Spring Wheat Roots Research Articles

Effects of Common Root Rot on Discoloration and Growth of the Spring Wheat Root System

Image analysis procedures were used to quantify the effect of common root rot on the growth and discoloration of the subcrown internode (SCI), crown roots, and seminal roots of spring wheat. Severe discoloration of the SCI was associated with diminished growth of the seminal and crown roots. The linkage of discoloration of the SCI to a reduction in root growth was most evident for the crown roots. Reduced growth of either the crown or seminal roots was not compensated for by increased growth of the other root system. The differences in root discoloration among different root rot categories were generally small. On average, the crown and seminal roots were whiter than the SCI in the healthy (nil) category. There was a weak negative relationship between discoloration of the SCI and the crown and seminal root systems. However, it was also observed that root discoloration usually increased with greater root length. Since plants with healthy SCIs usually had longer roots, they were more likely to be exposed to the pathogen and become discolored than were plants with severely diseased SCIs. The image analysis procedures developed in this study can be used to objectively and precisely measure damage caused by root diseases in other host species. This procedure validates the most commonly used field research method of rating plants for common root rot

Root growth and nitrate uptake by wheat (Triticum aestivumL.) following wetting of dry surface soil

The nitrate uptake capacity of surface roots of spring wheat (Triticum aestivum L. cv. Kulin) was investigated following wetting of dry surface soil. Plants were grown to stem elongation stage with adequate watering at depth while the surface soil was allowed to dry. Eight weeks after sowing, water or a l5 N-nitrate solution was added to the surface soil to simulate rainfall. Root growth and nitrate uptake were measured up to 4 d after wetting on plants with unconfined nodal root growth and on plants with the majority of nodal roots confined within small vials. Prior to wetting, plants from both nodal treatments had seminal roots with collapsed cortices along the upper 10 cm and many short, viable lateral roots. Nodal roots, where present, were only a few cm long and unbranched. Only plants with unconfined nodal roots were able to take up nitrate within the 24 h before any new root growth. By 2 d after wetting there was significant growth of the seminal lateral roots, and rapid growth and branching of nodal roots. From 2d after wetting, plants with confined nodal roots also took up nitrate, presumably due to the growth of the seminal lateral roots. Hence it appears as though the nodal roots in the unconfined treatment could immediately take up nitrate, but the seminal roots required new lateral root growth to become active in nitrate uptake. The plants with confined nodal roots had a lower nitrate uptake than those with unconfined nodal roots 4d after wetting, indicating that the seminal root system was not able to compensate for lack of nodal roots. Insufficient nitrate was taken up after 4 d, by plants from either nodal root treatment, to increase the shoot N concentration significantly.

Analyzing Root Competition with Dirichlet Tessellation for Wheat on Three Landscape Positions

AbstractThe underlying mechanisms for root competition are not completely understood; yet, it is important to accurately define the zone of influence around individual roots for nutrient or water uptake, particularly when modeling nutrient uptake processes. The objectives of this study were to investigate the use of the Dirichlet tessellation for quantifying soil polygons around roots of spring wheat (Triticum aestivum L. cv. Katepwa) grown on three landscape positions and to quantify the root spatial patterns. Roots were exposed on a horizontal soil plane at 2‐, 5‐, and 10‐cm depths and mapped on acetate sheets at 21, 45, and 88 days after planting (DAP) for shoulder, backslope, and footslope positions. Tessellation of scanned root maps showed that soil polygons decreased in size during the sampling period; however, polygon areas increased with soil depth regardless of slope position and ranged from 0.08 to 52.77 cm2. Eccentricity averaged 0.74 ± 0.01, indicating that polygons were more circular than elliptical and root displacement averaged one‐third the distance from the polygon center to the polygon edge. Root spatial patterns using R‐index values, showed that roots on shoulder positions had clumped to random patterns while roots at the footslope had random to regular patterns. Root spatial patterns and displacement for wheat violated the assumptions used in nutrient uptake modeling and should be incorporated into future modeling efforts. Dirichlet tessellation is an effective procedure for analyzing root competition and has promise for multispecies competition if different root systems can be weighted by morphological or physiological characteristics.

Control of the activity of plant plasma membrane MgATPase by the viscosity of the aqueous phase

The activity of plant plasma membrane (PM) MgATPase (EC 3. 6. 1. 35) was studied in PM vesicles purified from spring wheat (Triticum aestivum L. cv. Drabant) roots, winter wheat (Triticum aestivum L. cv. Martonvásári‐8) roots, and soybean (Glycine max L. cv. Williams) hypocotyls by aqueous polymer two‐phase partitioning. MgATPase from spring wheat roots was assayed at 23°C (a) in the absence and presence of Triton X‐100, (b) in the presence of either 1 mM or 3 mM MgATP2−, and in the presence of increasing concentration of sucrose from 10 mM upto 1. 2 M. Activity of MgATPase in PM vesicles from winter wheat roots was measured at 21°C at sucrose concentrations of 15 mM–1. 1 M in the presence of 3 mM MgATP2− and absence of Triton X‐100 only. MgATPase activity from soybean hypocotyls was studied (a) in the absence and presence of Triton X‐100, (b) both at 21 and 31°C, in the presence of 3 mM MgATP2− and varying concentrations of sucrose between 10 mM and 1. 1 M. In all cases, independently of the assay conditions and the source of PM, the MgATPase activity decreased with increasing sucrose concentration. Latency of the MgATPase activity depended only slightly on the concentration of sucrose. The Q10 value for the MgATPase activity from soybean hypocotyls (and thereby the Arrhenius activation energy of the enzymatic reaction) was independent of the sucrose concentration and of the presence of Triton X‐100. At optimal assay conditions, the ATP‐hydrolyzing activity of plant PM MgATPase (v) was inversely proportional to the m‐th power of the viscosity of aqueous phase (η) as predicted by the modified Kramers'theory of enzymatic catalysis: v ∝ (1/η)m, where m is an empirical parameter between 0 and 1. For the activity of MgATPase in the three species studied, m varied between 0. 5 and 1. 1 in good agreement with the theory. We thus conclude that (a) the activity of integral membrane enzyme‐proteins may be controlled not only by the property(ies) of the membrane lipid phase but also by the viscosity of the aqueous phase in the vicinity of such enzymes, and (b) the determination of vesicle sidedness based on enzyme latency may need a minor revision. Our interpretation is in agreement with the molecular dynamics approach of enzymatic catalysis worked out for soluble enzymes.

WHEAT AND TRITICALE ROOT DEVELOPMENT AS AFFECTED BY TRIFLURALIN

A growth chamber study was conducted to investigate the effects of trifluralin on root morphology of wheat and triticale seedlings. Five spring wheat cultivars, five durum wheat cultivars and three triticale cultivars were grown for 15 days in soil treated with 0, 0.4 and 0.8 ppm trifluralin. Root damage from trifluralin in both wheat and triticale was greater at 0.8 ppm than 0.4 ppm. The 0.4 ppm rate of trifluralin reduced dry weight of Canuck, Hercules and Carman compared to the control; however, at 0.8 ppm, root dry weight of all cultivars was reduced compared to the control. Trifluralin injury symptoms included increased number of seminal roots, decreased seminal root extension, increased root diameter, and reduced root dry weight. As a group, the roots of spring wheat were injured more by trifluralin than the roots of either durum wheat or triticale. Differences in root damage amongst the cultivars was more apparent after the appearance of the second radicle root. A negative correlation was obtained between caryopsis lipid content (μg lipid per caryopsis) and root dry weight among the cultivars at the 0.8 ppm trifluralin rate.Key words: Trifluralin, wheat, triticale, root morphology, lipid

Electrostatic surface properties of plasmalemma vesicles from oat and wheat roots. Ion binding and screening investigated by 9-aminoacridine fluorescence

Right-side-out and sealed plasmalemma vesicles were isolated from roots of spring wheat (Triticum aestivum L. cv. Drabant) and oat (Avena sativa L. cv. Brighton) by two-phase partition in a medium containing sucrose (0.25 mol l(-1)). Oat root plasmalemma vesicles were discovered to contain a strongly fluorescent compound with an emission maximum at 418 nm. The surface potential of the membranes was monitored by 9-aminoacridine fluorescence and the effect of protein concentration, mannitol versus sucrose, absence of osmoticum, concentrations of salt, and titrations with chelators investigated. It is concluded that i) protein concentrations of less than 50 μg ml(-1) for oat and 100 μg ml(-1) for wheat plasmalemma vesicles should be used to avoid serious problems with non-linearity of response of 9-aminoacridine fluorescence, ii) mannitol can be used instead of sucrose as the osmoticum, iii) the vesicles were ruptured in the absence of osmoticum allowing us to monitor both sides of the membranes, iv) plasmalemma vesicles from oat roots are more negative than vesicles from wheat roots, and v) oat and wheat root plasmalemma vesicles are isolated with about the same amounts of bound Ca(2+) and Mg(2+). These bound divalent cations may not, however, reflect the in-vivo conditions since the tissues were homogenised in the presence of ethylenediaminetetraacetic acid.

Allelopathic potential of wild oat (Avena fatua) on spring wheat (Triticum aestivum) growth

Wild oat plants may produce toxic substances that suppress the growth and development of desirable species, thus accounting for severe yield loss in infested fields. The purpose of this study was to determine the allelopathic potential of wild oat (Avena fatua) on the growth of spring wheat (Triticum aestivum var. Fieldwin) in the absence of plant competition. Wild oat and spring wheat plants were grown separately in 250-ml beakers in a sand medium. Root exudates were extracted from wild oat medium at the 1-, 2-, 3-, and 4-leaf stages of wild oat development and added to beakers containing spring wheat in temporally corresponding stages of development. Spring wheat root and leaf dry weights were measured to determine if one or more allelochemical agents were released from wild oat roots. Spring wheat leaf and root dry weights were significantly reduced by exudates from wild oat plants at the 2- and 4-leaf stages of development, respectively. Allelochemicals were isolated from wild oat root exudates at various stages of plant development. Paper chromatography analysis indicated that at least two unknown compounds were present.R f values in benzene-acetic acid-water of the two unknown compounds (0.825 and 0.930) were similar to scopoletin (7-hydroxy-6-methoxycoumarin) and vanillic acid (4-hydroxy-3-methoxybenzoic acid), respectively. Additional tests using diazotizedp-nitraniline, ultraviolet absorption spectra, and gas chromatography analysis also indicated that the unknowns were coumarin-related compounds such as scopoletin and vanillic acid.

Development of regulation mechanisms for SO42‐ influx in spring wheat roots

The development of SO42‐ influx in roots and sulfur transport to shoots was followed in 35S‐tracer experiments for sulfur‐deficient spring wheat (Triticum aestivum L. cv. Svenno) seedlings pretreated for various time periods (0–24 h) in nutrient solutions with SO42‐. Effects of the metabolic inhibitor 2,4‐dinitrophenol (DNP) and the protein synthesis inhibitor cycloheximide (CH) on SO42‐ influx were also evaluated. The SO42‐ influx appears feedback‐regulated by the internal sulfur level of the roots. Regulation may be achieved solely by a rapidly changed SO42‐ carrier activity through an allosteric effect by the intracellular SO42‐ concentration of the roots, followed first by induction of carrier synthesis and then by repression of carrier synthesis after transfer of the roots from SO42‐‐deficient nutrient solutions to solutions with SO42‐. A Hill plot of the partly sigmoidal relationship between SO42‐ influx and intracellular sulfur concentration in the roots gave a Hill coefficient of ‐4.2, indicating negative cooperativity between a minimum number of four interacting allosteric binding sites for sulfur on each carrier entity. DNP‐experiments showed that SO42‐ influx was mainly metabolic, especially after short pretreatment in SO42‐ at an external SO42‐ concentration of 0.1 mM. Pretreatment with CH rapidly prevented new SO42‐ carriers from being formed. Long CH pretreatment (24 h) and different SO42‐ pretreatments reduced SO42‐ influx below the non‐metabolic level obtained by uptake experiments with DNP, indicating the existence of SO42‐ carriers mediating passive SO42‐ transport across the plasmalemma of the root cells. SO42‐ influx was further decreased for the CH pretreated (24 h) plants by the presence of both CH and DNP in the experimental nutrient solution. This probably indicates the diffusive part of the non‐metabolic SO42‐ influx in the present experiments. Finally, it is suggested that there is a feedback signal between root and shoot, regulating sulfur transport upwards.

Separation of metabolic and non‐metabolic steps of Rb+ uptake in spring wheat roots with different K+ status

Uptake of Rb+ from a complete nutrient solution with 2.0 mM Rb+ was studied in roots of spring wheat seedlings (Triticum aestivum L. cv. Svenno) with different K+ levels. The relationship between Rb+ uptake and concentration of K+ in the roots indicated a negative feedback mechanism operating through allosteric control. The Rb+ uptake process in root cells was divided into two steps: (1) binding of the ion in the free space, and (ii) transmembrane transport into the cytoplasm. Metabolic and non‐metabolic components of uptake were separated by addition of the metabolic inhibitor 2,4‐dinitrophenol (DNP) to the nutrient solution. It is suggested that metabolic Rb+ uptake requires energy in two uptake steps (for binding to the carrier entity in the free space and for transmembrane transport) or in one step only (for transmembrane transport), dependent on the K+ status of the roots. The change from metabolic to non‐metabolic binding in the free space is accomplished by changing the conformational state of the carrier (slow/fast transitions). There may be a hysteretic effect on metabolic Rb+ uptake through a slow transition between carrier states. This is superimposed on the negative cooperativity, strengthening further cooperativity at intermediate K+ levels in the roots. Non‐metabolic Rb+ uptake probably consists of two components, a carrier‐mediated (facilitated diffusion) and a parallel diffusive component.