EFFECTS OF TISSUE VOLUME AND LOCATION ON THE MECHANICAL CONSEQUENCES OF DEHYDRATION OF PETIOLES

Data are presented on the mechanical consequences of dehydration for the petioles of two monocots and two dicots differing in leaf morphology (pinnate leaves ofChamaedorea erumpens and simple leaves of Spathiphyllum ‘clevelandii‘; pinnate leaves of Acer negundo and simple leaves of A. saccharum). The flexural stiffness EI of petioles decreased over a broad range of tissue water potential (– 10 < ψ_w <– 50 bars). Within the same range of ψ, the second moment of area I and the elastic modulus E were observed to decrease and increase, respectively. However, the mechanical alterations of Chamaedorea and A. negundo petioles were significantly less than those observed for Spathiphyllum and A. saccharum petioles. The increase in E of Spathiphyllum and A. saccharum petioles attending dehydration was linearly correlated with an increase in the relative volume fraction of tissues with lignified, thick cell walls (“support tissues”). The decrease in I of Spathiphyllum and A. saccharum petioles was linearly correlated with a decrease in the relative volume fraction of tissues with nonlignified, thin cell walls (“ground tissues”). Similar trends were observed for the petioles of C. erumpens and A. negundo but were found not to be statistically significant. Anatomical differences in the relative volume fraction and spatial locations of support tissues in the petioles of these four taxa appear to account for the differences observed in the mechanical consequences of petiole dehydration.     

THE PHLOEM OF ETAPTERIS LECLERCQII AND BOTRYOPTERIS TRIDENTATA

The phloem of Etapteris leclercqii and Botryopteris tridentata petioles is described from Lower Pennsylvanian coal balls. Petioles of B. tridentata are characterized in transverse section by an omega-shaped xylem trace, a phloem zone which extends from 2-10 cells in width, and 2-parted cortex. Etapteris leclercqii petioles exhibit a 4–9 cell-wide phloem zone surrounding the central clepsydroid xylem mass, and a 3-parted cortex. In both taxa a 1–2 cell layer parenchyma sheath separates the xylem from the extra-xylary tissues. The phloem of both species consists of sieve elements that average about 20 μm in diam by 200 μm in length in Botryopteris, and 100 μm in length in Etapteris, with horizontal-slightly oblique end walls. In transmitted light, the radial walls of the sieve elements form an irregular reticulate pattern enclosing elliptical lighter areas. With the scanning electron microscope, these areas appear as horizontal-slightly oblique furrows on the cell wall, with many small indentations lining the furrows. These indentations, because of their regular occurrence and size (from a few fractions of a micron up to 1.0 μm in diam), are interpreted as sieve pores, and the elliptical areas that enclose them as sieve areas. The phloem of E. leclercqii and B. tridentata is compared with that described for other fossil genera and with that of extant ferns.     

Light quality regulation of endogenous levels of auxin,abscisic acid and ethylene production in petioles and leaves of wild type and ACC deaminase transgenic <Emphasis Type="Italic">Brassica napus</Emphasis> seedlings

Brassica napus L. seedlings responded to low red to far-red (R/FR) ratio by elongating petioles and decreasing leaf expansion. These typical shade avoidance traits were correlated with significantly decreased endogenous indole-3-acetic acid (IAA) levels and significantly increased endogenous abscisic acid (ABA) levels and ethylene production. The transgenic (T) B. napus line bearing the bacterial ACC deaminase gene, did not respond to low R/FR ratio with altered petiole and leaf growth and less ethylene (especially by petioles) was produced. As with WT seedlings, T seedlings had significantly lower IAA levels in both petioles and leaves under low R/FR ratio. However, ABA levels of low R/FR ratio-grown T seedlings either increased (petioles) or were unaltered (leaves). Our results further suggest that low R/FR ratio regulates endogenous IAA levels independently of ethylene, but there may be an interaction between ABA and ethylene in leaf development.     

Are leaves ‘freewheelin'? Testing for a Wheeler‐type effect in leaf xylem hydraulic decline

A recent study found that cutting shoots under water while xylem was under tension (which has been the standard protocol for the past few decades) could produce artefactual embolisms inside the xylem, overestimating hydraulic vulnerability relative to shoots cut under water after relaxing xylem tension (Wheeler et al. 2013). That study also raised the possibility that such a ‘Wheeler effect’ might occur in studies of leaf hydraulic vulnerability. We tested for such an effect for four species by applying a modified vacuum pump method to leaves with minor veins severed, to construct leaf xylem hydraulic vulnerability curves. We tested for an impact on leaf xylem hydraulic conductance (K_x) of cutting the petiole and minor veins under water for dehydrated leaves with xylem under tension compared with dehydrated leaves after previously relaxing xylem tension. Our results showed no significant ‘cutting artefact’ for leaf xylem. The lack of an effect for leaves could not be explained by narrower or shorter xylem conduits, and may be due to lesser mechanical stress imposed when cutting leaf petioles, and/or to rapid refilling of emboli in petioles. These findings provide the first validation of previous measurements of leaf hydraulic vulnerability against this potential artefact.     

Transport of organic solutes in Phloem and xylem of a nodulated legume

Collections of xylem exudate of root stumps or detached nodules, and of phloem bleeding sap from stems, petioles, and fruits were made from variously aged plants of Lupinus albus L. relying on nodules for their N supply. Sucrose was the major organic solute of phloem, asparagine, glutamine, serine, aspartic acid, valine, lysine, isoleucine, and leucine, the principal N solutes of both xylem and phloem. Xylem sap exhibited higher relative proportions of asparagine, glutamine and aspartic acid than phloem sap, but lower proportions of other amino acids. Phloem sap of petioles was less concentrated in asparagine and glutamine but richer in sucrose than was phloem sap of stem and fruit, suggesting that sucrose was unloaded from phloem and amides added to phloem as translocate passed through stems to sinks of the plant. Evidence was obtained of loading of histidine, lysine, threonine, serine, leucine and valine onto phloem of stems but the amounts involved were small compared with amides. Analyses of petiole phloem sap from different age groups of leaves indicated ontogenetic changes and effects of position on a shoot on relative rates of export of sucrose and N solutes. Diurnal fluctuations were demonstrated in relative rates of loading of sucrose and N solutes onto phloem of leaves. Daily variations in the ability of stem tissue to load N onto phloem streams were of lesser amplitude than, or out of phase with fluctuations in translocation of N from leaves. Data were related to recent information on C and N transport in the species.     

THE ANATOMIC RESPONSES OF DAUCUS CAROTA TO THE ASTER YELLOWS VIRUS

Struckmeyer, B. Esther. (U. Wisconsin, Madison.) The anatomic responses of Daucus carota to the aster yellows virus. Amer. Jour. Bot. 50(9): 959–963. Ilus. 1963.—The leaves, petioles, and roots of carrots (Daucus carota) displaying aster yellows virus in the field and those infected with the aster yellows virus inoculated by the 6-spotted leafhopper were examined anatomically. Compared to the uninoculated, the young infected leaves displayed fewer layers of palisade cells and larger spongy parenchyma cells with a more compact arrangement. Mature leaves of infected plants sometimes were undulated and had few chloroplasts, many of which appeared fragmented. Hypertrophy and hyperplasia in the phloem tissue were associated with some necrosis and obliteration of cells. Long, needle-shaped crystalline inclusion bodies were present in the phloem in the leaves and roots. Most of the vascular bundles of the petiole were abnormal. Malformations included proliferating phloem cells, which in some instances almost encircled the bundle, hyperplasia of the phloem, hypertrophy of the parenchyma, and considerable necrosis and obliteration of these cells. Other responses included the division into 3 or 4 rows of the large outer phloem parenchyma by parallel walls so that a cambium-like layer was simulated. The tissue enclosed by this layer divided and underwent considerable necrosis and gummosis. Lacunae were found between the phloem bundle cap and the older phloem. Some of the cells in the phloem tissue differentiated into bundles with xylem. Numerous, short, lateral roots were conspicuous on the main root. The most noticeable response of the root tissue to this malady was hyperplasia and hypertrophy of the phloem followed by cellular disorganization, necrosis, and obliteration of cells. Some sieve tubes, companion cells, and parenchyma contained a gumlike deposit.     

Transmission of the Monocarpic Senescence Signal via the Xylem in Soybean

During monocarpic senescence in soybean (Glycine max [L.] Merrill cv. Anoka) there is a remobilization of nitrogen from the leaves to the seeds, and it has been hypothesized that this loss of nitrogen from the leaves induces foliar yellowing. The phloem in a small segment of the petiole between the pods and the target leaf can be inactivated with a jet of steam. When a plant is depodded except for a single pod cluster in the center of the plant, the pod cluster induces yellowing of the nearest leaf even if the petiole contains a zone of dead phloem, whereas most of the rest of the plant remains green. The nitrogen content of these leaves with a dead phloem zone in their petioles does not decrease greatly, even though the leaves turn yellow. A similar treatment of a single leaf on a fully depodded plant (leaves stay green) does not cause that leaf to turn yellow. Since nutrients would have to be withdrawn from the leaves via the phloem, the pods do not induce yellowing by pulling nutrients out of the leaf and must be able to exert their influence via the xylem.     

Correlative Bud Inhibition and Abscisic Acid in Acer pseudoplatanus and Syringa vulgaris

Growing shoots of Acer pseudoplatanus and Syringa vulgairs were decapitated and defoliated (“treated”) in June 1972–1975. During the 2–3 weeks after treatment the contents of abscisic acid (ABA) in the out-growing lateral buds at the upper-most node as well as in the petiole stumps and nodes were determined by means of gas-liquid chromatography. The concentration of ABA in lateral buds of intact shoots, calculated on a fresh weight basis, varied greatly from year but was consistently several times higher than in petioles and nodes. Defoliation and decapitation caused out-growth of the lateral buds. This was accompanied by a sharp decrease in the ABA concentration, which finally reached the level of petiole tissue. The concentration of ABA in controls (“untreated”) decreased also, but to a smaller extent, and remained higher than in petioles. In petioles and nodes of treated as well as of untreated shoots, the ABA concentration did not change. The absolute amount of ABA in the buds of treated shoots after 2–3 weeks varied greatly, but was apparently not different from the amount in buds of untreated controls or in buds at the beginning of the experiment. Therefore, the decrease of the ABA concentration was mainly due to fresh weight increase. The results are discussed in relation to a possible role of ABA in correlative bud inhibition.     

Paths and Mechanisms of Moisture Movements in Detached Leaves of White Clover(Trifolium repens L.): I. Losses of Petiole Moisture direct from Petioles and via Laminae

The experiments described were concerned with losses of moisturefrom laminae and petioles of leaves of white clover (Trifoliumrepens L.) detached from parent plants, and with the resistancesin the two pathways of loss of petiole moisture-via laminaeand direct from petiole surfaces. Methods involving determination of moisture losses from separatedlaminae and petioles were unsatisfactory and transpiration chamberswere therefore used to permit determinations with intact leaves. Up to 24 per cent of the total petiole moisture was lost viathe laminae, the amount frequently exceeding that initiallyresiding in the xylem of the petioles. Stomatal, cuticular, and external resistances were calculatedat several stages of wilting. Rates of loss of petiole moistureby both pathways were controlled by stomatal and external resistancesin the early stages and by cuticular and internal resistancesin the later stages. Under certain conditions, transpirationof petiole moisture via the lamina ceased earlier than mighthave been expected; estimates were made of the resistances involved.     

FOLIAR MORPHOLOGY AND ANATOMY OF THE GIGANTOPTERID PLANT DELNORTEA ABBOTTIAE,FROM THE LOWER PERMIAN OF WEST TEXAS

Delnortea is a monotypic genus (type-species: D. abbottiae) of Lower Permian gymnosperms based on leaves from uppermost Leonardian deltaic sediments exposed in the Del Norte Mountains, West Texas. The leaves are simple, symmetrical, mostly oblong or elliptical, and vary in length from 1.2 to about 35 cm. The petioles are short and stout, with a basally enlarged abscission zone. The margins are crenate, with a narrow, indurated border. Venation is in 4 orders: the secondaries and tertiaries are robust, unbranched, and pinnately arranged in a precise “herringbone” pattern, with the secondaries ending in the marginal sinuses; the quaternaries divide sparingly and fuse with others to form a dense reticulum of small meshes. Permineralized petiole and midrib material reflects a bifacial cambium, shown by a semicircular vascular arc, irregularly divided into several collateral bundles with secondary xylem and phloem. Delnortea is referable to the Gigantopteridaceae, a probably artificial family of gymnosperms incertae sedis with important venation features in common, but without known diagnostic reproductive organs. With Delnortea, the North American gigantopterids now include 5 genera, but Gigantopteris itself is lacking. Delnortea holds a relatively advanced evolutionary position among the American gigantopterids; its leaf morphology and gymnospermous anatomy entail intriguing points of comparison with Gnetum. The limited geographic and stratigraphic ranges and morphological distinctiveness of the American gigantopterids and associated taxa attest to rapid evolution and dispersal from a small area of origin in the southwestern United States during Leonardian time.     

THE ELASTIC MODULI AND MECHANICS OF POPULUS TREMULOIDES (SALICACEAE) PETIOLES IN BENDING AND TORSION

Changes attending leaf development in the mechanical behavior and elastic moduli of the petioles of Populus tremuloides Michx. were examined in terms of total leaf weight (Wt), lamina and petiole weight (Wl and Wp), petiolar length (L), and lamina surface area (A). A primary concern was the extent to which two elastic moduli (Young's modulus E and the shear modulus G) of petioles changed over time and were correlated with one another. E and G were measured by means of multiple resonance frequency spectra, and together with the dimensions of cross sections through petioles, these two elastic moduli were used to estimate the stiffness of petioles in simple bending and torsion. Petiolar bending was predicted by means of a model incorporating expressions for both the bending stiffness (El) and torsional rigidity (GJ), where I is the second moment of area and J is the torsional constant. The predictions from these models were compared to observed petiolar bendings due to Wl. Additionally, the frequency of the oscillatory motion of leaves (placed in a wind tunnel with a 1 m sec^-1 ambient wind speed, directed normal to the blade of the leaf) was determined. Results indicate that L, A, Wl, Wp, and Wt were positively correlated with the age of leaves (crudely estimated as a function of leaf plastochron index, LPI); these morphometric parameters were also correlated with the magnitudes of E and G. Also, G was positively and linearly correlated with E, and was, on the average, an order of magnitude less than E. EI and GJ were positively correlated with LPI. The relationships among E, G, EI, C and Wl, Wp, Wt are discussed in terms of leaf allometries.     

Cytokinins in the Phloem Sap of White Lupin (Lupinus albus L.)

Cytokinin-like activity in samples of xylem and phloem sap collected from field-grown plants of white lupin (Lupinus albus L.) over a period of 9 to 24 weeks after sowing was measured using the soybean hypocotyl callus bioassay following paper chromatographic separation. The phloem sap was collected from shallow incisions made at the base of the stem, the base of the inflorescence (e.g. stem top), the petioles, and the base and tip of the fruit. Xylem sap was collected as root exudate from the stump of plants severed a few centimeters above ground level. Concentration of cytokinin-like substances was highest in phloem sap collected from the base of the inflorescence and showed an increase over the entire sampling period (from week 10 [61 nanogram zeatin equivalents] to week 24 [407 nanogram zeatin equivalents]). Concentrations in the xylem sap and in the other phloem saps were generally lower. Relatively high concentrations of cytokinin-like substances in petiole phloem sap (70 to 130 nanogram zeatin equivalents per milliliter) coincided in time with high concentrations in sap from the base of the inflorescence (see above). Concentrations in sap (phloem or xylem) from the base of the stem were very much lower. This finding is consistent with movement of cytokinins from leaves into the developing inflorescence and fruit, rather than direct input to the fruit from xylem sap. However, an earlier movement of cytokinins from roots into leaves via the xylem cannot be ruled out. Sap collected at an 18-week harvest was additionally separated by sequential C₁₈ reversed-phase high performance liquid chromatography → NH₂ normal phase high performance liquid chromatography, bioassayed, and then analyzed by electron impact gas chromatography-mass spectrometry. Identification of zeatin riboside and dihydrozeatin as two of the major cytokinins in combined sap samples was accomplished by gas chromatography-mass spectrometry-selected ion monitoring.     

INFLUENCE OF PHLOEM BLOCKAGE ON CAMBIAL GROWTH OF SUGAR MAPLE

Circular patches of bark were surgically isolated on the sides of sugar maple (Acer saccharum Marsh.) trees at breast height at various times during the dormant and growing seasons. Subsequently, samples of wood and attached bark were taken from isolated and control sites to determine the effects of isolation of the bark on cambial activity and xylem and phloem development. In control sites cambial activity and xylem and phloem development occurred normally. Isolation of bark during the dormant season (in November, February, or March) prevented initiation of cambial activity and xylem and phloem development in isolated areas of half of the trees. Varying degrees of cambial activity (periclinal divisions) occurred in the remaining isolated areas, but normal cambial activity and xylem and phloem development were prevented. Isolation of bark after initiation of cambial activity and phloem differentiation, but prior to initiation of xylem differentiation, resulted in the formation of very narrow xylem and phloem increments with atypically short vessel members and sieve-tube members, respectively. The xylem increments consisted primarily of parenchyma cells. Isolation of bark after initiation of xylem differentiation resulted in curtailment of secondary wall formation in the last-formed part of many increments. The last-formed vessel members of all these xylem increments were atypically short. Similarly, the last formed sieve-tube members of corresponding phloem increments were atypically short. The atypically short cells in the xylem and phloem of isolated areas reflected the effect of isolation on the cambial region, viz., the subdivision of all fusiform cells into strands of cells. Ultimately, the strands of short fusiform cells lapsed into maturity, leaving only strands of parenchymatous elements between xylem and phloem.     

Sectorial Patterns in Leaves on Fruit Tree Shoots Produced by Radioactive Assimilates and Solutions

In vigorously growing shoots of apple and plum ¹⁴C-assimilateswere translocated from a ‘fed’ leaf to particularsectors of other leaves in a distribution pattern associatedwith the phyllotaxis; the same sectorial and distribution patternswere produced by ³²P phosphate solution taken into the shootthrough a cut petiole. The frequency with which a given sectorialpattern occurred at a particular position on the phyllotacticspiral was ascertained. Such patterns were not observed abovethe third rolled leaf in the apple shoot apex. Killing the phloem in the petiole prevented egress of labelledassimilate but not of ³²P solution. Barkringing above the sourceleaf reduced, but did not completely prevent, assimilate movementup the stem, suggesting some translocation in the xylem. Distribution of label from ⁴⁵CaCl₂, ⁸⁶RbCl and [³H]asparagine,incorporated through cut petioles, did not follow the same patternas label from ³²P solutions. Malus pumila Mill., apple, Prunus domestica L., Prunus insititia. L., leaf plum, patterns, transport of radioisotopes, vascular phyllotaxis     

Genomic fingerprinting of Frankia strains by PCR-based techniques. Assessment of a primer based on the sequence of 16S rRNA gene of Escherichia coli

Submergence stimulates elongation of the leaves of Rumex palustris and under laboratory conditions the maximum final leaf length (of plants up to 7 weeks old) was obtained within a 9 day period. This elongation response, mainly determined by petiole elongation, depends on the availability of storage compounds and developmental stage of a leaf. A starch accumulating tap root and mature leaves and petioles were found to supply elongating leaves with substrates for polysaccharide synthesis in expanding cell walls. Changes in the composition of cell wall polysaccharides of elongated petioles suggest a substantial cell wall metabolism during cell extension. Reduced starch levels or removal of mature leaves caused a substantial limitation of submerged leaf growth. From the 5th leaf onward enough reserves were available to perform submerged leaf growth from early developmental stages. Very young petioles had a limited capacity to elongate. In slightly older petioles submergence resulted in the longest final leaf lengths and these values gradually decreased when submergence was started at more mature developmental stages. Submerged leaf growth is mainly a matter of petiole elongation in which cell elongation has a concurrent synthesis of xylem elements in the vascular tissue. Mature petioles still elongated (when submerged) by cell and tissue elongation only: the annular tracheary elements stretched enabling up to 70% petiole elongation.     

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     

Gravity can induce epinastic bending of isolated leaves

Abstract Isolated leaves of Plectranthus fruticosus were grown in cubic plastic cuvettes, and were supplied via their cut petioles with nutrient solution and indole-3-acetic acid (10^?6m ). Holes bored in the cuvette walls allowed the petioles to be oriented at approximately 60°, 90° or 120° to the vertical. Growth of the leaves initially oriented at angles of 60° and 90°, which simulated the situation in the intact plant, did not result in epinastic bending of the petiole. Inversion of the leaves (adaxial surface of the petiole downwards) and orientation of the adaxial/abaxial surfaces of the horizontal petiole parallel to the gravity vector, however, yielded strong epinastic bending of the petioles. In the latter case, this bending was not in the direction of the gravity vector (evidence for point (iii), below). Furthermore, epinastic bending occurred, when the isolated leaves were rotated on a clinostat (petioles parallel to the rotation axis or inclined to the rotation axis at an angle of 30°; 3 r.p.m.). Since a possible influence of the shoot was excluded, it is concluded that (i) perception and response are restricted to the leaf, (ii) gravity alone is sufficient to induce epinasty, (iii) a gravitropic component of the response can probably be excluded. The clinostat induced epinasty may not have been caused by nullifying the effect of gravity but due to continuous gravistimulation of the leaf.     

EFFECT OF PETIOLE PHLOEM DISRUPTION ON STARCH AND MINERAL DISTRIBUTION IN SENESCING SOYBEAN LEAVES

Normally, starch (sugars) and minerals are redistributed from the leaves to the pods during monocarpic senescence in maturing soybean plants. Petiole phloem destruction (steam girdling), which blocked this redistribution by interrupting export through the petiole, altered the foliar senescence pattern producing a distinctive interveinal yellowing with green areas along the veins on pod-bearing plants. This suggests that blockage of the petiole phloem may cause nutrients to accumulate in the green zones along the leaf veins instead of being redistributed to the pods. In the leaves of untreated plants, starch showed the same distribution pattern as chlorophyll; however, starch was preserved in yellow areas as well as the green zones of the steam-girdled leaves. Mineral analyses of the veinal and interveinal zones of treated leaves and controls showed that the veinal green zones and interveinal yellowing in treated plants were not respectively enriched and depleted in minerals corresponding to a redistribution of minerals within the leaves. Depodding also blocked leaf yellowing, net mineral redistribution and starch breakdown. Thus, the pods are able to induce chlorophyll breakdown without net mineral redistribution or starch loss in leaves with petiole phloem destruction. This shows that chlorophyll breakdown is not obligatorily coupled with mineral redistribution or starch breakdown.     

Uptake and Utilization of Xylem-borne Amino Compounds by Shoot Organs of a Legume

Amino compounds representative of the major N solutes of xylem sap were pulse-fed (10 to 20 minutes) singly in ¹⁴C-labeled form to cut transpiring shoots of white lupin (Lupinus albus L.). ¹⁴C distribution was studied by autoradiography and radioassays of phloem sap, leaflet tissues, and shoot parts harvested at intervals after labeling. Primary distribution of N by xylem was simulated using a 20-minute labeling pulse followed by a 30-minute chase in unlabeled xylem sap. Shoots fed ¹⁴C-labeled asparagine, glutamine, valine, serine, or arginine showed intense labeling of leaflet veins and marked retention (35 to 78%) of ¹⁴C by stem + petioles. Shoots fed ¹⁴C-labeled aspartic acid or glutamic acid showed heaviest ¹⁴C accumulation in interveinal regions of leaflets and low uptake (11 to 20%) of ¹⁴C by stem + petioles. Departing leaf traces were major sites of uptake of all amino compounds, and the implications of this were evaluated. Fruits acquired only 1 to 5% of the fed label directly from xylem, but more than doubled their intake during the period 30 to 160 minutes after feeding through receipt of ¹⁴C transferred from xylem to phloem in stem and leaves. ¹⁴C-Labeled asparagine and valine transferred directly from xylem to phloem, but the ¹⁴C of ¹⁴C-labeled aspartic acid and arginine appeared in phloem mainly as metabolic products of the fed compound. The labeling of the soluble pool of leaflets reflected these differences. The significance of heterogeneity in distribution and metabolism of xylem amino compounds in the shoot was discussed.     

李砧木Marianna离体叶片再生体系优化研究

以李砧木‘Marianna’试管苗新梢顶端第1片叶为外植体,研究激素组合、基本培养基种类及外植体类型等对不定芽再生的影响。结果表明:1/2 MS基本培养基和WPM培养基再生率显著高于MS和SH培养基;叶片附带叶柄的外植体再生率和再生不定芽数显著高于叶柄和切除叶柄的叶片外植体;最佳再生培养基为1/2MS+2.0mg/L TDZ+0.1 mg/L IBA+0.25%琼脂+3.0%蔗糖,最高再生率和再生不定芽数分别为81.7%和7.46±1.38个;最佳生根培养基为1/2MS+0.5~1.0 mg/L IBA,能获得96.7%生根率、较高的生根数和根长。