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  • 1
    Electronic Resource
    Electronic Resource
    Control of root growth: effects of carbohydrates on the extension, branching and rate of respiration of different fractions of wheat roots (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 88 (1993), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Rates of extension, numbers of laterals and rates of respiration were measured in different fractions of wheat (Triticum aestivum L. cv. Alexandria) roots following changes in carbohydrate supply. The supply of carbohydrate was varied by selective pruning and exogenously fed sugars. Pruning shoots to a single leaf (leaf-pruning) reduced the rate of O2 uptake by intact roots. Rates were not stimulated by shortterm feeding of sucrose (25 mM), but were stimulated by the uncoupler p-trifluoro-methoxy(carbonylcyanide)phenylhydrazone (FCCP). Feeding glucose to roots of leaf-pruned and non-pruned plants for 16–24 h increased the rate of O2 uptake. It is concluded that respiration is under fine control by adenylates and coarse control by carbohydrate supply, with carbohydrates regulating directly the rate of some energy consuming process(es). These energy consuming processes are located in growing tissue fractions. Feeding glucose to leaf-pruned and non-pruned plants increased rates of O2 uptake in seminal root tips, the zone of developing lateral primordia and mature root sections with elongating laterals, but had no effect on mature sections from which the laterals had been excised. Leaf-pruning reduced the extension rate of seminal axes and first-order laterals when measured over 24 h. Feeding glucose to roots from the time of pruning increased the rate, but did not fully restore it to control values. Pruning roots to a single seminal axis (root-pruning) and feeding glucose to non-pruned plants had no effect on the extension rate of the seminal axis or its laterals over this time period, although rates were increased by root-pruning when measured over 3 days. The number of lateral root primordia was reduced by leaf-pruning and increased by root-pruning and feeding glucose. The results are discussed in terms of the role of carbohydrates in the control of root growth and branching.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1993.tb01772.x
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  • 2
    Electronic Resource
    Electronic Resource
    Regulation of respiration in roots of barley (1988)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 73 (1988), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The regulation of respiration in roots of barley [Hordeum distichum (L.) Lam. cv. Maris Mink] was examined in terms of the supply of carbohydrate and control by adenylates. The carbohydrate content of roots was modified by selective pruning and feeding sucrose (25 mM) and rates of O2 uptake were measured 16–24 h later. Pruning roots to a single seminal axis increased the soluble sugar content of the sole remaining root by 30% and its rate of O2 uptake by 24%: pruning shoots so that all but the second leaf was removed lowered the soluble sugar content of the roots by 39% and their rate of O2 uptake by 34%. Changes in the rate of O2 uptake were due largely to adjustments in activity of the cytochrome path (vcyt): these changes were accompanied by comparable adjustments in capacity of the path (Vcyt) so that it always operated close to full engagement (=90%). The capacity of the alternative path was unchanged and in no case was there any engagement. Since the alternative path failed to engage over a wide range of carbohydrate contents, we conclude that this path does not function as a simple energy overflow in barley roots. Irrespective of pruning treatment respiration appeared to be limited directly by the turnover of ATP since rates of O2 uptake were stimulated by the uncoupler FCCP, but not by short-term (〈 1 h) feeding of sucrose. However, long-term feeding of sucrose (16–24 h) to roots of leaf-pruned and control plants resulted in an increase in both vcyt and Vcyt. It is proposed that whilst the rate of O2 uptake is regulated directly by the turnover of ATP, some energy-consuming processes might be sensitive to the carbohydrate concentration: changes in supply of carbohydrate with selective pruning or sucrose feeding may alter rates of these processes and regulate vcyt through changes in energy demand. The nature of adjustments in Vcyt and the possible role of the alternative path are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1988.tb00598.x
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  • 3
    Electronic Resource
    Electronic Resource
    A comparison of the dynamics of root growth and biomass partitioning in wild oat (Avena fatua L.) and spring wheat (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Weed research 35 (1995), S. 0 
    Details
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The dynamics of early root growth and dry matter partitioning were compared in spring wheat (Triticum aestivum L.) and wild oat (Avena fatua L.) grown in solution culture. Total root length was greater in wheat than wild oat throughout the experiment; a result of a greater number of seminal axes and greater production of lateral root length per axis. The final number of adventitious roots was greater in wheat than in wild oat, but their length was similar. Relative growth rates were also similar as was shoot:root dry weight ratio and rate of root respiration. However, wheat used the dry matter partitioned to its roots more efficiently, producing a greater specific root length (SRL, length per unit weight). Caution must be exercised when relating these results to plants growing and compet-ing in the field, but three general points are raised. First, the initial number of seminal axes can have a profound effect on the rate of early root development; second, the adventitious root system of wild oat is not inherently more vigorous than that of wheat; and third, future studies should compare SRL of wheat and wild oat in the field. If differences similar to those in the present study are found they may contribute to the greater competitive ability of wheat.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3180.1995.tb02017.x
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  • 4
    Electronic Resource
    Electronic Resource
    Relationship between tissue sugar content, phloem import and lateral root initiation in wheat (1998)
    Copenhagen : Munksgaard International Publishers
    Physiologia plantarum 103 (1998), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Split-root experiments were conducted to test the hypothesis that adjustments in lateral root initiation, as might occur in response to localized soil conditions, are determined by the sugar content of the root and do not depend on changes in the import of phloem-translocated phytohormones. Wheat (Triticum aesticum L. cv. Alexandria) seedlings were grown in hydroponics with their seminal roots divided between two compartments within the culture vessel. Two seminal roots of treated plants were supplied with standard nutrient solution supplemented with 50 mM glucose, whilst the remaining three roots received nutrient solution without glucose. Control plants had their roots divided in the same ratio, but both ‘halves’ received nutrient solution without glucose. Feeding glucose to one ‘half’ of the root system increased the frequency (number per unit length) of lateral root primordia in the fed axes. The increase was first observed 15 h after the start of treatment and was located within the apical 30 mm of root. At this time there was no significant treatment effect on the frequency of primordia in non-fed axes. The enhanced initiation of lateral roots in glucose-fed root tips was associated with an increase in their concentration of glucose and sucrose plus low molecular mass fructans. In contrast, there was a reduction in partitioning of 14C-photosynthate to these root tips compared to the non-fed roots of treated plants and controls. The results indicate that lateral root initiation can be stimulated by sugars in the absence of an increase in phloem translocation. It is proposed that proliferation of lateral roots in response to localized soil conditions, such as nutrient patches, may be signalled by an increase in sugar content of the tissue, rather than an altered flux of phytohormones or other material co-transported with sucrose in the phloem.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1399-3054.1998.1030113.x
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  • 5
    Electronic Resource
    Electronic Resource
    Causes and location of non-specific effects of SHAM on O2 uptake by wheat roots (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 93 (1995), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Uptake of O2 by whole, detached, root systems of wheat (Triticum aestivum L. cv. Alexandria) was titrated with salicylhydroxamic acid (SHAM) in the presence and absence of cyanide. The resulting Qall plot was non-linear indicating that SHAM was acting non-specifically. The nature of the non-specific effects was investigated in reverse titration experiments. Uptake of O2 was titrated with KCN in the presence and absence of SHAM at 1 mM and 25 mM, which yielded Qcy1 values of 〈 1 and 〉 1, respectively. The results suggest that at 25 mM, SHAM inhibits the cytochrome pathway, but at 1 mM it stimulates an O2-consuming process which is likely to be a peroxidase. A SHAM-stimulated peroxidase could easily be washed from these roots. In vitro, the peroxidase was stimulated to a similar extent by low (1 mM) and high (25 mM) concentrations of SHAM. Failure to inhibit with high concentrations of SHAM distinguishes this peroxidase from those bitherto eluted from root tissue. Reverse titration experiments in the presence and absence of 1 mM SHAM indicated that there were no significant side effects of SHAM in root tips. These data are supported by the negligible peroxidase activity that was washed from this root fraction. In contrast, significant side effects occurred in vivo, and substantial peroxidase activity was measured in vitro, from sections 4–6 cm and 18–20 cm behind the seminal root apex. The greatest activity was found with the 4–6 cm section which may be associated with high rates of cell wall lignification. The implications of these results for measurements of root respiration are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1995.tb06839.x
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  • 6
    Electronic Resource
    Electronic Resource
    Extension rate and respiratory activity in the growth zone of wheat roots: Time-course for adjustments after defoliation (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 98 (1996), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The time-course for adjustments in the rate of extension of wheat (Triticum aestivum L. cv. Alexandria) roots, and the activity and capacity of respiratory pathways in the root apex, were determined after pruning the shoot to the ligule of the first leaf. Leaf pruning reduced the extension rate of both seminal and lateral roots. The onset of the response occurred within 1 h of pruning for laterals and between 2 and 3 h for seminals. The reduction in rate appears to be the result of a decrease in carbohydrate availability because (1) in seminal roots it was preceded by a decrease in soluble sugar content of the apical part of the growth zone (0–5 mm behind the root apex) and (2) supplying glucose (50 mM) to the roots of plants defoliated 24 h earlier led to a steady increase in extension rate of both seminal and lateral roots compared to non-fed controls. Supplying 3-O-methyl glucose had no effect. The reduction in extension rate of seminal roots was accompanied (or slightly preceded) by a reduction in respiratory O2 uptake in the apical part of the growth zone (0–5 mm). Changes in respiratory activity in the basal part of the growth zone (5–10 mm) only occurred several hours later. At the time root extension rate was reduced, the rate of O2 uptake could be stimulated with FCCP, which indicates that respiration was under the fine control of adenylates. From these results we suggest the following sequence of events occurs after defoliation. Firstly, defoliation reduces the supply of sugars to the root apex, this leads to a reduction in rate of extension through some form of coarse control by carbohydrates on cell division and expansion, which in turn reduces the rate of respiratory O2 uptake because of a smaller demand for ATP. The results also indicate that there is a rapid (〈1.5 h) reduction in respiratory capacity in the root apex after defoliation which occurs before any change in the overall rate of respiration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1996.tb00693.x
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  • 7
    Electronic Resource
    Electronic Resource
    Respiration of barley roots: Assessment of activity of the alternative path using SHAM (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 70 (1987), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The activity of the alternative path of O2 consumption in detached and intact roots of barley [Hordeum distichum (L.) Lam. cv. Maris Mink] was determined by titration with salicylhydroxamic acid (SHAM) in the presence and absence of cyanide. In the absence of cyanide, only high concentrations were inhibititory (〉 5 mM). whilst in its presence low SHAM concentrations (2.5–5.0 mM) gave maximum inhibition: the resulting ϱ Valt plots were non-linear. A SHAM-stimulated peroxidase could readily be washed from these roots, but non-linearity cannot be explained in terms of SHAM-stimulation of this peroxidase as it is not active in the absence of an exogenous supply of NADH. In detached roots the degree of inhibition of respiration with 25 mM SHAM was nearly double the capacity of the alternative path (measured as the degree of inhibition by SHAM in the presence of cyanide), suggesting non-specific inhibition. Effects of SHAM on cytochrome path activity in intact roots were examined by reverse titration with cyanide in the presence and absence of SHAM. At 5 mM SHAM had no effect on the cytochrome path, but at 25 mM it inhibited. We conclude that the only factor causing non-linearity of ϱValt plots in barley roots is non-specific inhibition of the cytochrome path by high concentrations of SHAM; consequently only low concentrations of SHAM (2.5–5.0 mM) are suitable for estimating alternative path activity in barley roots.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1987.tb02848.x
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  • 8
    Electronic Resource
    Electronic Resource
    Influence of root temperature on the potassium requirements of young tomato plants (1991)
    Springer
    Plant and soil 133 (1991), S. 227-237 
    Details
    ISSN: 1573-5036
    Keywords: critical-concentration ; potassium ; root temperature ; shoot: root ratio ; tomato ; utilization-efficiency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The effect of low root temperature on the growth and K requirements of young tomato (Lycopersicon esculentum Mill. cv Sonatine) plants was investigated. When K was supplied in solution at high concentration (5 mM), lowering the temperature of the root system from 25° to 15°C reduced the relative growth rate so that after ten days plant dry weight was 60% and leaf area 44% of that of controls maintained at 25°C. Shoot: root dry weight ratio was initially increased by cooling, but declined to 84% of controls after ten days. In spite of these changes in shoot: root ratio the concentration of K in whole plants, expressed on the basis of tissue water, was stable throughout the experiment and was significantly higher than that of controls. Further, the critical concentration of K for shoots (the concentration in the shoot associated with 90% maximum growth) was also increased at root temperatures of 15° and 30°C compared with 24°C. It is suggested that the higher concentration of K at low root temperature may reflect a real increase in requirement for the element at the physiological level. Preliminary measurements of the solute potential demonstrated a less osmotically active sap in leaves of root-cooled plants, thus there may be a greater reliance on K as an osmoticum in these individuals. When supplies of K limited growth, root-cooling had no effect on any of the parameters determining the efficiency of its use; the minimum concentration to which roots could deplete the solution of K was identical for cooled and control plants and at the same stage of visible deficiency there was no significant difference in the efficiency ratio (mg DW, mg-1 K) or utilization efficiency (mg DW mM -1 K), in spite of large differences in the partitioning of dry matter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00009195
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