Primary Lateral Root Research Articles

Changes in Structure and Hydraulic Conductivity for Root Junctions of Desert Succulents as Soil Water Status Varies

AbstractVariations in hydraulic conductivity (LP) and the underlying anatomical and morphological changes were investigated for main root‐lateral root junctions of Agave deserti and Ferocactus acanthodes under wet, dry, and rewetted soil conditions. During 21 d of drying, LP and radial conductivity (LR) increased threefold to fivefold at junctions of both species. The increase in LR was accompanied by the formation of an apoplastic pathway for radial water movement from the surface of the junction to the stele for A. deserti and by the rupture of periderm by emerging primordia of secondary lateral roots for F. acanthodes. During 7 d of rewetting, LR decreased for junctions of A. deserti, as apoplastic water movement was not apparent, but LR was unchanged for F. acanthodes. Axial conductance (Kh) decreased during drying for both species, largely because of embolism related to the degradation of unlignified cell wall areas in tracheary elements at the root junction. The resulting apertures in the cell walls of such elements would admit air bubbles at pressure differences of only 0.12‐0.19 MPa. Rewetting restored Kh for both species, but not completely, due to blockage of xylem elements by tyloses. About 40% of the primary lateral roots of the monocotyledon A. deserti abscised during 21 d of drying. For the dicotyledon F. acanthodes, which can form new conduits in its secondary xylem, only 10% of the primary lateral roots abscised during 21 d of drying, consistent with the much greater frequency of lateral roots that persist during drought in the field compared with the case for the sympatric A. deserti.

Hydraulic conductivity and anatomy along lateral roots of cacti: changes with soil water status.

To help understand root function for desert plants at different levels of water availability, cellular and water-conducting properties were examined for young lateral roots of Ferocactus acanthodes (Lem.) Britton & Rose and Opuntia ficus-indica (L.) Miller. Hydraulic conductivity (Lp ), radial conductivity (LR ), and axial conductance (Kh ) were determined for root segments in wet soil, during drought, and after rewetting. All three parameters increased with distance from the root tip under wet conditions and during drought for both species, with larger increases occurring under wet conditions. Lp decreased with drought duration up to 35 d for both species, due to dehydration of cortical cells, suberization of periderm, and embolism of xylem vessels; Lp and LB decreased more for O. ficus-indica, and Kh decreased more for F. acanthodes. The increase in Kh with distance from the root tip and the decrease with duration of drought were associated with the changes in the number of conducting xylem vessels. After 7 d of rewetting, new secondary lateral roots developed, enhancing water uptake, especially for O. ficus-indica. Rewetting also caused water uptake for primary lateral roots to return to approximately the original value under wet conditions, mainly because decreases in emboli led to recovery of axial flow.

The root morphology of Lupinus angustifolius in relation to other Lupinus species

Commercial L. angustifolius cultivation is restricted to acid to neutral coarse-textured soils in Australia. An unsuitable root system may be part of the reason for the poor performance on fine-textured or alkaline soils. As a first step to examine this question plants of 12 annual Lupinus species were grown in a coarse soil with the aim of describing the range of root morphologies within the genus and to compare these to commercial L. angustifolius. A wide range of rooting patterns were observed. The differences in the dominance of the taproot was pronounced between species. The commercial genotype of L. angustifolius occupied an extreme within the range of root morphologies of the species. Roots of L. angustifolius consisted of a dominant taproot and a relatively high number of primary lateral roots but few secondary roots. In contrast, the primary, secondary and tertiary lateral roots of L. pilosus, L. mutabilis, L. atlanticus, L. palaestinus and L. micranthus were more dominant than the taproot. The length and distribution of primary lateral roots along the taproot also varied between species. The number of primary lateral roots fell rapidly with depth in L. angustifolius and L. mutabilis, while the other species had a more even distribution. L. angustifolius had a less extensive root system and relatively thick roots when compared to species such as L. albus and L. mutabilis. L. luteus also had relatively thick roots. The relatively thick roots and less extensive lateral root system in commercial L. angustifolius may partially explain its poor growth on fine-textured soils, where a greater proliferation of finer, lateral roots may be necessary. Proteoid root formation was observed for L. albus, L. cosentinii, L. pilosus, L. palaestinus, L. micranthus, L. digitatus, L. princei and L. atlanticus. They were particularly numerous in L. micranthus and L. albus. The structure of proteoid root clusters varied between species.

Growth and root morphology of planted and naturally-regenerated Douglas fir and Lodgepole pine

Summary — Root system morphology and growth of Douglas fir (Pseudotsuga menziesii var glauca (Beissn) Franco) and Lodgepole pine (Pinus contorta var latifolia Engelm) saplings transplanted from containers to the field in 1979 were compared with naturally-regenerated saplings of the same species and age. Naturally-regenerated saplings of both species were significantly taller than planted trees, had greater leader growth in the previous year and height/diameter ratios, and smaller taproot diameters 10 cm below groundline. Naturally-regenerated saplings also had up to 2.3-fold the number of lateral roots compared with planted saplings. Seventy to 79% of all primary lateral roots of naturally-regenerated saplings occurred within the top 10 cm of the soil surface, compared with 3042% for the planted trees. The depth of the first structural lateral root associated with naturallyregenerated saplings was also significantly less than that of planted saplings. The shape of the container in which seedlings were raised in the nursery was clearly evident when root system architecture of planted saplings was examined. Many container-initiated seedling root systems exhibited conical shaping with little lateral root egress. A variety of root deformities which included constriction, coiling and kinkiness were detected in planted, but not naturally-regenerated saplings. These results are discussed in relation to potential difficulties arising from artificial forest regeneration with pine and Douglas fir.

Genetic variation for stress-related traits in guar

Eighty-two guar, Cyamopsis tetragonoloba (L.) Taub., germplasms were evaluated in laboratory and field studies for traits assumed to be associated with drought resistance. Primary root and lateral root lengths were measured in 10-day-old seedlings grown in polyethylene growth pouches at 35°C. Germplasms differed significantly in primary root and lateral root lengths, number of laterals, and in branching intensity (Experiment 1). Four vascular bundles were found in each germplasm with exception of a wild species, C. serrata Schinz, which had only three in each root. Germplasms differed significantly in canopy temperature and paraquat reaction (Experiment 2). Mean canopy temperatures exceeded air temperature ( T c − T a ), varying from 0.3 to 3.9°C in the 82 germplasms. Paraquat reaction (a relative measure of the plant's cellular antioxidant system) indicated five germplasms possessed a three-fold greater resistance to paraquat than the most susceptible germplasms. The uptake of paraquat was not significantly different in pubescent (non-waxy) and glabrous (waxy) germplasms. A stress index, designed to identify germplasms with vigorous root systems, high canopy temperature avoidance and resistance to paraquat, indicated 10 germplasms possessed relatively high levels of all traits. Seedling root characteristics, canopy temperature and paraquat reaction were not significantly correlated with grams seed −1 plant −1, suggesting that selection for improved yield using root and plant measurements described above would be non-productive.

Behavior of lateral roots in winter wheat as affected by temperature

The experiment was conducted to evaluate the effects of temperature on growth of laterals on the seminal roots of wheat ( Triticum aestivum L.). Wheat seedling root growth was measured on alternate days for 28 days beginning at 4 days after planting. The length, number, time of emergence, and the distance apart of primary lateral roots and the length of the unbranched axis were determined on the plants under air temperatures of 10, 20, 25 and 30°C. The primary lateral roots (i) emerged earlier with increased temperature, and developed closer to the tip of the seminal axis at 20 and 30°C than at 10 and 25°C, (ii) were more closely spaced along the seminal axis at the higher temperatures, (iii)_increased in density along a segment of root within a period of time after planting that varied with temperature, indicating that lateral root emergence did not follow an acropetal sequence, (iv) had a distribution in length that was unaffected by temperature, (v) were fewest in number and least in length at 10°C, greatest in number and length at 25°C, and were intermediate in length and number at 20 and 30°C, and (vi) had lengths that accounted for about 46, 83, 85 and 72% of the total seminal root length at 10, 20, 25 and 30°C, respectively.

Does Iron Deficiency in Pisum sativum Enhance the Activity of the Root Plasmalemma Iron Transport Protein?

Roots of Fe-sufficient and Fe-Deficient pea (Pisum sativum L.) were studied to determine the effect of Fe-deficiency on the activity of the root-cell plasmalemma Fe(2+) transport protein. Rates of Fe(III) reduction and short-term Fe(2+) influx were sequentially determined in excised primary lateral roots using Fe(III)-ethylene-diaminetetraacetic acid (Fe[III]-EDTA). Since the extracellular Fe(2+) for membrane transport was generated by root Fe(III) reduction, rates of Fe(2+) influx for each root system were normalized on the basis of Fe(III) reducing activity. Ratios of Fe(2+) influx to Fe(III) reduction (micromole Fe(2+) absorbed/micromole Fe[III] reduced) revealed no enhanced Fe(2+) transport capacity in roots of Fe-deficient peas (from the parental genotype, Sparkle) or the functional Fe-deficiency pea mutant, E107 (derived from Sparkle), relative to roots of Fe-sufficient Sparkle plants. Data from studies using 30 to 100 micromolar Fe(III)-EDTA indicated a linear relationship between Fe(2+) influx and Fe(III) reduction (Fe(2+) generation), while Fe(2+) influx saturated at higher concentrations of Fe(III)-EDTA. Estimations based on current data suggest the Fe(2+) transport protein may saturate in the range of 10(-4.8) to 10(-4) molar Fe(2+). These results imply that for peas, the physiological rate limitation to Fe acquisition in most well-aerated soils would be the root system's ability to reduce soluble Fe(III)-compounds.

Primary root and lateral root development in guar seedlings

Primary root and lateral root length of 7- and 10-day-old seedlings of three guar ( Cyamopsis tetragonoloba (L.) Taub.) seed sources were evaluated under several temperature and pre-germination seed treatment regimes to determine optimum conditions for root development. Seeds were germinated and seedlings grown in polyethylene growth pouches at constant temperatures in the dark. Primary root length, lateral root length and number of lateral roots were evaluated for 7 consecutive days after planting (DAP) in Experiment 1, and for 7 days with a final measurement at day 10 (DAP) in Experiment 2. In Experiment 1, seed sources differed significantly in primary root length, lateral root length, and number of lateral roots when grown at 30°C for 7 days. Mean primary root lengths were greatest (11.0 cm) for untreated seed grown in distilled water. Hot-water treated seed grown in distilled water produced the greatest number of lateral roots and total lateral root length. Hoagland's solution, in combination with either hot-water treated, sodium hypochlorite treated or no seed treatment, adversely affected primary root growth but increased branching intensity. Primary roots of all strains had four distinct xylem bundles. In Experiment 2 primary root length, number of laterals and lateral root length were greatest at 30–35°C. Branching intensity was greatest at 35°C. Primary root length was significantly correlated with number of laterals and lateral root length in all three seed sources and significantly correlated with branching intensity in the cultivar “Lewis”. The influence of the environment on mature seed during the pre-harvest period and its potential for masking genetic differences in primary root and lateral root development is discussed.

Root Growth Potential, First-Year Survival, and Growth of Shortleaf Pine Seedlings Show Effects of Life Date, Storage, and Family

Abstract Root growth potential (RGP), and first-year field survival and growth of shortleaf pine (Pinus echinata Mill.) seedlings were significantly affected by lift date, storage, and family. Seedlings lifted in December and January showed highest RGP, survival, and growth. Storage for 28 daysalways reduced survival and growth, and the effect was greatest for late-lifted seedlings. However, for late planting, the difference in performance between freshly lifted seedlings and earlier lifted and stored seedlings may be small. Large family differences existed for seasonal changesin RGP and survival, suggesting separate management by family may be beneficial. The presence of a terminal bud and secondary needles showed little value in predicting seedling performance, whereas RGP and number of primary lateral roots were strongly correlated with seedling survival. South.J. Appl. For. 13(4):163-169.

Soil Residual Properties of DPX-A7881 Under Laboratory Conditions

Growth chamber studies were conducted to examine the soil residual properties of DPX-A7881, a new sulfonylurea herbicide. The phytotoxic residue levels in the soil were determined by a lentil radicle bioassay. The duration of activity was prolonged in soil adjusted to pH 7.6 and 8.1 relative to more acidic levels. The rate of breakdown in the soil was enhanced with increased temperature and soil moisture content; a significant temperature by moisture interaction was noted over the duration of the incubation period. The dissipation of DPX-A7881 in soil obeyed first-order kinetics in both studies. An accelerated rate of breakdown in unsterilized versus sterilized soil (pH 7.6) indicated that microbial degradation was an important factor affecting the persistence in alkaline soils. Herbicide residues in the soil caused a reduction in taproot length and number of primary lateral roots of canola seedlings 15 days after planting but there were no other morphological effects observed on the root. The secondary laterals, however, had generally recovered by this time.

Root Excision and Dehydration Effects on Water Uptake in Four Range Species

Germinating seeds of crested wheatgrass (Agropyron desertorum), Russian wildrye (Elymusjunceus), alfalfa (Medicago sativa), and cicer milkvetch (A stragalus cicer) were dehydrated for 4 days at -22 MPa, and/or their roots were excised, and used as treated materials. In an experiment in root growth boxes, where the seedlings depended for 60 days on the initial soil water supply, seminal primary and seminal lateral roots of grasses penetrated to the same depth. Both types of roots were similarly effective in taking up water, mainly from the upper 50 cm of the soil profile. In a sealed pot experiment under favorable moisture conditions, water uptake increased with seedling age up to 34 and 41 days for crested wheatgrass and Russian wildrye, respectively, and up to the end of the experiment (53 days) for the legume species. Leaf area of grasses was not affected by root excision alone, but it decreased due to the combined effects of root excision and temporary dehydration. Leaf area was generally proportional to water uptake within each species. In all 4 species, root excision and temporary dehydration did not affect transportation rates, while transportation rate decreased as a function of age. Transportation rates were higher in legumes than grasses and were higher in Russian wildrye than crested wheatgrass.

Hydraulic conductance and anatomy of roots of Vicia faba plants infected by Uromyces viciae-fabae

Infection of faba bean ( Vicia faba L.) by rust [ Uromyces viciae-fabae (Pers.) Shroet.] inhibited increases in the length of tap and primary lateral roots both in soil columns and in solution culture. In whole root systems exicsed from plants grown in solution culture, rust infection reduced volume flux of water slightly but increased hydraulic conductance (Lp) per unit area of root or of endodermal surface; these changes occurred over a range of imposed hydrostatic pressures and temperatures. Rust-induced increases in Lp occurred in tissue produced after infection, but not in tissue produced before infection, the sub-terminal segment. Examination of lateral roots from the upper 18 cm of the soil profile showed infection reduced root diameter and increased specific root length (cm root mg −1 dry weight). In tissues formed after inoculation, infection had no effect on the diameter of the cortex or the number of cortical cells along a radius. However, the diameter of the endodermal cylinder was reduced in both tap and lateral roots. Since radial resistance to water flow is the major component of total root resistance in faba bean, it is proposed that these changes were responsible for the increased Lp caused by infection.

Pisolithus tinctorius increases the size of nursery grown red oak seedlings

Inoculation of nursery beds with vegetative mycelia of P. tinctorius (Pt) significantly increased the number of salable 1–0 red oak seedlings produced in two of three years and the average stem height and diameter each year. The percentage of Pt mycorrhizal primary lateral roots on seedlings in the inoculated plots was significantly correlated with stem diameter and weight of lateral roots. The high rates of colonization of short roots by Pt in inoculated plots suggested the test fungus could successfully compete with indigenous fungi in forming mycorrhizae.

Toppling in British Columbia's Lodgepole Pine Plantations: Significance, Cause and Prevention

Young trees sometimes lean, or topple by pivoting about a point below the ground. Geotropic curvature in the lower part of the stem restores the leading shoot to the vertical. The resultant stem bowing reduces potential lumber recovery, and is associated with reaction wood formation. Toppling has occurred in lodgepole pine (Pinus conforta Dougl.) plantations throughout British Columbia. Generally the number of trees affected has been small; although in the southern interior of the province the majority of trees in some plantations have toppled. In areas where toppling in planted trees has occurred, naturally established lodgepole pine is relatively stable. Since planted trees are usually of the native provenance, this suggests that toppling in plantations is primarily the result of nursery and planting effects on root morphology. More normal root morphogenesis, and hence greater stability can be achieved by planting young seedlings that retain the capacity to initiate primary lateral roots. Pruning the lateral roots of older stock provides another approach. A chemical method for pruning lateral roots of container-grown lodgepole pine seedlings has been developed and adopted commercially in British Columbia and elsewhere.

Predicting Soybean Rooting Depth as a function of Soil Temperature1

AbstractA two dimensional predictive simulation of rooting depth has been developed from data which describe the effects of root‐zone temperature on soybean [Glycine max (L.) Merr.] root development. The major inputs are equations which describe the rate of taproot and lateral root extension, node development, and the rooting angle as a function of time and temperature. The simulation predicts the extension of the taproot and 10 primary lateral roots for two groups of soybean cultivars. The output consists of a listing of serial rectangular coordinates for each root tip and a computer plot of the root system. The rooting depths predicted by the simulation agree well with field experimental data illustrating the importance of soil temperature in determining the depth of soybean root penetration in extrapolating greenhouse root extension data to a field situation.

Colchicine-light effects on growth and mitotic behaviour in germinating lettuce achenes.

Root and shoot growth were severely suppressed in colchicine-pretreated lettuce achenes germinated in the dark and under illumination of 150 lux. Abnormal nuclear morphology rather than normal-appearing restitution nuclei was evident in these drug-pretreated achenes, there being no evidence of normal mitotic behaviour or cytokinetic activity in the root and shoot tissues examined. Root extension and lateral root meristem differentiation were evident in colchicine-pretreated achenes germinated under an illumination of 3000 lux, normal-appearing anaphase figures and cytokinetic activity being evident in both the primary root apices and lateral root meristems. Thus, the growth and mitotic behaviour of germinating colchicine-pretreated lettuce achenes were observed to be influenced significantly by the environmental light intensity in which germination occurred.

The buckling of plant roots

The mechanical stresses required to buckle root tips were measured directly for seven plant species. For two of these, both seminal and primary lateral roots were measured. For four of the plant species investigated, the easier and more rapid method used to measure the buckling stresses of excised root tips gave results which agree closely with those obtained for the growing roots of intact plants. Values of buckling stress were also calculated from previously determined elastic properties of roots. The calculated and measured values of buckling stress are of the same magnitude only, and comparison for ten root types fails to show any consistent relationship between these two methods. From the results from three plant species it has been possible to define empirical functions to account for the observed changes in root buckling stress with air gap length and water stress. Buckling stresses are not significantly affected by the concentration of nitrate in the growth medium.

The Effect of Auxins on Pinus contorta Seedling Root Development

Primary lateral root production on Pinus contorta seedlings was increased 5–10 fold by immersion in auxin solutions. Watering auxin solutions onto P. contorta seedlings growing in soil or compost induced the development of large numbers of primary lateral roots in the root collar region. The number of primary lateral roots which developed depended mainly upon the auxin used and its application rate, seedling age and to a lesser extent on the soil characteristics. Instability of transplanted pines is partly due to their lack of primary lateral roots and their inability to regenerate new ones after planting out; this instability may be overcome by using auxin treated seedlings. Potential practical applications of this technique are discussed.

Elastic response of the roots of field crops

The elasticity of root tips was investigated in experiments of the static clamped‐beam type. The response was non‐linear. The results were interpreted in terms of a generalized elastic modulus M, and two parameters, α and β, which account for the non‐linearity.Seminal axes and primary lateral roots of 16 crop species grown in the laboratory show significant inter‐species differences but insignificant inter‐variety differences in the elastic properties. A smaller set of results for field‐grown roots with two tillage treatments shows that, in nearly all cases, the elastic modulus is smaller and the diameter is larger than with laboratory‐grown roots. Environmental factors such as water potential, and nutrition have significant influences on the diameters and elastic behaviour of roots.

Effects of Shading, Removal of Panicle and Foliar Application of Nutrient on the Formation of Superficial Roots of Rice Plants

Rice plants, cultivar "Mubo- Aikoku", were grown in Wagner pots under conditions of 50 per cent shade, removing about half of each panicle, foliar spraying with 5 per cent glucose or 1 per cent urea solution four times and control. Treatments were carried out during the period between young panicle formation stage and full ripe stage, at which the formation of superficial roots could be observed. Regarding shade grown plants, the length of both primary roots and secondary lateral roots as well as the density of both secondary and tertiary lateral roots were lower than those of control. Concerning panicles removing and foliage spraying grown plants, the opposite trend was true as compared with shade treatment, i.e., the investigated features of superficial roots formation were several times higher than those of control. With respect to the formation of lateral roots, visual observation showed that spraying grown plants branched up to forth or fifth order, while those of shade treatment branched only up to tertiary. The formation rate of "lion-tail-like root", was greatly different among the treatments, i.e., this rate was higher for shade plants than control, and the opposite was true with panicles removing grown plants. According to the conjecture that both panicles removing and foliar application of nutrients are favourable for the nutrio-physiological conditions of tested plants, while shade is hazard; from the above results, it can be concluded that the formation of superficial roots as well as "lion-tail-like roots" was closely connected with nutrio-physiological conditions.