Order Lateral Roots Research Articles

Genotypic Variation in the Development of Seminal Root System of Rice under Different Culture Conditions in vitro.

To elucidate genotypic variations in the root system architectures of rice, which are determined by the emergence (branching) and elongation of lateral roots, we compared the development of seminal root systems (seminal root axis and lateral roots) among seven cultivars with different ecotypes using an in vitro culture method which can simplify growth conditions. Four different culture treatments were prepared by combining two factors (nitrogen source in medium and presence/absence of shoot) to evaluate genotypic variations as a whole. After three weeks of culture, sampled seminal root systems were developmentally, topologically and geometrically analyzed. First, we researched the responses of root system development to culture conditions. It was especially notable that the responses of L-type and S-type first order lateral roots were completely different, and that root system size was affected by both the composition of medium and the presence/absence of shoot, while branching pattern was mainly controlled by the former. Though it was difficult to find a general trend in cultivar variations throughout the treatments, we characterized and classified the seven cultivars mainly based on the root system size and responses to culture conditions. Instinctive genotypic variations were clearly recognized under culture conditions as compared to soil conditions. Thus, this study showed the possibility that selection of genotypes focused on architecture could be facilitated using an in vitro culture method.

Effect of Drought During the Establishment Period on the Root System Development of Cassava.

The effect of different time and duration of progressive drought on cassava, during the establishment stage, i.e., from planting to about three months after planting, was studied with special attention to root system development. Plants exposed to drought, regardless of whether early (from 9-44 days after planting (DAP)) or late (from 44-82 DAP), in the establishment period had significantly fewer leaves and lower shoot dry weight (DW) than well-watered controls. Late droughted plants manifested similar inhibition of shoot growth with those continuously droughted from 9-82 DAP. With regards to root development, early drought caused reduction in the number and length of adventitious roots, number of first, second and third order lateral roots and total root DW. The value of these parameters generally increased after the plants were rewatered. Late drought caused reduction in the number and length of the adventitious roots, and the number of first and second order lateral roots, but not the third order lateral roots, which appeared to be promoted instead by drought. The total root DW also increased in late-droughted plants due to the thickening of adventitious roots. Overall, the results show that cassava has sensitivity to drought stress during its establishment period.

Modification of Root System Morphology in a Peanut Seedling Inoculated with Arbuscular Mycorrhizal Fungus, Gigaspora margarita Becker & Hall.

Modification of root system morphology caused by the inoculation of arbuscular mycorrhizal fungus (Gigaspora margarita Becker & Hall) was evaluated in peanut (Arachis hypogaea L.). Peanut plants were grown for 16 days in root boxes placed in a growth chamber with natural light. Inoculum of the fungus was uniformly mixed with the soil in root boxes, whereas in others, the soil was uninoculated to serve as a control. In each root system, the tap root axis was divided into 10-mm sections, where lateral roots remained intact, to evaluate the difference in lateral root development along the tap root. Two-way ANOVA in which the variation sources were divided into the inoculation treatment and section of tap root axis, showed significant effects of the inoculation on lateral root development. As for the root number, the effect was promotive for the 1st order lateral roots but inhibitive for the 2nd order ones, and as for the individual root length, inhibitive for the former but was not detected for the latter. Our conclusion is that the inoculation caused changes in root system morphology of peanut through lateral root development on the tap root, where the responses were different between 1st and 2nd order lateral roots.

Distribution of Arbuscular Mycorrhizas in Peanut Root System.

The distribution of arbuscular mycorrhizal colonies was assessed in a peanut (Arachis hypogaea L.) root system at early growth stage. Arbuscular mycorrhizal fungus (Gigaspora margarita Becker & Hall) was uniformly inoculated into non-sterilized soil. Peanut plants were grown in root boxes filled with the soil for 16 days inside a growth chamber. Approximately 66% of the total length of the mycorrhizal colonies was found on the 1st order latelral roots, while the rest was observed on the 2nd ones. In contrast, the tap root was scarcely colonized. On the 1st order lateral roots, regardless of the root length, it was evident that the frequency of the mycorrhizal colonies increased acropetally toward the root apex especially in the relatively aged roots that initiated on the proximal portion of tap root axis. In those lateral roots, the highest frequency of the mycorrhizal colony occurrence was recognized in the most apical part of the root, while many of relatively long colonies were found a little behind the root apex. However, the trend became unclear gradually in the relatively younger lateral roots initiated on the more distal potion of tap root axis. These facts clearly showed that in the 1st order lateral roots, the distribution and growth of mycorrhizal colonies are closely related with their initiating positions along tap root axis.

Plant growth and cell division in Pisum sativum L. and Picea sitchensis (Bong.) Carr. exposed to ozone

summaryPea (Pisum sativum L. cv. Feltham First) and clonal Sitka spruce plants (Picea sitchensis (Bong.) Carr.) were exposed to ozone concentrations of 0–90 ppb to investigate effects on both shoot and root growth and also cell division in the apical mm of roots. P. sativum plants were maintained under these conditions for 3 wk whilst P. sitchensis were left for 3 months. After 3 wk in the presence of 90 ppb ozone the mitotic index in the root apical mm of P. sativum was reduced compared with control plants (0 ppb ozone), whereas the number of primordia along the length of the main root in P. sativum plants increased at 90 ppb ozone. The smallest concentration of ozone (30 ppb) had no effect on leaf area, shoot dry weight and number of leaves of P. sativum. However, the number of second order lateral roots and total root dry weight were reduced at concentrations of 60 ppb and above while leaf size, plant height and shoot dry weight were only reduced in the presence of 90 ppb ozone. Cell doubling time in the root apical mm of P. sitchensis increased in plants which had been grown in the presence of 30 ppb ozone and decreased in those plants grown in chambers containing 90 ppb ozone. Ozone did not appear to have any other effects on those aspects of the cell cycle examined in either P. sativum or P. sitchensis.

Analysis of Timecourse Changes in Root System Morphology of Rice in Excised Root Culture.

The development of cultured seminal root system of rice was analyzed to determine the most appropriate culture period for the characterization of root system morphology. Excised seminal root tips of Taichung Native 1 (TN-1, indica type) and Yukara (japonica type), were cultured for six weeks with the conventional tissue culture method, and their growth was evaluated with developmental, topological and fractal analyses. Developmental root growth parameters, such as the number and length of each root system component, reached almost maximum values at the fourth week in TN-1, and the third week in Yukara. On the other hand, it was possible to characterize the root system morphology by the branching densities of L- and S-type first order lateral roots and the average length of S-type first order lateral roots at the third week. In the timecourse changes of a topological parameter (log a/log μ), which indicates the branching pattern, the difference between cultivars became clear at the third week. The fractal dimension (D), which indicates the complexity of root morphology, was higher in Yukara than in TN-1 throughout the experimental period. This suggested the possibility for characterizing the root system morphology of each cultivar by the D value. Therefore, we concluded that the most appropriate sampling time for the morphological research of cultured seminal root system was three weeks when the conventional excised root culture method is used.

Effects of Physiological and Morphological Characteristics of Root Tips Excised from Rice Seminal Roots on Subsequent Growth in vitro.

Tissue culture of excised root is a useful method with which genetic variation of plant root itself can be determined without the influence of shoot. We aimed to determine the effects of age and elongation rates of the seminal root axis of rice on subsequent growth in a culture medium. Taichung Native 1 (indica type) and Yukara (japonica type) were used in the experiments. The seminal root tips (1-cm-length) were sampled every day after bedding on agar and their morphological and physiological characteristics were monitored by recording the persence of lateral roots and primordia, dry weight and C·N content. Root tips with different ages or elongation rates were then cultured, and subsequent growth was observed after three week culture. Root tips which were older and had lower elongation rates showed inferior root growth in both cultivars. When a more than three-day-old seminal axis on which lateral roots started to emerge was excised, less L-type first order lateral roots was produced than that grown on the two-day-old axis, and this affected the total root number and length. The dry weight or C·N content of excised segments decreased as the excision day, and these characteristics showed a close correlation with the subsequent root growth. Thus, we concluded that the excision of root tip segments at an earlier stage ensures excellent development of seminal root system in vitro.

Morphology and Physiology of the Seminal Root System of Young Maize (Zea mays L.) Plants as Influenced by a Locally Restricted Nitrate Supply

AbstractIn water culture the effect of a locally restricted NO3 supply to the seminal root system of maize seedlings was studied. For this purpose plants were cultivated in containers with a wide‐bore polyethylene tube positioned horizontally. Roots were suited through small holes in this tube and after sealing the holes with a non‐toxic silicon putty, root segments in the tube could be exposed to a different nutrient solution from the rest of the root system in the outer compartment.In case of a locally restricted NO3 supply (NO3 was just supplied to the root segment within the tube), we observed an increase in root growth beginning at the fifth day after onset of the treatment. NO3 uptake rate (15N) within the tube was significantly higher than in control plants (receiving NO3 to the entire root system) as early as two days after onset of the treatment. One day later respiration (O2 consumption) of the root segment exposed to NO3 increased and at the same day we observed an accumulation of 14C activity (after pulse labelling of the shoots with 14CO2) suggesting an increased phloem unloading. It is argued that this leads to the measured increase in IAA activity (Radio Immuno Assay) in the zone of NO3 supply. Beginning at the fifth day we observed a stimulation of cell division rate (incorporation of 3H‐methylthymidine), accompanied by an increase in length of first order lateral roots.

Effects of high nitrogen concentrations on ectomycorrhizal structure and growth of seedlings of Picea abies (L.) Karst.

High nitrogen concentrations are known to affect ectomycorrhizal and ectomycorrhizal fungi in field and laboratory experiments. Using NH/ as a nitrogen source in the growth pouch system, a variety of structural modifications were documented on first order lateral roots of Picea abies (L.) Karst. seedlings. Root cells increased in size and number at high levels of NH4 + resulting in a hypertrophic appearance of roots in both uncolonized seedlings and in those inoculated with mycelia of the ectomycorrhizal fungus Hebeloma crustuliniforme (Bull, ex St. Amans) Quel. A fungal mantle surrounded short roots of inoculated seedlings, and the outer walls of epidermal and cortical cells were often thickened when in contact with fungal hyphae. No Hartig net developed, although intracellular penetration of fungal hyphae into epidermal and cortical cells frequently occurred. At moderate NH4 + concentrations, Hartig net development was incomplete, but occasional intracellular penetration of Hartig net hyphae into epidermal and cortical cells occurred. The addition of high levels of NH4 + after ectomycorrhizal development resulted in ectomycorrhizas with distinctly altered apical structures. None of the various NH4 + concentrations resulted in significantly different plant dry weights after two months of exposure, either with or without fungal inoculation. After four months, dry weight, root length and branching indices were higher in both inoculated plants and those exposed to high nitrogen. The root/shoot ratio and number of short roots per seedling were high with fungal inoculation. Shoot nitrogen levels after two and four months and the Ca levels after 4 months were higher with increasing NH4 + in the nutrient solution. Other mineral elements were not influenced by nitrogen concentrations and fungal inoculation.

Growth and Development of Roots of Grapevine (Vitis vinifera L.) in Relation to Water Uptake from Soil

Developmental patterns of lateral roots and their vascular differentiation were investigated for Vitis vinifera L. cv. Shiraz to assess the likely contribution of lateral roots to total water uptake of plants subjected to different irrigation regimes. Correlation analyses showed a significant positive correlation between main root diameter and the diameter of first order lateral roots of well-watered plants, but in water-stressed plants the two were not significantly correlated. The correlations between diameters of first order lateral roots and the diameters of main roots were greater than correlations between the lengths of first order laterals and the diameters of main roots. The suberised surface area of well-watered main roots increased from 4% of total surface area at 0·25 cm to 100% at 10 cm from the tip, whereas that of stressed plants increased from 15% at 0·25 cm to 100% at 5 cm from the tip. In all treatments the highest linear density of first order laterals was about 7 laterals cm-1 of main root. More than 50% of first order laterals had diameters less than 0·05 cm, and more than 90% of them had lengths less than 5 cm. Calculations of axial resistances based on xylem diameter measurements suggest that the axial resistances of root segments may not be uniform along roots as is often assumed in models of water uptake. Water flow into the main roots via the lateral root pathway is likely to be much smaller than that via the direct radial flow pathway as only about 1% of surface area of main roots is directly occupied by lateral roots, leaving the other 99% of main root surface area available for the direct radial flow pathway.

Growth and Development of Roots of Grapevine (Vitis vinifera L.) in Relation to Water Uptake from Soil

Developmental patterns of lateral roots and their vascular differentiation were investigated for Vitis vinifera L. cv. Shiraz to assess the likely contribution of lateral roots to total water uptake of plants subjected to different irrigation regimes. Correlation analyses showed a significant positive correlation between main root diameter and the diameter of first order lateral roots of well-watered plants, but in water-stressed plants the two were not significantly correlated. The correlations between diameters of first order lateral roots and the diameters of main roots were greater than correlations between the lengths of first order laterals and the diameters of main roots. The suberised surface area of well-watered main roots increased from 4% of total surface area at 0.25 cm to 100% at 10 cm from the tip, whereas that of stressed plants increased from 15% at 0.25 cm to 100% at 5 cm from the tip. In all treatments the highest linear density of first order laterals was about 7 laterals cm(-1) of main root. More than 50% of first order laterals had diameters less than 0.05 cm, and more than 90% of them had lengths less than 5 cm. Calculations of axial resistances based on xylem diameter measurements suggest that the axial resistances of root segments may not be uniform along roots as is often assumed in models of water uptake. Water flow into the main roots via the lateral root pathway is likely to be much smaller than that via the direct radial flow pathway as only about 1 % of surface area of main roots is directly occupied by lateral roots, leaving the other 99 % of main root surface area available for the direct radial flow pathway.

Growth reduction and root deformation of containerized lodgepole pine saplings 11 years after planting

Root system architecture and field performance of 90 twelve-year-old lodgepole pine ( Pinus contorta var. contorta Dougl.) saplings, initially raised in containers for one year (1979) before planting, were compared with 60 naturally regenerated lodgepole pine saplings of the same age. The naturally regenerated saplings were significantly taller, and leader increments for 1989–1990 and 1990–1991 indicated that they performed better than the planted saplings during the two most recent growing seasons. Planted saplings displayed root morphologies which differed markedly from their natural counterparts; these included poor structural lateral root symmetry, fewer first order lateral roots, a greater distance from the ground surface to the first structural lateral root, and a greater root collar diameter and concentration of lateral roots 10 cm below the groundline. In addition, root stocks of planted saplings possessed remnants of vertical container shaping and a number of deformed roots that were either constricted, coiled and/or kinked. Naturally regenerated saplings illustrated elaborate sinker root development, and an assortment of self-grafted roots which were not observed on planted saplings. Possible effects of containerization on root morphology are discussed in relation to difficulties which may arise from artificial regeneration of cut-over sites.

Specific colonization of the hypodermis of sorghum roots by an endophyte,Polymyxasp.

Abstract A number of clusters of resting spores of an endophyte were found to have colonized the nodal root axes and first order lateral roots of sorghum at the heading stage. The clusters with a diameter ranging 15 to 20 μm consisted of a number of spores with a diameter in the range of 2 to 5 μm. Based on the morphological characteristics, the endophyte was tentatively assigned to Polymyxa sp. The clusters were distributed in the epidermis and the hypodermis, but mostly in the latter. The clusters were absent in the tissues internal to the hypodermis. The number of cells colonized by the clusters in the hypodermis, the hypodermal cell lignification identified by the phloroglucinol-HCl test, and the cortical sclerenchyma development were examined acropetally in three nodal roots which emerged from the third node. The colonized cells accounted for less than about 10% of the total number of the hypodermal cells in the first 8 cm portion, but beyond this part, their number increased and they accounted for 10 to 35%. Hypodermal cell lignification and cortical sclerenchyma development were clearly recognized approximately in the first 9 and 6 cm portion, respectively, but they were not observed beyond this part. Even in this portion, however, no endophyte colonization was observed in any tissues internal to the hypodermis. These findings suggest that in sorghum the hypodermis itself, regardless of cell lignification, may function as a barrier to protect the inner tissues from further colonization by the spore clusters of Polymyxa sp.

Growth and development of sorghum roots after exposure to different periods of a hot root-zone temperature

Under natural conditions crop plants are often exposed to high soil temperature regimes during growth. To determine the influence of a hot root-zone temperature (RZT) on growth and development of root system components of plants, sorghum ( Sorghum bicolor Moench) was grown in nutrient solution with three temperature regimes. Maximum seminal root (SR) elongation and first order lateral root (LR) initiation and elongation occurred at 25°C (control). At 40°C SR elongation and first order LR initiation and elongation were severely inhibited. Less inhibition in root growth occurred at 40/25°C (day/night) RZT than at 40°C. The duration of exposure to 40°C (i.e. from 0 to 6 days) had a profound influence on subsequent root growth and development when the plants were returned to 25°C; the longer the 40°C period the greater the degree of root growth inhibition at 25°C. Nodal roots (NRs) which arose mainly from the first node of the stem were initiated regardless of their previous exposure to 40°C; the number and length increased as the exposure duration at 40°C increased.

Effects of soil compaction on the development of rice and maize root systems

The aim of this study was to determine the effects of soil compaction on the development of root system components of rice ( Oryza sativa L.) and maize ( Zea mays L.). Plants were grown for 4 weeks in root ☐es (24 cm long × 2 cm wide × 40 cm deep) with soil bulk densities of 1.33 g/cm 3 (control) and 1.50 g/cm 3 (compact). In the compact treatment the main root axes of rice never penetrated beyond the 10–15 cm soil layer even by the fourth week, while seminal and seminal adventitious roots of maize had penetrated 30–35 cm deep by the third week. Generally, growth of higher order (second and third) lateral roots compensated for the restricted growth of the main root axes in both species. The ratio of first order L-type laterals producing higher order laterals on their axes was greater in the compact treatment for rice, while that of maize was not significantly increased. The root growth responses of rice and maize to soil compaction were different in the downward penetration of the main axis and the growth of the higher order laterals.

Interspecific Differences of the Root System Structures of Four Cereal Species as Affected by Soil Compaction

Comparison of the root system structures of four cereal species as affected by soil compaction was conducted morphometrically. Plants were grown under two different soil bulk densities of 1.33g/cm3 (control)and 1.50g/cm3 (compact) for two weeks in the root box, and measurements were made on the number, length and diameter of all the roots from every component of the root system. Promoted or less restricted growth was recognized in the mean length and number of higher order laterals in every species under compact treatments. The increased occurrence of L-type lateral roots in the compact treatment contributed to the promoted growth of higher order laterals. Compared to upland rice and Job's tears, sorghum and maize showed higher restriction in both shoot and root growth. As for the occurrence ratio of L-type laterals in the compact treatment, the former two species had 1.5 to 3 times that of the latter two species. Regardless of root diameter, the species with longer root length showed higher restriction of total root length in both 1st and 2nd order laterals. It was suggested that the ability to produce L-type laterals and extension rate of each order lateral roots were closely related to root growth responses under mechanically impeded soil conditions.

Effect of seed provenance and fungal species on bead formation in roots of Piceamariana seedlings

The effects of both seed source and fungal species on the formation of beads in roots of Piceamariana (Mill.) B.S.P. were examined. Seed was collected from two sites near Chapleau, Ontario. One provenance was an upland site with sandy soil, the second a lowland site with peaty soil. Seedlings were grown under aseptic conditions in test tubes and inoculated with either Laccariabicolor (Maire), Laccarialaccata (Scop, ex Fr.), Laccariaproximo (Boud.) Pat., or agar plugs. Each constriction or striation on the root was counted as a single bead. These constricted regions were associated with the accumulation of a darkly stained substance and the absence of a Hartig net. Bead formation on first order lateral roots from each treatment was assessed and the data were analyzed for significance with a two-way factorial ANOVA. There was a significant interaction between seed source and fungal species on the numbers of beads formed. Bead formation was significantly more common on the lowland seed source in the L. laccata treatment only. L. laccata inoculation resulted in the greatest number of beads on first order lateral roots followed by control and L. proximo treatments. Colonization of seedlings with L. bicolor resulted in the formation of significantly fewer beads than in the control or any other treatment.

Effects of seed provenance and mycorrhizal fungi on early seedling growth in Piceamariana

The importance of provenance and fungal species effects on mycorrhiza formation in Piceamariana was determined. Seed was collected from two sites near Chapleau, Ontario. One provenance was collected from an upland site with sandy soil, the second from a lowland site with peaty soil. Seedlings were grown under aseptic conditions in test tubes. Two experiments were performed: in the first, seedlings were inoculated with Hebelomacylindrosporum, Laccarialaccata, or Paxillusinvolutus, whereas in the second, seedlings were inoculated with Laccariabicolor, Laccarialaccata, Laccariaproximo or noninoculated agar plugs. Counts of ectomycorrhiza and lateral root formation were analyzed for significance with two-way factorial ANOVAS. When inoculated with L. laccata, seedlings from the lowland seed source had significantly more mycorrhizal second order lateral roots than seedlings from the upland seed source. Lowland seedlings also had greater shoot dry weight and foliage length values. However, overall differences between provenances were small. In contrast, differences between fungal treatments were pronounced. Both L. laccata and L. bicolor initiated good ectomycorrhiza formation and increased seedling growth.

The effect of photoperiod and temperature on growth and frost resistance of winter rye root systems

Root growth, development and frost resistance were examined in winter rye (Secale cereale L. cv. Puma) plants grown under 6 combinations of temperature and photoperiod (20/16°C or 5/3°C, day/night; 8, 16‐ or 24‐h days). Overall root system growth is influenced by the interaction of temperature and photoperiod. Maximum shoot growth occurs at a 24‐h photoperiod in 20°C plants and at a 16‐h photoperiod in 5°C plants, and is correlated in both treatments with a high root:shoot ratio. Frost resistance of rye roots is affected by short photoperiods in 2 ways. First, short photoperiod and low temperature delay production of new adventitious roots so that newly developing roots are not exposed to freezing temperatures. Second, short photoperiod alone can induce several degrees of frost tolerance in existing roots during the lag phase of growth. Low temperature alone does not decrease the rate of dry weight accumulation in rye root systems, but cold temperature does retard developmental processes within the roots. Rye roots grown at 5°C develop first order lateral roots, differentiate metaxylem vessels and suberize endodermal cell walls more slowly than roots grown at 20°C.

Mutual relationship between patterns of soil penetration resistance and root radial expansion growth of upland rice.

The root boxes (24cm×2cm×40cm) filled with soil at two different soil bulk densities of 1.33 g/cm3 (control) and 1.50 g/cm3 (compact), were prepared for studying mutual relationship between the variation of penetration resistance as a function of soil depth and radial expansion growth of root axis. Upland rice was grown under both soil conditions for two weeks, and the root systems were sampled by pinboard method. Penetration resistance determined by a developed penetrometer showed several peaks of resistance throughout the entire depth of the root boxes caused by the presence of soil boundary layers resulting from the procedure of soil filling up. There were also found variations of root diameter of seminal axis and lst order lateral roots emerged from the seminal axis as a function of soil depth. In the compact plot, patterns of the penetration resistance corresponded well with those of root diameter. However, in the control, the correspondence of both patterns was not as clear as in the compact. These results indicated that patterns of soil mechanical impedance along the entire depth of the root box could be recorded in root axes as the history of radial expansion growth when root tips were exposed to higher mechanical impedance. The result obtained in this experiment suggested the necessity of considering the patterns of soil mechanical impedance in the growth media for the study of root-soil interaction.