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At least 19 recordsLinked to original sources
PubMed1984

Analysis and significance of gravity-induced asymmetric growth in the grass leaf-sheath pulvinus.

The negative gravitropic response in the grass leaf-sheath pulvinus is a consequence of cell elongation involving all cells except those of the uppermost region of the upper flank of an horizontally oriented pulvinus. The lowermost layer of cells elongate maximally, and the regions in between elongate to intermediate extents. The resulting curvatures of a responding pulvinus can be expressed mathematically by relating the angle of curvature (theta) to the original length (L0) and the maximal length of the lower surface (L1) and the diameter of the organ (D), using the equation, theta = (L1-L0)/D, where theta is in radians. The elongation response (S) of any individual cells within the pulvinus can be expressed by the equation, S = 0.5 - r cos theta, where r is the radius of the pulvinus and theta is in degrees. Microscopic measurement of cell lengths in different regions of the pulvinus supports the mathematical predictions. Indirect support is also obtained from the use of colchicine, coumarin, dichlorobenzonitrile (DCBN) and isopropyl N-chlorophenyl carbamate which exaggerate the inherent asymmetry during gravitropic response. Coumarin and DCBN also induce thickenings in the radial walls which appear first in the statenchyma, and later, in cells located towards the outer periphery of the pulvinus. The distribution patterns of these thickenings suggest that the asymmetric growth response of the pulvinus may be due to a differential and radial, centrifugal transport of growth promotors from the central statenchyma region.

Avena↗
PubMed1988

Competency for graviresponse in the leaf-sheath pulvinus of Avena sativa: onset to loss.

The development of the leaf-sheath pulvinus of oat (Avena sativa L. cv. Victory) was studied in terms of its competency to respond to gravistimulation. Stages of onset of competency, maximum competency and loss of competency were identified, using the length of the supertending internode as a developmental marker. During the early phases in the onset of competency, the latency period between stimulus and graviresponse decreased and the steady state response rate increased significantly. When fully competent, the latency period remained constant as the plant continued to develop, suggesting that the latency period is relatively insensitive to quantitative changes (e.g., in carbohydrate or nutrient availability) at the cell level within the plant. In contrast, the response rate was found to increase with plant development, indicating that graviresponse rate is more strongly influenced by quantitative cellular changes. The total possible graviresponse of a single oat pulvinus was confirmed to be significantly less than the original presentation angle. This was shown to not result from a loss of competency, since the graviresponse could be reinitiated by increasing the presentation angle. As a result of the low overall graviresponse of individual pulvini, two or more pulvini are required to bring the plant apex to the vertical. This was determined to occur though the sequential, rather than simultaneous, action of successive pulvini, since a given pulvinus lost competency to gravirespond shortly after the next pulvinus became fully competent.

Avena↗
PubMed1993

Kinetic induction of oat shoot pulvinus invertase mRNA by gravistimulation and partial cDNA cloning by the polymerase chain reaction.

An asymmetric (top vs. bottom halves of pulvini) induction of invertase mRNA by gravistimulation was analyzed in oat shoot pulvini. Total RNA and poly(A)+ RNA, isolated from oat pulvini, and two oligonucleotide primers, corresponding to two conserved amino acid sequences (NDPNG and WECPD) found in invertase from other species, were used for the polymerase chain reaction (PCR). A partial length cDNA (550 bp) was obtained and characterized. A 62% nucleotide sequence homology and 58% deduced amino acid sequence homology, as compared to beta-fructosidase of carrot cell wall, was found. Northern blot analysis showed that there was an obviously transient induction of invertase mRNA by gravistimulation in the oat pulvinus system. The mRNA was rapidly induced to a maximum level at 1 h after gravistimulation treatment and gradually decreased afterwards. The mRNA level in the bottom half of the oat pulvinus was significantly higher than that in the top half of the pulvinus tissue. The kinetic induction of invertase mRNA was consistent with the transient accumulation of invertase activity during the graviresponse of the pulvinus. This indicates that the expression of the invertase gene(s) could be regulated by gravistimulation at the transcriptional level. Southern blot analysis showed that there were two to three genomic DNA fragments which hybridized with the partial-length invertase cDNA.

Amino Acid Sequence↗
PubMed1991

Dynamics of auxin movement in the gravistimulated leaf-sheath pulvinus of oat (Avena sativa).

The role of auxin redistribution in the graviresponse of the leaf-sheath pulvinus of oat (Avena sativa L.) was assessed using 3H-indole-3-acetic acid (3H-IAA) preloaded into isolated pulvini. When pulvini were totally isolated from subtending nodal tissue as well as leaf-sheath and internode, gravistimulation failed to induce an asymmetric growth response. Presence of either the nodal tissue or the internode/leaf-sheath tissue was sufficient to restore a normal graviresponse. Gravistimulation of totally isolated pulvini inhibited basipetal export of label (i.e., 3H-IAA) without generating any asymmetry of label within the pulvinus. In contrast, gravistimulation of pulvini with nodes intact generated an asymmetric distribution of label (initiation by 1 h; final ratio, lower/upper = 1.5) as well as the upward bending response. The kinetics of formation of the asymmetry of label paralleled the kinetics of initiation of the asymmetric growth response. The addition of 0.1 M sucrose to all agar blocks shortened both the time to initiation of label redistribution and the time to initial upward bending. However, sucrose did not change the final magnitude of label asymmetry although it increased the final steady state bending rate four fold. The inhibitors of polar auxin transport N-1-naphthylphthalamaic acid (NPA), 2,3,5-triiodobenzoic acid (TIBA), morphactin, naringenin, kaempferol and myricetin all significantly decreased the bending response of oat pulvini, but this inhibition was less than 50%. In contrast, TIBA and naringenin (each at 100 micromoles), effectively eliminated the redistribution of label, but did not eliminate the bending response. These results indicate that the active basipetal export of auxin is inhibited by gravistimulation of the oat pulvinus, while active lateral transport is induced. It is concluded that, while lateral transport of auxin occurs following gravistimulation, it is not necessary for a graviresponse. Other processes, such as localized changes in tissue responsiveness or the conversion of conjugated hormone to free (active) hormone, may suffice to drive the graviresponse.

Avena↗
PubMed1989

Localization and pattern of graviresponse across the pulvinus of barley Hordeum vulgare.

Pulvini of excised stem segments from barley (Hordeum vulgare cv Larker') were pretreated with 1 millimolar coumarin before gravistimulation to reduce longitudinal cell expansion and exaggerate radial cell enlargement. The cellular localization and pattern of graviresponse across individual pulvini were then evaluated by cutting the organ in cross-section, photographing the cross-section, and then measuring pulvinus thickness and the radial width of cortical and epidermal cells in enlargements of the photomicrographs. With respect to orientation during gravistimulation, we designated the uppermost point of the cross-section 0 degrees and the lowermost point 180 degrees. A gravity-induced increase in pulvinus thickness was observable within 40 degrees of the vertical in coumarin-treated pulvini. In upper halves of coumarin-treated gravistimulated pulvini, cells in the inner cortex and inner epidermis had increased radial widths, relative to untreated gravistimulated pulvini. In lower halves of coumarin-treated pulvini, cells in the central and outer cortex and in the outer epidermis showed the greatest increase in radial width. Cells comprising the vascular bundles also increased in radial width, with this pattern following that of the central cortex. These results indicate (a) that all cell types are capable of showing a graviresponse, (b) that the graviresponse occurs in both the top and the bottom of the responding organ, and (c) that the magnitude of the response increases approximately linearly from the uppermost point to the lowermost. These results are also consistent with models of gravitropism that link the pattern and magnitude of the graviresponse to graviperception via statolith sedimentation.

Cell Division↗
PubMed1977

Phytochrome and Circadian Clocks in Samanea: Rhythmic Redistribution of Potassium and Chloride within the Pulvinus during Long Dark Periods.

Previous investigations with the electron microprobe reveal that the movements of Samanea leaflets are correlated with massive redistribution of K within the pulvinus. Evidence is now presented that Cl moves with K, whether plants are in white light or darkness, whether or not the amplitude of free running oscillations has damped, and whether or not the rhythm has been rephased by phytochrome photoconversion. The mid-extensor to mid-flexor ratio of K + Cl is correlated with leaflet angle under all conditions. Total Cl in both inner cortex and motor region is approximately 0.6 as high as K. The stoichiometry between Cl and the migratory fraction of K is close to, but not precisely 1:1 in all regions of the pulvinus, suggesting that other ions or systems may also be involved in the balancing of electrical charges.

Journal Article↗
PubMed1992

The role of calcium in growth induced by indole-3-acetic acid and gravity in the leaf-sheath pulvinus of oat (Avena sativa).

Leaf-sheath pulvini of excised segments from oat (Avena sativa L.) were induced to grow by treatment with 10 micromoles indole-3-acetic acid (IAA), gravistimulation, or both, and the effects of calcium, EGTA, and calcium channel blockers on growth were evaluated. Unilaterally applied calcium (10 mM CaCl2) significantly inhibited IAA-induced growth in upright pulvini but had no effect on growth induced by either gravity or gravity plus IAA. Calcium alone had no effect on upright pulvini. The calcium chelator EGTA alone (10 mM) stimulated growth in upright pulvini. However, EGTA had no effect on either IAA- or gravity-induced growth but slightly diminished growth in IAA-treated gravistimulated pulvini. The calcium channel blockers lanthanum chloride (25 mM), verapamil (2.5 mM), and nifedipine (2.5 mM) greatly inhibited growth as induced by IAA (> or = 50% inhibition) or IAA plus gravity (20% inhibition) but had no effect on gravistimulated pulvini. Combinations of channel blockers were similar in effect on IAA action as individual blockers. Since neither calcium ions nor EGTA significantly affected the graviresponse of pulvini, we conclude that apoplastic calcium is unimportant in leaf-sheath pulvinus gravitropism. The observation that calcium ions and calcium channel blockers inhibit IAA-induced growth, but have no effect on gravistimulated pulvini, further supports previous observations that gravistimulation alters the responsiveness of pulvini to IAA.

Avena↗
PubMed1990

Cell wall and enzyme changes during the graviresponse of the leaf-sheath pulvinus of oat (Avena sativa).

The graviresponse of the leaf-sheath pulvinus of oat (Avena sativa) involves an asymmetric growth response accompanied by several asymmetric processes, including degradation of starch and cell wall synthesis. To understand further the cellular and biochemical events associated with the graviresponse, changes in cell walls and their constituents and the activities of related enzymes were investigated in excised pulvini. Asymmetric increases in dry weight with relatively symmetric increases in wall weight accompanied the graviresponse. Starch degradation could not account for increases in wall weight. However, a strong asymmetry in invertase activity indicated that hydrolysis of exogenous sucrose could contribute significantly to the increases in wall and dry weights. Most cell wall components increased proportionately during the graviresponse. However, beta-D-glucan did not increase symmetrically, but rather increased in proportion in lower halves of gravistimulated pulvini. This change resulted from an increase in glucan synthase activity in lower halves. The asymmetry of beta-D-glucan content arose too slowly to account for initiation of the graviresponse. A similar pattern in change in wall extensibility was also observed. Since beta-D-glucan was the only wall component to change, it is hypothesized that this change is the basis for the change in wall extensibility. Since wall extensibility changed too slowly to account for growth initiation, it is postulated that asymmetric changes in osmotic solutes act as the driving factor for growth promotion in the graviresponse, while wall extensibility acts as a limiting factor during growth.

Avena↗
PubMed1985

Effects of Ethephon, 1-Aminocyclopropane-1-carboxylic Acid, and Inhibitors of Ethylene Synthesis on the Gravitropically Induced Movement of Mimosa pudica Pulvinus.

Primary pulvini of Mimosa pudica L. displaced from their position display gravitropic movements beginning about 15 minutes after their reorientation. Ethephon, an ethylene-releasing compound, and 1-aminocyclopropane-1-carboxylic acid, an intermediate in ethylene biosynthesis, enhance these movements at a concentration as low as 10 nanomolar. Inhibitors of ethylene synthesis (l-alpha-(2-aminoethoxyvinyl)glycine, (aminooxy)acetic acid, and Co(2+)) reduce the amplitude of the movements. The promotive action of 1-aminocyclopropane-1-carboxylic acid is abolished by l-alpha-(2-aminoethoxyvinyl)glycine. These results permit one to conclude that ethylene may modify the curvature movement but not the initiation of the gravitropic reaction. With reference to the pulvinus functioning based on turgor variations and ion migrations inside the organ, namely K(+) acting as the osmoticum, the data suggest that ethylene may act by increasing the membrane permeability to water and/or by altering an ion pump.

Journal Article↗
PubMed1998

Growth dynamics and cytoskeleton organization during stem maturation and gravity-induced stem bending in Zea mays L.

Characterization of gravitropic bending in the maize stem pulvinus, a tissue that functions specifically in gravity responses, demonstrates that the pulvinus is an ideal system for studying gravitropism. Gravistimulation during the second of three developmental phases of the pulvinus induces a gradient of cell elongation across the non-growing cells of the pulvinus, with the most elongation occurring on the lower side. This cell elongation is spatially and temporally separated from normal internodal cell elongation. The three characterized growth phases in the pulvinus correspond closely to a specialized developmental sequence in which structural features typical of cells not fully matured are retained while cell maturation occurs in surrounding internodal and nodal tissue. For example, the lignification of supporting tissue and rearrangement of transverse microtubules to oblique that occur in the internode when cell elongation ceases are delayed for up to 10 d in the adjacent cells of the pulvinus, and only occurs as a pulvinus loses its capacity to respond to gravistimulation. Gravistimulation does not modify this developmental sequence. Neither wall lignification nor rearrangement of transverse microtubules occurs in the rapidly elongating lower side or non-responsive upper side of the pulvinus until the pulvinus loses the capacity to bend further. Gravistimulation does, however, lead to the formation of putative pit fields within the expanding cells of the pulvinus.

Cell Wall↗
PubMed2002

Gravity-stimulated changes in auxin and invertase gene expression in maize pulvinal cells.

Maize (Zea mays) stem gravitropism involves differential elongation of cells within a highly specialized region, the stem internodal pulvinus. In the present study, we investigated factors that control gravitropic responses in this system. In the graviresponding pulvinus, hexose sugars (D-Glc and D-Fru) accumulated asymmetrically across the pulvinus. This correlated well with an asymmetric increase in acid invertase activity across the pulvinus. Northern analyses revealed asymmetric induction of one maize acid invertase gene, Ivr2, consistent with transcriptional regulation by gravistimulation. Several lines of evidence indicated that auxin redistribution, as a result of polar auxin transport, is necessary for gravity-stimulated Ivr2 transcript accumulation and differential cell elongation across the maize pulvinus. First, the auxin transport inhibitor, N-1-naphthylphthalamic acid, inhibited gravistimulated curvature and Ivr2 transcript accumulation. Second, a transient gradient of free indole-3-acetic acid (IAA) across the pulvinus was apparent shortly after initiation of gravistimulation. This temporarily free IAA gradient appears to be important for differential cell elongation and Ivr2 transcript accumulation. This is based on the observation that N-1-naphthylphthalamic acid will not inhibit gravitropic responses when applied to pulvinus tissue after the free IAA gradient peak has occurred. Third, IAA alone can stimulate Ivr2 transcript accumulation in non-gravistimulated pulvini. The gravity- and IAA-stimulated increase in Ivr2 transcripts was sensitive to the protein synthesis inhibitor, cycloheximide. Based on these results, a two-phase model describing possible relationships between gravitropic curvature, IAA redistribution, and Ivr2 expression is presented.

Gene Expression Regulation, Enzymologic↗
PubMed1999

Transient and sustained increases in inositol 1,4,5-trisphosphate precede the differential growth response in gravistimulated maize pulvini.

The internodal maize pulvinus responds to gravistimulation with differential cell elongation on the lower side. As the site of both graviperception and response, the pulvinus is an ideal system to study how organisms sense changes in orientation. We observed a transient 5-fold increase in inositol 1,4,5-trisphosphate (IP3) within 10 s of gravistimulation in the lower half of the pulvinus, indicating that the positional change was sensed immediately. Over the first 30 min, rapid IP3 fluctuations were observed between the upper and lower halves. Maize plants require a presentation time of between 2 and 4 h before the cells on the lower side of the pulvinus are committed to elongation. After 2 h of gravistimulation, the lower half consistently had higher IP3, and IP3 levels on the lower side continued to increase up to approximately 5-fold over basal levels before visible growth. As bending became visible after 8-10 h, IP3 levels returned to basal values. Additionally, phosphatidylinositol 4-phosphate 5-kinase activity in the lower pulvinus half increased transiently within 10 min of gravistimulation, suggesting that the increased IP3 production was accompanied by an up-regulation of phosphatidylinositol 4, 5-bisphosphate biosynthesis. Neither IP3 levels nor phosphatidylinositol 4-phosphate 5-kinase activity changed in pulvini halves from vertical control plants. Our data indicate the involvement of IP3 and inositol phospholipids in both short- and long-term responses to gravistimulation. As a diffusible second messenger, IP3 provides a mechanism to transmit and amplify the signal from the perceiving to the responding cells in the pulvinus, coordinating a synchronized growth response.

Cell Membrane↗
PubMed1987

How cereal grass shoots perceive and respond to gravity.

The leaf-sheath pulvinus of grasses presents a unique system for studying gravitropism, primarily because of its differences from other organs. The mature pulvinus is a discrete organ specialized for gravitropism: it is nongrowing in the absence of gravistimulation and capable of displaying a graviresponse independent of the rest of the plant. In this paper we present a model for gravitropism in pulvini based on recent findings from studies on the mechanisms of graviperception and graviresponse. According to this model, amyloplasts play an essential role in perceiving a change in the orientation of the pulvinus. The perception of this reorientation leads to the enhanced synthesis and release from conjugate of the auxin IAA, and the increased conjugation of gibberellin, on a localized basis. Because there is a graded growth promotion across the gravistimulated pulvinus, it is suggested that the observed hormonal asymmetry is actually an indication of a linear gradient of hormone concentration, as well as hormone response, across the pulvinus. It is further suggested that the linear gradient of hormone concentration may be predominantly the result of local changes in hormone level, rather than a product of hormonal movement into or across the pulvinus.

Edible Grain↗
PubMed2001

A role for inositol 1,4,5-trisphosphate in gravitropic signaling and the retention of cold-perceived gravistimulation of oat shoot pulvini.

Plants sense positional changes relative to the gravity vector. To date, the signaling processes by which the perception of a gravistimulus is linked to the initiation of differential growth are poorly defined. We have investigated the role of inositol 1,4,5-trisphosphate (InsP(3)) in the gravitropic response of oat (Avena sativa) shoot pulvini. Within 15 s of gravistimulation, InsP(3) levels increased 3-fold over vertical controls in upper and lower pulvinus halves and fluctuated in both pulvinus halves over the first minutes. Between 10 and 30 min of gravistimulation, InsP(3) levels in the lower pulvinus half increased 3-fold over the upper. Changes in InsP(3) were confined to the pulvinus and were not detected in internodal tissue, highlighting the importance of the pulvinus for both graviperception and response. Inhibition of phospholipase C blocked the long-term increase in InsP(3), and reduced gravitropic bending by 65%. Short-term changes in InsP(3) were unimpaired by the inhibitor. Gravitropic bending of oat plants is inhibited at 4 degrees C; however, the plants retain the information of a positional change and respond at room temperature. Both short- and long-term changes in InsP(3) were present at 4 degrees C. We propose a role for InsP(3) in the establishment of tissue polarity during the gravitropic response of oat pulvini. InsP(3) may be involved in the retention of cold-perceived gravistimulation by providing positional information in the pulvini prior to the redistribution of auxin.

Avena↗
PubMed1978

[Mimosa pudica adenosine triphosphatase].

The morphological structure (pulvinus P1, P2 and P3) directly involved in the seismonastic movements of the Mimosa pudica leaf have been used to isolate: 1) "soluble" ATPase, loosely bound to pulvinus structures; 2) Ca, Mg-dependent ATPase, which is tightly bound to pulvinus structures and is extracted by a saline solution of high ionic strength, used to isolate actomyosin from muscles and non-muscle motile cells; 3) ATPase bound to the pulvinus membrane structures, which is solubilized by the detergents, e. g. Triton X-100 and Tween-80, and is similar to membrane ATPase. Physico-chemical and kinetic studies of the APSases have shown that Ca,Mg-ATPase is similar to the ATPases from muscle and non-muscle motile cells in a number of characteristics, e. g. solubility in saline solution of high ionic strength, aggregability in a solution of lower ionic strength, activation by bivalent metal ions, pH-optimum, specificity for substrates, etc. The protein composition of the ATPases has been determined by gel-electrophoresis in polyacrylamide gel. The molecular weight of purified Ca,Mg-ATPase from Mimosa pudica pulvinus is found to be 139 000. The role of ATPases in seismonastic movements of the Mimosa pudica leaf is discussed.

Adenosine Triphosphatases↗
PubMed1988

Altered growth response to exogenous auxin and gibberellic acid by gravistimulation in pulvini of Avena sativa.

Pulvini of excised segments from oats (Avena sativa L. cv Victory) were treated unilaterally with indoleacetic acid (IAA) or gibberellic acid (GA3) with or without gravistimulation to assess the effect of gravistimulation on hormone action. Optimum pulvinus elongation growth (millimeters) and segment curvature (degrees) over 24 hours were produced by 100 micromolar IAA in vertical segments. The curvature response to IAA at levels greater than 100 micromolar, applied to the lower sides of gravistimulated (90 degrees) pulvini, was significantly less than the response to identical levels in vertical segments. Furthermore, the bending response of pulvini to 100 micromolar IAA did not vary significantly over a range of presentation angles between 0 and 90 degrees. In contrast, the response to IAA at levels less than 10 micromolar, with gravistimulation, was approximately the sum of the responses to gravistimulation alone and to IAA without gravistimulation. This was observed over a range of presentation angles. Also, GA3 (0.3-30 micromolar) applied to the lower sides of horizontal segments significantly enhanced pulvinus growth and segment curvature, although exogenous GA3 over a range of concentrations had no effect on pulvinus elongation growth or segment curvature in vertical segments. The response to GA3 (10 micromolar) plus IAA (1.0 or 100 micromolar) was additive for either vertical or horizontal segments. These results indicate that gravistimulation produces changes in pulvinus responsiveness to both IAA and GA3 and that the changes are unique for each growth regulator. It is suggested that the changes in responsiveness may result from processes at the cellular level other than changes in hormonal sensitivity.

Avena↗
PubMed2001

Transient dissociation of polyribosomes and concurrent recruitment of calreticulin and calmodulin transcripts in gravistimulated maize pulvini.

The dynamics of polyribosome abundance were studied in gravistimulated maize (Zea mays) stem pulvini. During the initial 15 min of gravistimulation, the amount of large polyribosomes transiently decreased. The transient decrease in polyribosome levels was accompanied by a transient decrease in polyribosome-associated mRNA. After 30 min of gravistimulation, the levels of polyribosomes and the amount of polyribosome-associated mRNA gradually increased over 24 h up to 3- to 4-fold of the initial value. Within 15 min of gravistimulation, total levels of transcripts coding for calreticulin and calmodulin were elevated 5-fold in maize pulvinus total RNA. Transcripts coding for calreticulin and calmodulin were recruited into polyribosomes within 15 min of gravistimulation. Over 4 h of gravistimulation, a gradual increase in the association of calreticulin and calmodulin transcripts with polyribosomes was seen predominantly in the lower one-half of the maize pulvinus; the association of transcripts for vacuolar invertase with polyribosomes did not change over this period. Our results suggest that within 15 min of gravistimulation, the translation of the majority of transcripts associated with polyribosomes decreased, resembling a general stress response. Recruitment of calreticulin and calmodulin transcripts into polyribosomes occurred predominantly in the lower pulvinus one-half during the first 4 h when the presentation time for gravistimulation in the maize pulvinus is not yet complete.

Biological Transport↗