Girdling-induced nutrient accumulation in above ground tissue of peanuts and subsequent feeding by Spissistilus festinus, the three-cornered alfalfa hopper

Changes in nutrient partitioning in stems and leaves of peanut (Arachis hypogaea L.) were examined after girdling of stems by Spissistilus festinus (Say) (Homoptera:Membracidae), the three-cornered alfalfa hopper. Under field conditions amino acids increased more than 12-fold in concentration in the 2 cm stem section above the girdle compared to below the girdle or control stems for newly formed girdles (less than 7–11 days). Asparagine and proline were the predominant amino acids, and increased 40- and 60-fold, respectively, above the girdle compared to below the girdle. There was no buildup of nutrient assimilates for the older girdled stems that had callused (and presumably recovered from feeding injury). A time course from 1–11 days was followed under greenhouse conditions, and girdled regions remained enriched in sugars for one day and amino acids for four days after girdle formation. After girdle formation most S. festinus responded to nutrient sinks by feeding within 5 mm above the girdle. This behavior was most pronounced one day after girdle formation, but persisted for seven days after girdle formation. During this period a new girdle was often formed within 10 mm above the original girdle. Under field conditions, stems and leaves derived from stems that had sustained an early or late season girdle generally had a reduced dry weight, total nitrogen content, and total carbon content; however, significant differences did not always occur. Thus, although temporary changes occurred in nutrient partitioning in girdled stems, there appears to be longer term negative growth effects on leaves and stems.     

Transport of [3H]IAA label in gravistimulated primary roots of maize

The curvature of roots in response to gravity is attributed to the development of a differential concentration gradient of IAA in the top and bottom of the elongation region of roots. The development of the IAA gradient has been attributed to the redistribution of IAA from the stele to cortical tissues in the elongation region. The gravistimulated redistribution of IAA was investigated by applying [³H]IAA to the cut surface of 5 mm apical primary root segments. The movement of label from the stele-associated [³H]IAA into the root, tip, root cap, and cortical tissues on the top and bottom of the elongation region was determined in vertically growing roots and gravistimulated roots. Label from the stele moved into the region of cell differentiation (root tip) prior to accumulating in the elongation region. Little label was observed in the root cap. Gravistimulation did not increase the amount of label moving from the stele; but gravistimulation did increase the amount of label accumulating in cortical tissues on the lower side of the elongation region, and decreased the amount of label accumulating in cortical tissues on the upper side of the elongation region. Removal of the cap prior to or immediately following gravity stimulation rendered the roots partially insensitive to gravity and also prevented gravity-induced asymmetric redistribution of label. However, removal of the root cap following 30 min of gravistimulation did not alter root curvature or the establishment of an IAA asymmetry across the region of root elongation. These results suggest that a signal originating in the root cap directs auxin redistribution in tissues behind the root cap, leading to the development of an asymmetry of IAA concentration in the elongation region that in turn causes the differential growth rate in the elongation region of a graviresponding root.     

Transport of [3H]IAA label in gravistimulated primary roots of maize

The curvature of roots in response to gravity is attributed to the development of a differential concentration gradient of IAA in the top and bottom of the elongation region of roots. The development of the IAA gradient has been attributed to the redistribution of IAA from the stele to cortical tissues in the elongation region. The gravistimulated redistribution of IAA was investigated by applying [³H]IAA to the cut surface of 5 mm apical primary root segments. The movement of label from the stele-associated [³H]IAA into the root, tip, root cap, and cortical tissues on the top and bottom of the elongation region was determined in vertically growing roots and gravistimulated roots. Label from the stele moved into the region of cell differentiation (root tip) prior to accumulating in the elongation region. Little label was observed in the root cap. Gravistimulation did not increase the amount of label moving from the stele; but gravistimulation did increase the amount of label accumulating in cortical tissues on the lower side of the elongation region, and decreased the amount of label accumulating in cortical tissues on the upper side of the elongation region. Removal of the cap prior to or immediately following gravity stimulation rendered the roots partially insensitive to gravity and also prevented gravity-induced asymmetric redistribution of label. However, removal of the root cap following 30 min of gravistimulation did not alter root curvature or the establishment of an IAA asymmetry across the region of root elongation. These results suggest that a signal originating in the root cap directs auxin redistribution in tissues behind the root cap, leading to the development of an asymmetry of IAA concentration in the elongation region that in turn causes the differential growth rate in the elongation region of a graviresponding root.     

Seasonal variations in the polar-transport pathways and retention sites of [3H]indole-3-acetic acid in young branches ofFagus sylvatica L.

Branches were cut from young beeches (Fagus sylvatica L.) at various stages of the annual cycle and [³H]indole-3-acetic acid (0.35 nmol) was applied to the whole surface of the apical section of each branch, just below the apical bud. The labelled pulse (moving auxin) and the following weakly radioactive zone (auxin and metabolites retained by the tissues) were localized by counting: microautoradiographss were made using cross sections from these two regions. During the second fortnight of April, auxin was transported by nearly all the cells of the young primary shoot, but the label was more concentrated in the vascular bundles. Auxin transport became the more localized: the cortical parenchyma appeared to lose its ability to transport the hormone (end of April), followed in turn by the pith parenchyma (May). Polar auxin movement at that time was limited to the outer part of the bundle (cambial zone and phloem) and to the inner part (protoxylem parenchyma). Later protoxylem parenchyma ceased to carry auxin. During the whole period of cambial activity, auxin was transported and retained mainly by the cambial zone and its recent derivatives. In September, before the onset of dormancy, and in February, at the end of the resting period, the transport pathways and retention sites for auxin were mainly in the phloem, where sieve tubes often completely lacked radiolabel. When cambial reactivation occurred in the one-year shoot, auxin was mainly carried and retained again in the cambial zone and differentiating derivatives.Abbreviation IAA indole-3-acetic acid     

Microsurgical removal of epidermal and cortical cells: evidence that the gravitropic signal moves through the outer cell layers in primary roots of maize

There is general agreement that during root gravitropism some sort of growth-modifying signal moves from the cap to the elongation zone and that this signal ultimately induces the curvature that leads to reorientation of the root. However, there is disagreement regarding both the nature of the signal and the pathway of its movement from the root cap to the elongation zone. We examined the pathway of movement by testing gravitropism in primary roots of maize (Zea mays L.) from which narrow (0.5 mm) rings of epidermal and cortical tissue were surgically removed from various positions within the elongation zone. When roots were girdled in the apical part of the elongation zone gravitropic curvature occurred apical to the girdle but not basal to the girdle. Filling the girdle with agar allowed curvature basal to the girdle to occur. Shallow girdles, in which only two or three cell layers (epidermis plus one or two cortical cell layers) were removed, prevented or greatly delayed gravitropic curvature basal to the girdle. The results indicate that the gravitropic signal moves basipetally through the outermost cell layers, perhaps through the epidermis itself.     

Apical callus formation and plant regeneration controlled by plant growth regulators on axenic culture of the red alga Gracilariopsis tenuifrons (Gracilariales, Rhodophyta)

Axenic cultures of Gracilariopsis tenuifrons (Bird et Oliveira) Fredericq et Hommersand (Gracilariales, Rhodophyta) were established in ASP12‐NTA solid medium (0.4% agar and 1.0% sucrose) supplemented with plant growth regulators to evaluate the effects on apical callus formation and plant regeneration. Indole‐3‐acetic acid (IAA), 2,4‐dichlorophenoxyacetic acid (2,4‐D) and 6‐benzylaminopurine (BA) were added individually or in combinations (IAA : BA) over a range of concentrations from 0.5 to 5 mg L^?1. Growth of apical and intercalary segments was stimulated by high concentrations of 2,4‐D (5 mg L^?1) and a high IAA to BA ratio (IAA : BA = 5:1 mg L^?1) respectively. Apical calluses were originated from divisions of apical and cortical cells located at apical regions of thallus segments and lateral branches. Low concentration of IAA (0.5 mg L^?1) or a high IAA to BA ratio (IAA : BA = 5:1 mg L^?1) were the optimal treatments for inducing apical callus formation in apical segments, while high concentration of IAA (5 mg L^?1) stimulated the highest callus induction rate in intercalary segments. Conversely, equal parts IAA and BA (IAA : BA = 1:1 mg L^?1) and low concentration of 2,4‐D (0.5 mg L^?1) stimulated growth of apical calluses from apical and intercalary segments, respectively. Two processes of regeneration were observed: direct regeneration (upright axis originated from cells of proximal region of intercalary segments) and indirect regeneration (adventitious plantlet originated from cells of apical calluses). Direct regeneration was promoted significantly by treatment with a low IAA to BA ratio (IAA : BA= 1:5 mg L^?1), and treatments with IAA (0.5 mgL^?1) or 2,4‐D (0.5 or 5 mg L^?1) significantly stimulated the elongation of upright axis. Plant growth regulators are essential to inducing indirect regeneration, and a high concentration of IAA (5 mg L^?1) and BA (5 mg L^?1) were the optimal treatments for inducing the regeneration of plantlets from apical calluses in apical and intercalary segments, respectively. Regenerating plantlets grew into plants morphologically similar to those formed from germinating spores, and became fertile after 6 weeks. The results suggest that auxins and cytokinins are involved in developmental regulatory processes in G. tenuifrons. The regeneration process from calluses in species of Gracilariales was observed for the first time in the present study. The culture system described for G. tenuifrons could be useful for micropropagation and for biotechnological applications in agarophytic algae.     

In vivo metabolism of labelled indole-3-acetic acid during polar transport in etiolated hypocotyls of Lupinus albus: Relationship with growth

The in vivo metabolism of indole-3-acetic acid (IAA) in etiolated hypocotyls of lupin (Lupinus albus L., from Bari, Italy) was investigated by appliying IAA labelled with two radioisotopes ([1-¹⁴C]-IAA+[5-³H]-IAA) to the apical end of decapitated seedlings, followed by extraction of the radioactivity in the different regions along the hypocotyl. This method allowed detection of IAA decarboxylation in zones distant from the cut surface and, therefore, containing intact cells. When IAA was added directly in solution to the cut surface, decarboxylation was high especially in those hypocotyl regions where transient accumulations characteristic of the polar transport of IAA occurred. In 10-day-old seedlings such accumulations were observed both in the elongation zone (2^nd, 3^rd, and 4^th cm) and in the non elongating basal zone (8^th, 9^th and 10^th cm). When the IAA, instead, was applied with an agar block deposited on the cut surface, IAA metabolism (decarboxylation as well as conjugation) was increased but almost exclusively in tissues within 10 mm of the cut surface. In both kinds of experiment, the increase in IAA decarboxylation seemed to coincide with a decrease in the transport of IAA, since in the assay without agar the transient accumulations of radioactivity were probably due to a decrease in the transport velocity, while in the assay with agar the transport intensity was much lower than in the assay without agar. These results point to a competitive relationship between IAA metabolism and transport. Consequently, it is suggested that hypocotyl regions that probably use auxin for development processes (e.g., cell elongation and differentiation) may have a more intense IAA metabolism in parallel with their higher IAA concentrations.     

Effects of activated charcoal, explant size, explant position and sucrose concentration on plant and shoot regeneration of Lilium longiflorum via young stem culture

An efficient system for the in vitro plant and shootregeneration of Lilium longiflorum was developed andaccomplished using transverse thin cell layers (tTCL) of young stems.tTCLs were cut transversely along young stems from which the shoot-tipshad been removed. Sections were measured accurately using a graded gridand were cut in 4 mm × 4 mm × 1 mm cubes, eliminatingepidermal tissue, and were cultured on one-half MS medium containing 8 gl^–1 agar, different sucrose concentrations (10, 20, 30 or 40g l^–1), and with or without 1 mg l^–1 activatedcharcoal (AC). Plants formed on the surface of tTCLs within 60 days onone-half MS medium containing 8 g l^–1 agar and 20 gl^–1 sucrose. Sections of 1 mm taken just below the apicalarea developed buds within 15 days, whereas the sections closer to thebase required about 45 days. Shoot regeneration was enhanced whensucrose concentration was used at 30 or 40 g l^–1 after 60days of culture. No root formation occurred. Both shooting and rootingoccurred when sucrose was used at 20 g l^–1. The plantletswere transferred to soil and grew well under greenhouseconditions.     

Untersuchung des Einflusses der Temperatur auf die Photosynthese-Induktion bei Chlorella vulgaris mit radioaktivem CO2

Summary The lateral bud of Solanum andigena has the potentiality to develop as a stolon or as a leafy, orthotropic shoot. Natural stolons are normally only produced from underground nodes, but aerial stolons can be induced to form by the application of a combination of indole-3-acetic acid and gibberellic acid (IAA/GA₃) paste to the cut surface; under some conditions both natural or induced stolons are converted to upright, leafy shoots. The presence of roots was found to be necessary for the conversion of a natural stolon to a leafy shoot, but this root effect could be replaced by the synthetic cytokinin, 6-benzylaminopurine (BAP). By using -¹⁴C-BAP it was demonstrated that cytokinin accumulates in the tip of an induced stolon, prior to its conversion to a leafy shoot caused by withdrawal of the IAA/GA₃ paste. The application of IAA/GA₃ to decapitated plants was shown to influence both the distribution and metabolism of the cytokinin. The possibility that the role of auxin in apical dominance, at least in part, is to control the distribution and metabolism of cytokinins is discussed.     

The vertical zonation of adpressed diatoms and other epiphytic algae on Phragmites australis

The seasonal colonization and vertical zonation of adpressed and upright algae on Phragmites stems in Lake Belau, Germany, was investigated from November 1988 to October 1991. During the autumns and winters from 1988 to 1990 the dominant adpressed species included the diatoms Epithemia adnata, E. sorex, E. turgida and Rhopalodia gibba, while during the same seasons in 1990 and 1991, Cocconeis placentula var. euglypta was abundant. The upright diatoms were most abundant on the middle sections of the stems, whereas those epiphytes with most of their cell surfaces directly in contact with the substratum constituted the greatest part of the biomass on the lowest sections of the stems. Epithemia spp. and R. gibba attained their highest abundances near the sediment as well as buried beneath the most dense periphyton aggregations, while there were dense populations of C. placentula var. euglypta on the entire surface of the stems. Cocconeis is able to tolerate higher light intensities, with photosynthetically active radiation (PAR) values averaging 38?μmol?m^?2?s^?1, than Epithemia and Rhopalodia, which settle at a significantly lower PAR (26 and 20?μmol?m^?2?s^?1, respectively). The change in dominance among the adpressed species from Epithemia and Rhopalodia to Cocconeis can be explained by changes in the grazing habits of the snail Acroloxus lacustris.     

Cu2+ inhibition of gel secretion in the xylem and its potential implications for water uptake of cut Acacia holosericea stems

Maintaining a high rate of water uptake is crucial for maximum longevity of cut stems. Physiological gel/tylosis formation decreases water transport efficiency in the xylem. The primary mechanism of action for post‐harvest Cu²⁺ treatments in improving cut flower and foliage longevity has been elusive. The effect of Cu²⁺ on wound‐induced xylem vessel occlusion was investigated for Acacia holosericea A. Cunn. ex G. Don. Experiments were conducted using a Cu²⁺ pulse (5 h, 2.2 mM) and a Cu²⁺ vase solution (0.5 mM) vs a deionized water (DIW) control. Development of xylem blockage in the stem‐end region 10 mm proximal to the wounded stem surface was examined over 21 days by light and transmission electron microscopy. Xylem vessels of stems stood into DIW were occluded with gels secreted into vessel lumens via pits from surrounding axial parenchyma cells. Gel secretion was initiated within 1–2 days post‐wounding and gels were detected in the xylem from day 3. In contrast, Cu²⁺ treatments disrupted the surrounding parenchyma cells, thereby inhibiting gel secretion and maintaining the vessel lumens devoid of occlusions. The Cu²⁺ treatments significantly improved water uptake by the cut stems as compared to the control.     

Rapidly Induced Wound Ethylene from Excised Segments of Etiolated Pisum sativum L., cv. Alaska: III. Induction and Transmission of the Response

Increased ethylene synthesis was rapidly induced throughout the apical meristematic region of etiolated seedlings of Pisum sativum L., cv. Alaska by cuts made 1 centimeter from the apical hook. The wound signal was transmitted at about 2 millimeters per minute. Accumulation of substance(s) at the cut surfaces of excised sections, as the result of interrupted translocation, did not initiate or significantly contribute to wound-induced ethylene synthesis, nor was the cut surface the site of enhanced ethylene synthesis. Cutting subapical sections into shorter pieces showed that cells less than 2 millimeters from a cut surface produced about 30% less ethylene than cells greater than 2 millimeters from a cut surface.     

THE ATLANTIC SPECIES OF SOLIERIA (GIGARTINALES,RHODOPHYTA): THEIR MORPHOLOGY,DISTRIBUTION AND AFFINITIES1

Solieria chordalis (C. Agardh) J. Agardh and S. tenera (J. Agardh) Wynne et Taylor exhibit multiaxial growth from a cluster of four to eight obconical apical cells. A single periaxial cell is cut off from each axial cell and successive periaxial cells are rotated 120° in a zig-zag pattern along each axial filament. Periaxial cells produce branched, laterally diverging filaments which form the cortex. The medulla is composed of axial cells, elongate cells of lateral filaments, stretched interconnecting cells, and secondary rhizoids. The two species are nonprocarpic. Carpogonial branches are 3-celled, inwardly directed, with a reflexed trichogyne. The auxiliary cell together with associated darkly-staining inner cortical cells form an association, the auxiliary cell complex, that is recognizable prior to diploidization. A single, unbranched, non-septate connecting filament issues from the fertilized carpogonium and fuses with the inner, lateral side of an auxiliary cell. Production of an involucre from surrounding vegetative cells is stimulated and a gonimoblast initial is cut off toward the interior of the thallus which divides to form a compact cluster of gonimoblast cells. A fusion cell is produced through fusion of inner gonimoblast cells with the auxiliary cell that, in turn, fuses progressively with cells of the lateral file bearing the auxiliary cell. Mature cystocarps have terminal carposporangia cut off from gonimoblast cells at the periphery of the fusion cell and are surrounded by an involucre with a distinct ostiole. Tetrasporangia are cut off laterally from surface cortical cells which then cut off one or two additional derivatives toward the outside. A lectotype is designated for Solieria chordalis, but the lectotypification of S. tenera is questioned. We conclude that Solieria is closely related to Rhabdonia and place the Rhabdoniaceae in synonomy with the Solieriaceae.     

Electrophysiological properties of cellular and paracellular conductive pathways of the rabbit cortical collecting duct

Summary Microelectrode techniques were applied to the rabbit isolated perfused cortical collecting duct to provide an initial quantitation and characterization of the cell membrane and tight junction conductances. Initial studies demonstrated that the fractional resistance (ratio of the resistance of the apical cell membrane to the sum of the resistances of the apical and basolateral membranes) was usually independent of the point along the tubule of microelectrode impalement—implicating little cell-to-cell coupling—supporting the application of quantitative techniques to the cortical collecting duct. It was demonstrated that in the presence of amiloride, either reduction in the luminal pH or the addition of barium to the perfusate selectively reduced the apical membrane potassium conductance. From the changes inG ^te and fractional resistance upon reducing the luminal pH or addition of barium to the perfusate, the transepithelial, apical membrane, basolateral membrane and tight junction conductances were estimated to be 9.3, 6.7, 8.1 and 6.0 mS cm^–2, respectively. Ninety to ninety-five percent of the apical membrane conductance reflected the barium-sensitive potassium conductance in the presence of amiloride with an estimated potassium permeability of 1.1×10^–4 cm sec^–1. Reduction in the perfusate pH to 4.0 caused a 70% decrease in the apical membrane potassium conductance, implying a blocking site with an acidic group having a pK _a near 4.4. It is concluded that both the transcellular and paracellular pathways of the cortical collecting tubule have high ionic conductances, and that the apical membrane conductance primarily reffects a high potassium conductance. Furthermore, both reduction in the perfusate pH and addition of barium to the perfusate selectively block the apical potassium channels, although the site of inhibition likely differs since the two ions display markedly different voltage-dependent blocks of the channel.     

Synthesis of glycoproteins in the Golgi complex of the mouse gallbladder epithelium during fasting,refeeding, and gallstone formation

Summary The mouse gallbladder epithelium was studied with light microscopic autoradiography and quantitative electron microscopy during fasting, refeeding and experimental gallstone formation. To determine the intracellular pathway of glycoproteins, H³-galactose was injected at different time intervals into the mice. At 10, 25 and 40 min after an intraperitoneal injection the gallbladders were fixed and prepared for light microscopy. As early as 10 min after injection, label was observed in supranuclear cytoplasmic regions and at 25 min, an increased radioactivity was present throughout the apical cytoplasm. At 40 min, silver grains were mainly present at the cell surface. Autoradiographs processed 25 min after an intraperitoneal H³-galactose injection after fasting for 48 h showed decreased supranuclear and apical radioactivity. After refeeding (12 h) there was an enhanced activity in both these regions. Animals fed a lithogenic diet for one month showed a marked increase of radioactive label mainly in cells of crypts and invaginations of the mouse gallbladder mucosa.Morphometric measurements of the Golgi apparatus revealed that deprivation of food significantly diminished the volume density of the Golgi apparatus. Refeeding the animals restored the volume density values to normal levels. In the course of gallstone formation there was a further significant increase in the volume density of the Golgi complexes as compared to controls.     

CELL DIVISION AND THE ROLE OF THE PRIMARY WALL IN THE FILAMENTOUS DESMID ONYCHONEMA LAEVE (CHLOROPHYTA)1

Cell division and the role of the primary wall in filament formation in the desmid Onychonema laeve Nordst. were investigated by transmission and scanning electron microscopy. In addition, sequential chemical extractions and enzyme treatments were performed, on cell walls of intact filaments. Interphase cells are deeply constricted, consisting of two semicells, each elliptical in front view and circular in side view. In addition to two short lateral spines, each semicell has two apical processes that originate on opposite sides at an angle of about 15° from the central axis and overlap the adjacent cell. Division is initiated as in other desmids by a slight separation of the semicells and development of a girdle of primary wall material at the isthmus. In O. laeve the girdle of primary wall expands to form a spherical vesicle (termed a division vesicle) between the separating semicells. Nuclear division and septum formation occur in this vesicle when it is nearly the full diameter of the filament. Morphogenesis of the apical processes begins with completion of the septum, before the secondary wall appears. At maturity each apical process is surrounded by a thick layer of both secondary and primary wall, except that its capitate tip protrudes through the shroud of primary wall. Sequential treatment with hot ammonium oxalate, 4% NaOH, 17.5% NaOH and 10% chromic acid or various enzyme solutions did not cause filament breakage. SEM and TEM views of O. laeve after these treatments show intact secondary walls and intact primary wall material covering and connecting the apical processes of adjacent cells. It is the persistence of the primary wall between cells and around the apical processes that maintains the long, unbranched filamentous morphology of Onychonema laeve.     

Distribution of actin microfilaments in frog skin epithelial granular cells

Summary— Microfilaments were localised by immunofluorescence and immunogold cytochemistry to examine their distribution in granular cells of the isolated frog skin epithelium. Strongly fluorescent bundles of actin were observed beneath the plasma membrane with little evidence for actin in the central regions. Higher resolution offered by cytochemistry revealed that bundles of actin filaments comprised a substantial portion of the cortical cytoskeleton. Quantitative analysis of the frequency of gold label revealed an extremely rich array of filaments beneath the apical membrane of granular cells, with markedly less babel along the basolateral membrane and in the central cytoplasm. Treating cells with cytochalasin B or arginine vasopressin caused an apparent disruption of the apical actin fibres, concurrent with a decrease in gold label density. Assumably these signs are indicative of depolymerization of the filaments. Although the significance of this distribution is unknown, the apical polarisation of actin is consistent with a role in regulating the Na⁺ permeability of the apical membrane. The data are discussed in relation to possible roles of the cytoskeleton in the regulation of transepithelial sodium transport by vasopressin.     

Nitrate movement in xylem of lucerne plants

Nitrate content in lucerne stems and leaf blades immersed by cut ends in distilled water or in KNO₃ solution increased with the increase in KNO₃ concentration and with the duration of exposure under irradiance of 100 or 230 W m^?2 PAR. The nitrate content increased from basal stem parts to apical stem parts and leaves. Nitrate was transported mainly with transpiration stream. Some flow variations occurred in stems causing time changes in nitrate content in different parts of stems.     

Pruning-induced tylose development in stems of current-year shoots of Vitis vinifera (Vitaceae)

Tyloses form in xylem vessels in response to various environmental stimuli, but little is known of the kinetics or regulation of their development. Preliminary investigations indicated that wounds seal quickly with tyloses after pruning of grapevine shoots. In this study, tylose development was analyzed qualitatively and quantitatively at different depths and times from pruning cuts along current-year shoots of grapevines at basal, middle, and apical stem regions. Tyloses developed simultaneously within a single vessel but much separated in time among vessels. Pruning caused prodigious tylosis in vessels of grape stems, extending to approximately 1 cm deep and to 7 d after wounding, but about half of the vessels did not become completely occluded. The fraction of vessels forming tyloses was greatest in basal (85%) and least in apical (50%) regions. The depth of maximum density of tyloses was 4 mm from the cut in the basal region and 2 mm from the cut in the middle and apical regions. Tylose development was faster in the basal and middle than in the apical region. The pattern of tylose development is discussed in the context of wound repair and pathogen movement in grapevines.     

Graviresponsiveness of surgically altered primary roots of Zea mays

We examined the gravitropic responses of surgically altered primary roots of Zea mays to determine the route by which gravitropic inhibitors move from the root tip to the elongating zone. Horizontally oriented roots, from which a 1-mm-wide girdle of epidermis plus 2-10 layers of cortex were removed from the apex of the elongating zone, curve downward. However, curvature occurred only apical to the girdle. Filling the girdle with mucilage-like material transmits curvature beyond the girdle. Vertically oriented roots with a half-girdle' (i.e. the epidermis and 2-10 layers of the cortex removed from half of the circumference of the apex of the elongating zone) curve away from the girdle. Inserting the half-girdle at the base of the elongating zone induces curvature towards the girdle. Filling the half-circumference girdles with mucilage-like material reduced curvature significantly. Stripping the epidermis and outer 2-5 layers of cortex from the terminal 1.5 cm of one side of a primary root induces curvature towards the cut, irrespective of the root's orientation to gravity. This effect is not due to desiccation since treated roots submerged in water also curved towards their cut surface. Coating a root's cut surface with a mucilage-like substance minimizes curvature. These results suggest that the outer cell-layers of the root, especially the epidermis, play an important role in root gravicurvature, and the gravitropic signals emanating from the root tip can move apoplastically through mucilage.