Basipetal Direction Research Articles

Radial and axial gradients of lead concentration in bark and xylem of hardwoods.

The bark and wood tissues ofRobinia pseudoacacia L.,Tilia cordata Mill., andAcer platanoides L., grown in different localities of Munich with varying traffic intensity, were quantitatively analyzed for lead content in both radial and axial directions. In comparison to the non-heartwood-forming genera (Tilia, Acer) the heartwood-formingRobinia showed distinct differences in radial distribution of lead: the sapwood ofRobinia had higher lead contamination than the heartwood. The innermost heartwood zone of this species had a higher lead content than did the younger heartwood tissue. InTilia andAcer, the wood zones of different ages did not exhibit significant differences in their lead concentrations. The bark surface showed a high lead concentration which could be washed off to a large extent with water. The lead concentration in the trunk ofRobinia was found to increase in basipetal direction. The lead content in bark and sapwood of this species was proportional to the traffic intensity in the neighborhood. The results are discussed in relation to the possible translocation of lead within the trees.

Cytochemical and Subcellular Organization of the Shoot Apical Meristem of Dry and Germinating Jack Pine Embryos

Water added to dry seeds of jack pine evoked changes at the shoot apex which reflected the mobilization and consumption of food reserves for the synthesis of new protoplasm and for the formation of the prospective shoot. In shoot apices the distal zone contained large cells having nuclei with low affinity for stains. Flank and subapical zones had smaller cells with densely stained nuclei. These features did not alter during imbibition nor after the first wave of mitosis at 96 h when radicles emerged from seeds. Cells in the distal zone divided rarely. Mitosis, most abundant in subapices, decreased acropetally to the distal zone.In dry seeds, protein bodies and amyloplasts increased in size and frequency per cell from the distal zone in the basipetal direction towards the flanks and subapical zone. During imbibition most proteinaceous reserves, rich in arginine N, disappeared from all cells of the shoot apex. Lipid bodies in distal cells were small, numerous, and disappeared slowly as germination proceeded. Proplastids, mitochondria, and unidentified pleomorphic bodies were distributed in close proximity to the nucleus particularly in apical cells.Products of imbibed tritiated water (nonexchangeable tritium), and tritiated D-glucose, thymine, thymidine, and uracil were localized at the shoot apex and revealed assimilatory patterns consistent with cytochemical zonation. The covalent incorporation of tritium from water, while spread through most cells, was greatest in nuclei of flank and subapical cells. The radioactivity from glucose was found mainly in cell walls. Labelling by uracil, thymine, and thymidine by salvage mechanisms was especially abundant in nuclei of the flanks. These events coincided with dense RNA and DNA staining during germination. Collectively, observations indicated that at the flanks, water and seed reserves were concentrated at specific binding sites for the synthesis and dispersion of macromolecules before the visual production of leaf primordia.

Ontogeny of xylem transfer cells inHieracium floribundum

The ontogeny of transfer cells associated with tracheary elements in the rhizome of the rosette plant,Hieracium floribundum is described. The events preceding the initiation of wall ingrowths in parenchymatous cells associated with tracheary elements determining them as transfer cells vary with the type of tracheary element and the position within the rhizome. Parenchyma cells adjacent to protoxylem and metaxylem elements close to the rhizome apex usually divide before wall ingrowth formation whereas this tendency is decreased in the basipetal direction in the rhizome. When parenchyma cells do not divide before wall ingrowth formation, the wall ingrowths are poorly developed and the cells remain vacuolated. If cell division does occur, the daughter cell next to the tracheary element always becomes a transfer cell and the other develops as a xylem parenchyma cell. Within a vascular bundle there is a gradient in intensity of wall ingrowth formation, with the transfer cells associated with protoxylem elements having the most elaborate wall ingrowths, and the transfer cells associated with the late metaxylem elements having few or no wall ingrowths. Parenchyma cells associated with secondary xylem elements lack wall ingrowths. At the end of primary growth and the establishment of secondary growth within a bundle, successive cytological changes occur in the xylem transfer cells, leading ultimately to the loss of wall ingrowths, the thickening of cell walls and the complete vacuolation of the once-richly cytoplasmic cells. Although the thickened walls of other primary xylem parenchyma cells become lignified at this time, the transfer cell walls remain unlignified until the rhizome is very old.

Transmission of action potentials inBiophytum

By cooling or by electrical stimulus an action potential, (60 to 100 mv negative) was propagated throughout the length of a pinna-rachis or a peduncle ofBiophytum sp. A cutting stimulus evoked a series of two to four transmission of actions of action potentials. The transmission did not pass through the base of the leaf or peduncle. The velocity of the transmission in the rachis and penduncle was about 0.2 cm/sec, and no difference in the velocity was found between the acropetal and basipetal directions. In the stimulated site a local response (a negative bulge of potential) was seen with threshold stimulus. The absolute refractory period for the transmission of action potential was estimated at 20 to 50 sec, and the relative one at 30 to 70 sec. The mechanism of the transmission seemed to be similar to that inMimosa pudica.

Leaf development and phloem transport in Cucurbita pepo: Transition from import to export

The capacity of a growing leaf blade of Cucurbita pepo L. to import (14)C-labelled photoassimilate is lost in a basipetal direction. Import into the lamina tip stops when the blade is 10% expanded. Development of the leaf progresses linearly with time and the lamina base stops importing when the blade is 45% expanded. Export capacity also develops basipetally and follows immediately the loss of import capacity, at least in the lamina base. The small amount of material initially exported from the leaf tip is redistributed to the still-importing leaf base, delaying export from the lamina until the blade is 35% expanded. Loss of import capacity by the petiole is both basipetal and dorsoventral. The proximal, adaxial portion of the petiole is the last region to cease importing (14)C. Leaves of Beta vulgaris L. and Nicotiana tabacum L. also lose import capacity in a basipetal direction.

Untersuchungen zur Translokation von Magnesium (28Mg) in Sonnenblumenpflanzen

Investigations on translocation of magnesium (28Mg) in sunflower plants.1. The translocation and retranslocation of Mg respectively 28Mg in sunflower plants of different age have been investigated. The focus of this investigation was on the influence of the composition of the uptake solution and the age of plants on the uptake of Mg respectively 28Mg through the roots or through the leaves and on Mg translocation (distribution).2. After sunflower plants were grown in Mg‐deficient 1/2‐Hoagland solution Mg in the plants were redistributed. The Mg in the roots, stems, cotyledons, primary and secondary leaves was retranslocated to the youngest leaves.3. In isolated, secondary‐rooted sunflower shoots grown in Mg‐deficient solution, plant Mg was retranslocated into the new roots and into the youngest shoots.4. The 28Mg‐uptake from the 0,2 mM MgSO4 solution was usually higher than from the 1/10‐Hoagland solution. The composition of the uptake solution had little influence on the distribution of 28Mg. Independent of the age plants had the highest 28Mg content in the young and the lowest in the old leaves.5. Root uptake of 28Mg resulted in a more uniform distribution in the plant than leaf uptake. The old leaves had a higher 28Mg content by root uptake than by leaf uptake of 28Mg. This is probably influenced by transpiration, in combination with the xylem transport of 28Mg after root uptake, which differs from leaf uptake and translocation in basipetal direction.6. With increased age of plants, the content of 28Mg/10 gr. fresh weight decreased and the difference in content between the parts of plant was higher. The decrease of Mg content in the oldest leaves was the highest.7. The results showed that Mg was transportable in the phloem. The magnitude and the direction of Mg transport was determined as primarily through the assimilation stream, which is coupled with Mg transport in plants.

1-N-naphthylphthalamic acid and 2,3,5-triiodobenzoic acid

Auxin transport in corn coleoptile sections was inhibited by 2,3,5-triiodobenzoic acid (TIBA) as well as by 1-N-naphthylphthalamic acid (NPA); this inhibition was effected within 1 min of application.A particulate cell fraction-presumably plasma-membrane vesicles-specifically binds NPA and properties of these binding sites were studied using (3)H-NPA and a pelletting technique. The saturation kinetics of the physiological NPA effect, i.e. the inhibition of auxin transport, is similar to that of the specific in-vitro NPA binding. Half saturation of the inhibitory effect was found with about 5×10(-7) M TIBA and with 10(-7) M NPA. Both substances also decreased the speed of movement of auxin pulses within coleoptile sections.NPA dissociates from its binding site when the particulate cell material is centrifuged through an NPA-free cushion. The NPA that is washed from its binding site can be used in another binding test without any apparent change and is chromatographically unaltered. Therefore, the NPA binding is probably reversible and non-covalent. Inhibition of auxin transport by TIBA or NPA could also be reversed when the coleoptile sections were washed in buffer.The movement of (131)I-TIBA in corn coleoptiles appears to be polar in a basipetal direction. Higher concentrations of indoleacetic acid or TIBA inhibited this polar movement, suggesting that TIBA moves in the same channels as auxin. With (3)H-NPA, however, no polar transport could be detected. Together with the in-vitro binding results, these data indicate that TIBA acts directly at the auxin receptor while NPA has a different receptor site.The effect of TIBA and NPA on elongation, with or without auxin, is neglegible in comparison to their effects on auxin transport.

Patterns of translocation and metabolism of 14C-labelled IAA in the phloem of Willow

When 2-(14)-C-labelled IAA was applied to an isolated segment of Willow via a bark abrasion the pathway of transport of this compound was found to be located in the sieve elements as evidenced by the pattern of activity found in honeydew excreted by individuals of Tuberolachnus salignus (Gmelin) feeding on the segment.Further experiments have established that polarity of transport of (14)C-IAA occurs in a basipetal direction when isolated segments of willow are orientated in a vertical position, with the morphological apex uppermost. No polarity was found when segments were orientated in a vertical position with the morphological base uppermost, or when the segments were orientated in a horizontal position. The metabolism of (14)C-IAA was also studied with respect to orientation. It was shown that the conversion rate of IAA to IAA aspartate was influenced by the orientation of the segment. It is considered that this is not a direct effect of orientation on the rate of metabolism of IAA.

Sulfur Dioxide and IAA Transport in Isolated Bean Petiole Sections

The uptake and movement of IAA-l-Cl4 in 5 mm sections from the middle of petioles of primary bean leaves was studied under five concentrations of SO2 (0.0, 0.1, 1.0, 10.0 and 100.0 ppm) by suspending the sections horizontally between donor agar blocks containing C14 labeled IAA and plain agar receiver blocks and measuring radioactivity in the blocks after 6 hr by scintillation counting. Movement was strictly polar in a basipetal direction. There was no signiScant effect of SO2, petiole size) or interaction between these two variables on IAA movement or IAA loss from donor blocks. It is therefore unlikely that SO2 damage to plants results from any effect on IAA movement.

Studies on the movement of indole auxins in willow (Salix viminalis L.)

Auxin activity was detected in honeydew obtained from the aphid Tuberolachnus salignus (Gmelin) feeding on willow (Salix viminalis). Active uptake of (14)C-indolyl-3-acetic acid (IAA) into the sieve tubes was demonstrated by irrigating the cambial surface of willow bark with (14)C-IAA solution and assaying aphid stylet exudate. When, however, (14)C-IAA was applied to the peridermal tissues of the bark or to a mature leaf most of the radioactivity (collected in honeydew or stylet exudate) co-chromatographed with indolyl-3-acetyl-aspartic acid (IAAsp). The presence of IAAsp in honeydew was not affected by extraction procedure or by aphid metabolism. Honeydew obtained from willow treated with (14)C-tryptophan contained only (14)C-tryptophan. When (14)C-IAA was applied in agar to the cut end of willow segments the radioactivity was found to move in a basipetally polar manner. The direction of movement of radioactivity in the sieve tubes, however, was found to be influenced by the proximity of the roots. Nevertheless, there was evidence that endogenous auxin in the sieve tubes does move in a predominantly basipetal direction.

THE INFLUENCE OF ACROPETALLY TRANSPORTED INDOLEACETIC ACID ON THE GEOTROPISM OF INTACT PEA ROOTS AND ITS MODIFICATION BY 2, 3, 5-TRIIODOBENZOIC ACID

SUMMARY The geotropic response of horizontal intact pea seedling roots was rapidly influenced by indole-3-acetic acid (IAA), which was applied in narrow rings of lanolin paste a few cm from the apex. The applied auxin thus likely was transported in the acropetal direction in these roots. The influence of IAA was strongly reduced when 2, 3, 5-triiodobenzoic acid (TIBA) was applied to the roots at the apical side of the IAA-ring. When TIBA was applied alone at various distances from the apex of the horizontal roots it also inhibited the geotropic curvature. The transport of auxin in the apical region of horizontal roots probably occurred both in the acropetal and in the basipetal direction.

Transport and Metabolism of Indole-3-Acetic Acid in Coleus Petiole Segments of Increasing Age

Transport and metabolism of IAA-1-(14)C in Coleus blumei Benth. was studied by means of a combination of liquid scintillation counting, autoradiography and thin-layer chromatography. Transport of IAA in petiole segments of increasing age (No. 2-8) was strictly polar in a basipetal direction. No acropetal movement occurred in either young or old tissues. The greatest amount, expressed as a percentage of the radioactivity lost from the donor block, was found in basal receivers on petiole number 2. There was gradually less transport in older segments. The recovery as a percentage of the radioactivity not accounted for by donor and receiver blocks, measured by counting the radioactivity in an acetonitrile-extract of petiole segments, was low: 25 to 50%. In this acetonitrile-soluble fraction evidence for different radioactive compounds was found, depending on the age of the tissue. A possible relationship between the amounts of auxin transported in the tissue and its corresponding metabolism is discussed.

The shoot apex and the ontogeny of axillary buds in Cuminum cyminum L

The structure and plastochronic changes of the shoot apex, and the origin, development, procambialization, and vascular relationships of the axillary bud in Cuminum cyminium were investigated. Pre-leaf initiation, leaf initiation, and post-leaf initiation phases of the shoot apex are identified. The inflorescence is axillary. During flowering the main vegetative shoot apex is semispherical, stratified, and devoid of any distinction between the central and peripheral zones. The vegetative axillary bud is differentiated from the peripheral zone of the shoot apex at the second node. It is delimited by an arcuate shell zone which helps in changing the apical position of the bud to foliar. The emergence of the bud is effected by the meristematic activity of tunica and corpus cells. A single prophyll is formed at right angles to the axillant leaf. Usually the bud trace procambium is differentiated during prophyll initiation. Occasionally it may be seen earlier, but not in connection with the earliest visible bud meristem. There are four to six strands of the bud trace directly interconnecting not only the strands of the prophyll and axillant leaf traces but also those of the second or sometimes even the third bud leaf and the axillant leaf. The bud trace procambial connection is formed by basipetal and acropetal differentiation of procambium in which the bud meristem cells and vacuolated ground meristem cells below the bud are involved. The cells of the peripheral zone of the bud apex below the prophyll primordium procambialize in a basipetal direction. As a continuation from the strand of the axillant leaf trace, the adjacent vacuolated ground meristem cells below the bud acropetally differentiate into procambial cells in the direction of the basipetal procambium and they make connection with it. All the strands of the bud trace are not simultaneously developed. The vegetative and inflorescence buds show varying vascular relationships between the strands of the leaf traces and those of the bud traces. The node differentiated during the vegetative phase of the plant is trilacunar and the one formed at flowering time is tetra- or pentalacunar. The nature and number of bud trace strands, however, suggest fundamental similarities between vegetative and inflorescence buds.

The Translocation of Two Organic Arsenicals in Purple Nutsedge

The translocation of disodium methanearsonate (DSMA) and amine methanearsonate (hereinafter referred to as AMA) in purple nutsedge (Cyperus rotundus L.) was studied following foliar applications. Tracer techniques with DSMA-14C and chemical analyses for elemental arsenic (hereinafter referred to as As) suggested apoplastic and symplastic movement of both arsenicals. Chromatographic studies of extracts from DSMA-14C-treated plants indicated that the compound was not readily broken down. The carbon-arsenic bond appeared to remain largely intact, although some 14C activity was found in respiratory CO2 several days after treatment. A comparison between the Rf value of the radioactive plant extract to that of standard DSMA-14C suggested that a plant extract-DSMA complex may have been formed. Over 85% of the material applied to the plant remained in the treated shoots. DSMA moved in both acropetal and basipetal directions, and such movement within a single leaf was not influenced by relative leaf age. The arsenicals were not redistributed in the shoot or in the tuber system, but As was accumulated in terminal tubers following repeated applications.

Thresholds for Georesponse to Acceleration in Gravity-Compensated Avena Seedlings

The magnitude of acceleration required to induce growth responses in Avena seedlings grown in the absence of tropic response to earth gravity has been investigated. For this purpose, a clinostat was developed that imposes accelerations from about 10(-9) g to 3 g upon the seedling; simultaneously, it nullifies, or compensates for, response to the directional component of the gravitational-force vector by rotating the seedling on a horizontal axis. When accelerations less than 10(-3) g are applied in either the acropetal or the basipetal direction, the growth in length and weight of the various organs is not materially different from that of compensated seedlings to which no longitudinal force is applied. At accelerations between 10(-3) and 10(-2) g, differences in growth become highly significant. When the centrifugal forces are transverse to the seedling during compensation, the threshold acceleration range for geoperception, as manifest by shoot reorientation, is again between 10(-3) and 10(-2) g. Geotropic reorientation of the root becomes apparent after exposures between 10(-4) and 10(-3) g.

Photoperiodic studies on growth and development of Impatiens balsamina L.

In the short-day plant Impatiens balsamina it was found that, while floral buds are initiated with 3 short-day (SD) cycles, at least 8 such cycles are required for flowering. The numbers of floral buds and open flowers bear a linear relationship with the number of SD cycles. The induced floral buds revert to vegetative growth unless the plants receive the minimum number of SD cycles needed for flowering, this reversion occurring in a basipetal direction. The rate of extension growth of the stem increases with increasing numbers of SD cycles. The high rate is maintained longer in plants receiving 32 or more SD cycles, but the subsequent fall is also steeper in these plants than in plants receiving less inductive cycles. Senescence also occurs in these plants and appears to be related to the magnitude of reproductive development and the high rate of extension growth.

MODIFIED REMNANTS OF CENTRIPETAL XYLEM IN THE LEAF TRACE OF CEPHALOTAXUS

A study of the leaf traces at the nodes in various species and varietal forms of Taxus, Torreya, Amentotaxus and Cephalotaxus reveals, only in Cephalotaxus, an unusual type of parenchymatous tissue associated with the xylem of the leaf trace. The cells of this tissue occur in one to three layers, have abundant cytoplasm and conspicuous nuclei. The thin walls of these cells are devoid of pits and show spiral or spiral‐reticulate thickenings. These thickenings, although readily taking the counterstain, reveal the presence of lignin as determined by the phloroglucin test and by fluorescence microscopy. This tissue is always internal—that is, adaxial—to the protoxylem of the trace. From the node it accompanies the trace for a short distance into the leaf base, where it gives way centrally to the typical leaf parenchyma and laterally to the transfusion tissue on the flanks of the bundle. In the basipetal direction it is in contact with the inner face of the annular protoxylem of the stele, eventually disappearing in the typical pith parenchyma. This tissue occasionally reveals instances of well‐lignified tracheid‐like centripetal elements. On the basis of the characteristics of this tissue, it is suggested that its origin lies in former centripetal xylem. The significance of this tissue to the evolution of the stele and the systematic position of Cephalotaxus is discussed.

Polarity of IAA Effect on Sieve-Tube and Xylem Regeneration in Coleus and Tomato Stems

A technique is described for the processing of regenerated xylem and sieve tubes from the same wound area for microscopic and quantitative comparison.Regeneration was examined in internodes of 2 developmental stages in Coleus: internode 2, elongating, characteristic of primary growth; and internode 5, non-elongating, characteristic of secondary growth.Transport of indoleacetic acid (IAA) in excised number 5 internodes of Coleus is strictly polar, in a basipetal direction, judging by a regeneration bioassay involving both sieve tube strands and xylem cells. Similar results were obtained with tomato.If isolated number 5 Coleus internodes are not treated with hormone, they regenerate no xylem cells and a small number of sieve tube strands. With increasing concentrations of IAA added apically, the number of regenerated sieve tube strands (and, with higher concentrations, of xylem cells) increases progressively up to 1% IAA, the highest concentration applied.Internode 2 of Coleus regenerates fewer xylem cells or sieve tube strands than internode 5, whether on the otherwise intact plant or with a given concentration of IAA added apically. The amount of regenerated xylem increases with added apical IAA, except that the highest concentration gives no further increase. The number of xylem cells regenerated in intact plants occurs at the same interpolated IAA concentration as in number 5 internodes. No concentration of IAA tried provided replacement of intact number of sieve tube strands in internode 2.IAA can exert a regenerative stimulus on both xylem and sieve tubes in the area immediately adjacent to the site of its application.

Auxin Transport in Explants of Coleus

alpha-Naphthaleneacetic acid-C(14), labeled in the carboxyl group, was applied in blocks of agar to the distal and to the proximal (either apical or basal) ends of explants of Coleus. The radioactivity in receiver blocks at the opposite ends was measured. Acropetal transport was slight, only 4% of the basipetal transport.Translocation of NAA-C(14) was polar in basipetal direction. Only 1.4% of the radioactivity lost from donor blocks at the apical position reached the receiver blocks; the greatest part remained in the tissue and was immobilized there. All activity found in receiver blocks at the basal end appeared to be still in the form of NAA. There were no differences between petiole tissue and stem tissue, so far as the transport of NAA is concerned.

Polarity of Transport of Benzyladenine, Adenine and Indole-3-acetic Acid in Petiole Segments of Phaseolus vulgaris

Polarity in plant tissues is recognizable externally from the pattern of growth. For example, segments of stem tissues suitably cultured produce buds only toward the ends which are nearest to the apex in the intact stem, while root initials are normally produced only at the opposite or basal ends. Within the tissues of young shoots polarity is manifested by a greater movement of endogenous or applied auxin in the basipetal direction, away from the apex, than in the acropetal direction, towards the apex. Until 1964, only the natural or synthetic auxins were known to move in this polar way. The relative concentrations of auxins and other hormonal regulators of growth, control the development of different plant parts. Examples of interactions between auxins and kinins include regulation of growth and differentiation in plant tissue culttures (11) and the control of apical dominance and lateral b)ud growth (6). It is, therefore, pertinent to consider the movement of kinins in plant tissues, and how this movement might be influenced by auxin. The observation that 1 kinin, benzyladenine (BA) is transported in petiole segments of Phaseolus vulgaris in a basipetally polar direction and that this movement is enhanced by indole-3-acetic acid (IAA) has already been reported briefly for benzyladenine labeled in 2 different positions (8, 9). Kinin activity in plants is shown by many 6-substituted adenine compounds (6) and it would appear that the adenine moiety is essential for such activity. Adenine itself, however, is poorly active in evoking a kinin response (11). The present paper reports the results of experiments on the transport of C14-labeled benzyladenine, adenine and indole-3-acetic acid which emphasize the difference in mobility between benzyladenine and adenine and provide evidence for an interaction between the movement of auxins and kinins.