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PubMed2004

Nonlegumes, legumes, and root nodules harbor different arbuscular mycorrhizal fungal communities.

Legumes are an important plant functional group since they can form a tripartite symbiosis with nitrogen-fixing Rhizobium bacteria and phosphorus-acquiring arbuscular mycorrhizal fungi (AMF). However, not much is known about AMF community composition in legumes and their root nodules. In this study, we analyzed the AMF community composition in the roots of three nonlegumes and in the roots and root nodules of three legumes growing in a natural dune grassland. We amplified a portion of the small-subunit ribosomal DNA and analyzed it by using restriction fragment length polymorphism and direct sequencing. We found differences in AMF communities between legumes and nonlegumes and between legume roots and root nodules. Different plant species also contained different AMF communities, with different AMF diversity. One AMF sequence type was much more abundant in legumes than in nonlegumes (39 and 13%, respectively). Root nodules contained characteristic AMF communities that were different from those in legume roots, even though the communities were similar in nodules from different legume species. One AMF sequence type was found almost exclusively in root nodules. Legumes and root nodules have relatively high nitrogen concentrations and high phosphorus demands. Accordingly, the presence of legume- and nodule-related AMF can be explained by the specific nutritional requirements of legumes or by host-specific interactions among legumes, root nodules, and AMF. In summary, we found that AMF communities vary between plant functional groups (legumes and nonlegumes), between plant species, and between parts of a root system (roots and root nodules).

DNA, Fungal↗
PubMed2005

A 2-year follow-up of root coverage using sub-pedicle acellular dermal matrix allografts and subepithelial connective tissue autografts.

BACKGROUND: Coverage of roots exposed by gingival recession is one of the main objectives of periodontal reconstructive surgery. A large variety of mucogingival grafting procedures are available. However, the long-term effectiveness of this procedure is still not clear. This study compared the effectiveness of sub-pedicle acellular dermal matrix allografts with subepithelial connective tissue autografts in achieving root coverage 2 years postoperatively. METHODS: One hundred one (101) patients were treated with dermal matrix allografts (mean age, 28.4+/- 0.7 years; mean recession, 4.2 mm) and 65 patients treated with connective tissue graft (mean age, 30.1+/- 1.4 years; mean recession, 4.9 mm). All patients underwent full periodontal evaluation and presurgical preparation, including oral hygiene instruction and scaling and root planing. The exposed roots were thoroughly planed and covered by a graft without any further root treatment or conditioning. There were no differences in the average age, time of follow-up, or gender between the two groups. Patients were evaluated periodically between 1 and 2 years. Residual recession and defect coverage were assessed. RESULTS: Mean residual root recession after root coverage with acellular dermal matrix allograft was 0.2 +/- 0.04 mm, with defect coverage of 95.9% +/- 0.9%. Frequency of defect coverage was 82.2%. Root coverage was 98.8% +/- 0.2%, resulting in a frequency of root coverage of 100%. Gain in keratinized gingiva was 2.2+/- 0.04 mm and attachment gain was 4.5+/- 0.1 mm per patient. Connective tissue autografts resulted in mean residual root recession of 0.1+/- 0.04 mm, with percent defect coverage of 97.8%+/- 0.6% and frequency of defect coverage of 95.4%. Root coverage was 99.1%+/- 0.2%, and frequency of root coverage was 100%. Gain in keratinized gingiva was 3.0+/- 0.1 mm and attachment gain was 5.3+/- 0.2 mm per patient. No significant differences in final recession and root coverage between the two treatment methods were found. However, autografts resulted in significant increases in defect coverage, keratinized gingival gain, attachment gain, and residual probing depth. The clinical results were stable for the 2-year follow-up period. CONCLUSIONS: These results indicate that coverage of root by sub-pedicle acellular dermal matrix allografts or subepithelial connective tissue autografts is a very predictable procedure which is stable for 2 years postoperatively. However, subepithelial connective tissue autografts resulted in significant increases in defect coverage, keratinized gingival gain, attachment gain, and residual probing depth.

Adult↗
PubMed2001

[Experimental study on combining selective rhizotomy of different anterior and posterior sacral roots for restoration of bladder function after spinal cord injury].

OBJECTIVE: To investigate an alternative procedure for complete denervation of bladder in the supra-cone cord injury to restore the bladder function. METHODS: Sixteen dogs were included in this study after their spinal cords were transected above the cone. They were divided into 6 groups and performed the rhizotomy of L7 to S3 root in different combination respectively. The bladder and urethra pressure change by electrostimulation during operation and cystometrogram change after operation were tested. RESULTS: 1. Electrostimulation study: for bladder innervation, S2 was the most important and S1 was secondary. While for urethra innervation, S1 was more important than S2. When the anterior and posterior roots of S1 and S2 were intact with rhizotomy of posterior roots of L7 and S3, stimulated the common or posterior root of S1 and S2, the change of pressure in bladder and urethra was the same. When the anterior roots of S1 and S2 were resected with rhizotomy of posterior roots of L7 and S3, the pressure in bladder and urethra was significant decreased compared to stimulating the corresponding posterior roots. 2. Cystometrogram (CMG) study: in the complete deafferented group, resecting the posterior roots of L7 to S3, the bladder became flaccid. While resecting the posterior root of S2 and anterior root of S1 or, resecting the posterior root of S1 and anterior root of S2, combining with rhizotomy of posterior roots of L7 and S3, the CMG curve was similar to the complete deafferented group. In the S1 and S2 intact group, the bladder became spastic. CONCLUSION: Combining rhizotomy of anterior and posterior sacral root in different level has the same effects on bladder as complete deafferentation.

Animals↗
PubMed1977

[Investigations about cause of specific replant disease of fruit trees. VI. Proof of actinomycetes in feeder roots of apple seedlings in soils with different digrees of soil sickness (author's transl)].

Microscopic analysis of longitudinal sections of feeder roots of apple seedlings from soil with experimentally prepared different degrees of soil sickness led to the following results: 1. A colonization of root-barks by actinomycetes could be pointed out in injured and in macroscopic not visible injured feeder roots of apple seedlings from sick soil. 2. The frequency of the colonization of root-pieces of the two highest root classes was in the sick soil at 47.3% and in the two soils with a less degree of soil sickness at 32.4%. In the non-sick soil the root were at a frequency of 0.3% nearly free from actinomycetes. 3. Feeder roots colonizated by actinomycetes showed injuries in the cell-bandage. Increasing injuries of the roots were obtained with increasing intensity of colonization by actinomycetes. In heavy injured feeder roots the proof of actinomycetes was difficult or no more possible. As the share of heavy injured roots was increasing with increasing degree of soil sickness can be supposed that the real frequency of root colonization by actinomycetes is substantially higher than it was observed in roots seeming to be healthy macroscopically. 4. The results obtained support our hypothesis that soil sickness of apple trees is caused by actinomycetes. The injuries of the roots appearing as a consequence of the colonization may explain both, the soil sickness in the case of replanting and the development of soil sickness in growing apple plantations. 5. Since until now there is no proof that actinomycetes cause injuries in roots of fruit-trees further examinations have to be aspired to confirm our results.

Actinomycetales↗
PubMed1992

Resistance to fracture of endodontically treated roots.

The root canals of 48 single-canal canine teeth were prepared by four different methods. The coronal lingual wall and root canal space were lowered to 2 mm below the buccal wall of the roots. The prepared root was placed into acrylic resin so that 12 mm of buccal root was exposed. A slowly increasing force was applied at the junction of the buccal wall and root canal space until fracture occurred. The force of fracture of the buccal root wall of each root was recorded and the results in each group were compared. All teeth fractured at the buccal wall/acrylic resin junction. Instrumentation of the root canals significantly weakened the roots. Obturation of the canals in conjunction with Roth's 801 sealer did not strengthen the roots. Obturation of the canals in conjunction with a glass ionomer sealer significantly strengthened the roots as compared with roots instrumented but not obturated and those obturated with gutta-percha and Roth's 801 Sealer.

Analysis of Variance↗
PubMed1989

Differential growth and hormone redistribution in gravireacting maize roots.

When growing roots are placed in a horizontal position gravity induces a positive curvature. It is classically considered to be the consequence of a faster elongation rate by the upper side compared to the lower side. A critical examination indicates that the gravireaction is caused by differential cell extension depending on several processes. Some of the endogenous regulators which may control the growth and gravitropism of elongating roots are briefly presented. The growth inhibitors produced or released from the root cap move preferentially in a basipetal direction and accumulate in the lower side of the elongation zone of horizontally maintained roots. The identity of these compounds is far from clear, but one of these inhibitors could be abscisic acid (ABA). However, indol-3y1 acetic acid (IAA) is also important for root growth and gravitropism. ABA may interact with IAA. Two other aspects of root cell extension have also to be carefully considered. An elongation gradient measured from the tip to the base of the root was found to be important for the growth of both vertical and horizontal gravireactive roots. It was changed significantly during the gravipresentation and can be considered as the origin of the differential elongation. Sephadex beads have been used as both growth markers and as monitors of surface pH changes when they contain some pH indicator. This technique has shown that the distribution of cell extension along the main root axis is related to a pH gradient, the proton efflux being larger for faster growing parts of roots. A lateral movement of calcium is obtained when Ca2+ is applied across the tips of horizontally placed roots with a preferential transport towards the lower side. Endogenous calcium, which may accumulate inside the endoplasmic reticulum of some cap cells, may also act in the gravireception. These observations and several others strongly suggest that calcium may play an essential role in controlling root growth and several steps of the root gravireaction.

Abscisic Acid↗
PubMed2004

Root resorption: the possible role of extracellular matrix proteins.

During maxillary permanent canine eruption, the deciduous canine root is selectively resorbed while the adjacent permanent lateral incisor root is left intact. An understanding of this selective resorption could provide insights into the cause of moderate to severe iatrogenic root resorption during orthodontic tooth movement. This study investigated the possible role of extracellular matrix (ECM) proteins in the selective resorption process. The spatial expression patterns of 2 ECM proteins, osteopontin (OPN) and bone sialoprotein (BSP), were assessed within the periodontal ligament (PDL) surrounding root surface areas of deciduous and permanent teeth. Intact and resorbed root surface areas from 14 deciduous roots and intact root surface areas from 12 permanent tooth roots were examined. In the deciduous roots, BSP and OPN were locally expressed in the cell layer adjacent to the root surface and most intensely concentrated in areas surrounding and within odontoclasts proximal to the resorptive lacunae. In contrast, BSP and OPN were expressed in a generalized pattern throughout the PDL of permanent roots. These preliminary findings suggest a differential expression of ECM proteins on deciduous versus permanent tooth roots, which could act as a signal for selective odontoclast adhesion to, and subsequent resorption of, deciduous root surfaces.

Extracellular Matrix Proteins↗
PubMed1995

Risk factors for apical root resorption of maxillary anterior teeth in adult orthodontic patients.

The purpose of this study was to identify risk factors for apical root resorption in adult orthodontic patients. Standardized periapical radiographs of maxillary anterior teeth and cephalograms made before and after treatment and treatment charts of 343 adults, representing groups of consecutively treated patients from four orthodontic practices, were examined. Apical root resorption was calculated by subtracting posttreatment tooth length measurements from the corresponding pretreatment measurements. Root width was measured from the mesial to the distal outline of the roots 4 mm from the apex. Root form was scored subjectively as normal, pointed, eroded, blunt, bent, and bottle shaped. Root movement was calculated from measurements of superimposed tracings of pretreatment and posttreatment cephalograms. Proximity of the central incisor roots to the palatal cortical bone was scored subjectively as present or absent. Severity of initial malocclusion and treatment variables were collected from the charts. Multiple linear regression analyses revealed that amount of root movement, long roots, narrow roots, abnormal root shape, and use of Class II elastics were significant risk factors. However, the statistical model had a low explained variance, strongly suggesting a weak prediction power. No association was found between type of initial malocclusion, treatment time, use of rectangular arch wires, proximity of the root to the palate or treatment with maxillary osteotomy, and root resorption. Endodontic treatment was a preventive factor.

Adult↗
PubMed2001

An in vitro study comparing root-end cavities prepared by diamond-coated and stainless steel ultrasonic retrotips.

AIM: This study compared the appearance of root-end cavity preparations and the time required to prepare them using prototype ultrasonic diamond-coated (DC) and stainless-steel (SS) retrotips. METHODOLOGY: In 12 maxillary and 12 mandibular molar teeth 48 root-end cavities were prepared ultrasonically in the palatal, mesio-buccal, distal and mesial root-ends using DC and SS retrotips, alternately. Replicas of the resected root tips and the root-end cavities were examined under a scanning electron microscope (SEM), recording (i) incidence and extent of dentine cracks (ii) minimum remaining thickness of the dentine walls and (iii) surface quality of the resected root-ends. The time taken to complete the preparation was also recorded. Means of these parameters were compared for both types of retrotips using nonparametric tests. RESULTS: No resected root-ends had cracks before preparation. However, after preparation one root-end cavity shaped by an SS retrotip had a microcrack visible at 23x magnification. Four and seven other root-ends had crazed surfaces in the DC and SS groups, respectively (P > 0.05). Remaining minimum dentine thickness was 0.56 +/- 0.28 mm and 0.71 +/- 0.24 for the DC and SS groups, respectively, and this difference was significant (P < 0.05). A root-end cavity in one specimen in the DC group was perforated. Preparation times ranged from 25 s to 361 s and were significantly lower for DC tips (P < 0.01) than the SS tips. The time required to prepare root-end cavities also differed between roots; root-end preparation in mandibular molars was more time consuming. CONCLUSIONS: A better quality surface was produced by the prototype diamond-coated retrotips, in less time than the SS retrotips, which in turn caused fewer cracks than previously reported. DC retrotips removed more dentine than SS retrotips and should therefore be used with care to avoid overpreparation or perforation.

Apicoectomy↗
PubMed2002

Positional effect of cell inactivation on root gravitropism using heavy-ion microbeams.

When primary root apical tissues of Arabidopsis thaliana were irradiated by heavy-ion microbeams with 120 microm diameter, strong inhibition of root elongation and curvature were observed at the root tip. Irradiation of the cells that become the lower part of the root cap after gravistimulation showed strong inhibition of root curvature, whereas irradiation of the cells that become the upper part of the root cap after gravistimulation did not show severe damage in either root curvature or root growth. Further analysis using smaller area microbeams with 40 microm diameter indicated that the greatest inhibition of curvature occurred at the root tip and the next greatest inhibition occurred in the cells in the lower part of the root cap. These results indicate not only that the root tip and columella cells are the most sensitive sites for root gravity, but also that signalling of root gravity would go through the lower part of the cap cells after perception.

Arabidopsis↗
PubMed1988

Effects of cations on hormone transport in primary roots of Zea mays.

We examined the influence of aluminum and calcium (and certain other cations) on hormone transport in corn roots. When aluminum was applied unilaterally to the caps of 15 mm apical root sections the roots curved strongly away from the aluminum. When aluminum was applied unilaterally to the cap and 3H-indole-3-acetic acid was applied to the basal cut surface twice as much radioactivity (assumed to be IAA) accumulated on the concave side of the curved root as on the convex side. Auxin transport in the apical region of intact roots was preferentially basipetal, with a polarity (basipetal transport divided by acropetal transport) of 6.3. In decapped 5 mm apical root segments, auxin transport was acropetally polar (polarity = 0.63). Application of aluminum to the root cap strongly promoted acropetal transport of auxin reducing polarity from 6.3 to 2.1. Application of calcium to the root cap enhanced basipetal movement of auxin, increasing polarity from 6.3 to 7.6. Application of the calcium chelator, ethylene-glycol-bis-(beta-aminoethylether)-N,N,N',N'-tetraacetic acid, greatly decreased basipetal auxin movement, reducing polarity from 6.3 to 3.7. Transport of label after application of tritiated abscisic acid showed no polarity and was not affected by calcium or aluminum. The results indicate that the root cap is particularly important in maintaining basipetal polarity of auxin transport in primary roots of corn. The induction of root curvature by unilateral application of aluminum or calcium to root caps is likely to result from localized effects of these ions on auxin transport. The findings are discussed relative to the possible role of calcium redistribution in the gravitropic curvature of roots and the possibility of calmodulin involvement in the action of calcium and aluminum on auxin transport.

Abscisic Acid↗
PubMed2006

Radiographic technical quality of root fillings performed by dental students in Turkey.

AIM: To evaluate the radiographic technical quality of root fillings performed by undergraduate students at a dentistry faculty in Turkey. METHODOLOGY: A random sample of 2000 records of patients who received dental treatment at the Faculty of Dentistry, University of Gazi between 2000 and 2003 was investigated. The final sample consisted of 1,893 root-filled teeth with 3,692 root canals in 1,654 dental patients. For each root-filled tooth, at least three periapical radiographs were examined: preoperative, working length determination and postoperative. The length, density and taper of root fillings were recorded. The length of root fillings was recorded as adequate, short or overfilled. Density of root fillings was recorded as adequate or inadequate. Taper of root fillings was recorded as adequate or inadequate. Results were evaluated statistically using one-way analysis of variance (anova) and chi-square analysis. RESULTS: Sixty-nine per cent, 53.2% and 68.3% of root fillings had adequate length, density and taper, respectively; only 33% of teeth fulfilled these three criteria at the same time. The relationship between the length, density and taper of the root filling and the presence of canal curvature was statistically significant (P < 0.001). There was no significant difference between maxillary and mandibular teeth according to the adequacy of the root fillings. The highest percentage of adequate root fillings was found in maxillary canines (51.5%). CONCLUSIONS: The percentage of adequate root fillings performed by undergraduate students was only 33%.

Adult↗
PubMed1984

Potentials for root resorption during periodontal wound healing.

The present study was undertaken to examine whether (1) the process of resorption, which invariably affects periodontitis involved reimplanted roots facing bone or gingival connective tissue during healing, is a transient phenomenon and, (2) root resorption can be prevented by permitting downgrowth of epithelium along the root surface. A total of 24 teeth in 2 monkeys (Macaca cynomolgus) was subjected to experimental periodontal tissue breakdown by the placement of elastic ligatures around the teeth. The ligatures were left in situ until about 50% of the supporting tissues had been lost. Following removal of the ligatures, the teeth were extracted and the denuded portions of the roots were scaled and planed. The crowns of the teeth were resected and the root canals filled with guttapercha. The roots were subsequently implanted into sockets prepared in the jaw bone in such a way that each root was embedded in bone except for a portion which was in contact with gingival connective tissue. 1 month prior to sacrifice of the animals, the cut surface of the coronal part of the roots was exposed by removal of the covering soft tissue. The epithelium was thereby allowed to migrate into the wound. Implantation of the roots was scheduled to provide healing periods of 1, 2, 3, 4, 8, 12, 16, 20 and 24 weeks before exposure of the roots. The histologic examination of the implant specimens disclosed that replacement resorption was a progressive process which eventually resulted in the elimination of the transplanted roots. It was possible to prevent root resorption in this model by permitting apical downgrowth of epithelium along the root surface during the initial phase of healing. The results are discussed in relation to procedures used in periodontal therapy.

Animals↗
PubMed1985

Movement of calcium across tips of primary and lateral roots of Phaseolus vulgaris.

Calcium (Ca) movement across tips of primary and lateral roots of Phaseolus vulgaris was determined by applying 45Ca2+ to one side of the root and collecting radioactivity in an agar receiver block on the opposite side of the root. The ratios of cpm in receiver blocks on the bottom of primary roots : cpm in receiver blocks on the top of the primary roots were 1.87 and 2.47 after 1 and 2 hr, respectively. This polar transport of Ca across tips of primary roots correlated positively with a graviculture of 43 degrees after 2 hr. The ratio of cpm in receiver blocks on the bottom of lateral roots : cpm in receiver blocks on the top of lateral roots was 1.20 after 2 hr. The decreased polar movement of Ca across tips of lateral roots correlated positively with lateral roots being nongraviresponsive. These data 1) support the suggestion that gravistimulation induces polar movement Ca toward the lower side of tips of primary roots, and 2) suggest that the reduced polar movement of Ca across tips of lateral roots may be involved in uncoupling gravistimulation from gravicurvature in lateral roots.

Biological Transport↗
PubMed1983

Geoperception in primary and lateral roots of Phaseolus vulgaris (Fabaceae). I. Structure of columella cells.

Primary roots of Phaseolus vulgaris (Fabaceae) are positively geotropic, while lateral roots are not responsive to gravity In order to elucidate the structural basis for this differential georesponse, we have performed a qualitative and quantitative analysis of the ultrastructure of columella cells of primary and lateral roots of P. vulgaris. Root systems were fixed in situ so as not to disturb the ultrastructure of the columella cells. The columellas of primary roots are more extensive than those of lateral roots. The volumes of columella cells of primary roots are approximately twice those of columella cells of lateral roots. However, columella cells of primary roots contain greater absolute volumes and numbers of all cellular components examined than do columella cells of lateral roots. Also, the relative volumes of cellular components in columella cells of primary and lateral roots are statistically indistinguishable. The endoplasmic reticulum is sparse and distributed randomly in both types of columella cells. Both types of columella cells contain numerous sedimented amyloplasts, none of which contact the cell wall or form complexes with other cellular organelles. Therefore, positive geotropism by roots must be due to a factor(s) other than the presence of sedimented amyloplasts alone. Furthermore, it is unlikely that amyloplasts and plasmodesmata form a multi-valve system that controls the movement of growth regulating substances through the root cap.

Endoplasmic Reticulum↗
PubMed2004

[Comparison of the clinical effects of three root canal treatments.].

PURPOSE: To compare the clinical effects of three root canal treatments. METHODS: The patients were randomly divided into A,B,C groups. Group A: profile preparation of the root canal, then the root canal was filled with maillefer thermafil. Group B: profile preparation of the root canal, iodoform cataplasm and gutta percha point was used to fill root canal. Group C: preparation of the root canal with stainless steel hand-operated root canal magnified instrument, iodoform cataplasm and gutta percha point was used to fill the root canal. RESULTS: Through X ray and clinical evaluation, the root canal therapy result in group A was superior to group B, group B was superior to group C. CONCLUSION: The work efficiency of preparative instrument of profile flexible nickel-titanium root canal is high. The successful rate of maillefer thermafil for results root canal therapy is superior to the other methods. Root canal preparation by profile can get satisfying effects.

Barium Sulfate↗
PubMed1995

Characterization of the growth and auxin physiology of roots of the tomato mutant, diageotropica.

Roots of the tomato (Lycopersicon esculentum, Mill.) mutant (diageotropica (dgt) exhibit an altered phenotype. These roots are agravitropic and lack lateral roots. Relative to wild-type (VFN8) roots, dgt roots are less sensitive to growth inhibition by exogenously applied IAA and auxin transport inhibitors (phytotropins), and the roots exhibit a reduction in maximal growth inhibition in response to ethylene. However, IAA transport through roots, binding of the phytotropin, tritiated naphthylphthalamic acid ([3H]NPA), to root microsomal membranes, NPA-sensitive IAA uptake by root segments, and uptake of [3H]NPA into root segments are all similar in mutant and wild-type roots. We speculate that the reduced sensitivity of dgt root growth to auxin-transport inhibitors and ethylene is an indirect result of the reduction in sensitivity to auxin in this single gene, recessive mutant. We conclude that dgt roots, like dgt shoots, exhibit abnormalities indicating they have a defect associated with or affecting a primary site of auxin perception or action.

Biological Transport↗
PubMed1991

Computer-based video digitizer analysis of surface extension in maize roots: kinetics of growth rate changes during gravitropism.

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.

Computer Systems↗