Changes in phloem export of sucrose in leaves in response to phosphorus, potassium and magnesium deficiency in bean plants

The effect of varied phosphorus (10 and 250 mmol P m^–3potassium (50 and 2010 mmol K m^–3) and magnesium (20 and1000 mmol Mg m^–3 supply on sucrose, reducing sugars, aminoacids, P, K, and Mg in phloem exudate was studied in bean (Phaseolusvulgaris L.) plants over a 12 d growth period in nutrient solution.Phloem exudates were collected from detached primary leavesusing the EDTA-promoted exudation technique. Compared with controlnutrient-sufficient plants, sucrose export in the phloem exudatewas drastically decreased by K deficiency and, particularly,by Mg deficiency, whereas P deficiency either had no effector stimulated sucrose export. In Mg-deficient plants the rateof sucrose export was decreased to 10–20% of the controlplants. There was a close Inverse relationship between phloemexport and leaf concentration of sucrose: higher leaf concentrationsof sucrose were accompanied by lower phloem export of sucrose.In contrast to sucrose, reducing sugars in the exudates werevery low and not affected by P, K and Mg deficiency. The phloemexport of amino acids was strongly depressed by Mg deficiency,but only slightly by P and K deficiency. Resupplying Mg to Mg-deficientplants for 12 h during the dark or light periods rapidly stimulatedsucrose export. After resup ply of Mg for 24 h and 48 h therate of sucrose export was comparable with the rate in the controlplants. The results demonstrate a key role for Mg in phloem loadingand export of photosynthates from source leaves, especiallysucrose. Inhibition of root growth and development of visualsymptoms of chlorosis in Mg-deficient plants are suggested asconsequences of Impaired phloem loading. In agreement with thisin P-deficient plants where phloem loading was not impaired,chlorosis was absent and root growth was maintained at a highlevel. Key words: Bean, carbon partitioning, magnesium nutrition, phloem transport, phosphorus nutrition, potassium nutrition     

Effects of Abscisic Acid on the Growth Pattern of the Shoot Apical Meristem and on Flowering in Chenopodium rubrum L.

Abscisic acid (ABA) at 1 x 10^–4 M or 3 x 10^–4 Mwas applied to the apical buds of Chenopodium rubrum plantsexposed to different photoperiodic treatments and showing differentpatterns of floral differentiation. Stimulation of growth inwidth of the apical meristem of the shoot and/or inhibitionof growth in length was obtained under all photoperiodic treatments.This change of growth pattern was followed by different effectson flowering. In non-induced plants grown under continuous light ABA stimulatedpericlinal divisions in the peripheral zone and the initiationof leaves as well as the growth in width of bud primordia. Inplants induced by two short days reduced growth of the meristemcoincided with ABA application. Longitudinal growth of the meristemwas inhibited in this case and only a temporary stimulationof inflorescence formation took place. In plants induced ata very early stage, ABA exerted a strong inhibitory effect onflowering. A permanent and reproducible stimulatory effect onflowering was obtained in plants induced by three sub-criticalphotoperiodic cycles if ABA was applied to apices released fromapical dominance. In this case formation of lateral organs andinternodes was promoted by ABA and was followed by stimulatedinflorescence formation. Gibberellic acid (GA2) at 1x 10^–4M or 3 x 10^–4 M brought about a similar effect on floweringas ABA, although the primary growth effect was different, i.e.GA₂ stimulated longitudinal growth. The effects of ABA and GA₂ on floral differentiation have beencompared with earlier results obtained from auxin and kinetinapplications. These growth hormones are believed to regulateflowering by changing cellular growth within the shoot apex.Depending on the actual state of the meristem identical growthresponses may result in different patterns of organogenesisand even in opposite effects on flowering. Shoot apex, flowering, photoperiodic induction, abscisic acid, gibberellic acid, Chenopodium rubrum L.     

In Vitro Culture and Plant Regeneration in Vicia faba subsp. Equina (var. Spring Blaze)

Explants of stem, leaves, roots, and cotyledons from etiolatedaxenically grown Vicia faba seedlings were cultured on a rangeof media. Shoot organogenesis was only obtained with nodal stemand cotyledonary node explants when cultured on MS medium with3% sucrose, 2.0 mg 1^–1 BAP and 02 mg 1^–1 NAA. Callusproliferation accompanied shoot organogenesis from nodal stemexplants. Successive subculture of nodal stem callus resultedin proliferation of regenerative callus which contained severalshoot bud initials. The capacity for shoot regeneration fromthis callus was maintained for 9 months. Histological studiesreveal de novo formation of meristematic centres in callus andtheir further development into bud primordia. High frequencyrooting of these adventitious shoots was obtained on half-strengthMS medium with 1.5% sucrose, 0.1 mg 1^–1 NAA and 0.5 mg1^–1 kinetin. Key words: Vicia faba, adventitious shoots, axillary shoots, de novomeristem formation, organogenesis, tissue culture     

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     

Light Quality and Vernalization Interact in Controlling Late Flowering in Arabidopsis Ecotypes and Mutants

The late flowering ecotypes of Arabidopsis thaliana L. (Heyn.)Eifel, Pitztal and Innsbruck responded to 10 d vernalization(cold treatment) by flowering earlier with less with less thanhalf the number of leaves of non-induced plants. The vernalizationresponse was cumulative: increased numbers of days of vernalizationinduced earlier flowering up to an apparent saturation in responseafter 30 to 40 d. The ratio of red:far-red (R:FR) light alsoaffected non-vernalized time-to-flower. When grown under fluorescentplus incandescent lamps (R:FR = 1·0), time-to-flowerwas approximately half that required by plants grown under fluorescentlamps (R:FR = 5·8) at the same photon flux density andphotoperiod. Leaf production rate was unaffected by either vernalizationor light quality changes and time-to-flower and leaf numberwere highly correlated (r² = 0·973). The late flowering mutants of Landsberg erecta were grown underlighting which displayed a gradient of R:FR. Some mutants likeco, flowered at the same time in all R:FR treatment, while otherlike fca took nearly twice as long to flower, with double thenumber of leaves at R:FR ratio of 5·8 compared with theR:FR = 1 treatment. The ranking of the response from least tomost responsive was co, fe, gi, WT, fd, fwa, ft, fha, fpa, fy,fve and fca. Vernalization of these Landsberg mutants always resulted inearlier flowering, although only fca, fve, fy and fpa were significantlymore sensitive to thermoinduction than the wild type parent.There was a high correlation (r² = 0·89 between the responseto thermoinduction and to R:FR ratio. Vernalization of fca for24 d largely eliminated the R:FR time-to-flower response. Vernalizationand photoinduction similarly affect late flowering and can substitutefor each another.Copyright 1993, 1999 Academic Press Light quality, vernalization, flowering, Arabidopsis thaliana, phytochrome, thermoinduction, photoperiod, photoinduction, growth conditions, photon flux density, daylength, spectral quality, far-red light     

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     

Hormonal Control of Morphogenesis in Leaf Explants of Perilla frutescens Britton var. crispa Decaisne f. viridi-crispa Makino

Leaf discs of Perilla frutescens var. crispa f. viridi-crispawere cultured on a defined medium to investigate factors influencingbud and root formation, callus induction, somatic embryogenesis,and floral bud formation. Addition of naphthalene-acetic acid(NAA) to the culture medium caused compact callus whereas 2,4-dichlorophenoxyacetic acid (2,4-D) promoted soft and friable callus formationon the surface of the explants. Benzyladenine, when appliedwith auxin, suppressed callus and root formation. Somatic embryogenesisoccurred, when the explants were first grown on nutrient mediumcontaining 2,4-D and organic elements, and then transferredto the 2,4-D free medium. Treatments with cytokinins, N-phenyl-N'-(4-pyridyl)urea and its derivatives induced bud formation. A low concentrationof NAA and naphthoxy-acetic acid promoted bud development. Occasionalfloral bud formation was observed depending on the originalleaf positions on mother plants from which the leaf discs wereexcised. A gradient of floral bud forming capacity along thestem was noted. Perilla frutescens, tissue culture, embryogenesis, morphogenesis, benzyl adenine, kinetin, naphthalene-acetic acid, naphthoxy-acetic acid, 2,4-dichlorophenoxy acetic acid, indol-3yl-acetic acid, cytokinins, auxins     

Pathway of phloem loading in the C3 tropical orchid hybrid Oncidium Goldiana

The apoplast of mature leaves of the tropical orchid OncidiumGoldiana was perfused with 0.5 mM p-chloromercuribenzenesulphonicacid (PCMBS) via the transpiration stream in order to test themode of phloem loading. The efficacy of introducing PCMBS byperfusion was shown by saffranin O dye movement in the veinsand leaf apoplast in control experiments. Photoassimilate exportas the result of phloem loading was measured by collection of¹⁴CO₂-derived photoassimilates from the basal cut-ends of intactleaves. Phloem loading and translocation of photoassimilates was inhibitedby 89% in leaves perfused with PCMBS for 1 h. The effect ofPCMBS on leaf photosynthesis was minimal. The amount of radiocarbonfixed by PCMBS-treated leaves averaged 89% of control leavesperfused with distilled water. A negative correlation betweenthe total amount of photoassimilate exuded and the calculatedconcentration of PCMBS in the leaf apoplast was also observed.The results indicate that phloem loading in Oncidium Goldianaoccurs via the apoplastic pathway. Key words: Phloem loading, apoplast, PCMBS, tropical orchid     

Studies in Sieve-tube Exudation through Aphid Mouth-parts: The Effects of Light and Girdling

Exudation from the mouth-parts of the willow aphid Tuberolachnussalignus (Gmelin) inserted in the phloem of Salix sp. was studied.Leafy rooted cuttings 80–100 cm. in length were grownin artificial light. Exuding mouth-parts were located on thestem below the crown of leaves and the rates of exudation andconcentration of sucrose in the exudate measured whilst theleaves were alternately illuminated (600–800 f.c.) anddarkened. In darkness the rate of sap and sucrose exudationincreased and the concentration fell, relative to the valuesin the light. Similar effects were produced by girdling thestem just beneath the crown of leaves. These were shown to besecondary effects due to a lessening of transpirational tensionsduring darkness or after girdling. They were eliminated if changesin water tension were avoided. Direct effects of light and girdling on exudation were demonstratedby allowing the leaves to assimilate ¹⁴CO₂ and measuring thespecific activity of the exudate. These changes in radioactivityseen against the constancy in total sugar exudation demonstratea switch in source from leaf to stem. An attempt is made toexplain the pattern of changes in specific activity of the exudateduring light and dark periods in terms of shifts in the locationof contributing sources. The rate of translocation between two aphid colonies situateda measured distance apart was estimated by noting the timeswhen the honeydew from each reached a certain level of radioactivity.A mean figure of 28 cm./hr. was obtained.     

Photoassimilate translocation in the petiole of Cyclamen and Primula is independent of lateral retrieval

Phloem translocation of photoassimilates between source andsink is considered to be linked with active retrieval of sugarsleaked to the vascular apoplast. This hypothesis was evaluatedby studying photo-assimilate movement in petioles of intactplants of Cyclamen persicum and Primula obconica in the presenceof inhibitors affecting sucrose retrieval (PCMBS, CCCP). Inhibitorsolutions were applied by rinsing locally isolated petiole bundlesor by injection into the petioe parenchyma. PCMBS and CCCP reduced[¹⁴C]sucrose retrieval from the petiole apoplast by the vascularcells and altered the distribution pattern of ¹⁴C-photoassimilateswithin the petiole tissues. However, these treatments did notaffect translocation through the petiole phloem. Evidence isprovided that the reagents were present in the vascular apoplastsurrounding the translocating phloem. It was concluded thatassimilate movement in the petiole of Cyclamen and Primula wasindependent of apoplastic retrieval. Key words: Cyclamen, Primula, phloem, transport, path, sucrose, retrieval     

Flower-Inducing Activity of Phloem Exudates from Pharbitis cotyledons Exposed to Various Photoperiods

The phloem exudate prepared from the cotyledons of Pharbitisseedlings that had been exposed to a single dark period (oflonger than 10 h) induced flowering in cultured apices excisedfrom non-induced seedlings. The flower-inducing activity ofthe exudate increased as the seedlings were exposed to longerperiods of darkness. The highest activity was associated withthe exudate taken from cotyledons exposed to a single 16-h darkperiod. The activity of the exudate taken from cotyledons exposedto an inductive dark period was clearly reduced by interruptionof the dark period. The addition of exudate taken from threecotyledons to 10 ml of medium resulted in the highest flower-inducingactivity. About 50% of cultured apex explants formed floralbuds, even when the concentration of the exudate was reducedto 0.1 cotyledon equivalents per 10 ml of medium. The flower-inducingactivity of the exudate appeared to be heat-stable. (Received December 13, 1991; )     

Characteristics of Sugar, Amino Acid and Phosphate Release from the Seed Coat of Developing Seeds of Vicia faba and Pisum sativum

After removal of the embryo from developing seeds of Vicia fabaL. and Pisum sativum L., the ‘empty’ ovules werefilled with a standard solution (pH 5.5). Seed coat exudatesof both species were collected during relatively long experiments(up to about 12 h) and the concentration of sugar (mainly sucrose),amino acids and phosphate in the exudate measured. A discussionis presented on the amino acid/sugar ratio and the phosphate/sugarratio in the seed coat exudate. A pretreatment (15 min) withp-chloromercuribenzenesulphonic acid (PCMBS) reduced the releaseof sugar, amino acids and phosphate from broad bean seed coats.After excision of ‘empty’ ovules of Vicia faba andPisum sativum from the maternal plant, 2–4 h after thistreatment a strong difference became visible between sucroserelease from excised seed coats and sucrose release from attachedseed coats. Similarly, when the rate of phloem transport ofsucrose into an ‘empty’ ovule of Vicia faba or Pisumsativum was reduced by a sub-optimal mannitol concentrationin the solution, a reduced rate of sugar release from the seedcoat could be observed. Excision and treatment with a sub-optimalmannitol concentration reduced the release of amino acids toa lesser extent than for sucrose. These treatments did not reducethe rate of phosphate release from the seed coat. Key words: Seed development, Seed coat exudate, Phloem transport     

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     

Flower-Inducing Activity of Phloem Exudate in Cultured Apices from Pharbitis Seedlings

Phloem exudate from cotyledons of photoperiodically inducedPharbitis plants induced flowering in apices excised from non-inducedseedlings and cultured in vitro. The exudate also stimulatedflowering in apices excised from photo-induced seedlings andcultured under long-day conditions. The application of benzoicacid had similar effects. Both the exudate from non-inducedplants and gallic acid suppressed flowering in apices from photo-inducedseedlings. It appears that the phloem exudate contains flower-inducingor flower-suppressing substance(s), depending on the plant materialsfrom which it was collected. (Received August 15, 1989; Accepted May 14, 1990)     

The Relationship between Sugar and Amino Acid Export to the Phloem in Young Wheat Plants

The relationship between amino acid and sugar export to thephloem was studied in young wheat plants (Triticum aestivumL. ‘Pro-INTA, Isla Verde’) using the EDTA-phloemcollection technique. Plants grown with a 16 h photoperiod showeda rapid decrease in the concentration of sugars and amino acidsin the phloem exudate from the beginning of the dark period.When plants grown with a 16 h photoperiod were kept in the darkfor longer than 8 h the free amino acid content in leaves andexudate (on a dry weight basis) increased continually throughoutthe 72 h of darkness. During the first 24 h of darkness thesugars in the phloem exudate decreased to 30% of the initialvalue, and returned to the control level when plants were returnedto light. When plants grown under low light intensity for 10d were transferred to high light intensity, they showed an increasein leaf sugar content (dry weight basis) after 3 d but therewere no differences in leaf free amino acid content (dry weightbasis) compared to low-light plants. The sugar concentrationin the phloem exudate was increased by higher light intensities,but there was no difference in the amino acid concentrationof the phloem exudate, and thus the amino acid:sugar ratio inthe phloem decreased in the high-light plants. The present resultssuggest that amino acids can be exported to the phloem independentlyof the export of sugars. Copyright 1999 Annals of Botany Company Sugar exudation, amino acid transport, nitrogen, phloem, transport, wheat, Triticum aestivum L.     

Obligatory short‐day plant,Perilla frutescens var. crispa can flower in response to low‐intensity light stress under long‐day conditions

An obligatory short‐day plant, Perilla frutescens var. crispa was induced to flower under long‐day conditions when grown under low‐intensity light (30 µmol m^?2 s^?1). Plant size was smaller under lower light intensity, indicating that the low‐intensity light acted as a stress factor. The phenomenon is categorized as stress‐induced flowering. Low‐intensity light treatment for 4 weeks induced 100% flowering. The plants responded to low‐intensity light immediately after the cotyledons expanded, and the flowering response decreased with increasing plant age. The induced plants produced fertile seeds, and the progeny developed normally. The plants that flowered under low‐intensity light had greener leaves. This greening was because of the decrease in anthocyanin content, and there was a negative correlation between the anthocyanin content and percent flowering. Treatment with L‐2‐aminooxy‐3‐phenylpropionic acid, an inhibitor of phenylalanine ammonia‐lyase (PAL), did not induce flowering under non‐inductive light conditions and inhibited flowering under inductive low‐intensity light conditions. The metabolic pathway regulated by PAL may be involved in the flowering induced by low‐intensity light.     

The Cellular Pathway of Radial Transfer of Photosynthates in Stems of Phaseolus vulgaris L.: Effects of Cellular Plasmolysis and p-Chloromercuribenzene Sulphonic Acid

Cellular plasmolysis with l M solutions of mannitol appearedto sever plasmodesmatal interconnections between all cells ofthe stems of Phaseolus vulgaris plants except the sieve element-companioncell (se—cc) complexes. Phloem loading and uptake of [¹⁴C]sucroseby the storage cells of the stems was unimpaired by cellularplasmolysis followed by rehydration of the stem tissues. Accumulationof phloem-transported ¹⁴C-photosynthates of the treated stemswas inhibited in summer-grown plants and unaffected in winter-grownplants indicating that phloem unloading follows a symplasticand a free-space route respectively depending on growth season.At a concentration that did not interfere with cellular metabolism,p-chloromercuribenzene sulphonic acid (PCMBS) applied to thestems blocked [¹⁴C]sucrose loading into the phloem and storagecells of the stem, but had no effect on the pool size of free-spacesugars. This latter response is consistent with a facilitatedmechanism of sugar unloading to the stem free-space. Accumulationof phloem-transported ¹⁴C-photosynthates was stimulated by PCMBSand this effect was most pronounced in winter-grown plants.Cellular plasmolysis followed by rehydration abolished the PCMBSaction on ¹⁴C-photosynthate accumulation. This effect is consistentwith a PCMBS induction of phloem unloading through the stemsymplast. It is proposed that phloem unloading in bean stemsmay follow either a free-space or symplastic route and thatthe latter route is entrained under sink-limited conditions. Phaseolus vulgaris, french bean, stem, phioem unloading, free-space, symplast     

Concentrations and Transport of Solutes in Xylem and Phloem along the Leaf Axis of NaCl-treated Hordeum vulgare

Hordeum vulgare cv. California Mariout was established in sandculture at two different NaCl concentrations (0.5 mol m^–3‘control’ and 100 mol m^–3) in the presenceof 6.5 mol m^–3 K ⁺. Between 16 and 31 d after germination,before stem elongation started, xylem sap was collected by useof a pressure chamber. Collections were made at three differentsites on leaves 1 and 3: at the base of the sheath, at the baseof the blade, i.e. above the ligule, and at the tip of the blade.Phloem sap was collected from leaf 3 at similar sites throughaphid stylets. The concentrations of K ⁺, Na⁺, Mg2⁺ and Ca²⁺were measured. Ion concentrations in xylem sap collected at the base of leaves1 and 3 were identical, indicating there was no preferentialdelivery of specific ions to older leaves. All ion concentrationsin the xylem decreased from the base of the leaf towards thetip; these gradients were remarkably steep for young leaves,indicating high rates of ion uptake from the xylem. The gradientsdecreased with leaf age, but did not disappear completely. In phloem sap, concentrations of K⁺ and total osmolality declinedslightly from the tip to the base of leaves of both controland salt-treated plants. By contrast, Na⁺ concentrations inphloem sap collected from salt-treated plants decreased drasticallyfrom 21 mol m^–3 at the tip to 7.5 mol m^–3 at thebase. Data of K/Na ratios in xylem and phloem sap were used to constructan empirical model of Na⁺ and K⁺ flows within xylem and phloemduring the life cycle of a leaf, indicating recirculation ofNa⁺ within the leaf. Key words: Hordeum vulgare, xylem transport, phloem transport, NaCl-stress     

Influence of Carbohydrates on Photosynthesis in Single, Rooted Soybean Leaves Used as a Source-Sink Model

The single rooted leaf of soybean (Glycine max L. Merr.) wasused to study source-sink relationships in photosynthesis. Whenthe leaves were kept under a regime of 10 h light (410–480µmol photons m^–2, 400–700 nm)–14 h dark,they did not expand, the increase in leaf dry weight almoststopped, and photosynthetic activity remained at a high andconstant level for 8 d while the dry weight of the roots increasedat a constant rate throughout the period. Thus, under this conditionthe leaf and the root system served as the only source and sinkorgans, respectively. When leaves grown for 7 d under this conditionwere placed under continuous light to alter the source/sinkbalance in photosynthate, the root dry weight increased at aconstant rate equal to that found under the 10 h light–14h dark condition. The leaf dry weight markedly increased andby day 5 of continuous light had increased 1.6-fold, mainlyas a consequence of accumulation of starch and sucrose, whichwere not translocated for root growth. The continuous lightcaused an abrupt decrease in the photosynthetic activity (40%of initial value by day 5). However, the activity recoveredalmost completely after a 32-h transfer to darkness. Significantnegative correlations existed between photosynthetic activityand the sucrose and starch contents in the rooted leaves placedunder continuous light. When the plants were treated with variouslight conditions, there was no significant difference (p<0.01)among the regression line slopes for photosynthetic activityon the sucrose content, but there was some deviation among thosefor the photosynthetic activity on the starch content. Thisresult suggests that sucrose accumulated in the leaf has a moredirect influence on photosynthetic activity when the source/sinkbalance was altered. (Received September 9, 1985; Accepted February 21, 1986)     

Bl?tenbildung bei Lemna paucicostata 6746 durch kombinierte Anwendung von Abscisins?ure und GCG

To a certain extent the flowering of Lemna paucicostata 6746is evoked in continuous light by application of abscisic acid(ABA) and CCC. Moreover, the action of the combined substancesappears in two separate concentration ranges. In the range ofABA 2?10^–9 M/CCC 10^–7–10^–6 M floweringis initiated without inhibition of vegetative growth and proceedsonly in the presence of high intensity light and sucrose. Acombination of ABA 2?10^–5 M/CCC 10^–3M simultaneouslycauses a strong inhibition of frond multiplication. Here theeffect can be observed also under low intensity light conditionsand without sucrose in the medium. A range with flower inhibitingactivity lies between the two flower promoting concentrationranges. (Received November 16, 1972; )