autolysis in the pith region. In etiolated pea seedlings, α-amylase activity increased sequentially in the first, second, and third internodes. In light-grown seedlings, the increase was initially observed in the first internode, then simultaneously in the second and third internodes. In all internodes, these changes were observed in regions undergoing cellular autolysis in the cortex region. As in bean hypocotyls, α-amylase activity occurred in tissues virtually devoid of starch. Sequential accumulation and then decline in protein and sugar concentrations in each internode indicate a remobilization of materials from nongrowing regions of the stem. These results are consistent with the hypothesis that regulation of α-amylase activity is related to this remobilization.     

Regeneration of Diploid and Polyploid Plants from the Stem Pith Explants of Diploid Marrow Stem Kale (Brassica oleracea L.)

Viable plants of kale (Brassica oleracea L.) have been regeneratedfrom stem pith explants grown on complex agar media. About 80per cent of kale plants cv. Krasa gave explants which differentiatedroots and shoots. Analysis of stomatal length, pollen grainmorphology and estimation of chromosome number in PMC and somaticcells showed that a set of 71 regenerated plants derived fromfive diploid mother plants contained 6 di-, 54 tetra-, and 11octoploid regenerates. Utilization of this method in plant breedingis discussed.     

Internode Length in Pisum. A New Allele at the le Locus

In Pisum sativum L. a third, more severe, allele at the internodelength locus le is identified and named le^d. Plants homozygousfor le^d possess shorter internodes and appear relatively lessresponsive to GA₂₀ than comparable le (dwarf) plants. Gene le^dmay act by reducing the 3ß-hydroxylation of GA₂₀ tothe highly active GA₁ more effectively than does gene le. Theresults indicate that le is a leaky mutant and therefore thatendogenous GA₁ influences internode elongation in dwarf (le)plants. Pisum sativum, peas, internode length, genetics, gibberellin, dwarf elongation     

FACTORS INFLUENCING SEED WEIGHT IN IMPATIENS CAPENSIS (BALSAMINACEAE)

I analyzed within- and between-plant variation in seed weight from one greenhouse and four natural populations of Impatiens capensis Meerb. Most variation in seed size in natural populations occurred within populations and within plants. Weights of seeds from cleistogamous flowers on greenhouse plants increased with height on the plant and proximity to the main stem, a result that may be related to the local supply of photosynthate. Mean seed weight in the natural populations declined during seed set, then increased again. Seeds from chasmogamous flowers were significantly larger in one of the four populations. Maternal parents differed significantly in both mean seed weight and the relative size of the two types of seeds. Combined genetic and general environmental effects accounted for 26% of the total phenotypic variance, which provides an outside estimate of the heritability of this character.     

Abscisic Acid and Apical Dominance in Phaseolus coccineus L. The Role of Tissue Age

Abscisic acid (ABA) applied to the decapitated second internodeof runner bean plants enhanced outgrowth of lateral buds onlywhen internode stumps were no longer elongating. Applied toelongating internodes of slightly younger plants, ABA causesinhibition of bud outgrowth. Together with 10^–4 M indol-3-ylacetic acid (IAA), ABA stimulated internode elongation and interactedadditively in the inhibition of bud outgrowth. A mixture of10^–5 M ABA and 10^–6 M gibberellic acid (GA₃ ) causedsimilar effects on internode growth as IAA + ABA, but was mutuallyantagonistic in effect on growth of the lateral buds. Abscisic acid, apical dominance, gibberellic acid, indol-3yl acetic acid, Phaseolus coccineus, bean     

DEVELOPMENT OF CHAMBERED PITH IN STEMS OF PHYTOLACCA AMERICANA L. (PHYTOLACCACEAE)

An integrated microscopic (light and electron microscopy) and macroscopic investigation of chambered pith development was made of Phytolacca americana L. Terminal internodes have a solid pith cylinder in contrast to the alternating diaphragms and chambers occurring in subjacent pith. Macroscopically, chambers and diaphragms of any one internode are of equal size. Microscopically, diaphragms vary in height within an internode (from 1–6 cells high). Nevertheless, all diaphragms become thicker circumferentially (5–12 cells high) and connect with long files of intact peripheral pith cells. Diaphragm cells have a large centrally positioned vacuole with a thin, parietal layer of cytoplasm; nuclei, mitochondria, endoplasmic reticulum, and unidentified organelles differentiate in the cytoplasm of diaphragm cells. Although schizogenous activity has most often been implicated as the mechanism by which chambered pith develops in vegetative organs of angiosperms, the results of this study show that cavities in pokeweed result from both schizogenous and lysigenous mechanisms. Schizogeny is suggested by the fact that central pith cells of terminal internodes are longer and thinner walled than peripheral pith cells arranged in vertical files, thus indicating elongation of cells as a possible result of internode elongation. The precise developmental pattern and arrangement of chambers and diaphragms also suggest schizogenous processes. Lysigenous or enzymatic activity is indicated by the fact that cavities are bounded by broken cells, and wall fragments and organelles are often found within enlarging cavities. Chamber formation occurs continuously acropetally and centrifugally in the central pith. A comparison of diaphragms is made with Liriodendron tulipifera and Juglans nigra in an attempt to resolve differences in structure and terminology regarding the differentiation of chambered and diaphragmed pith.     

Quantitative Analysis of Intercellularly-Transported Photoassimilates in Chara corallina

Using a thin-layer chromatographic technique, we have identifiedthe photoassimilates that are transported intercellularly frombranchlets to internodes in Chara corallina. An internode-branchletcomplex having a primary apex was used in these experiments.After feeding 1 mol m³ NaH¹⁴CO₃ to a branchlet for 10 min, the¹⁴C-labelled photoassimilates (¹⁴C-photoassimilates) found inthe sol endoplasm of the branchlet were composed of sucrose,amino acids, malate, and sugarphosphates. The composition ofthe ¹⁴C-photoassimilates transported from the source branchletto the sink internode in 10 min was the same as that in thesol endoplasm of the source branchlet. From the proportion ofeach ¹⁴C-photoassimilate in both the source branchlet and thesink internode, it was deduced that the main photoassimilatesinvolved in the intercellular transport were sucrose and aminoacids. We found previously that polar transport of photoassimilatesoccurs from a branchlet to an internode with an apex. Determinationof the amount of sucrose, amino acids, glucose-6-phosphate,and malate in both branchlet and internode with or without anapex revealed that there were gradients in the concentrationsof sucrose, serine, and glutamic acid between the sol endoplasmof the two cells. The levels were higher in the branchlet andlower in the internode and the gradients decreased when theapex was detached. Therefore, it is concluded that sucrose andthese amino acids are the compounds involved in the polar intercellulartransport. Key words: Chara corallina, intercellular transport, photoassimilates, ¹⁴C     

Shaping the shoot: the relative contribution of cell number and cell shape to variations in internode length between parent and hybrid apple trees

Genetic control of plant size and shape is a promising perspective,particularly in fruit trees, in order to select desirable genotypes.A recent study on architectural traits in an apple progeny showedthat internode length was a highly heritable character. However,few studies have been devoted to internode cellular patterningin dicotyledonous stems, and the interplay between the two elementarycell processes that contribute to their length, i.e. cell divisionand elongation, is not fully understood. The present study aimedat unravelling their contributions in the genetic variationof internode length in a selection of F₁ and parent genotypesof apple tree, by exploring the number of cells and cell shapewithin mature internodes belonging to the main axes. The resultshighlighted that both the variables were homogeneous in samplescollected either along a sagital line or along the pith width,and suggest that cell lengthening was homogeneous during internodedevelopment. They allowed the total number of cells to be estimatedon the internode scale and opened up new perspectives for simplifyingtissue sampling procedures for further investigations. Differencesin internode length were observed between the genotypes, inparticular between the parents, and partly resulted from a compensationbetween cell number and cell length. However, genetic variationsin internode length primarily involved the number of cells,while cell length was more secondary. These results argue foran interplay between cellular and organismal control of internodeshape that may involve the rib meristem. Key words: Elongation, growth, histogenesis, Malusxdomestica Borkh, pith Received 2 January 2008; Revised 22 January 2008 Accepted 29 January 2008     

Drift happens: Molecular genetic diversity and differentiation among populations of jewelweed (Impatiens capensis Meerb.) reflect fragmentation of floodplain forests

Landscape features often shape patterns of gene flow and genetic differentiation in plant species. Populations that are small and isolated enough also become subject to genetic drift. We examined patterns of gene flow and differentiation among 12 floodplain populations of the selfing annual jewelweed (Impatiens capensis Meerb.) nested within four river systems and two major watersheds in Wisconsin, USA. Floodplain forests and marshes provide a model system for assessing the effects of habitat fragmentation within agricultural/urban landscapes and for testing whether rivers act to genetically connect dispersed populations. We generated a panel of 12,856 single nucleotide polymorphisms and assessed genetic diversity, differentiation, gene flow, and drift. Clustering methods revealed strong population genetic structure with limited admixture and highly differentiated populations (mean multilocus F_ST = 0.32, F_ST’ = 0.33). No signals of isolation by geographic distance or environment emerged, but alleles may flow along rivers given that genetic differentiation increased with river distance. Differentiation also increased in populations with fewer private alleles (R² = 0.51) and higher local inbreeding (R² = 0.22). Populations varied greatly in levels of local inbreeding (F_IS = 0.2–0.9) and F_IS increased in more isolated populations. These results suggest that genetic drift dominates other forces in structuring these Impatiens populations. In rapidly changing environments, species must migrate or genetically adapt. Habitat fragmentation limits both processes, potentially compromising the ability of species to persist in fragmented landscapes.     

Stimulatory and Inhibitory Effects of Sucrose Concentration on Xylogenesis in Lettuce Pith Explants; Possible Mediation by Ethylene Biosynthesis

Numbers of tracheary elements differentiating in lettuce pithexplants rose with increase in concentration of sucrose in themedium up to an optimal concentration of 0·2%, and fellwith further increase in concentration to about one-tenth maximalat 3% sucrose. Although a few tracheary elements formed withoutexogenous sucrose, a very low concentration of sucrose (0·001%)was sufficient to stimulate additional xylogenesis. Pretreatmentof explants with 3% sucrose caused a persisting inhibition ofxylogenesis, especially in tissue that had been near the siteof sucrose application (sandwich technique). The requirementfor adequate, but not inhibitory, concentrations of sucrosefor xylogenesis may underlie the development of xylem alongsidethe sucrose-rich phloem in normal apical morphogenesis. For callus growth the response to sucrose was different: theoptimal concentration was 3%, with a broad plateau from 1 to4% sucrose. Sucrose concentrations of 2 to 3%, used in manytissue culture media, are thus roughly optimal for callus growth,but ten times the optimum for xylogenesis in lettuce pith explants. It is surprising that 0·001% (0·03 mM) sucrose,applied exogenously, can stimulate xylogenesis: endogenous sugarconcentrations are normally higher. Perhaps the stimulationis mediated by ethylene biosynthesis, which is known to be xylogenic.Rates of ethylene production per explant rose with increasingsucrose concentration from about 0·1 nl h^-1 at 0% sucroseto a slightly (significantly) higher level at 0·004%sucrose and to about 0·5 nl h^-1 at 3% sucrose. D -glucoseresembled sucrose in its effects on xylogenesis and ethyleneproduction, but L-glucose yielded no xylogenesis and littlestimulation of ethylene biosynthesis.Copyright 1994, 1999 AcademicPress Lactuca sativa, Coleus blumei, Nicotiana tabacum, lettuce pith explants, tracheary element differentiation, sucrose, glucose, ethylene     

Transgenic expression of trehalulose synthase results in high concentrations of the sucrose isomer trehalulose in mature stems of field‐grown sugarcane

Sugarcane plants were developed that produce the sucrose isomers trehalulose and isomaltulose through expression of a vacuole‐targeted trehalulose synthase modified from the gene in ‘Pseudomonas mesoacidophila MX‐45’ and controlled by the maize ubiquitin (Ubi‐1) promoter. Trehalulose concentration in juice increased with internode maturity, reaching about 600 mm , with near‐complete conversion of sucrose in the most mature internodes. Plants remained vigorous, and trehalulose production in selected lines was retained over multiple vegetative generations under glasshouse and field conditions.