In Vitro Regeneration from Seedling Organs of Brassica oleracea var. italica Plenck cv. Green Comet I. Effect of Plant Growth Regulators

The calabrese cultivar Brassica oleracea var. italica cv. GreenComet was used in a study of the effects of exogenous hormoneson the growth and differentiation of seedling organs in vitro.Four types of explants were tested: hypocotyl segments, rootsegments, primary leaf discs and cotyledon discs. These explantswere incubated on media containing factorial combinations ofBAP x IBA, BAP x NAA, KN x IBA and KN x NAA (all at 0, 0.1,10 and 10.0mg l^–1). Hypocotyls were the most regenerativeexplants; shoot production was favoured by cytokinin: auxinratios greater than one and was decreased by IBA at 10 mg l^–1when callus was produced. Shoot formation from root explantsoccurred either in the absence of hormones or with low concentrations;no shoot was produced when any hormone was present at 10 mgl^–1. In contrast, shoot production from primary leaf diseswas favoured by high concentrations of both auxin and cytokininwith the combination of BAP and IBA the most effective. Shootproduction from cotyledon discs was sporadic with no consistentresponse on any auxin/cytokinin combination. After further experimentson the optimization of hormone concentration, the followingcombinations were chosen as allowing reliable regeneration:0.1 mg l^–1 BAP+0.1mg l^–1 IBA for hypocotyl segments,0.075 mg l^–1 KN +0.025 mg l^–1 IBA for root segments,and 5.0 mg l^–1 BAP+5.0 mg l^–1 IBA for leaf discs. Brassica oleracea var. italica, calabrese, tissue culture, seedling, auxin, cytokinin     

Establishment of Isolated Root Cultures of Brassica Species and Regeneration from Cultured-root Segments of Brassica oleracea var. italica

Isolated root cultures which could be maintained over severalmonths by serial subculture were established from Brassica oleraceavar. italica cv. Green Comet F₁. A modified White's medium wasfound to be the best of several salt compositions tested. Theeffects on isolated root growth of the following were also examined;nutritional components, culture vessel type and closure, pHof the medium and auxin type and concentration. Using a mediumdevised for Green Comet, root cultures were established fromsix other B. oleracea, B. napus and B. campestris cultivars. It was possible to regenerate shoots from segments of culturedroots by incubation on agar-solidified media containing cytokininand auxin. The effects on regeneration of various auxins andcytokinins were investigated; the combination of Picloram withKN gave the highest frequency of shoot formation. It was demonstratedthat isolated roots retained their regenerative ability overa period of 5 months in culture. Brassica oleracea var. italica, Brassica napus, Brassica campestris, isolated root culture, shoot regeneration, organ culture     

The Composition of Phloem Exudate and Xylem Sap from Broccoli (Brassica oleracea var. italica) Supplied with NH4+, NO""3 or NH4NO3

Shelp, B. J. 1987. The composition of phloem exudate and xylemsap from broccoli (Brassica oleracea var. italica) suppliedwith NH⁺₄, NO₃ or NH₄NO₃.—J. exp. Bot. 38: 1619–1636. The detailed composition of xylem sap and exudate from stemincisions of attached inflorescences of broccoli (Brassica oleraceavar. italica) was compared in plants supplied with NH⁺₄, NO₃or NH₄NO₃. A phloem origin for the exudate was suggested fromthe high levels of sugars (71–133 mg cm^-3), amino acids(8·1-26·7 mg cm³) and K. (2·3–3·8mg cm³), the low levels of NO₃ and Ca, the high C: N (w/w) ratios(8·3–33), and the alkaline pH (7·2–7·3).In contrast, the xylem sap was mildly acidic (pH 5·6–6·0),and possessed lower levels of all organic and inorganic solutesbut NO₃ and Ca, and lower ratios of K: Ca, Mg: Ca and C: N (0·6–4·4). Glutamine was the predominant o-phthalaldehyde-reactive aminocompound in both transport fluids with the next most abundantamino acids dependent on sap type and N-form. Together witharginine, -aminobutyric acid, which was found only in the xylemstream, was enhanced by NH⁺₄compared to NO₃ -nutrition suggestingthat glutamate metabolism was stimulated in the roots. Underlimiting N the amino acid concentrations in the transport fluidswere greater with NH⁺₄ than with NO₃. NO₃ reduction occurredin both the root and shoot with the latter site predominatingover the entire N range (0-300 mol m³). Even though the compositionof nitrogenous solutes in the xylem was dependent on cultivarand N source, the composition of the phloem streams supplyingthe developing inflorescence was relatively unaffected. The data on the element composition of organs and phloem sapare interpreted to suggest that, in spite of the restrictedmobility of some elements such as B and Mn, a significant proportionof their total supply to developing sinks is carried in thephloem stream. Key words: Transport fluid composition, plant nutrition, phloem mobility.     

In vitro Shoot Regeneration from Seedling Root Segments of Brassica oleracea and Brassica napus Cultivars

Root segments taken from aseptically-grown seedlings of Brassicaoleracea var. italica cv. Green Comet were used in an investigationof factors affecting in vitro regeneration. Shoot regenerationwas found to increase with seedling age and to be highest inroot segments adjacent to the hypocotyl and lowest in segmentsadjacent to the root tip. In a comparison of a range of mediaand agar concentrations shoot formation was favoured by complexmedia containing reduced nitrogen and was higher on gelled mediathan in liquid medium. The effects of various cytokinins andauxins were investigated; KN was the best cytokinin and IAAand Picloram the best auxins for shoot induction. Root segmentsfrom six other Brassica cultivars were grown on the medium devisedfor Green Comet; shoots were regenerated from two B. oleraceacultivars and two B. napus cultivars, but not from the B. campestriscultivars tested. Brassica oleracea var. italica, Brassica napus, Brassica campestris, seedling root culture, shoot regeneration     

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     

Plant Characteristics and Nutrient Composition and Mobility of Broccoli (Brassica oleracea var. italica) Supplied with NH4+, NO3"" or NH4NO3

Shelp, B. J. 1987. Plant characteristics and nutrient compositionand mobility of broccoli (Brassica oleracea var. italica) suppliedwith NH⁺₄, NO₃ or NH₄NO₃.—J. exp. Bot. 38: 1603–1618. The effects of varying NH⁺₄, NO₃ or NH₄NO₃ concentration onthe final plant characteristics, element composition, and accumulationof NO₃-N, NH⁺₄-N and organic-N were evaluated in broccoli (Brassicaoleracea var. italicacv. Futura and Premium Crop) plants culturedin vermiculite under greenhouse conditions supplemented withlight. NH⁺₄-grown plants were stunted and exhibited signs ofmarginal necrosis on the old leaves, accompanied by an accumulationof NH4. The tissue levels of N, P, Mn, Cu, Zn and B were generallyincreased by NH⁺₄ versus NO₃ nutrition whereas the reverse wastrue for Ca; Mg and K were only slightly affected, if at all.These results are attributed to: changes in element availabilityresulting from reduced rhizosphere pH due to NH⁺₄uptake ratherthan NO ₃uptake; competition of Ca uptake by NH⁺₄; and dilutionof N by increased vegetative growth with NO₃-nutrition. Theelement concentrations of N, P or K were similar in all tissueswhereas Ca, B and Mn were markedly less in the florets and youngleaves compared to mature leaves; this supports literature indicatingthat the former elements are phloem-mobile whereas the latterare not. Assuming that the nutrient supply for mature leavesis delivered principally via the xylem stream, the data suggestthat nutrients for developing leaves and florets are suppliedpredominantly in the phloem. If so, under our experimental conditions.Zn and Cu were also readily mobile in the phloem whereas Mgmovement was restricted. NH₄⁺ versus NO₄⁺ J nutrition alteredthe distribution of these elements. The two broccoli cultivarstested under the greenhouse environment differed in NH⁺₄ toleranceand in the distribution of K and Cu suggesting there was a geneticbasis for cultivar variation in mineral acquisition and redistribution. Key words: Plant nutrition, phloem mobility, elemental composition.     

Evidence of phloem boron transport in response to interrupted boron supply in white lupin (Lupinus albus L. cv. Kiev Mutant) at the reproductive stage

The present study investigates whether previously acquired boron(B) in mature leaves in white lupin can be retranslocated intothe rapidly growing young reproductive organs, in response toshort-term (3 d) interrupted B supply. In a preliminary experimentwith white lupin in soil culture, B concentrations in phloemexudates remained at 300–500 µM, which were substantiallyhigher than those in the xylem sap (10–30 µM). Thehigh ratios of B concentrations in phloem exudates to thosein the xylem sap were close to values published for potassiumin lupin plants. To differentiate ‘old’ B in theshoot from ‘new’ B in the root, an experiment wascarried out in which the plants were first supplied with 20µM ¹¹B (99.34% by weight) in nutrient solution for 48d after germination (DAG) until early flowering and then transferredinto either 0.2 µM or 20 µM ¹⁰B (99.47% by weight)for 3 d. Regardless of the ¹⁰B treatments, significant levelsof ¹¹B were found in the phloem exudates (200–300 µMin 20 µM ¹⁰B and 430 µM in 0.2 µM ¹⁰B treatment)and xylem sap over the three days even without ¹¹B supply tothe root. In response to the 0.2 µM ¹⁰B treatment, thetranslocation of previously acquired ¹¹B in the young (the uppermostthree leaves), matured, and old leaves was enhanced, coincidingwith the rise of ¹¹B in the xylem sap (to >15 µM) andphloem exudates (430 µM). The evidence supports the hypothesisthat previously acquired B in the shoot was recirculated tothe root via the phloem, transferred into the xylem in the root,and transported in the xylem to the shoot. In addition, somepreviously acquired ¹¹B in the leaves may have been translocatedinto the rapidly growing inflorescence. Phloem B transport resultedin the continued net increment of ¹¹B in the flowers over 3d without ¹¹B supply. However, it is still uncertain whetherthe amount of B available for recirculation is adequate to supportreproductive growth until seed maturation. Key words: ¹⁰B, ¹¹B, B recirculation, Lupinus albus L., phloem exudate, xylem sap Received 9 October 2007; Revised 28 November 2007 Accepted 30 November 2007     

Long Distance Transport of Abscisic Acid in NaCI-Treated Intact Plants of Lupinus albus

Plants of Lupinus albus were grown for 51 d under control (1.1mol m^–3 NaCl) and saline (40 mol m^–3 NaCl) conditions.Plants were harvested and changes of carbon, nitrogen and abscisicacid (ABA) contents of individual organs were determined 41d and 51 d after germination. In the period between the twoharvests xylem and phloem saps were collected and respirationand photosynthesis of individual organs were measured. Usingflows of carbon, C/ABA ratios and increments of ABA flows ofABA in phloem and xylem and rates of biosynthesis and degradationof ABA were calculated. Both under control and saline conditionsnet biosynthesis occurred in the root, the basal strata of leavesand in the inflorescence. Metabolic degradation of ABA tookplace in the stem internodes and apical leaf strata. Salt stress increased xylem transport of ABA up to 10-fold andphloem transport to the root up to 5-fold relative to that ofthe controls. A considerable amount of ABA in the xylem saporiginated from biosynthesis in the roots, i.e. 55% in salt-treatedand smaller than 28% in control plants. The remaining part ofABA in the xylem sap originated from the shoot: it was translocatedin the phloem from fully differentiated leaves towards the rootand from there it was recirculated back to the aerial partsof the plant. The data suggest that ABA may serve as a hormonalstress signal from the root system. Key words: Lupinus albus, salt stress, abscisic acid, long distance transport     

The Composition of Phloem Exudate and Xylem Sap from Tree Tobacco (Nicotiana glauca Grah.)

The composition of xylem sap and exudate from stem incisionsof Nicotiana glauca Grah. was compared in detail. Exudationfrom stem incisions occurred over a 5 min period in certainplants, enabling collection of 5–30 µl of sap. Therate of exudation showed an exponential decline. Exudate hada high dry matter content (170–196 mg ml^–1) andhigh sugar (sucrose) levels. Xylem sap had a low pH (5.8) andexudate a pH of 7.9. Glutamine dominated the amino compoundsin xylem sap and exudate, and K⁺ was the major cation. Totalamino compounds in stem exudate reached 10.8 mg ml^–1 whereasxylem sap contained much lower levels (0.28 mg ml^–1).All mineral elements and amino compounds with the exceptionof calcium were more concentrated in stem exudate than in xylemsap. Sucrose was labelled heavily in stem exudate following pulsingof an adjacent leaf with ¹⁴CO₂. A concentration gradient ofsugar (2.1 bar m^–1) was recorded for stems. Levels ofsucrose, amino compounds and K⁺ ions in stem exudate showeda diurnal periodicity. Each commodity reached maximum concentrationat or near noon and minimum concentration about dawn. The evidencesuggests that exudate from stem incisions of N. glauca is arepresentative sample of solutes translocated in the phloem. Nicotiana glauca Grah., phloem sap, xylem sap, sucrose, amino compounds, mineral ions     

Broccoli Stunt,a New Disease in Broccoli Plants Associated with Three Distinct Phytoplasma Groups in Brazil

Since 2007, a new disease in broccoli (Brassica oleracea var. italica Plenck) has been observed in the São Paulo state, Brazil. The characteristic symptoms of the disease are plant stunting, inflorescence malformation, reddening of the leaves and phloem necrosis. Nested polymerase chain reaction with P1/Tint and F2n/R2 primer pairs revealed the presence of phytoplasmas in diseased broccoli plants. Restriction fragment length polymorphism and phylogenetic analysis of the 16S rDNA gene showed that phytoplasmas belonging to 16SrI, III and XIII groups were associated with the plants. To the best of our knowledge, this is the first report of phytoplasmas in this Brassica species in Brazil, as well the first time phytoplasmas of 16SrIII and XIII groups have been associated with broccoli plants.     

Flavanoids in Pollen and Stigma of Brassica oleracea and Their Effects on Pollen Germination In Vitro

Brassica oleracea pollen was applied to a basic medium of 1.5per cent agar and 15 per cent sucrose to which flavanoids wereadded at three concentrations. Two types of agar were used;with agar 1, quercetin at a concentration of 0.5 x 10^–3per cent gave an increase in percentage germinating grains.With agar 2, an increase in germination occurred with kaempferoland naringin at concentrations of 0.5 x 10^–3 and 0.5 x10^–1 per cent respectively. Increase in pollen tube lengthoccurred with agar 2 and quercetin at a concentration of 0.5x 10^–3 per cent. The stigma tissue of B. oleracea contains at least three andthe pollen at least one glycoside of quercetin. The sugars inthe glycosides were not identified. Pollen germination and pollentube extension were not stimulated exclusively by the flavanoidspresent in the stigma. The flavanoid composition of the stigmadid not vary amongst five different S-allele genotypes, indicatingthat flavanoids are probably not directly involved in the incompatibilityreaction of B. oleracea.     

Cation and Chloride Partitioning through Xylem and Phloem within the Whole Plant of Ricinus communis L. under Conditions of Salt Stress

Uptake and partitioning through the xylem and phloem of K⁺,Na⁺, Mg²⁺ , Ca²⁺ and Cl^– were studied over a 9 d intervalduring late vegetative growth of castor bean (Ricinus communisL.) plants exposed to a mean salinity stress of 128 mol m^–3NaCl. Empirically based models of flow and utilization of eachion within the whole plant were constructed using informationon ion increments of plant parts, molar ratios of ions to carbonin phloem sap sampled from petioles and stem internodes andpreviously derived information on carbon flow between plantsparts in xylem and phloem in identical plant material. Salientfeatures of the plant budget for K⁺ were prominent depositionin leaves, high mobility of K⁺ in phloem, high rates of cyclingthrough leaves and downward translocation of K⁺ providing theroot with a large excess of K⁺ . Corresponding data for Na⁺showed marked retention in the root, lateral uptake from xylemby hypocotyl, stem internodes and petioles leading to low intakeby young leaf laminae and substantial cycling from older leavesback to the root. The partitioning of the anionic componentof NaCl salinity, Cl^–, contrasted to that of Na⁺ in thatit was not substantially retained in the root, but depositedmore or less uniformly in stem, petiole and leaf lamina tissues.The flow pattern for Mg²⁺ showed relatively even depositionthrough the plant but some preferential uptake by young leaves,generally lesser export than import by leaf laminae, and a returnflow of Mg²⁺ from shoot to root considerably less than the recordedincrement of the root. Ca²⁺ partitioning contrasted with thatof the other ions in showing extremely poor phloem mobility,leading to progressive preferential accumulation in leaf laminaeand negligible cycling of the element through leaves or root.Features of the response of Ricinus to salinity shown in thepresent study were discussed with data from similar modellingstudies on white lupin (Lupinus albus L.) and barley (Hordeumvulgare L.) Key words: Ricinus communis L, potassium, sodium, chloride, calcium, magnesium, phloem, xylem, transport, partitioning, salinity     

A Model of the Influence of Air Temperature and Solar Radiation on the Time to Maturity of Calabrese Brassica oleracea var italica

The concept of thermal time is applied to the prediction ofduration from sowing to maturity of calabrese (Brassica oleraceavar italica cv. Corvet), using a multiple linear regressionmodel. Given daily records of maximum and minimum air temperatureand total solar radiation, maturity could be predicted to within±7 d for nine out of ten crops over the four years considered.Within any one year the precision improved to ±5 d. Calabreseappeared to stop developing at a base temperature of 0 °C.Thermal time accounted for 74·3 per cent of the variationin reciprocal total duration and solar radiation a further 17·7per cent. Model, weather, calabrese, broccoli, thermal time, solar radiation     

Retranslocation of boron in broccoli and lupin during early reproductive growth

The objective of the present study was to determine if boron (B) retranslocation depends on plant-B status and external-B supply. The stable ¹⁰B isotope was supplied to the root system of broccoli ( Brassica oleracea var. italica Plenck cv. Commander) and lupin ( Lupinus albus L. cv. Ultra) plants to provide a quantitative picture of B distribution during early reproductive development. Regardless of the B regime (i.e. continuous supply with luxury, sufficient or deficient B; transfer at inflorescence emergence from either a luxury- or sufficient-B supply to a deficient one) and whether ¹⁰B was acquired before or during inflorescence development, a significant proportion of the B recovered in broccoli florets and lupin fruit was ¹⁰B enriched. B acquired during inflorescence development was an important source of B for reproductive structures, but the relative importance of B acquired before and after inflorescence emergence appeared to be species dependent. The occurrence of B retranslocation was not dependent upon the induction of B deficiency. The concentrations of B in phloem exudates (0.38 to 0.03 mM) were 4- to 23-fold those in xylem sap, and more similar to the concentrations in the reproductive structures (0.86 to 0.07 mM) than those in source leaves (2.4 to 0.19 mM). The decreasing acropetal gradient of tissue-B concentrations with luxury-B supply declined dramatically or was reversed in plants grown with sufficient or deficient B. The data are consistent with B being a phloem-mobile element, and suggest that newly acquired B is particularly important during the early reproductive growth of plants.     

The distribution of BoCAL-a alleles in Brassica oleracea is consistent with a genetic model for curd development and domestication of the cauliflower

The characteristic curd of cauliflower (Brassica oleracea var. botrytis L.) consists of proliferating, arrested inflorescence and floral meristems. However, the origins and events leading to the domestication of this important crop trait remain unclear. A similar phenotype observed in the ap1-1/cal-1 mutant of Arabidopsis thaliana led to speculation that the orthologous genes from B. oleracea may be responsible for this characteristic trait. We have carried out a detailed molecular and genetic study, which allows us to present a genetic model based on segregation of recessive alleles at specific, mapped loci of the candidate genes BoCAL and BoAP1. This accounts for differences in stage of arrest between cauliflower and Calabrese broccoli (B. oleracea var. italica Plenck), and predicts the intermediate stages of arrest similar to those observed in Sicilian Purple types. Association of alleles of BoCAL-a with curding phenotypes of B. oleracea is also demonstrated through a survey of crop accessions. Strong correlations exist between specific alleles of BoCAL-a and discrete inflorescence morphologies. These complementary lines of evidence suggest that the cauliflower curd arose in southern Italy from a heading Calabrese broccoli via an intermediate Sicilian crop type. PCR-based assays for the two key loci contributing to curd development are suitable for adoption in marker-assisted selection.     

Modelling Nitrogen Content and Distribution in Cauliflower (Brassica oleracea L.botrytis )

A model of nitrogen uptake and distribution is presented whichdescribes these processes in relation to the amount of availablesoil nitrate and the rate of plant growth. Nitrogen uptake iseither sink or source limited. Sink limitation is based on maximumN-concentrations of plant compartments. The N-uptake model iscombined with a photosynthesis model based on the productivity-nitrogenrelationship at the single-leaf level. The model is parameterizedusing cauliflower as an example crop. Applied to an independentdata set, the combined model was able to predict leaf, stemand inflorescence nitrogen concentrations with correlation coefficientsbetween predicted and simulated values of 0.89, 0.66 and 0.86,respectively. The influence of nitrogen supply and light intensityon leaf nitrate-N could also be predicted with good accuracy(r² = 0.87). Dry matter production based on the productivity-Nrelationship and the partitioning into leaf, stem and inflorescencewas also reproduced satisfactorily (r² = 0.91, 0.93 and 0.92,respectively). Copyright 2000 Annals of Botany Company Brassica oleracea L. botrytis, cauliflower, nitrogen, nitrate, nitrogen supply, nitrogen uptake, nitrogen distribution, model     

Boron Mobility in Two Coniferous Species

In contrast to earlier beliefs, it is now known that boron (B)can be retranslocated complexed with sugar alcohols in someplant species. Conifers had been thought not to translocatesugar alcohols in the phloem. However, 1 d after applying¹⁰Benriched boric acid to shoots of Scots pine and Norway spruceseedlings, we found increases in both the amount and proportionof¹⁰B in the root systems in both species. We conclude thatB is translocated in the phloem from shoots to roots in spruceand pine, and therefore it is possible that these species retranslocateB. Copyright 2000 Annals of Botany Company Scots pine, Pinus sylvestris, Norway spruce, Picea abies, conifers, boron retranslocation, roots, stable isotopes, sugar alcohols, boron complexes, mineral nutrition, forest trees     

Phloem Mobility of Boron is Species Dependent: Evidence for Phloem Mobility in Sorbitol-rich Species

Boron is generally considered to be phloem immobile or to haveonly limited phloem mobility in higher plants. Evidence suggests,however, that B may be mobile in some species within thePyrus,Malus andPrunusgenera. These genera utilize sorbitol as a primarytranslocated photosynthate and it has been clearly demonstratedthat B forms stable complexes with sorbitolin vitro.In the researchpresented here we demonstrate, further, that B is freely phloemmobile inPyrus, MalusandPrunusspecies and suggest that thisis mediated by the formation and transport of B-sorbitol complexes. The pattern of B distribution within shoot organs and the translocationof foliar-applied, isotopically-enriched¹⁰B was studied in sixtree species. Results demonstrate that in species in which sorbitolis a major sugar (sorbitol-rich), B is freely mobile while inspecies that produce little or no sorbitol (sorbitol-poor) Bis largely immobile. The sorbitol-rich species used here werealmond [Prunus amygdalusB. syn.P. dulcis(Mill.)], apple (MalusdomesticaB.) and nectarine (Prunus persicaL. B. var.nectarinaM.),sorbitol-poor species included fig (Ficus caricaL.), pistachio(Pistacia veraL.) and walnut (Juglans regiaL.). In sorbitol-richspecies foliar applied¹⁰B was transported from the treated leavesto adjacent fruit and specifically to the fruit tissues (hull,shell or kernel) that developed during the experimental period.Whereas, foliar-applied¹⁰B was rapidly translocated out of leaves,only a small percentage of the¹¹B present in the leaf at thetime of foliar application was retranslocated. In sorbitol-richspecies, B concentrations differed only slightly between oldand young leaves while fruit tissue had significantly greaterB concentrations than leaves. In contrast, sorbitol-poor specieshad significantly higher B concentrations in older leaves thanyoung leaves while fruit tissue had the lowest B concentration.This occurred irrespective the source of plant B (soil, solutionor foliar-applied). In a subsequent experiment the growth ofapple trees in solutions free of applied B was maintained solelyby foliar applications of B to mature leaves. These resultsindicate that B is mobile in species that produce significantamounts of sorbitol. We propose that the mobility of B in thesespecies is mediated by the formation of B-sorbitol complexes. Almond; Prunus amygdalus ; apple; Malus domestica; nectarine; Prunus persica; fig; Ficus carica; pistachio; Pistacia vera; walnut; Juglans regia; boron; phloem mobility; deficiency; toxicity; inductively coupled plasma-mass; spectrometer     

The Role of the Stem in the Partitioning of Na+ and K+ in Salt-Treated Barley

Hordeum vulgare cv. California Mariout was grown for 50 d insand culture at 100 mol m^–3 NaCl. Xylem sap was collectedthrough incisions at the base of individual leaves along thestem axis by applying pressure to the root system. K⁺ concentrationsin the xylem sap reaching individual leaves increased towardsthe apex, while concentrations of Na⁺, NO₃^–, and Cl^–declined. Phloem exudate was obtained by collecting into Li₂EDTAfrom the base of excised leaves. K/Na ratios of phloem exudatesincreased from older to younger leaves. K/Na ratios in xylem sap and phloem exudate were combined withchanges in ion content between two harvests (38 and 45 d aftergermination) and the direction of phloem export from individualleaves, to construct an empirical model of K⁺ and Na⁺ net flowswithin the xylem and phloem of the whole plant. This model indicatesthat in old leaves, phloem export of K⁺ greatly exceeded xylemimport. In contrast, Na⁺ export was small compared to importand Na⁺ once imported was retained within the leaf. The direction of export strongly depended on leaf age. Old,basal leaves preferentially supplied the root, and most of theK⁺ retranslocated to the roots was transferred to the xylemand subsequently became available to the shoot. Upper leavesexported to the apex. Young organs were supplied by xylem andphloem, with the xylem preferentially delivering Na⁺ , and thephloem most of the K⁺ . For the young ear, which was still coveredby the sheath of the flag leaf, our calculation predicts phloemimport of ions to such an extent that the surplus must havebeen removed by an outward flow in the xylem. Within the culm,indications for specific transfers of K⁺ and Na⁺ between xylemand phloem and release or absorption of these ions by the tissuewere obtained. The sum of these processes in stem internodes and leaves ledto a non-uniform distribution of Na⁺ and K⁺ within the shoot,Na⁺ being retained in old leaves and basal stem internodes,and K⁺ being available for growth and expansion of young tissues. Key words: Hordeum vulgare L., K⁺, Na⁺, stem, salt stress