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PubMed2000

Aortic root asymmetry in marfan patients; evaluation by magnetic resonance imaging and comparison with standard echocardiography.

BACKGROUND: Patients with Marfan syndrome may develop aortic root dissection despite only mild aortic root dilation as shown by standard echocardiography, which may be due to aortic root asymmetry. Purpose of the present study was to investigate aortic root asymmetry by magnetic resonance (MR) imaging in patients with Marfan syndrome and to compare these measurements with standardly performed echocardiography. METHODS: Eighty-seven Marfan patients (mean age 31 +/- 8 years) underwent MR imaging. From this population, 15 patients (mean age 29 +/- 3 years) were selected in whom both echocardiography and MR imaging had been performed within 3 months. With echocardiography, the aortic root was measured according to the recommendations of the American Society of Echocardiography. With MR imaging, a short axis view of the aortic root was obtained to measure distances between the noncoronary, right coronary and left coronary cusps and the aortic root area. Correlations between aortic root area and diameters were assessed, and 95% confidence intervals (95% CIs) calculated. RESULTS: No difference in the standardly measured noncoronary to right coronary cusp diameter between MR imaging and echocardiography was shown (42 +/- 6 mm). Largest aortic root diameter on the MR images was the right to left coronary cusp diameter (46 +/- 7 mm, p < 0.02). For a given noncoronary to right coronary cusp diameter, 95% confidence intervals revealed a variation of -20 to +20% in the aortic root area. CONCLUSIONS: The majority of Marfan patients show asymmetric dilation of the aortic root by MR imaging. This phenomenon may go unnoticed when standard echocardiography is performed. The asymmetry of the aortic root might be of clinical importance in unexpected aortic root dissection.

Adult↗
PubMed2002

Harlequin (hlq) and short blue root (sbr), two Arabidopsis mutants that ectopically express an abscisic acid- and auxin-inducible transgenic carrot promoter and have pleiotropic effects on morphogenesis.

Plant growth and development is regulated by complex interactions among different hormonal, developmental and environmental signalling pathways. Isolation of mutants in these processes is a powerful approach to dissect unknown mechanisms in regulatory networks. The plant hormones abscisic acid (ABA) and auxin are involved in vegetative, developmental and environmental growth responses, including cell division and elongation, vascular tissue differentiation and stress adaptation. The uidA (beta-glucuronidase; GUS) reporter gene driven by the carrot (Daucus carota) late embryogenesis-abundantDc3 promoter in transgenic Arabidopsis thaliana seedlings is ABA-inducible in the root zone of elongation and vasculature. We show here that the ABA-insensitive2-1 mutation (abi2) reduces ABA-inducible Dc3-GUS expression in these root tissues. Dc3-GUS expression is also induced in root cortex cells by indole-3-acetic acid. We mutagenized, with ethyl methane sulfonate, 5100 M1 abi2/abi2 homozygous plants of a line that carries two independent Dc3-GUS reporter genes and screened M2 clonal lines for ABA-inducible Dc3-GUS expression in roots. We isolated two novel single-gene nuclear mutants, harlequin (hlq) and short blue root (sbr), that ectopically express Dc3-GUS in roots and have pleiotropic effects on morphogenesis. The hlq mutant expresses Dc3-GUS in a checkered pattern in epidermis of roots and hypocotyls, accumulates callose and has deformed and collapsed epidermal cells and abnormal and reduced root hairs and leaf trichomes. It (hlq) is also dwarfed, skotomorphogenic and sterile. The sbr mutant is a seedling-lethal dwarf that over-expresses Dc3-GUS in the root and has radially swollen epidermal cells in the root and hypocotyl, supernumerary cell number in the root cortex and epidermis, abnormal vasculature, and abnormal epidermal cell patterning in cotyledons and leaves. It (sbr) also exhibits a semidominant root phenotype of reduced growth and lateral root initiation. The hlq and sbr mutants are not rescued by exogenous application of plant growth regulators. The hlq and sbr mutants do not require the abi2-1 mutant gene for their phenotypes and map to chromosome III and I, respectively. Further characterization of the hlq and sbr phenotypes and genes may provide insights into the relationship of hormone- and stress-regulated gene expression to morphogenesis and plant growth.

Abscisic Acid↗
PubMed2003

Results of surgery for aortic root aneurysm in patients with Marfan syndrome.

OBJECTIVES: This study was undertaken to examine the long-term results of surgery for aortic root aneurysm in patients with Marfan syndrome. METHODS: Forty-four patients underwent aortic root replacement and 61 underwent aortic valve-sparing operations for aortic root aneurysm. Patients who underwent aortic root replacement had more severe symptoms, worse left ventricular function, more severe aortic insufficiency, and larger aortic root aneurysms than did patients who had aortic valve-sparing operations. Two types of valve-sparing operations were performed: reimplantation of the aortic valve in 39 patients and remodeling of the aortic root in 22 patients. Echocardiography was performed annually during follow-up. The mean follow-ups were 75 +/- 54 months for the aortic root replacement group and 49 +/- 38 months for the aortic valve-sparing group. RESULTS: There were 1 early death and 7 late deaths; 6 deaths were in the aortic root replacement group and 2 were in the aortic valve-sparing group. Survivals at 10 years were 87% in the aortic root replacement group and 96% in the aortic valve-sparing group (P =.3). Freedoms from reoperation at 10 years were 75% in the root replacement group and 100% in the valve-sparing group (P =.1). Freedoms from valve-related mortality and morbidity were 65% after root replacement and 100% after valve-sparing operation (P =.02). Freedom from aortic insufficiency greater than 2+ after aortic valve-sparing operations was 75% at 10 years and was similar for both types of valve-sparing operations; however, the diameters of the aortic annulus and neoaortic sinuses increased only after the remodeling procedure. CONCLUSIONS: This study suggests that aortic valve-sparing operations provide similar survival but lower rates of valve-related complications than aortic root replacement for patients with Marfan syndrome. Reimplantation of the aortic valve may be more appropriate than remodeling of the aortic root to prevent dilation of the aortic annulus, and for this reason we now use only this technique to treat patients with Marfan syndrome.

Adolescent↗
PubMed1992

Carbon dioxide efflux from roots of calamodin and apple.

The specific rate of CO(2) efflux (respiration) from roots of intact fruiting calamodin plants (Citrus madurensis Lour.) showed no diel trend, and did not respond significantly to short-term (2 day) changes in shoot irradiance. Mean root respiration rate was about 8.4 nmol CO(2) g(-1) s(-1) at 20 degrees C, and increased with temperature with a Q(10) of about 2. In calamodin plants, the proportion of total root length that was white averaged 6.0 mm m(-1). Respiration of roots of apple plants (Malus domestica Borkh.), planted in spring as rootstocks and grown at high irradiance and N supply, declined from about 5.3 to 2.8 nmol CO(2) g(-1) s(-1) between 46 and 138 days after bud burst. At 50% irradiance, root respiration was reduced more than 25% at 46 and 92 days after bud burst, but was not significantly affected later in the season. Reducing shoot irradiance reduced the proportion of total root length that was white, e.g., from 217 to 146 mm m(-1) at 46 days after bud burst. For plants previously grown at low irradiance, increasing shoot irradiance for 6 days increased the rate of root respiration by 5 to 10%. For plants previously grown at high irradiance, reducing shoot irradiance for 6 days reduced root respiration by about 20% early in the season, but had no significant effect later in the season. For plants grown with low-N supply (5% of the high-N), root respiration was reduced early in the season, but was not significantly affected later. Reducing the N supply increased slightly the proportion of total root length that was white. For plants previously grown with low-N, increasing the N supply for 6 days reduced further the rate of root respiration. For plants previously grown with high-N, reducing the N supply for 6 days did not significantly affect the rate of root respiration. Specific respiration rates of root systems excised from mature trees growing outdoors peaked in June, at about 2.4 nmol CO(2) g(-1) s(-1), and then declined for the remainder of the growing season.

Journal Article↗
PubMed1992

Influence of hydroponic culture method on morphology and hydraulic conductivity of roots of honey locust.

The morphology and hydraulic conductivity of root systems of Gleditsia triacanthos L. var. inermis Willd. (honey locust) grown hydroponically in sand and solution cultures were compared. Total root system length was similar in the two cultures. However, root systems grown in solution had longer primary roots, fewer lateral roots and root hairs, and a greater distance between the tip of the primary root and the junction of the youngest secondary root and the primary root than root systems grown in sand. Hydraulic conductivities of root systems grown hydroponically for 21 or 35 days in sand or solution culture were similar. These findings show that different methods of hydroponic culture can affect root morphology without altering root resistance to water transport.

Journal Article↗
PubMed1992

Root growth and water use efficiency of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and lodgepole pine (Pinus contorta Dougl.) seedlings.

One-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and lodgepole pine (Pinus contorta Dougl.) seedlings were grown for 17 weeks in 100-cm deep, 7.8-liter containers. Two Douglas-fir provenances, one from a wet and one from a dry site in coastal British Columbia, and two lodgepole pine provenances, one from a wet and one from a dry site in interior British Columbia, were grown in wet (522% water content) or dry (318% water content) peat/vermiculite soil in a factorial design. Each container was sealed so that water loss occurred only through the seedling. Five harvests were made at three to five week intervals and water use, dry matter increment, root length and root weight were determined at each harvest. Stomatal conductance and shoot water potentials were measured during the last 12 weeks of the experiment. Lodgepole pine seedlings had greater dry matter production, water use, stomatal conductance and new root length than Douglas-fir seedlings. New root weight of lodgepole pine seedlings exceeded that of Douglas-fir seedlings during the last five weeks of the experiment, and specific root length (root length per unit root weight) of new roots was higher for lodgepole pine seedlings throughout the experiment. Douglas-fir seedlings showed higher water use efficiency (WUE) than lodgepole pine seedlings, and both species showed higher WUE in the dry soil treatment. Douglas-fir seedlings had lower water potentials and higher water uptake rates per unit of new root length than lodgepole pine seedlings, although water uptake rates per unit of root dry weight showed little difference between species. Soil water treatment influenced specific root length of new roots, water uptake per unit of new root length, and WUE in Douglas-fir seedlings more than in lodgepole pine seedlings.

Journal Article↗
PubMed1993

Early and late root formation in epicotyl cuttings of Pinus sylvestris after auxin treatment.

Auxin stimulated rooting of epicotyl cuttings of Pinus sylvestris irrespective of the physiological stage of the plant from which the cuttings were taken. The epicotyl cuttings were divided into two groups, those that differentiated roots early (within 6 weeks after cutting) and those that differentiated roots late (more than 6 weeks after cutting). Auxin treatment significantly stimulated the frequency of early rooting of epicotyl cuttings, whereas it had no effect on the frequency of late rooting of epicotyl cuttings. The number of roots per rooted cutting was significantly higher after auxin treatment both on early and late rooted cuttings. Anatomical studies showed that most of the roots on both early and late rooted cuttings developed from wound tissue. However some types of rooting were found only after auxin treatment of early rooted cuttings, e.g., roots that developed from resin duct wound tissue or from vascular tissue or in the pith.

Journal Article↗
PubMedDate not supplied

First-order root development from cuttings of Populus trichocarpa x P. deltoides hybrids.

We studied first-order root development of field-grown plants of 44 F(1) Populus trichocarpa x P. deltoides hybrids as well as 15 clones of P. trichocarpa (T) and 20 clones of P. deltoides (D) during their first growing season. The cuttings were planted in the field on May 11-12, 1988 and destructively sampled in July, August and September. By September 12, hybrids had an average of 50 first-order roots per cutting (range = 32 to 85) with an average of 25% dead roots (range = 10 to 51%). The longest roots of hybrids averaged 107 cm (range = 58 to 182 cm) and originated at the base of the cutting. Roots originating at the side of the cutting averaged 54 cm in length (range = 12 to 96 cm). For most aboveground and root parameters measured, the values for hybrids exceeded those for both parent species clones. For all clones, aboveground weights were positively correlated with weights of collected roots (R(2) = 0.66 to 0.86). In contrast, aboveground weights were negatively (but poorly) correlated with root/shoot ratios (R(2) = 0.08 to 0.21). Roots differed allometrically depending on their location on the cutting. Total weight of roots originating along the sides of the cutting was not correlated with aboveground weight (R(2) = 0.001 to 0.27), whereas total weight of roots originating at the base of the cutting was correlated with aboveground weight (R(2) = 0.52 to 0.80). Basal roots dominated the first-order root systems of most clones in terms of maximum length and total mass, but not in total numbers of roots.

Journal Article↗
PubMedDate not supplied

Sap flow measurements of lateral tree roots in agroforestry systems.

Successful extension of agroforestry to areas of the semi-arid tropics where deep reserves of water exist requires that the tree species be complementary to the associated crops in their use of water within the crop rooting zone. However, it is difficult to identify trees suitable for dryland agroforestry because most existing techniques for determining water uptake by roots cannot distinguish between absorption by tree and crop roots. We describe a method for measuring sap flow through lateral roots using constant temperature heat balance gauges, and the application of this method in a study of complementarity of water use in agroforestry systems containing Grevillea robusta A. Cunn. Sap flow gauges were attached to the trunks and roots of Grevillea with minimum disturbance to the soil. Thermal energy emanating from the soil adversely affected the accuracy of sap flow gauges attached to the roots, with the result that the uncorrected values were up to eightfold greater than the true water uptake determined gravimetrically. This overestimation was eliminated by using a calibration method in which nonconducting excised root segments, with sap flow gauges attached, were placed adjacent to the live roots. The power consumption and temperature differentials of the excised roots were used to correct for external sources and internal losses of heat within the paired live root. The fraction of the total sap flow through individual trees supplied by the lateral roots varied greatly between trees of similar canopy size. Excision of all lateral roots, except for one to which a heat balance gauge was attached, did not significantly increase sap flow through the intact root, suggesting that it was functioning at near maximum capacity.

Journal Article↗
PubMed1996

Foliage, fine-root, woody-tissue and stand respiration in Pinus radiata in relation to nitrogen status.

We measured respiration of 20-year-old Pinus radiata D. Don trees growing in control (C), irrigated (I), and irrigated + fertilized (IL) stands in the Biology of Forest Growth experimental plantation near Canberra, Australia. Respiration was measured on fully expanded foliage, live branches, boles, and fine and coarse roots to determine the relationship between CO(2) efflux, tissue temperature, and biomass or nitrogen (N) content of individual tissues. Efflux of CO(2) from foliage (dark respiration at night) and fine roots was linearly related to biomass and N content, but N was a better predictor of CO(2) efflux than biomass. Respiration (assumed to be maintenance) per unit N at 15 degrees C and a CO(2) concentration of 400 micro mol mol(-1) was 1.71 micro mol s(-1) mol(-1) N for foliage and 11.2 micro mol s(-1) mol(-1) N for fine roots. Efflux of CO(2) from stems, coarse roots and branches was linearly related to sapwood volume (stems) or total volume (branches + coarse roots) and growth, with rates for maintenance respiration at 15 degrees C ranging from 18 to 104 micro mol m(-3) s(-1). Among woody components, branches in the upper canopy and small diameter coarse roots had the highest respiration rates. Stem maintenance respiration per unit sapwood volume did not differ among treatments. Annual C flux was estimated by summing (1) dry matter production and respiration of aboveground components, (2) annual soil CO(2) efflux minus aboveground litterfall, and (3) the annual increment in coarse root biomass. Annual C flux was 24.4, 25.3 and 34.4 Mg ha(-1) year(-1) for the C, I and IL treatments, respectively. Total belowground C allocation, estimated as the sum of (2) and (3) above, was equal to the sum of root respiration and estimated root production in the IL treatment, whereas in the nutrient-limited C and I treatments, total belowground C allocation was greater than the sum of root respiration and estimated root production, suggesting higher fine root turnover or increased allocation to mycorrhizae and root exudation. Carbon use efficiency, the ratio of net primary production to assimilation, was similar among treatments for aboveground tissues (0.43-0.50). Therefore, the proportion of assimilation used for construction and maintenance respiration on an annual basis was also similar among treatments.

Journal Article↗
PubMed1998

Responses of citrus fine roots to localized soil drying: a comparison of seedlings with adult fruiting trees.

We studied the responses of citrus (Citrus volkameriana Tan. & Pasq.) roots to 15 weeks of soil drying. A comparison was made between the fine roots of 1-year-old seedling root systems (seedling) and the fine roots of woody laterals of 6-year-old grafted trees (adult). Each seedling and woody lateral root system was established in a pair of vertically separated and independently irrigated soil compartments located in field root chambers excavated adjacent to the trees to which the woody laterals were attached. Root + soil respiration and fine root survival of seedlings and adults were similar for the first 5 weeks. However, eight weeks after termination of irrigation to the upper soil compartments, mortality of fine roots was high in adults but not seedlings. Fine roots of adults exposed to dry soil for 5, 8 and 15 weeks exhibited 2, 26 and 33% mortality, respectively, whereas the corresponding values for fine roots of seedlings were 2, 6 and 8%. Although root + soil respiration rates of adults and seedlings were similar before the soil drying treatment, rates for adults were only 25% of those for seedlings after 15 weeks of soil drying. We conclude that, although fine roots of adults and seedlings are similar in form, they respond differently to soil drying.

Journal Article↗
PubMed2001

Prenatal localization of the dorsal root ganglion in different segments of the normal human vertebral column.

STUDY DESIGN: Vertebral columns from 11 normal human fetuses (10-24 weeks of gestation) derived from spontaneous abortions were examined as part of the legal autopsy procedure including spinal cord analysis. OBJECTIVES: To study the localization of the dorsal root ganglion in the normal fetal spine and to relate the dorsal root ganglion location to the ossification of the vertebral bodies and vertebral arches. SUMMARY OF BACKGROUND DATA: The normal and pathologic ossification pattern of the fetal human spine has been studied. There has been no study addressing the localization of the dorsal root ganglion in normal and pathologic axial development. METHODS: The dorsal root ganglion were studied by using histology (horizontal sections) and morphometric measurement. RESULTS: The study showed: 1) The dorsal root ganglion appeared before ossification of the spine; 2) The dorsal root ganglion had an oval shape in all cases; 3) The longitudinal axis of dorsal root ganglion was directed anterolaterally in the cervical and lumbosacral segments and mainly laterally in the thoracic segment; 4) During development, the dorsal root ganglion changed position according to the body axis; and 5) The para-axial ossification protected the dorsal root ganglion differently in the different axial segments. CONCLUSIONS: The dorsal root ganglion appeared before ossification. The distance from the dorsal root ganglion to the body axis increased during development. In the different segments of the spine, different orientations and different locations of the dorsal root ganglion were observed in relation to osseous spine components. The results can be used as reference data for future studies on the dorsal root ganglion in pathologic spines.

Ganglia, Spinal↗
PubMed2001

Effect of nucleus pulposus on the neural activity of dorsal root ganglion.

STUDY DESIGN: This study was designed to investigate, using neurophysiologic techniques in an in vivo rat model, the effect of application of nucleus pulposus to the nerve root on the neural activity of the dorsal root ganglion and the corresponding receptive fields. OBJECTIVES: To assess a further role of the dorsal root ganglion in mechanisms of radicular pain in lumbar disc herniation. SUMMARY OF BACKGROUND DATA: It has been suggested that the epidural application of autologous nucleus pulposus without mechanical compression causes nerve root inflammation and related radicular pain in lumbar disc herniation. Concerning the dorsal root ganglion, its mechanical hypersensitivity and potential for generating ectopic discharges have been reported. However, the effect of autologous nucleus pulposus on the dorsal root ganglion is uncertain. METHODS: In adult Sprague-Dawley rats spontaneous neural activity was recorded from the surgically exposed L5 dorsal root using electrophysiologic techniques, and the mechanosensitivity of L5 dorsal root ganglia and corresponding receptive fields on the hind paw were measured using calibrated nylon filaments. Autologous nucleus pulposus from the tail or fat was implanted at the L5 nerve root. Neural activity was monitored for 6 hours. RESULTS: Spontaneous neural activity in the nucleus pulposus group gradually increased and showed significant differences compared with the fat group from 2.5 to 6 hours after exposure. The mechanosensitivity of the dorsal root ganglia showed significant increases compared with the fat group. CONCLUSIONS: After application of nucleus pulposus to the nerve root, the dorsal root ganglion demonstrated increased excitability and mechanical hypersensitivity. These results suggest that nucleus pulposus causes excitatory changes in the dorsal root ganglion.

Animals↗
PubMed1998

Meristem-specific suppression of mitosis and a global switch in gene expression in the root cap of pea by endogenous signals

Two functionally distinct sets of meristematic cells exist within root tips of pea (Pisum sativum): the root apical meristem, which gives rise to the body of the root; and the root cap meristem, which gives rise to cells that differentiate progressively through the cap and separate ultimately from its periphery as border cells. When a specific number of border cells has accumulated on the root cap periphery, mitosis within the root cap meristem, but not the apical meristem, is suppressed. When border cells are removed by immersion of the root tip in water, a transient induction of mitosis in the root cap meristem can be detected starting within 5 min. A corresponding switch in gene expression throughout the root cap occurs in parallel with the increase in mitosis, and new border cells begin to separate from the root cap periphery within 1 h. The induction of renewed border cell production is inhibited by incubating root tips in extracellular material released from border cells. The results are consistent with the hypothesis that operation of the root cap meristem and consequent turnover of the root cap is self-regulated by a signal from border cells.

Journal Article↗
PubMed1976

Transmembrane electropotential in barley roots as related to cell type, cell location, and cutting and aging effects.

Transmembrane electropotential difference (PD) was measured in whole roots of barley (Hordeum vulgare L. cvs. Compana and Himalaya). Seedlings were grown 4 to 5 days in aerated 0.5 mm CaSO(4) or a nutrient solution. Measurements of PD were made with roots bathed in CaSO(4), KCl + CaSO(4), or the nutrient solution. The following results were found. (a) There was a radial PD gradient with epidermal cells being 10 to 58 millivolts less negative than cells in the third layer of the cortex (outside to inside). There was no longitudinal PD gradient in the region 0.5 to 4 cm from the root tip, nor was there any difference between the PD of young root hairs and other epidermal cells. (b) Cell PD in excised whole roots was not detectably different from that found in roots attached to the shoot, and was unchanged for 2 hours from excision. (c) In 1-centimeter sections of root, cell PD at the freshly cut surface was depolarized by 90 millivolts from that in the intact root; cells farther than 1 millimeter from the cut surface were not depolarized. The PD of cells at the cut surface became more negative upon aging the segment in 0.5 mm CaSO(4), eventually becoming greater by -25 millivolts than that in cells of intact roots. Cells in segments to which the root tips were attached had less negative PDs after aging than those in subapical segments, indicating a possible hormonal effect. PDs in aged, excised segments are not equivalent to those in intact roots. (d) Creeping of cytoplasm over electrode tips inserted into the vacuole gave measurements of vacuole-to-cytoplasm PD of + 9 millivolts in 0.5 mm CaSO(4) and + 35 millivolts in 1 mm KCl + 0.5 mm CaSO(4). Most of the cell PD was across the plasmalemma. (e) The reducing sugar content of roots in CaSO(4) solution was greater than that of roots in the nutrient solution in which ion uptake, particularly K(+) occurred.

Journal Article↗
PubMed1984

Metabolic response of river birch and European birch and European birch roots to hypoxia.

Flood tolerance of woody plants has been attributed to internal oxygen diffusion from shoot to root, metabolic adaptation within the root, or both. The purpose of this study was to compare several biochemical and physiological responses of birch roots to hypoxia in order to determine the nature of root metabolic adaptation to low oxygen tension. One-year-old seedlings of flood-tolerant river birch (Betula nigra L.) and flood-intolerant European birch (Betula pendula Roth) were transferred to solution culture, and the solutions were bubbled with air or nitrogen. After 18 days of hypoxia, total adenosine phosphate and ATP contents of river birch roots were 35% and 23% of controls, respectively, whereas those of European birch roots were 13% and 8%. Adenylate energy charge of river birch roots decreased between 6 and 12 days of hypoxia. In contrast, energy charge of European birch roots decreased after only 1 day of hypoxia. In vitro activity of cytochrome c oxidase and oxygen consumption capacity of excised roots from both birch species decreased under hypoxia. In vitro activity of alcohol dehydrogenase from roots of both species increased after 1 day of hypoxia. However, alcohol dehydrogenase activity from river birch roots increased 25-fold after 6 days of hypoxia, whereas that from European birch decreased back to control levels. Hypoxia decreased malate content of roots from both species. Metabolic adaptation within the root, rather than internal oxygen diffusion, appears to be responsible for the relative tolerance of river birch to hypoxia.

Journal Article↗
PubMed1990

High Sensitivity to Auxin is a Common Feature of Hairy Root.

The responses to auxin of Lycopersicon esculentum roots transformed by (T(l)+T(r))-DNA of the Ri plasmid of agropine-type Agrobacterium rhizogenes strain 15834 and Catharanthus trichophyllus roots transformed by the (T(l)+T(r))-DNA, and by T(l)- or T(r)- DNA alone of the same bacterial strain were compared to that of their normal counterparts. The transmembrane electrical potential difference of root protoplasts was measured as a function of the concentration of exogenous naphthalene acetic acid. The sensitivity to auxin expressed by this response was shown to be independent of the measurement conditions and of the basal polarization of isolated protoplasts. According to this electrical response, as well as to the modulation by auxin of proton excretion by root tips and root tip elongation, roots transformed by (T(l)+T(r)) DNA are 100 to 1000 times more sensitive to exogenous auxin than normal roots, as is the case with normal and transformed roots from Lotus corniculatus (WH Shen, A Petit, J Guern, J Tempé [1988] Proc Natl Acad Sci USA 85: 3417-3421). Further-more, transformed roots of C. trichophyllus are not modified in their sensitivity to fusicoccin, illustrating the specificity of the modification of the auxin sensitivity. Roots transformed by the T(r)-DNA alone showed the same sensitivity to auxin as normal roots, whereas the roots transformed by the T(l)-DNA alone exhibited an auxin sensitivity as high as the roots transformed by (T(l)+T(r))-DNA. It was concluded that the high sensitivity to auxin is controlled by the T(l)-DNA in agropine type Ri plasmids.

Journal Article↗
PubMed1990

Correlation of Pectolytic Enzyme Activity with the Programmed Release of Cells from Root Caps of Pea (Pisum sativum).

In many plant species, the daily release of hundreds to thousands of healthy cells from the root cap into the soil is a normal process, whose function is unknown. We studied the separation of the cells in pea (Pisum sativum) using an aeroponic system in which separated cells were retained on the root until they were washed off for counting. We found that cell separation is a developmentally regulated, temperature-sensitive process that appears to be regulated independently of root growth. No cells were released from very young roots. When plants were grown aeroponically, cell numbers increased with increasing root length to a mean of 3400 cells per root, at which point the release of new cells ceased. The process could be reset and synchronized by washing the root in water to remove shed cells. Cell separation from the root cap was correlated with pectolytic enzyme activity in root cap tissue. Because these cells that separate from the root cap ensheath the root as it grows and thus provide a cellular interface between the root surface and the soil, we propose to call the cells "root border cells."

Journal Article↗