Effect of Localized Anoxia on Phaseolus vulgaris L. Root Growth

Heterogeneity within the root environment results in differentialgrowth within root systems. The response of five Phaseolus vulgarisL. cultivars to non-uniform root aeration was evaluated. Threetreatments were applied to a split root system for a periodof 72 h. Treatments consisted of an aerated control, a non-aeratedcontrol (both halves non-aerated, using N₂). and localized anoxia(one-half the root system aerated and the remaining half subjectedto N₂). Shoot and root growth were reduced in the anoxic controlbut not in the aerated control or localized anoxia treatment. Root growth was greatest in the aerated portion of the localizedanoxia treatment for all genotypes. Contributions of the rootcomponents to the compensatory responses differed dependingon the plant cultivar examined. The growth of branched and lateralroots present before the treatment period increased by 65% inline 31908. A 50% increase in the growth of lateral roots whichemerged during the treatment period occurred in another line(Swan Valley). Other genotypes responded in an intermediatemanner. These observations indicate differences in cultivarresponses to localized soil stress. Key words: Phaseolus vulgaris L., Anoxia, Root growth     

Effect of Lateral Root Formation on the Vascular Pattern of Barley Roots

The vascular pattern in the root of barley (Hordeum vulgare L.), characterized by discontinuous xylem, is markedly affected by its branching. The roots become divided into unbranched segments alternating with branched segments with a more complex vascular pattern, formed by two systems differing in origin and age: the primary vascular system derived from the procambium and ontogenetically younger connective vascular system derived from stelar parenchyma. Adjacent to the sites of the lateral root initiation, reprogramming of parent stelar parenchyma for connective vascular elements occurs. The connecting phloem is represented by small sieve elements and companion cells, the connecting xylem is composed of small vessel elements with reticulate or scalariform-reticulate wall thickenings and simple perforations. Development of the connective vascular system secures continuous lateral and axial vascular connection between lateral root and parent root. The extent of the vascular connection in the parent root increases in an acropetal direction. Hydraulic effects of connective vascular tissue formation and parent root segmentation are discussed.     

Anoxia Tolerance in a Root Hair Defective Mutant of Rice

Anoxia tolerance of rice (Oryza sativa L.) seedlings was investigated using wild type (WT) and root hair defective mutant RH2. The elongation of both RH2 and WT roots was suppressed by anoxia, but this suppression was less in RH2 than in WT roots. The anoxic treatment increased the activity of alcohol dehydrogenase in both RH2 and WT roots, but the induction was greater in RH2 roots. These results suggest that anoxia tolerance of RH2 roots is greater than that of WT roots, indicating that root hairs may interfere with the anoxia tolerance of rice roots.     

Hypoxic Induction of Anoxia Tolerance in Root Tips of Zea mays

When root tips of fully aerobic, intact maize (Zea mays L.) seedlings are made anaerobic, viability normally is only 24 hours or less at 25°C. We find that viability can be extended to at least 96 hours if seedlings are given a hypoxic pretreatment for 18 hours by sparging the solution with 4% O₂ in nitrogen (v/v) before anoxia. Fully aerobic root tips (sparged with 40% O₂) had very low alcohol dehydrogenase (ADH) activity (per gram root fresh weight), and the level remained low under anoxia. In hypoxically pretreated roots, however, high levels of ADH activity were induced, and activity rose further during the initial 24 hours of anoxia, and then remained high at about 20 times that of controls in 40% O₂. ADH activity in roots in solution sparged with air (21% O₂) was about three times that in 40% O₂. Improved viability of hypoxically pretreated root tips was associated with maintenance of a high energy metabolism (ATP concentration, total adenylates, and adenylate energy charge). Roots that were not pretreated lost 94% of the total adenylates and ATP at 24 hours of anoxia. The relation between induced ADH activity, energy metabolism, and improved anoxia-tolerance in acclimated maize root tips is discussed.     

Effect of Anoxia on Carbohydrate Metabolism in Rice Seedlings

The metabolism of carbohydrates was investigated in rice (Oryza sativa L.) seedlings grown under anoxia. Two phases can be recognized in the utilization of carbohydrates: during the first days of germination under anoxia, the metabolism of sugars is mainly degradative, whereas after the induction of [alpha]-amylase (EC 3.2.1.1) has taken place, the increased presence of glucose and sucrose indicates that both starch degradation and sucrose synthesis operate. The analysis of the enzymes involved in carbohydrate metabolism indicates that anoxic rice seedlings possess a set of enzymes that allow the efficient metabolism of starch and sucrose to fructose-6-phosphate. We propose that cytosolic sucrose metabolism in anoxic rice seedlings takes place mainly through a sucrose synthase (EC 2.4.1.13) pathway with nucleoside diphosphate kinase (EC 2.7.4.6), allowing the cycling of urydilates needed for the operation of this pathway.     

Root Density and Water Potential Gradients near the Plant Root

The models of Gardner (1960) and Cowan (1965) for water transferto the plant root are used to estimate the differences in waterpotential between the root and the bulk soil for a wide rangeof root densities and water extraction rates at a series ofmatric potentials for a Yolo light clay. For root densities and extraction rates reported both in theliterature and in this paper there is good evidence to suggestthat the large potential gradients originally predicted by Gardnerand Cowan are restricted to situations involving very low rootdensities and high extraction rates in relatively dry soil.     

Loss of Potential Aquatic-Terrestrial Subsidies Along the Missouri River Floodplain

Ecosystems - The floodplains of large rivers have been heavily modified due to riparian development and channel modifications, both of which can eliminate shallow off-channel habitats. The...     

Rapid Changes in the Pattern of Electric Current around the Root Tip of Lepidium sativum L. following Gravistimulation

Using a highly sensitive vibrating electrode, the pattern of naturally occurring electric currents around 1-day-old primary roots of Lepidium sativum L. growing vertically downward and the current pattern following gravistimulation of the root has been examined. A more or less symmetrical pattern of current was found around vertically oriented, downward growing roots. Current entered the root at the root cap, the meristem, and the beginning of the elongation zone and left the root along most of the elongation zone and in the root hair zone. After the root was tilted to a horizontal position, we observed current flowing acropetally at the upper side of the root cap and basipetally at the lower side within about 30 seconds in most cases. After a delay of several minutes, acropetally oriented current was also found flowing along the upper side of the meristematic zone. The apparent density of the acropetal current in the root cap region increased and then decreased with time. Gravitropic curvature was first visible approximately 10 minutes after tilting of the root to the horizontal position. Since the change in the pattern of current in the root cap region precedes bending of the root and is different for the upper and lower side, a close connection is suggested between the current and the transduction of information from the root cap to the elongation zone following graviperception in the cap.     

Carbon Transport and Root Respiration of Split Root Systems of Phaseolus vulgaris Subjected to Short Term Localized Anoxia

The influence of anoxia on carbon transport and root respiration was evaluated by applying [U-¹⁴C]sucrose to the foliage. Translocation patterns to the root systems of two dry edible bean genotypes (Phaseolus vulgaris L.) were examined after a 3-day exposure to aerated and nonaerated environments. Localized anoxia of root systems was simulated by growing roots in split configurations and exposing half of the system to anoxic conditions. Anoxia of the root system for 72 hours reduced the movement of ¹⁴C label into the roots with concurrent accumulations in the hypocotyl region. The translocation of ¹⁴C label to anoxic roots was less than 50% of the aerated controls of both genotypes. Most of the ¹⁴C label translocated to anoxic root systems was excluded from respiratory metabolism during the 3-hour pulse/chase period and was an order of magnitude less than the aerated controls. These observations suggest that the bulk of ¹⁴C label which entered the root during the anoxic period was unavailable for metabolism by the enzymes of glycolysis and/or was diluted by a relatively large metabolite pool. A higher percentage of ¹⁴C label was translocated to the aerated half of the localized anoxia treatment relative to the half of the aerated controls. The proportion of ¹⁴C label translocated to the root system in the aerated control was 20 and 16% compared to 28 and 25% in the aerated localized anoxia treatment for the genotypes Seafarer and line 31908, respectively. Line 31908 partitioned a greater percentage of ¹⁴C-labeled compounds to the actively growing fraction of the root system in the localized anoxia treatment than did Seafarer. This suggests a greater reliance on previously stored carbohydrate for immediate root growth in Seafarer than in line 31908.     

Modelling the Population Dynamics of Root Hemiparasitic Plants Along a Productivity Gradient

Root hemiparasitic plants interact with their host plants through parasitism and competition. The interactions can be divided into aboveground and belowground interactions. Because both groups of plants are autotrophic, they compete for light aboveground. Belowground interactions are more complex. The host plants compete for resources in the soil and the hemiparasitic plants prey on the host plants through haustoria, using the hosts as the main source of water and nutrients. In this paper, we modeled the relationship between these two plant types, extending the well-known Rosenzweig-MacArthur predator-prey model to cover both light competition and intra-specific parasitism among hemiparasites. We included a realistic relationship of carrying capacity to environmental productivity and followed model behavior on a productivity gradient. The model shows that, at very low productivities, there are only a few poor hosts and hemiparasites have no chance to persist. As productivity increases, there is a range of productivity where both plant types coexist. A further increase in productivity gets the system out of the coexistence range, and only host plants survive. This final prediction successfully explains patterns observed in empirical data, contrary to the results of an earlier, oversimplified model of the explored interaction. Comparison of various models demonstrates that the model is able to reproduce the decline of hemiparasites with increasing productivity only when competition for light is included.     

Effect of Anoxia on the Expression and Molecular Form of the Pyrophosphate Dependent Phosphofructokinase

Induction of pyrophosphate dependent phosphofructokinase (PFP)activity in the cotyledons of C. lanatus coincides with onlyan increase in the ß-subunit content. After normoxicinduction of PFP activity a subsequent exposure to anoxia causesa sharp decline in activity and the ß-subunit content. (Received March 18, 1991; Accepted August 13, 1991)     

Primary Root Growth and the Pattern of Root Apical Meristem Organization are Coupled

Root apical meristems (RAMs) in dicotyledonous plants have two organizational schemes; closed (with highly organized tiers) and open (tiers lacking or disorganized). These schemes are commonly believed to remain unchanged during the growth of the root axis. Individual roots are commonly thought to have indeterminate growth. We challenge these two generalizations through the study of five species with closed apical organization: Clarkia unguiculata L., Oxalis corniculata L., Dianthus caryophyllus L., Blumenbachia hieronymi Urb., and Salvia farinaceae Benth. cv. “Strata”. These roots have phased growth patterns where early growth is followed by deceleration, after which the initial cells stop dividing, elongation ceases, and the root reaches its determinate length. At or before reaching determinacy, the root apical meristem stops maintaining its closed organization and becomes less organized. These observations will be placed in context with observations from the literature to suggest two new generalizations, namely, that apical organization does change over the growth phases of roots, and that roots are determinate.     

Effect of Root Position on Measured Root Position on Measured Root Membrane Potentials

Root membrane potentials were measured by interposing a plantroot between two KCI solutions of different concentrations.The potentials measured across the two calomel electrodes werefound to depend on the position of the root. The potentialswere found to be lower when the root tip rather than the rootbase was in contact with the more concentrated solution. Thisindicates that the two parts of the root do not have the samein transport properties. Using an approximate theoretical treatmentthe observed potentials could be accounted for.     

节瓜蓟马空间分布图式研究

对节瓜蓟马在节瓜上的空间分布状况进行了调查和分析,结果表明,该虫的空间分布型前期符合奈曼分布,后期符合负二项分布;其空间图式是聚集的,分布的基本成分是个体群;在节瓜不同叶位上分布差异显著。明显向心叶聚集,在瓜栅向光面与背光面虫口比例方面,均以向光面较多。     

Spatial Analysis of Antibiotic Resistance Along Metal Contaminated Streams

The spatial pattern of antibiotic resistance in culturable sediment bacteria from four freshwater streams was examined. Previous research suggests that the prevalence of antibiotic resistance may increase in populations via indirect or coselection from heavy metal contamination. Sample bacteria from each stream were grown in media containing one of four antibiotics—tetracycline, chloramphenicol, kanamycin, and streptomycin—at concentrations greater than the minimum inhibitory concentration, plus a control. Bacteria showed high susceptibilities to the former two antibiotics. We summarized the latter two more prevalent (aminoglycoside) resistance responses and ten metals concentrations per sediment sample, by Principal Components Analysis. Respectively, 63 and 58% of the variability was explained in the first principal component of each variable set. We used these multivariate summary metrics [i.e., first principal component (PC) scores] as input measures for exploring the spatial correlation between antibiotic resistance and metal concentration for each stream sampled. Results show a significant and negative correlation between metals PC scores versus aminoglycoside resistance scores and suggest that selection for metal tolerance among sediment bacteria may influence selection for antibiotic resistance differently in sediments than in the water column. Our most important finding comes from geostatistical cross-variogram analysis, which shows that increasing metal concentration scores are spatially associated with decreasing aminoglycoside resistance scores—a negative correlation, but holds for contaminated streams only. We suspect our field results are influenced by metal bioavailability in the sediments and by a contaminant promoted interaction or “cocktail effect” from complex combinations of pollution mediated selection agents.     

Further Study on the Statistical Test to Detect Spatial Pattern

In the study of spatial patterns, the statistic I' = (n — 1)s²/x was commonly used. In this paper, we found that x — s² has an approximated normal distribution with zero mean if the x_i's (i = 1 to n) are independent identically distributed Poisson variables. Based on this conclusion, the hypothesis that a point pattern is completely random can be tested directly. And a method for the test of spatial patterns was proposed which can be sued as an alternative to the Chi-square based dispersion index test.     

Spatial Pattern Analysis of Plant-Parasitic Nematodes

Spatial patterns of Meloidogyne incognita, Tylenchorhynchus claytoni, Helicotylenchus dihystera, and Criconemella ornata were analyzed using Hill''s two-term local quadrat variance method (TTLQV), spectral analysis, and spatial correlation. Data were collected according to a systematic grid sampling plan from seven tobacco fields in North Carolina. Different estimates of nematode cluster size were obtained through TTLQV and spectral analysis. No relationship was observed between either estimate and nematode species, time of sampling (spring vs. fall), or mean density. Cluster size estimates obtained from spectral analysis depended on sampling block size. For each species examined, spatial correlations among nematode population densities were greater within plant rows than across rows, indicating that clusters were ellipsoidal with long axes oriented along plant rows. Analysis of mean square errors indicated that significant gains in sampling efficiency resulted from orienting the long axis of sampling blocks across plant rows. Spatial correlation was greater in the fall than in spring and was greater among 1 × 1-m quadrats than among 3 × 3-m quadrats.     

The Effect of Coumarin on Root Growth and Root Histology

The effect of coumarin on the root growth was studied on roots from intact plants, isolated roots and isolated elongating zones. All material was cultivated aseptically. A new method was developed for sterile culture of intact plants in flowing nutrient medium. The effects on cell division and cell elongation were studied separately. An effect on both these processes can be established at all concentrations that affect the root growth. The concentration-growth curve has an “all-or-none” appearance. Coumarin inhibits the transverse divisions in all cell layers; the perivascular layers seem to be more sensitive. Also the mitotic activity that is involved in the initiation of laterals is inhibited. The longitudinal divisions within the stele are enhanced. Coumarin decreases the cell length in all cell layers, most likely with greater relative sensitivity in the perivascular layers. Studies on the time course of cell elongation in both attached corn roots and isolated elongating zones reveal that the decrease in cell length is caused exclusively by a decrease in the maximal rate of elongation, whereas the duration of the elongation is unchanged. With each decrease of the cell length, the cell diameter is increased. The two changes are intimately connected within the greater part of the active region of concentration. Studies on the time course of the radial expansion in isolated elongating zones show a strict connection in time between cell elongation and radial expansion. The radial expansion leads to unchanged or increased cell volume at most concentrations and for most cell types. Coumarin causes an inhibition of the longitudinally directed processes and a stimulation of the radially directed ones. This is interpreted as indicating that the formative system is disengaged or reorientated, i.e., the polarity of the cells is changed. Through experiments partly with isolated elongating zones and partly by disruption of the linear phase by means of mannitol, the inhibitory effect of coumarin could be localized to the first non-linear phase of the elongation. The results were compared with earlier findings in the literature. The microtubuli are proposed as a conceivable main Component in the formative system common to both cell division and cell elongation. These are assumed to be affected by changes in the SH/SS balance produced by coumarin.     

The Electrical Potential Difference Across the Tonoplast of Root Cells

Changes in electrical potential, measured as a microelectrodewas advanced into epidermal cells and from cell to cell in rootsof Lolium multiflorum and Zea mays, are described. The recordingssuggest that the electrical potential difference between thecytoplasm and vacuole, E_vc is of the order of a few millivolts,the vacuole tending to be the more positive. E_vc appeared tobe approximately the same for epidermal, cortical, endodermal,and pericycle cells.