Light touch and medio-lateral postural stability during short distance gait.

While standing, light fingertip touch on an external stable object attenuates sway and improves balance in healthy adults as well as in individuals with poor postural control. The effect of light touch on balance during gait is, however, not well known. Therefore, the purpose of this work was to study the effects of light fingertip touch on balance during gait. We hypothesized that similar to its effect during stance light touch would increase postural stability. Forty healthy young adults were tested under four gait conditions: (1) eyes open (EO), (2) eyes closed (EC), (3) eyes closed while lightly touching a static object on the right side of the walking lane (ECLTS), (4) eyes closed while lightly touching a dynamic object, namely, a stick that was moved forwards by the subject with the right hand (ECLTD). The main outcome measure was medio-lateral step width variability, a well established indicator of gait balance in the medio-lateral plane. During the EC condition, light touch of an external static object (ECLTS) decreased medio-lateral variability (i.e., balance improved); however, this stabilizing effect was not observed with light touch on the stick. The availability of self positional and spatial cues when touching a static external reference, and their absence when touching a stick that is moved forwards by the subject as he walks, can explain the different effects of light touch in the ECLTS vs the ECLTD gait conditions.

Analysis of FcgammaRIIA cytoplasmic tail requirements in signaling for serotonin secretion: evidence for an ITAM-dependent, PI3K-dependent pathway.

The human Fc receptor, FcgammaRIIA, is known to mediate phagocytosis and endocytosis, yet the greatest numbers of these receptors are expressed on the surface of non-phagocytic platelets, where they are involved in serotonin secretion. FcgammaRIIA harbours three tyrosine (Y) residues within its cytoplasmic domain. Y1 is upstream of both Y2 and Y3, which are contained within an immunoreceptor tyrosine-based activation motif (ITAM), required for many signaling events. We have demonstrated that the two ITAM tyrosines are required for phagocytic signaling and that mutation of a single ITAM tyrosine decreases but does not abolish phagocytic signaling. Furthermore, we have identified that the YMTL motif is required for endocytosis. These observations suggest that FcgammaRIIA utilizes different sequences for various signaling events. Therefore, we investigated the sequence requirements for another important FcgammaRIIA-mediated signaling event, serotonin secretion, using Rat Basophilic Leukemia (RBL-2H3) cells transfected with wildtype (WT) FcgammaRIIA or mutant FcgammaRIIA. Stimulation of cells expressing WT FcgammaRIIA induced release of serotonin at a level 7-fold greater than that in nonstimulated WT FcgammaRIIA-transfected cells or nontransfected RBL cells. Mutation of either ITAM tyrosine (Y2 or Y3) to phenylalanine was sufficient to abolish serotonin secretion. Further, while inhibition of Syk with piceatannol blocked phagocytosis as expected, it did not inhibit serotonin secretion. Additionally, inhibition of phosphoinositol-3-kinase (PI3K) with wortmannin only had a partial effect on serotonin signaling, despite the fact that the concentrations used completely abolished phagocytic signaling. These data suggest that the requirements for serotonin secretion differ from those for phagocytosis mediated by FcgammaRIIA.

Activation of selected frontal trunk and extremities muscles during rolling from supine to side lying in healthy subjects and in post-stroke hemiparetic patients.

The purpose of this work was to get insight into the role of frontal trunk and proximal extremity muscles in rolling from supine to side lying. Participants were seventeen hemiparetic patients and 14 healthy subjects. Electromyographic (EMG) activity of the Sternocleidomasoid (ScM), Pectoralis Major (PM), External Oblique (ExO) and Rectus Femoris (RF) muscle pairs was recorded during rolling performance. Analysis included the establishment of EMG response times and magnitudes. For all muscles, initiation of EMG activity was delayed in the patients as compared with the controls. Among the healthy subjects, EMG activity level of the SCM was more enhanced on the mobile than on the stable body side, while activation level of the PM muscle was larger on the stable body side. In the hemiparetic group, the SCM demonstrated similar results as the controls yet, PM activity on the paretic side was lower than on the non-paretic side regardless of rolling direction. The difference in activation level between the corresponding ExO and RF muscles showed inconsistency among the healthy subjects, whereas in the hemipareic group the muscles on the paretic side never displayed higher activation levels than on the non-paretic side. In conclusion, rolling sideways in hemiparetic subjects is characterized by a normal relationship between activation levels of the SCM muscles while the relationship between the corresponding PM, ExO and RF muscles is hampered due to reduced activation level of the muscles on the paretic body side.

Effects of light fingertip touch on postural responses in subjects with diabetic neuropathy.

OBJECTIVES: To investigate the potential benefits from lightly touching an external supporting device on automatic postural responses to support surface translations, in subjects with profound sensory neuropathy in the feet due to diabetes mellitus (DM-PN). METHODS: Eight subjects with DM-PN and 10 age matched controls were tested under randomly ordered conditions of no fingertip touch (NT), light touch (LT; <1 N), and heavy touch (HT, as needed) of a stationary touch plate, during three backward translation velocities of the support surface at 10, 20, and 30 cm/s. Dependent variables included response latencies, CoP velocity, and the slope of the relation between centre of pressure (CoP) velocity and translation velocity as a measure of response scaling. RESULTS: Postural response latencies were significantly longer and scaling of initial response magnitude in proportion to translation velocity was significantly smaller in the DM-PN subjects compared to the control subjects. LT had no significant effect on response latencies of the DM-PN patients. Fingertip touch increased the slope of the scaling of postural response magnitude in both groups. However, DM-PN subjects had to use HT to improve response scaling, whereas control subjects improved scaling with LT as well as HT. LT significantly increased rightward CoP velocity towards the touch plate in all subjects. CONCLUSIONS: LT did not reduce the latency or improve the scaling of automatic postural responses in subjects with peripheral neuropathy. The major effect of LT on the automatic postural responses of the DM-PN subjects was in increasing CoP velocity towards the side of the supporting device. HT in neuropathy subjects and LT in age matched control subjects increased the sensitivity of initial postural response scaling, suggesting that somatosensory substitution from a cane in the hand could be used to improve the magnitude of medium latency postural responses to slips and trips.

Fingertip touch improves postural stability in patients with peripheral neuropathy.

The purpose of this work was to determine whether fingertip touch on a stable surface could improve postural stability during stance in subjects with somatosensory loss in the feet from diabetic peripheral neuropathy. The contribution of fingertip touch to postural stability was determined by comparing postural sway in three touch conditions (light, heavy and none) in eight patients and eight healthy control subjects who stood on two surfaces (firm or foam) with eyes open or closed. In the light touch condition, fingertip touch provided only somatosensory information because subjects exerted less than 1 N of force with their fingertip to a force plate, mounted on a vertical support. In the heavy touch condition, mechanical support was available because subjects transmitted as much force to the force plate as they wished. In the no touch condition, subjects held the right forefinger above the force plate. Antero-posterior (AP) and medio-lateral (ML) root mean square (RMS) of center of pressure (CoP) sway and trunk velocity were larger in subjects with somatosensory loss than in control subjects, especially when standing on the foam surface. The effects of light and heavy touch were similar in the somatosensory loss and control groups. Fingertip somatosensory input through light touch attenuated both AP and ML trunk velocity as much as heavy touch. Light touch also reduced CoP sway compared to no touch, although the decrease in CoP sway was less effective than with heavy touch, particularly on the foam surface. The forces that were applied to the touch plate during light touch preceded movements of the CoP, lending support to the suggestion of a feedforward mechanism in which fingertip inputs trigger the activation of postural muscles for controlling body sway. These results have clinical implications for understanding how patients with peripheral neuropathy may benefit from a cane for postural stability in stance.

Accuracy of reproducing hand position when using active compared with passive movement.

BACKGROUND AND PURPOSE: Evaluating proprioception is relevant to physical rehabilitation because of its significance in motor control. One method of proprioceptive testing involves having subjects either imitate or point at a joint position or movement which was presented via a passive movement. However, as the muscle spindles are subject to central fusimotor control, the proprioceptive system may be better-tuned to movements created by active muscular contraction than to passive movements. The objective of the present study was to determine whether accuracy of reproducing hand position is dependent on whether proprioceptive input is obtained via an active or a passive movement. METHOD: Thirty-nine healthy volunteers (mean age (+/- SD) 24.6 (+/- 3.6) years) participated in the study. Subjects' right hands, which were obscured from view, were acoustically guided to five targets on a digitizer tablet with either an active or passive upper extremity movement. Subjects were then asked to reproduce the targets' location by either reaching to them with the unseen hand or by use of a laser beam. Distance from target and angular deviations were calculated in both absolute and relative terms. Repeated measures analysis of variance (ANOVA) was performed for each variable followed by predetermined contrasts. RESULTS: Comparison between the active and passive conditions when reconstruction of target location was guided kinaesthetically indicates significant differences in absolute distance, range and angular deviation. The comparison when reconstruction of target location was guided visually indicates significant differences in absolute distance, absolute angle and angular deviation. CONCLUSIONS: The ability to reproduce hand position accurately is enhanced when position is encoded by active upper extremity movement compared with passive movement. The results have implications for the design of strategies for evaluating as well as treating patients with impaired proprioception and limited movement.

The effect of treadmill training on the ambulation of stroke survivors in the early stages of rehabilitation: a randomized study.

The objective of this study was to compare the effects of conventional over-ground gait training with treadmill training on the restoration of gait in people with hemiparesis following a stroke. Twenty-five individuals in the early stages of rehabilitation were alternately assigned to one of two treatment groups. In addition to conventional physical therapy, the experimental group participated in 15 treadmill-training sessions in which a handrail was used for external support. The control group received the same number of equal length sessions of over-ground ambulation. Treatment effects were established by pre- and posttreatment assessment of: 1) functional walking ability, 2) walking speed, 3) stride length, 4) temporal characteristics of gait, and 5) electromyographic activity of calf muscles. Normal values were obtained from eight healthy individuals of approximately the same age as the stroke survivors. The study demonstrates that individuals following a stroke are well able to tolerate treadmill training in the early stage of their rehabilitation process without the use of a weight support apparatus. Furthermore, the findings suggest that treadmill training may be more effective than conventional gait training for improving some gait parameters such as functional ambulation, stride length, percentage of paretic single stance period, and gastrocnemius muscular activity.

Time-related changes in motor performance of the upper extremity ipsilateral to the side of the lesion in stroke survivors.

OBJECTIVE: The objective of the present study was to examine time-related changes in motor performance of daily tasks of the upper extremity ipsilateral to the side of lesion in poststroke hemiparetic patients. METHODS: Nine patients after an acute uniliteral cerebrovascular accident and 10 age-matched healthy controls were studied. Functional motor abilities of the upper extremity ipsilateral to side of lesion were examined over a 4-month time course, using validated measurement tools (Jebsen test of hand function, nine-hole peg test, and three functional activities of daily living). RESULTS: The results indicated a significant impairment in the motor function of the hand ipsilateral to the side of brain lesion in comparison with the matched extremity in control subjects. They also pointed to time-related improvement in performance speed, implying that the deterioration in the functional performance of the upper extremity on the uninvolved body side of poststroke hemiparetic patients is not static and may improve with time. The findings further suggested that the left hand of patients with an intact right cerebral hemisphere improves more than does the right hand of their peers whose left cerebral hemisphere is intact. CONCLUSIONS: Due to the small sample size and methodologic considerations, further and more extensive work is required to determine difference in improvement in motor abilities of the ipsilateral left versus the ipsilateral right upper extremities in stroke survivors.

Activation of flexor and extensor trunk muscles in hemiparesis.

OBJECTIVE: The purpose of this work was to study the bilateral activity of trunk flexor and extensor muscles in post-stroke hemiparetic patients. DESIGN: Criterion variables were degree of temporal synchronization and level of electromyographic activity in pertinent muscle pairs during two symmetrical tasks: (1) from reclined sitting, bringing the trunk forward; (2) during upright sitting, shrugging shoulders, and extending back. The recti abdomini and external oblique muscles were tested as prime movers of the first task, and the lumbar erector spinae and latissimus dorsi muscles were tested in the second task. Electromyographic recordings from these muscles during three repetitions of each exercise were used for analysis. RESULTS: Cross-correlation analysis pointed to higher temporal synchronization between the abdominal muscles than between the back extensor muscles and in axial compared with para-axial muscles. Differences between patients and controls were found only for the erector spinae muscle pair, which indicates less synchronous activity between the two sides in the patients. The average electromyographic activity level was comparable for corresponding abdominal muscles, both in the patients and in the control subjects. Regarding the back extensor, side differences were detected for the latissimus dorsi muscles in both groups, with the paretic and right side less active in the patients and controls, respectively. CONCLUSIONS: Altogether, the findings do not support the claim of unilateral deficits in the function of trunk muscles in post-stroke hemiparetic patients. They emphasize the need for further characterization of the impairment of trunk extensor and flexor muscles in post-stroke patients.

Weight-bearing shifts of hemiparetic and healthy adults upon stepping on stairs of various heights.

OBJECTIVE: To examine and compare the effect of stepping on stairs of various heights on lower extremity weight bearing in hemiparetic patients. SETTING: Flieman Geriatric Rehabilitation Hospital, Haifa, Israel. SUBJECTS: Fifteen ambulatory hemiparetic patients following an acute cerebrovascular accident, and 16 age-matched healthy controls. INTERVENTIONS: Each subject was tested twice on two consecutive days in five weight-bearing positions which included level stance and stepping with either leg on 10-cm- and 17-cm-high steps. Data concerning weight distribution on the lower extremities were collected by two computerized forceplates. MAIN OUTCOME MEASURE: Weight borne by each foot expressed as percentage of overall body weight. RESULTS: In the attempted symmetrical level stance, the percentage of body weight borne by the paretic limb of the stroke patients was significantly lower than that of the nonparetic limb. Placing one foot on a step induced a weight shift to the foot placed on the floor regardless of step height. Weight shifting to the paretic limb was, however, significantly lower than to the nonparetic limb. Weight shifting to the nonparetic limb was significantly lower than to the corresponding limb of healthy individuals. Step height had no significant effect on weight distributions on the feet. CONCLUSIONS: Raising a foot on a step appears to be an appropriate strategy for weight shift training of stroke patients. Since weight shifting to both the paretic and nonparetic limb of stroke patients is impaired, treatment strategies should include training in weight shifting to both lower extremities.

Postural sway of the affected and nonaffected pelvis and leg in stance of hemiparetic patients.

OBJECTIVES: To study potential differences between sway of the paretic and of the nonparetic pelvis and leg in standing hemiparetic patients by comparing measurements of corresponding bilateral waist and leg sites, and by comparing the results to those of healthy control subjects. DESIGN AND SETTING: Anterior-posterior and mediolateral sway of 15 hemiparetic patients and 13 healthy control subjects was measured with the eyes open and closed during quiet stance. Data were collected via an ultrasonic-based system that continuously monitored the position of four transducers mounted bilaterally on the anterior aspect of the pelvis and on each tibial tuberosity. Sway of each transducer marker was calculated by the standard deviation around its mean position and by its mean speed. Descriptive statistics, analysis of variance, and cross-correlation analysis were used for comparing hemiparetic patients with healthy subjects, as well as for determining the effects of body level, body side, and vision on postural sway. RESULTS: For all four measurement sites and in both the anterior-posterior and mediolateral axes, the hemiparetic patients had larger sways than the control subjects. Patients' sway on the paretic side was larger than on the nonparetic side, whereas no side differences were detected in the control subjects. For both groups, waist sway was larger than legs' sway. Cross-correlation values between sway of the ipsilateral waist and leg on each body side, as well as between the two legs, were substantially lower in the patients than in healthy subjects. CONCLUSIONS: Postural sway of standing hemiparetic patients is characterized by an asymmetrical profile that is expressed both in larger sway values of the paretic than of the nonparetic side, and in low temporal synchronization between sway of the legs and of the pelvis as well as between the two legs. Impairment in the ability to stabilize the distal segments of the lower extremity on the paretic side, rather than in stabilization of the pelvis, appears to underlie the enhanced postural sway of hemiparetic patients during stance.

Activation of selected trunk muscles during symmetric functional activities in poststroke hemiparetic and hemiplegic patients.

OBJECTIVE: To compare the EMG activity between the recti abdominii muscles and between the lumbar erector spinae muscles in hemiparetic and hemiplegic patients during functional symmetric trunk movements and to compare patients' EMG activity profiles with those of healthy controls. METHODS: EMG activity from the selected muscles was recorded during three symmetric and time controlled trunk exercises. Data analysis was based on values of cross correlations and of ratios between EMG activity of the bilateral corresponding muscles. RESULTS: In all groups, the highest cross correlations were obtained for both muscles when the muscles acted as prime movers. For the recti abdominii muscles, these values in the patients were comparable with those of the healthy subjects, whereas for the extensor muscles, the highest synchronous activity was displayed in healthy subjects and the lowest in hemiplegic patients. Laterality differences in the amount of EMG activity of the recti abdominii muscles were not biased towards one side. For the extensor muscles, in the controls, the activation levels were higher in the left erector spinae muscle than in the right one in two of the three exercises. Similarly, in the extensor muscles of the hemiparetic patients, activity on the paretic side was higher than on the non-paretic side in two exercises. CONCLUSIONS: In patients with a supratentorial poststroke hemiparesis or hemiplegia, bilateral corresponding axial trunk muscles co-contract during symmetric trunk activities. Synchronous activation is at its highest level during voluntary dynamic tasks and is greater in the recti abdominii than in the erector spinae muscles. For both muscles, EMG activation levels on the paretic side were not lower than on the non-paretic side. Thus, the assertion that the muscles on the paretic side are activated to a lesser extent than their counterparts on the non-paretic side during symmetric trunk movements was not confirmed.

Total knee arthroplasty in the elderly: patients' self-appraisal 6 and 12 months postoperatively.

The objective of this work was to study patients' self-appraisal of total knee arthroplasty (TKA) 6 and 12 months postoperatively, and to establish which factors determine dissatisfaction from surgery. The study group consisted of 79 patients subjected to TKA who underwent rehabilitation in a specialized institution from which they were discharged home after becoming independently ambulatory and capable of independent home care. Data were collected by interviews and physical examinations which were conducted upon admission to the rehabilitation program and at the patients' homes 6 and 12 months postoperatively. Descriptive statistics and logistic regression were applied for data analysis. Results of the 1-year follow-up indicated a decrease in the prevalence of pain in the postoperated knee and improvement in ambulatory capacities. The frequency of reliance on a walking aid and the prevalence of pain in the nonoperated knee were not substantially changed, however. In 27% of the subjects pain in the nonoperated knee had worsened at 1 year. One third of the respondents expressed dissatisfaction from the operation. Outcomes of the logistic regression analysis pointed to pain in both the ipsi- and contralateral knee and to the limitations in using stairs as the variables which significantly affected the levels of dissatisfaction 1 year postoperatively. Dissatisfaction could have resulted from inappropriate expectations from either misinterpretations or limited prior knowledge of the likely results of the operation.

Repetitive practice of a single joint movement for enhancing elbow function in hemiparetic patients.

The primary goal of this study was to assess whether repetitive practice of flexion-extension movements of the affected elbow in hemiparetic patients enhances performance and to compare the effects of this practice mode to the effects of the physical therapy variable exercise program which is routinely applied during sessions. Subjects were 27 poststroke hemiparetic patients, residents of a rehabilitation institute, divided into an experimental (n = 15) and a control group (n = 12). The former were treated with 800 repeated elbow movements in a maximal predetermined amplitude of 80 degrees, provided in 8 equal sessions every other day. The latter received 10 min. of conventional physical therapy for the paretic upper extremity at similar time intervals. Pre- and posttreatment assessments included the bilateral measurements of kinematic variables and activation latencies of the biceps and triceps brachi muscles as well as motor and functional tests. For all criterion variables, the findings pointed to comparable improvement in both groups. It was concluded that repetitive elbow movements had no unique training effect on the kinematics of movement and on activation latencies of the primary muscles controlling elbow function in hemiparetic patients. Further, transfer of the effects of training to execution of movements towards and from the mouth was also comparable in both groups, pointing again to there being no particular advantage in using repetitive movements as a training mode for enhancement of elbow function in hemiparetic patients.

Somatosensory evoked potentials of the posterior tibial nerve in hemiparetic patients: relation to stance balance and walking ability.

OBJECTIVES: To examine the association between stance ability and walking performance of poststroke hemiplegic patients and their posterior tibial nerve somatosensory evoked potentials (SEPs). DESIGN AND SETTING: Fifteen patients, residents of a geriatric rehabilitation hospital, were evaluated twice, with a 2-week interval between sessions. In each session, clinical tests of stance balance and walking ability were performed, and bilateral SEPs to stimulation of the posterior tibial nerve were recorded. Eight healthy, age-matched control subjects underwent the same tests in a single session, but SEPs were recorded unilaterally. Correlation analysis and analysis of variance (ANOVA) were used for studying the prognostic value of the initial posterior tibial nerve SEP measurements as well as the within- and between-sessions relationships between the clinical-functional tests and the SEP data. RESULTS: No significant correlations between the initial SEP values and functional improvement were established. Within each session, positive significant correlations existed between decreased latencies of several of the medium-latency SEP waves and the performance of stance and gait tasks. However, the between-sessions improvement in stance balance was not correlated with a decrease in latency of the SEP peaks or with an increase in their amplitudes. As to walking ability, in those patients whose gait significantly improved, a significant shortening of P37 and P54 latencies took place. CONCLUSIONS: The association between the initial and/or the 2-week changes in SEP of the posterior tibial nerve and improvement in stance and walking abilities is equivocal. In addition, the applicability of SEP measurements is limited by patients' physical status and cooperation. The clinical significance of posterior tibial nerve SEP testing in poststroke hemiparetic patients is therefore debatable.

Electromyographic and positional changes in the elbows of spastic hemiparetic patients during walking.

The displacement of the paretic elbow of hemiparetic patients into flexion during walking is an acknowledged associated reaction characteristic of upper limb spasticity. The main purpose of this study was to examine the step-dependent pattern and magnitude of the angular and electromyographic changes which take place during this flexion movement. Steps-related changes in elbow angle were measured on the paretic side of 14 hemiparetic patients during walking with a 4-point cane. The EMG activity of the ipsilateral biceps and triceps brachii muscles was concomitantly recorded. The activity of the brachioradialis muscle in 8 patients was monitored as well. In another trial, the angular and electromyographic activities were measured bilaterally in 7 patients during free walking. Flexion movement on the paretic side was characterized by a steep increase in flexion occurring during the first 4 steps, followed by a more gradual rise with successive stepping. Neither the electromyographic activity of the elbow flexor nor that of the extensor muscles was related to that flexion movement. The excursion into flexion on the non-paretic side was smaller than on the paretic side and incorporated flexion-extension fluctuations. The associated reaction at the paretic elbow during walking is a postural response which is triggered by the balance perturbation in the gait activity. It starts with a steep rise in flexion which seems to be reflexive in nature. The preservation of elbow flexion during walking may be an expression of stiffening of the elbow flexor muscles fibers.

Somatosensory evoked potentials in aphasic patients.

The purpose of this study was to employ evoked potentials to evaluate the function of the somatosensory system in a group of right hemiplegic aphasic patients in whom conventional physical examination was inapplicable. Bilateral somatosensory evoked potentials (SEPs) in response to stimulation of the median nerve were recorded in 20 patients, and unilateral recordings were performed with 20 healthy, aged, matched controls. The major abnormality, present in 13 patients, was absence or reduction of the amplitude of the cortical components N19 and P22 in the lesioned side of the brain. Consequently, the only significant difference between the lesioned versus nonlesioned brain side in patients, and between patients and control subjects was in the amplitude of the cortical components. Since a strong correlation exists between the detected abnormality and impaired somatosensory function, it is concluded that it is highly probable that many aphasic patients suffer somatosensory deficits which, being difficult to assess, are overlooked by the medical personnel.

An ultrasonic-operated kinematic measurement system for assessment of stance balance in the clinic.

This study describes the application of a kinematic measurement system based on ultrasonic technology to enable the assessment of stance balance in the clinic. The system is composed of 1-8 ultrasonic transducer markers which transmit ultrasonic waves, and three ultrasonic receivers. The spatial position of each marker is monitored by calculation of the time interval between transmission and reception of the wave. Sway data from the waist of 44 healthy subjects and 15 hemiparetic patients were collected during quiet stance. The results distinguished between data collected with and without vision, between patients and controls, and between the two sides of the body. The findings were found to be valid and reliable in repeated measurements. RELEVANCE:--Assessment of stance balance in the clinic is a requisite for quantifying disability and measuring improvement in patients with postural control deficits. Due to high costs and complexity of operation, the use of prevailing equipment for these purposes is mainly confined to research facilities. This paper describes a unique kinematic measurement system whose low price and ease of operation make it feasible for clinical use.

The Auxin Transport Inhibitor N-(1-Naphthyl)phthalamic Acid Elicits Pseudonodules on Nonnodulating Mutants of White Sweetclover.

The collection of symbiotic (sym) mutants of white sweetclover (Melilotus alba Desr.) provides a developmental sequence of mutants blocked early in infection or nodule organogenesis. Mutant phenotypes include non-nodulating mutants that exhibit root-hair deformations in response to Rhizobium meliloti, mutants that form ineffective nodules lacking infection threads, and mutants that form infection threads and ineffective nodules. Mutant alleles from both the sym-1 and the sym-3 loci exhibited a non-nodulating phenotype in response to R. meliloti, although one allele in the sym-1 locus formed ineffective nodules at a low frequency. Spot-inoculation experiments on a non-nodulating allele in the sym-3 locus indicated that this mutant lacked cortical cell divisions following inoculation with R. meliloti. The auxin transport inhibitor N-(1-naphthyl)phthalamic acid elicited development of pseudonodules at a high frequency on all of the sweetclover sym mutants, including the non-nodulating mutants, in which the early nodulin ENOD2 was expressed. This suggests that N-(1-naphthyl)phthalamic acid activates cortical cell divisions by circumventing a secondary signal transduction event that is lacking in the non-nodulating sweetclover mutants. The sym-3 locus and possibly the sym-1 locus appear to be essential to early host plant responses essential to nodule organogenesis.