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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 22 (1969), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Lowering the water potential of culture solutions from −0.4 to −5.4 atm reduced both phosphorus and bromide transport to the shoot, hut the content in the roots was not affected. Reductions in phosphorus transport to the shoot were measured during the first four hours of treatment and were related to concurrent decreases in water flow and not to an impairment of active phosphorus transport. The effect of low water potential on phosphorus transport to shoots was similar at external phosphorus concentrations between 0.6 and 15 mg/l.Phosphorus transport was greater in the dark at −0.4 atm than in the light at −5.4 atm even when these treatments gave the same overall rates of water flow; this is attributed to a different pattern of water flow through the various root zones. The results suggest that the main effect of water flow on anion transport to shoots occurred after the ions had been actively adsorbed by the roots and was not due to mass flow increasing ion delivery to sites of active uptake.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 22 (1969), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Measurements were made of phosphorus uptake by intact tomato plants from solutions labelled with 32P. The plants were exposed to low water potentials by the addition of mannitol to culture solutions. The amounts of labelled phosphorus in the roots and in the shoots wore determined after a one- or two-hour period. Down to -5.4 atmospheres, the amount of labelled phosphorus in the roots remained constant, hut the amount transported to the shoots was reduced. However, potentials of -10.4 atm reduced the amount of labelled phosphorus in both the root and the shoot. Similar results were obtained when plants were tested immediately after water stress was imposed and when tested after water potentials had been lowered gradually.Plants were treated for one hour at low water potentials and then returned to control solutions (−0.4 atm). For a considerable time, these plants had a much lower phosphorus uptake than plants which had remained continuously at −0.4 atm. These data support the idea that a disturbance in mineral nutrition is partly responsible for reduced growth in plants which experience a moderate water deficit.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 21 (1968), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Cyclic fluctuations in stomatal aperture, transpiration rate and leaf water potential under constant environmental conditions have been investigated in intact plants of cotton, pepper, and sunflower. Stomatal aperture and transpiration rate were least when leaf water potential was high and were greatest when leaf water potential was low.Lowest leaf water potential values lagged behind the occurrence of highest transpiration rates, and high overall resistance to water flow occurred in cycling plants. Both of these are considered essential for the occurrence of persistent cyclic behaviour. Hydropassive opening of stomates as the leaves wilted facilitated cycling in cotton and pepper, but not in sunflower, where hydropassive opening did not occur.The roots were identified as the site of the major resistance to water flow in the plant and further experiments directly showed the importance of this root resistance in initiating cycling by causing water stress in the leaves as the stomates opened.Root resistance varied diurnally, becoming increasingly important at night. Root resistance naturally rose to high levels in cotton. High levels were induced in pepper or sunflower by having the roots in deionized water for several days or by anoxia.Quantitative measurements of overall plant resistance were made from leaf water potential and transpiration rate data.The results are discussed and it suggested that plant resistance may indirectly be of importance in the movement of water from the plant to the air.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Planta 83 (1968), S. 119-136 
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The effects of water flow on phosphorus uptake by roots and on its subsequent translocation to shoots were separated by giving short-term pulses of 32P-labelled nutrient to intact tomato plants. At the end of a 5 min pulse, all the 32P taken up by the plants was confined to the roots. Only about half of this 32P was later translocated to shoots; there was very little translocation after 4 hours. Experiments after long-term labelling showed that only a small part of the total P in the root is readily translocated to shoots. This P appears to be in part of the symplast and contributes about 75% of the P transported to the xylem sap. The rest is presumably derived by leakage from vacuoles. A slow rate of water flow reduced both uptake into the symplast and the translocation to the shoots of P which had already been absorbed by the roots. This was conclusively demonstrated by giving a 32P pulse before reducing the rate of water flow; 32P not translocated to shoots was partly retained by the roots and partly lost to the external solution. Water flow also accelerates transport to the xylem of previously-absorbed P in excised roots. It is concluded that the major effect of water flow on phosphorus transport to shoots occurs after phosphorus uptake by the roots, probably during radial transport to the xylem.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Planta 80 (1968), S. 129-141 
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In excised roots of barley and tomato plants, lowering the water potential of nutrient solutions to-10.4 and-20.4 atm decreased the uptake of bromide and phosphorus while increasing the loss of these ions to the external solutions. Lowering the water potential greatly increased the rate of loss of potassium and bromide from the cytoplasm, but the increases in loss from the vacuoles were much smaller. The results suggest that the mechanisms of ion uptake are not affected by low water potential and that the decrease in ion accumulation is caused by the increased leakage from the cells.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Planta 80 (1968), S. 142-146 
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Tomato plants were treated for one hour in nutrient solutions at-10.4 atm. Roots were excised, transferred to solutions at-0.4 atm and put into a pressure chamber to induce rates of water flow similar to those in transpiring plants. For roots continuously at-0.4 atm, the xylem sap had much higher phosphorus concentrations than the external solution, which contained 6 p.p.m. phosphorus. Roots previously treated at-10.4 atm had much lower concentrations in the sylem sap than in the external solution and the amount of phosphorus transported and the water flow were linearly related. This phosphorus transport was due to passive movement as shown by measuring transport of both 32P and 14C mannitol. Thus transport to the xylem mediated by active processes was abolished even though uptake by the roots remained substantial. These results obtained after plasmolysis support the view that radial transport to the xylem includes uptake into and movement through the symplast.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1573-5036
    Keywords: Development ; Model ; Root ; Shoot ; Thermal time ; Wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary A model has been developed of root growth in winter wheat based on cumulative thermal time with description of the extension and branching of individual age classes of seminal and crown root axes. The model requires, as input, the sowing date and average monthly mean air temperatures and gives, as output, the maximum depth of penetration of each age class of root and the root length density or root weight in any 10 cm layer of soil contributed by main axes, first-order and second-order laterals on any calendar date. The impact of soil temperature on root length density distributions with time was assessed by comparing a warm site (Perth, Australia) with a cool site (Rothamsted Experimental Station, England). Simulated values of root length density for plants with six leaves were consistently high when soil temperature was held constant at 10°C, but variable soil temperatures at each site resulted in rooting profiles characteristic for the two sites, although root length densities were larger than commonly observed at either location. The model simulates well described sequences of root production and permits calculation of maximal root development rates for unstressed plants growing in moist soil with no mechanical impedance to growth. It allows the co-development of root and shoot to be modelled and since it uses only about 5 K bytes of computer memory could be easily used for the assessment of management practices in the field.
    Type of Medium: Electronic Resource
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