Choice of leaf for estimation of K status by analysis of petiole sap

Burns, Ian G.; Hutsby, Wendy

doi:10.1002/jsfa.2740370204

Cited by 4 publications

(1 citation statement)

References 11 publications

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“…where A is the initial amount of K (mmol) within the total shoot sap and V is the total volume of this sap (1). V changes with the growth of the plant:…”

Section: Theorymentioning

confidence: 99%

Determination of critical K concentrations in sap from individual leaves or from whole plants using K-interruption experiments

Burns¹

1986

Plant Soil

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Summary A new method is described for estimating critical K concentrations from K interruption experiments using only 2 treatments. Frequent measurements are made of the growth and K concentration of plants subjected to either continued or interrupted K supply and the data used to define the relation between relative yield and K concentration for the K-deficient plants. Critical concentrations are estimated from the results using a mathematical model of plant growth to interpolate over the critical concentration region of the curve. The method has the advantage that the critical concentrations are determined at the exact time that growth is affected.The method was tested using data from previously published experiments with lettuce in which the concentrations of K were measured in sap from both the total shoot and from individual leaf petioles. The model accurately predicted the form of the relationship between relative yield and K concentration for the total shoot and for young expanding leaves, but consistently deviated from the data for recently matured ones. Average estimates of critical concentration ranged from ca. 18 to 34 mmol 1-~ in the young leaves and from 48 to 67 mmoll-l in the mature ones when Na salts were present or absent respectively. The values for total shoot sap were similar to those for mature leaves. The critical concentrations for young expanding leaves were virtually identical to the minimum believed to be needed for the maintenance of important biochemical processes in individual cells, and suggests that a single critical K concentration for plant sap might apply to a wide range of crops provided an actively growing part of the plant is sampled.

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“…where A is the initial amount of K (mmol) within the total shoot sap and V is the total volume of this sap (1). V changes with the growth of the plant:…”

Section: Theorymentioning

confidence: 99%

Determination of critical K concentrations in sap from individual leaves or from whole plants using K-interruption experiments

Burns¹

1986

Plant Soil

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Cation replacement of potassium in the total shoot of lettuce and its effect on growth during K deficiency

Burns¹,

Hutsby²

1986

J Sci Food Agric

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The growth and inorganic ion composition of K-sufficient lettuce shoots were measured after withholding K or K and Na from transplanting in sand culture experiments in the glasshouse. Initial reductions in shoot growth occurred shortly after transplanting in both K-deficient treatments when the K concentrations were still well above that known to limit enzymic activity. These early growth effects coincided with a rapid decline in total ionic strength within the plants caused by the fall in K concentration which could not be compensated for by increases in the uptake of Na, Mg or Ca, even when adequate concentrations of all of these ions were available. Further rapid reductions in growth rate occurred when the concentration of K declined below about 600 mmol kg-' in both K-deficient treatments. These results support the hypothesis of a dual mechanism for the effect of K concentration on growth during K deficiency. The primary effect was caused by a rapid decline in ionic concentration shortly after the K became unavailable which severely affected the mechanisms controlling turgor pressure within the plant. The secondary effect was caused by a reduction in enzymic activity and only became important when the K status of the plant was relatively low.

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The uptake of na and its redistribution between leaves during the development and alleviation of K deficiency

Burns¹,

Hutsby²

1986

J Sci Food Agric

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Changes in the concentration of Na in the shoot dry matter and in the petiole sap of individual leaves of lettuce were measured in order to determine the extent to which Na was able to replace K within the plants during K deficiency. The results were used to estimate changes in the distribution of the total ionic concentration between leaves and to make deductions about likely variations in osmotic potential within the shoots and their effect on plant growth. Measurements of Na concentration revealed both a pronounced delay in the uptake of additional amounts of Na and in its translocation within the K-deficient plants. Sodium concentrations increased most rapidly in the young expanding leaves during the onset of K deficiency but the changes in its concentration were ultimately larger in the middle to older ones. Elevated Na concentrations in the younger leaves of K-deficient plants also declined more rapidly than those in any of the other leaves following reintroduction of the K supply. Although the pattern of these changes broadly mirrored the corresponding changes in K concentration within the shoots there were significant reductions in the combined K+Na concentrations during the onset and development of K deficiency. The deficit in K+Na was initially greatest in the young leaves but subsequently disappeared more quickly when either the uptake of Na was increased or the K supply was resumed. Since the combined concentrations of K+Na were directly related to the changes in total ionic concentrations within the shoots, the results suggest that during K deficiency, plants adopt a strategy which reduces the effects of a decline in ionic strength at the most actively growing sites in order to minimise the damage to normal growth processes from changes in the internal osmotic pressure.

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Choice of leaf for estimation of K status by analysis of petiole sap

Cited by 4 publications

References 11 publications

Determination of critical K concentrations in sap from individual leaves or from whole plants using K-interruption experiments

Determination of critical K concentrations in sap from individual leaves or from whole plants using K-interruption experiments

Cation replacement of potassium in the total shoot of lettuce and its effect on growth during K deficiency

The uptake of na and its redistribution between leaves during the development and alleviation of K deficiency

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