Abstract
The effect of varied phosphorus (10 and 250 mmol P m−3 potassium (50 and 2010 mmol K m−3) and magnesium (20 and 1000 mmol Mg m−3 supply on sucrose, reducing sugars, amino acids, P, K, and Mg in phloem exudate was studied in bean (Phaseolus vulgaris L.) plants over a 12 d growth period in nutrient solution. Phloem exudates were collected from detached primary leaves using the EDTA-promoted exudation technique. Compared with control nutrient-sufficient plants, sucrose export in the phloem exudate was drastically decreased by K deficiency and, particularly, by Mg deficiency, whereas P deficiency either had no effect or stimulated sucrose export. In Mg-deficient plants the rate of sucrose export was decreased to 10–20% of the control plants. There was a close Inverse relationship between phloem export and leaf concentration of sucrose: higher leaf concentrations of sucrose were accompanied by lower phloem export of sucrose. In contrast to sucrose, reducing sugars in the exudates were very low and not affected by P, K and Mg deficiency. The phloem export of amino acids was strongly depressed by Mg deficiency, but only slightly by P and K deficiency. Resupplying Mg to Mg-deficient plants for 12 h during the dark or light periods rapidly stimulated sucrose export. After resup ply of Mg for 24 h and 48 h the rate of sucrose export was comparable with the rate in the control plants. The results demonstrate a key role for Mg in phloem loading and export of photosynthates from source leaves, especially sucrose. Inhibition of root growth and development of visual symptoms of chlorosis in Mg-deficient plants are suggested as consequences of Impaired phloem loading. In agreement with this in P-deficient plants where phloem loading was not impaired, chlorosis was absent and root growth was maintained at a high level.
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Claims 15
Claim · model-written summary
K deficiency drastically decreased sucrose export relative to nutrient sufficient plants.
Verbatim
e0“Compared with control nutrient-sufficient plants, sucrose export in the phloem exudate was drastically decreased by K deficiency”
t0“bean plants”
Claim · model-written summary
Mg deficiency drastically decreased phloem sucrose export.
Not reportedComparator
Verbatim
e0“sucrose export in the phloem exudate was drastically decreased by K deficiency and, particularly, by Mg deficiency”
t0“bean plants”
Claim · model-written summary
P deficiency had no effect or stimulated sucrose export.
Not reportedComparator
Verbatim
e0“P deficiency either had no effect or stimulated sucrose export”
t0“bean plants”
Claim · model-written summary
Mg deficiency lowered sucrose export to 10–20% of control.
Verbatim
e0“In Mg-deficient plants the rate of sucrose export was decreased to 10–20% of the control plants.”
t0“bean plants”
Claim · model-written summary
Leaf sucrose concentration was inversely associated with phloem sucrose export.
Verbatim
e0“higher leaf concentrations of sucrose were accompanied by lower phloem export of sucrose”
t0“bean plants”
Claim · model-written summary
Reducing sugars in exudates were very low.
Verbatim
e0“reducing sugars in the exudates were very low”
t0“bean plants”
Claim · model-written summary
P, K and Mg deficiency did not affect reducing sugars in exudates.
- Taxon
- bean plantst0
- Treatment
- P, K and Mg deficiencye0
- Outcome
- reducing sugars in the exudatese0
- Direction
- not affectede0
Not reportedComparator
Verbatim
e0“reducing sugars in the exudates were very low and not affected by P, K and Mg deficiency”
t0“bean plants”
Claim · model-written summary
Mg deficiency strongly depressed phloem amino acid export.
Not reportedComparator
Verbatim
e0“The phloem export of amino acids was strongly depressed by Mg deficiency”
t0“bean plants”
Claim · model-written summary
P deficiency slightly depressed phloem amino acid export.
Not reportedComparator
Verbatim
e0“phloem export of amino acids was strongly depressed by Mg deficiency, but only slightly by P and K deficiency”
t0“bean plants”
e1“P deficiency either had no effect or stimulated sucrose export”
Claim · model-written summary
K deficiency slightly depressed phloem amino acid export.
Not reportedComparator
Verbatim
e0“phloem export of amino acids was strongly depressed by Mg deficiency, but only slightly by P and K deficiency”
t0“bean plants”
Claim · model-written summary
Mg resupply for 12 hours rapidly stimulated sucrose export in deficient plants.
Verbatim
e0“Resupplying Mg to Mg-deficient plants for 12 h during the dark or light periods rapidly stimulated sucrose export”
t0“bean plants”
Claim · model-written summary
After 24 and 48 hours of Mg resupply sucrose export was comparable to controls.
Verbatim
e0“After resup ply of Mg for 24 h and 48 h the rate of sucrose export was comparable with the rate in the control plants”
t0“bean plants”
Claim · model-written summary
The authors interpret Mg as key to phloem loading and photosynthate export.
Verbatim
e0“The results demonstrate a key role for Mg in phloem loading and export of photosynthates from source leaves, especially sucrose”
t0“bean plants”
Claim · model-written summary
Impaired phloem loading was suggested to cause reduced root growth and chlorosis in Mg deficient plants.
Verbatim
e0“Inhibition of root growth and development of visual symptoms of chlorosis in Mg-deficient plants are suggested as consequences of Impaired phloem loading”
t0“bean plants”
Claim · model-written summary
P deficient plants lacked chlorosis and maintained high root growth.
Verbatim
e0“in P-deficient plants where phloem loading was not impaired, chlorosis was absent and root growth was maintained at a high level”
t0“bean plants”
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Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.