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1.
We have earlier published observations showing that endogenous alterations in growth rate during gravitropism in maize roots (Zea mays L.) are unaffected by the orientation of cuts which remove epidermal and cortical tissue in the growing zone (Björkman and Cleland, 1988, Planta 176, 513–518). We concluded that the epidermis and cortex are not essential for transporting a growth-regulating signal in gravitropism or straight growth, nor for regulating the rate of tissue expansion. This conclusion has been challenged by Yang et al. (1990, Planta 180, 530–536), who contend that a shallow girdle around the entire perimeter of the root blocks gravitropic curvature and that this inhibition is the result of a requirement for epidermal cells to transport the growth-regulating signal. In this paper we demonstrate that the entire epidermis can be removed without blocking gravitropic curvature and show that the position of narrow girdles does not affect the location of curvature. We therefore conclude that the epidermis is not required for transport of a growth-regulating substance from the root cap to the growing zone, nor does it regulate the growth rate of the elongating zone of roots.  相似文献   

2.
Gravitropism in roots has been proposed to depend on a downward redistribution of calcium across the root cap. However, because of the many calcium-binding sites in the apoplast, redistribution might not result in a physiologically effective change in the apoplasmic calcium activity. To test whether there is such a change, we measured the effect of gravistimulation on the calcium activity of statocyte cell walls with calcium-specific microelectrodes. Such a measurement must be made on a tissue with gravity sensing cells at the surface. To obtain such a tissue, decapped maize roots (Zea mays L. cv. Golden Cross Bantam) were grown for 31 h to regenerate gravitropic sensitivity, but not root caps. The calcium activity in the apoplasm surrounding the gravity-sensing cells could then be measured. The initial pCa was 2.60 ± 0.28 (approx 2.5 mM). The calcium activity on the upper side of the root tip remained constant for 10 min after gravistimulation, then decreased 1.7-fold. On the lower side, after a similar lag the calcium activity increased 1.6-fold. Control roots, which were decapped but measured before recovering gravisensitivity (19 h), showed no change in calcium activity. To test whether this gradient is necessary for gravitropic curvature, we eliminated the calcium activity gradient during gravitropism by applying a mobile calcium-binding site (di-nitro-BAPTA; 1,2-bis(2-amino-5-nitro-phenoxy)ethane-N,N,N,N-tetraacetic acid) to the root cap; this treatment eliminated gravicurvature. A calcium gradient may be formed by proton-induced calcium desorption if there is a proton gradient. Preventing the formation of apoplastic pH gradients, using 10 and 50 mM 2-(N-morpholino)ethanesulfonic acid (Mes) buffer or 10 mM fusicoccin to stimulate proton excretion maximally, did not inhibit curvature; therefore the calcium gradient is not a secondary effect of a proton gradient. We have found a distinct and rapid differential in the apoplasmic calcium activity between the upper and lower sides of gravistimulated maize root tips which is necessary for gravitropism.Abbreviations BAPTA 1,2-bis(2-aminophenoxy)ethane-N,N,N,N-tetraacetic acid - FC fusicoccin - Mes 2-(N-morpholino)ethanesulfonic acid The authors thank Phyllis Woolwine for drawing Fig. 1, Dr. Sarbjit Virk for assistance with total calcium measurements, Dr. Paul Sampson for statistical advice, and Michael Newton for developing the EM algorithm to analyze the time-series data. This work was supported by NASA grant NAGW-1394 and by a NASA Research Associateship to T.B. through NASA grant NAGW-70.  相似文献   

3.
Sailer H  Nick P  Schafer E 《Planta》1990,180(3):378-382
Gravitropic stimulation of maize (Zea mays L.) seedlings resulted in a continuous curvature of the coleoptiles in a direction opposing the vector of gravity when the seedlings were rotated on a horizontal clinostat. The orientation of this response, however, was reversed when the gravitropic stimulation was preceeded by symmetric preirradiation with blue light (12.7 mol photons·m–2). The fluence-response curve of this blue light exhibited a lower threshold at 0.5 mol·m–2, and could be separated into two parts: fluences exceeding 5 mol·m–2 reversed the direction of the gravitropic response, whereas for a range between the threshold and 4 mol·m–2 a split population was obtained. In all cases a very strong curvature resulted either in the direction of gravity or in the opposite orientation. A minor fraction of seedlings, however, curved towards the caryopsis. Furthermore, the capacity of blue light to reverse the direction of the gravitropic response disappeared with the duration of gravitropic stimulation and it depended on the delay time between both stimulations. Thistonic blue-light influence appears to be transient, which is in contrast to the stability observed fortropistic blue-light effects.This work was supported by the Deutsche Forschungsgemeinschaft.  相似文献   

4.
Primary roots of maize (Zea mays L.) and pea (Pisum sativum L.) exhibit strong positive gravitropism. In both species, gravistimulation induces polar movement of calcium across the root tip from the upper side to the lower side. Roots of onion (Allium cepa L.) are not responsive to gravity and gravistimulation induces little or no polar movement of calcium across the root tip. Treatment of maize or pea roots with inhibitors of auxin transport (morphactin, naphthylphthalamic acid, 2,3,5-triiodobenzoic acid) prevents both gravitropism and gravity-induced polar movement of calcium across the root tip. The results indicate that calcium movement and auxin movement are closely linked in roots and that gravity-induced redistribution of calcium across the root cap may play an important role in the development of gravitropic curvature.Abbreviations 9-HFCA 9-hydroxyfluorenecarboxylic acid - NPA naphthylphthalamic acid - TIBA 2,3,5-triiodobenzoic acid - IAA indole-3-acetic acid  相似文献   

5.
Björkman T  Cleland RE 《Planta》1988,176(4):513-518
In order to determine the role of the epidermis and cortex in gravitropic curvature of seedling roots of maize (Zea mays L. cv. Merit), the cortex on the two opposite flanks was removed from the meristem through the growing zone; gravitropic curvature was measured with the roots oriented horizontally with the cut flanks either on the upper and lower side, or on the lateral sides as a wound control. Curvature was slower in both these treatments (53° in 5 h) than in intact roots (82°), but there was no difference between the two orientations in extent and rate of curvature, nor in the latent time, showing that epidermis and cortex were not the site of action of the growth-regulating signal. The amount of cortex removed made no difference in the extent of curvature. Curvature was eliminated when the endodermis was damaged, raising the possibility that the endodermis or the stele-cortex interface controls gravitropic curvature in roots. The elongation rate of roots from which just the epidermis had been peeled was reduced by 0.01 mM auxin (indole-3-acetic acid) from 0.42 to 0.27 mm h-1, contradicting the hypothesis that only the epidermis responds to changes in auxin activity during gravistimulation. These observations indicate that gravitropic curvature in maize roots is not driven by differential cortical cell enlargement, and that movement of growth regulator(s) from the tip to the elongating zone is unlikely to occur in the cortex.Abbreviations df degrees of freedom - IAA indole-3-acetic acid  相似文献   

6.
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.  相似文献   

7.
Immunofluorescence labeling of cortical microtubules (MTs) was used to investigate the relationship between MT arrangement and changes in growth rate of the upper and lower sides of horizontally placed roots of maize (Zea mays L. cv. Merit). Cap cells and cells of the elongation zone of roots grown vertically in light or darkness showed MT arrangements that were transverse (perpendicular) to the growth direction. Microtubules of cells basal to the elongation zone typically showed oblique orientation. Two hours after horizontal reorientation, cap cells of gravicompetent, light-grown and curving roots contained MTs parallel to the gravity vector. The MT arrangement on the upper side of the elongation zone remained transverse but the MTs of the outer four to five layers of cortical cells along the lower side of the elongation zone showed reorientation parallel to the axis of the root. The MTs of the lower epidermis retained their transverse orientation. Dark-grown roots did not curve and did not show reorientation of MTs in cells of the root cap or elongation zone. The data indicate that MT depolymerization and reorientation is correlated with reduction in growth rate, and that MT reorientation is one of the steps of growth control of graviresponding roots.Abbreviations MT microtubule - QC quiescent center This work was supported by National Science Foundation grant IBN-9118094.  相似文献   

8.
Ishikawa H  Hasenstein KH  Evans ML 《Planta》1991,183(3):381-390
We used a video digitizer system to measure surface extension and curvature in gravistimulated primary roots of maize (Zea mays L.). Downward curvature began about 25 +/- 7 min after gravistimulation and resulted from a combination of enhanced growth along the upper surface and reduced growth along the lower surface relative to growth in vertically oriented controls. The roots curved at a rate of 1.4 +/- 0.5 degrees min-1 but the pattern of curvature varied somewhat. In about 35% of the samples the roots curved steadily downward and the rate of curvature slowed as the root neared 90 degrees. A final angle of about 90 degrees was reached 110 +/- 35 min after the start of gravistimulation. In about 65% of the samples there was a period of backward curvature (partial reversal of curvature) during the response. In some cases (about 15% of those showing a period of reverse bending) this period of backward curvature occurred before the root reached 90 degrees. Following transient backward curvature, downward curvature resumed and the root approached a final angle of about 90 degrees. In about 65% of the roots showing a period of reverse curvature, the roots curved steadily past the vertical, reaching maximum curvature about 205 +/- 65 min after gravistimulation. The direction of curvature then reversed back toward the vertical. After one or two oscillations about the vertical the roots obtained a vertical orientation and the distribution of growth within the root tip became the same as that prior to gravistimulation. The period of transient backward curvature coincided with and was evidently caused by enhancement of growth along the concave and inhibition of growth along the convex side of the curve, a pattern opposite to that prevailing in the earlier stages of downward curvature. There were periods during the gravitropic response when the normally unimodal growth-rate distribution within the elongation zone became bimodal with two peaks of rapid elongation separated by a region of reduced elongation rate. This occurred at different times on the convex and concave sides of the graviresponding root. During the period of steady downward curvature the elongation zone along the convex side extended farther toward the tip than in the vertical control. During the period of reduced rate of curvature, the zone of elongation extended farther toward the tip along the concave side of the root. The data show that the gravitropic response pattern varies with time and involves changes in localized elongation rates as well as changes in the length and position of the elongation zone. Models of root gravitropic curvature based on simple unimodal inhibition of growth along the lower side cannot account for these complex growth patterns.  相似文献   

9.
The occurrence and distribution of abscisic acid (ABA), xanthoxin (Xa) and the carotenoid violaxanthin (Va) were investigated in root tips of maize (Zea mays L. cv. Merit). In roots grown in the dark, Va and ABA were present in relatively high amounts in the root cap and in low amounts in the adjacent terminal 1.5 mm of the root. Xanthoxin was present in equal concentrations in both regions. In roots exposed to light, the ABA distribution was reversed, with relatively low levels in the root cap and high levels in the adjacent 1.5-mm segment. Light also caused a decrease in Va in both regions of the root and an increase in Xa, especially in the cap. In the maize cultivar used for this work, light is necessary for gravitropic curving. This response occurs within the same time frame as the light-induced ABA redistribution as well as the changes in the levels of Va and Xa. These data are consistent with a role for ABA in root gravitropism and support the proposal that Xa may arise from the turnover of Va.Abbreviations ABA abscisic acid - GC gas chromatography - HPLC high-performance liquid chromatography - GC-MS gas chromatography-mass spectroscopy - Va violaxanthin - Xa xanthoxin  相似文献   

10.
Membranes isolated from pea buds contain protein-kinase activity which is greatly activated by low concentrations of calcium ions. This paper describes a simple purification of this enzyme with a novel means of detecting enzyme activity by Western blotting. The purified enzyme appears to autophosphorylate primarily on serine residues, is activated by bovine calmodulin and additional evidence from phase partitioning indicate most of this enzyme to be located in the plasma membrane.Abbreviations PAGE polyacrylamide-gel electrophoresis - SDS sodium dodecyl sulphate  相似文献   

11.
12.
Randy Moore  James D. Smith 《Planta》1985,164(1):126-128
The abscisic-acid (ABA) content of roots of the carotenoid-deficient w-3, vp-5, and vp-7 mutants of Z. mays was analyzed using gas chromatography-mass spectrometry with an analysis sensitivity of 6 ng ABA g–1 fresh weight (FW). Roots of normal seedlings of the same lines were characterized by the following amounts of ABA (as ng ABA g–1 FW,±standard deviation): w-3, 279±43; vp-5, 237±26; vp-7, 338±61. We did not detect any ABA in roots of any of the mutants. Thus, the lack of carotenoids in these mutants correlated positively with the apparent absence of ABA. Primary roots of normal and mutant seedlings were positively gravitropic, with no significant differences in the curvatures of roots of normal as compared with mutant seedlings. These results indicate that ABA 1) is synthesized in maize roots via the carotenoid pathway, and 2) is not necesary for positive gravitropism by primary roots of Z. mays.Abbreviation ABA abscisic acid  相似文献   

13.
Nick P  Schafer E 《Planta》1988,173(2):213-220
The influence of gravitropic stimulation upon blue-light-induced first positive phototropism for stimulations in the same (light source and center of gravity opposite to each other) and in opposing directions was investigated in maize cole-optiles by measuring fluence-response patterns. As a result of gravitropic counterstimulation, phototropic bending was transient with maximum curvature occurring 100 min after stimulation. On a horizontal clinostat, however, the seedlings curved for 20 h. Gravistimulation in the opposite direction acted additively upon blue-light curvature. Gravistimulation in the same direction as phototropic stimulation produced a complex behaviour deviating from simple additivity. This pattern can be explained by a gravitropically mediated sensitization of the phototropic reaction, an optimal dependence of differential growth on the sum of photo-and gravistimulation, and blue-light-induced inhibition of gravitropic curvature at high fluences. These findings indicate that several steps of photo-and gravitransduction are separate. Preirradiation with red light desensitized the system independently of applied gravity-treatment, indicating that the site of red-light interaction is common to both transduction chains.Abbreviations BL blue light - G+ stimulation by light and gravity in the same direction (i.e. light source and center of gravity opposite to each other) - G- stimulation by light and gravity in opposing directions  相似文献   

14.
Chimeric Ca2+/calmodulin-dependent protein kinase (CCaMK) was cloned from developing anthers of lily (Lilium longiflorum Thumb. cv. Nellie White) and tobacco (Nicotiana tabacum L. cv. Xanthi). Previous biochemical characterization and structure/function studies had revealed that CCaMK has dual modes of regulation by Ca2+ and Ca2+/calmodulin. The unique structural features of CCaMK include a catalytic domain, a calmodulin-binding domain, and a neural visinin-like Ca2+-binding domain. The existence of these three features in a single polypeptide distinguishes it from other kinases. Western analysis revealed that CCaMK is expressed in a stage-specific manner in developing anthers. Expression of CCaMK was first detected in pollen mother cells and continued to increase, reaching a peak around the tetrad stage of meiosis. Following microsporogenesis, CCaMK expression rapidly decreased and at later stages of microspore development, no expression was detected. A tobacco genomic clone of CCaMK was isolated and transgenic tobacco plants were produced carrying the CCaMK promoter fused to the β-glucuronidase reporter gene. Both CCaMK mRNA and protein were detected in the pollen sac and their localizations were restricted to the pollen mother cells and tapetal cells. Consistent results showing a stage-specific expression pattern were obtained by β-glucuronidase analysis, in-situ hybridization and immunolocalization. The stage- and tissue-specific appearance of CCaMK in anthers suggests that it could play a role in sensing transient changes in free Ca2+ concentration in target cells, thereby controlling developmental events in the anther. Received: 29 January 1999 / Accepted: 12 February 1999  相似文献   

15.
Roots of Zea mays were maintained in a vertical orhorizontal position and the local elongation rate and H+ fluxes were measured using Sephadex beads containing a pH indicator. When the roots were kept horizontally, the growth of the lower side was strongly inhibited and that of the upper side slightly stimulated as compared with vertical roots. The H+ extrusion, which was greatest in the elongation zone, was strongly inhibited on the lower side and slightly stimulated on the upper side as compared with vertical roots.  相似文献   

16.
Membranes from the buds of Pisum sativum L. contain a protein kinase which is activated 5- to 15-fold by micromolar levels of calcium. Best calcium activations were found with light-membrane fractions, and on density gradients these band at a similar position to the plasma membrane. Other heavier membranes, however, also contain a calcium-dependent protein kinase. The activity of the calcium-dependent protein kinase is inhibited by added phospholipids and phospholipase, in contrast to protein-kinase C. Calcium-dependent protein-kinase activity can be inhibited by 40% by low concentrations of the calmodulin inhibitor, trifluoperazine, but inhibitions are detected only after prior incubation of the membranes for some hours in ethylene glycol-bis-(-aminoethyl ether)-N,N,N,N-tetraacetic acid. Substantial calcium-dependent protein-kinase activity remains uninhibited by trifluoperazine indicating that there may be calmodulin-dependent and calmodulin-independent, but calcium-activated, protein kinases in pea membranes. The calcium-activated protein kinase seems to be intrinsically bound to membranes and only slight or partial solubilisation is obtained by the detergents nonidet P-40, (3-[(3-cholamidopropyl)-dimethyl-ammonio]-1-propanesulfonate or octyl glucose. Better solubilisation is obtained by acetone treatment. There is some retention of calcium activation after partial solubilisation. A calcium-independent protein kinase has also been detected in membrane preparations; it has a substrate specificity different from that the calcium-dependent enzyme. Our results indicate, therefore, that there may be at least three protein kinases attached to pea shoot membranes.Abbreviations EGTA ethylene glycol-bis(-aminoethyl ether)-N,N,N,N-tetraacetic acid - Hepes 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid - TFP trifluoperazine  相似文献   

17.
Nick P  Sailer H  Schafer E 《Planta》1990,181(3):385-392
The interaction of photo- and gravitropic stimulation was studied by analysing the curvature of maize (Zea mays L.) coleoptiles subjected to rotation on horizontal clinostats. Gravitropic curvature in different directions with respect to the stimulation plane was found to be transient. This instability was caused by an increasing deviation of response direction from the stimulation plane towards the caryopsis. The bending angle as such, however, increased steadily. This reorientation of the gravitropic response towards the caryopsis is thought to be caused by the clinostat-elicited nastic curvature found in maize coleoptiles. In contrast, the response to phototropic stimulation was stable, in both, orientation and curving. Although stimulation by gravity was not capable of inducing a stable tropistic response, it could inhibit the response to opposing phototropic stimulation, if the counterstimulation was given more than 90 min after the onset of gravistimulation. For shorter time intervals the influence of the phototropic stimulus obscured the response to the first, gravitropic stimulation. For time intervals exceeding 90 min, however, the phototropic effects disappeared and the response was identical to that for gravity stimulation alone. This gravity-induced inhibition of the phototropic response was confined to the plane of gravity stimulation, because a phototropic stimulation in the perpendicular direction remained unaffected, irrespective of the time interval between the stimulations. This concerned not only the stable phototropic curving, but also the capacity of the phototropic induction to elicit a stable directional memory as described earlier (P. Nick and F. Schäfer, 1988b, Planta 175, 380–388). This was tested by a second bluelight pulse opposing the first. It is suggested that gravity, too, can induce a directional memory differing from the blue-light elicited memory. The mechanisms mediating gravi- and phototropic directional memories are thought to branch off the respective tropistic signal chains at a stage where photo- and gravitropic transduction are still separate.This work was supported by the Deutsche Forschungsgemeinschaft and a grant of the Studienstiftung des Deutschen Volkes to P. Nick.  相似文献   

18.
N. H. Battey  M. A. Venis 《Planta》1988,176(1):91-97
Crude Ca2+-activated protein kinase from membranes of apple (Malus domestica L. Borkh., Cox's Orange Pippin) fruit can be partially purified to yield a Ca2+-dependent protein kinase whose activity is apparently not regulated by calmodulin. The autophosphorylating catalytic subunit of this protein kinase shows a Ca2+-dependent mobility shift of approx. 10 kilodaltons (kDa) on sodium dodecyl sulphate-polyacrylamide gel electrophoresis; in the absence of added Ca2+ or ethylene glycol-bis(-aminoethyl ether)-N,N,N,N-tetraacetic acid (EGTA) its apparent molecular mass is approx. 50 kDa. The Ca2+-dependent protein kinase is inhibited by the calmodulin antagonists N-(6-aminohexyl)-5-chloro-1-naphthalenesulphonamide and trifluoperazine with IC50 values of approx. 45 M and 15 M, respectively. These similarities between the protein kinase and calmodulin indicate that the kinase may be a calmodulin-like protein.Abbreviations DEAE diethylaminoethyl - EGTA ethylene glycol-bis(-aminoethyl ether)-N,N,N,N-tetraacetic acid - Hepes 4-(-2-hydroxyethyl)-1-piperazineethanesulphonic acid - kDa kilodalton - PAGE polyacrylamide gel electrophoresis - SDS sodium dodecyl sulphate - W7 N-(6-aminohexyl)-5-chloro-1-naphthalenesulphonamide - W5 N-(6-aminohexyl)-naphthalenesulphonamide  相似文献   

19.
Horizontal primary roots of Zea mays L. were photographed during the course of their gravireaction and during a preceding growth period in the vertical orientation. The displacement, by root elongation, of marker particles on the root surface was recorded. The particle-displacement rates were used to estimate the distribution of elemental elongation rates along opposite sides of the growing root apex. In the temperature range 21–25°C there was a stimulation of local elongation rates along the upper side of a gravireacting root and a reduction (and sometimes a cessation) of elongation along the lower side. Elemental elongation rates have been related to the development of root curvature, and the magnitude of the differential growth between upper and lower sides required for a particular rate of bending has also been estimated. The results complement, and are compatible with, findings relating to the distribution of certain endogenous growth regulators believed to participate in the gravireaction.Abbreviation RELEL relative elemental rate of elongation  相似文献   

20.
Plasma membranes have been purified from roots of maize (Zea mays L.) using a two-phase aqueous polymer system, dextran-polyethylene glycol. The plant material was homogenized in the presence of a mixture of natural protease inhibitors from potato (Solanum tuberosum L.); these inhibitors have been shown to be more effective than phenylmethylsulfonyl fluoride in suppressing the endogenous proteases in maize roots. Inhibition of proteolysis in the homogenization medium markedly increased (about tenfold) the number of lowaffinity binding sites for fusicoccin (FC). In addition, storage of plasma membranes at −20° C decreased both the number of the low-affinity sites and their dissociation constant (KD); this effect was in all probability caused by lipid peroxidation. The presence of EDTA throughout isolation and storage of the plasma membranes stabilized the parameters of FC binding to the membranes. The kinetics of binding of [3H]dihydroFC and the competition between [3H]dihydroFC and FCs A, C, J, and H were determined for the low-affinity sites. It was found that (i) the rate constant of association between FC and the low-affinity binding sites is about two orders of magnitude lower than that for the high-affinity sites; (ii) different FCs can be arranged in the order of decreasing avidity for the low-affinity FCbinding site: FC A>FC C>FC J>FC H. The authors are indebted to Dr. L.M. Krasnopolskaya (Institute of Agricultural Biotechnology, Moscow, Russia) for fusicoccins A, C, J, and H, and to Dr. A.V. Galkin (Institute of Agricultural Biotechnology, Moscow, Russia) for valuable comments and ren dering the paper into English.  相似文献   

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