Abstract
Abstract The objective of this study was to investigate the effect of aluminum (Al) on NO3 − and NH4 + uptake and on activity/expression of the N‐assimilating enzymes glutamine synthetase (GS1, GS2, and GSr isoforms, EC 6.3.1.2), glutamate synthase (NADH‐GOGAT, EC 1.4.7.14; ferredoxin‐GOGAT, EC 1.4.7.1), and glutamate dehydrogenase (GDH, EC 1.4.1.2) of maize (Zea mays L.) genotypes contrasting in tolerance to Al toxicity. Seeds were germinated on paper towels, screened for uniformity and allowed to grow for 5–6 d in a modified Steinberg nutrient solution, pH 5.5, in a glasshouse, under natural light. Immediately after transference to a growth chamber (12 h photoperiod, 26°C ± 0.5/18°C ± 0.9 day/night temperature, 72% RH and 540 µ Em−2 s−1 quantum flux density) Al stress was imposed by lowering pH to 4.5 and addition of 166 µmoles L−1 AlCl3. Control plants were grown in the same nutrient solution without Al, pH 4.5. Aluminum inhibited NO3 − and NH4 + uptake and decreased shoot dry matter yield in all genotypes used in this investigation. Irrespective of their tolerance to Al toxicity, Al‐treated plants had less nitrogen (N), phosphorus (P), calcium (Ca), magnesium (Mg), and sulfur (S) in their leaves. In roots, Al treatment did not affect dry matter weight but decreased accumulation of N, Ca, and Mg. Phosphorus and potassium (K) tended to accumulate in roots of Al‐treated plants, suggesting that Al inhibited P translocation to the leaves. In roots, Al induced anaplerotic GDH and phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) activities, but inhibited GS activity. Moreover, in the apex (0–5 mm) and in the 6–15 mm segment of the elongation zone of most genotypes, Al tended to inhibit expression of GSr and favor expression of GS1. This increase in GS1 expression concomitantly with decreased N uptake and elevated deaminating GDH activity are indicative of metabolic changes usually associated with plant senescence. In leaves, Al did not influence GOGAT and GS activities and expression of GS isoforms suggesting it does not disturb assimilation of nitrogenous compounds translocated from roots to leaves. Nonetheless, lower leaf PEPC activity suggests that Al intoxicated plants had lower CO2 − fixation rates. The inverse effect of Al treatment on the activities of GDH and PEPC in roots and leaves, indicates that whereas increased activities in roots were induced by stress related stimuli, decreased activities in leaves were caused by a reduced nitrogen supply to the leaves. Because the earliest effects observed in this investigation appeared only after 24 h of exposure to Al and were similar in both tolerant and sensitive genotypes, it is concluded that the changes observed in N uptake and assimilation into plant amino acids were downstream of the initial, primary Al toxicity event.
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Claims 14
Claim · model-written summary
Aluminum inhibited nitrate and ammonium uptake in all maize genotypes.
Zea maysNot reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Aluminum inhibited NO3 − and NH4 + uptake and decreased shoot dry matter yield in all genotypes used in this investigation.”
t0“Maize”
Claim · model-written summary
Aluminum decreased shoot dry matter yield in all genotypes.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Aluminum inhibited NO3 − and NH4 + uptake and decreased shoot dry matter yield in all genotypes used in this investigation.”
t0“Maize”
Claim · model-written summary
Aluminum-treated maize had less N, P and Ca in leaves.
- Organ / stage
- leavese0
- Treatment
- Al‐treatede0
- Outcome
- nitrogen (N), phosphorus (P), calcium (Ca)e0
- Direction
- lesse0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Al‐treated plants had less nitrogen (N), phosphorus (P), calcium (Ca), magnesium (Mg), and sulfur (S) in their leaves.”
t0“Maize”
Claim · model-written summary
Aluminum-treated maize had less magnesium and sulfur in leaves.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Al‐treated plants had less nitrogen (N), phosphorus (P), calcium (Ca), magnesium (Mg), and sulfur (S) in their leaves.”
t0“Maize”
Claim · model-written summary
Aluminum did not affect root dry matter weight.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In roots, Al treatment did not affect dry matter weight but decreased accumulation of N, Ca, and Mg.”
t0“Maize”
Claim · model-written summary
Aluminum decreased root N, Ca and Mg accumulation.
- Organ / stage
- rootse0
- Treatment
- Al treatmente0
- Outcome
- accumulation of N, Ca, and Mge0
- Direction
- decreasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In roots, Al treatment did not affect dry matter weight but decreased accumulation of N, Ca, and Mg.”
t0“Maize”
Claim · model-written summary
Phosphorus and potassium tended to accumulate in roots after aluminum treatment.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Phosphorus and potassium (K) tended to accumulate in roots of Al‐treated plants”
t0“Maize”
Claim · model-written summary
Aluminum induced root GDH and PEPC activities.
- Organ / stage
- rootse0
- Treatment
- Ale0
- Outcome
- anaplerotic GDH and phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) activitiese0
- Direction
- inducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In roots, Al induced anaplerotic GDH and phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) activities, but inhibited GS activity.”
t0“Maize”
Claim · model-written summary
Aluminum inhibited root GS activity.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In roots, Al induced anaplerotic GDH and phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) activities, but inhibited GS activity.”
t0“Maize”
Claim · model-written summary
Aluminum tended to inhibit GSr expression in root apex and elongation zone.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“in the apex (0–5 mm) and in the 6–15 mm segment of the elongation zone of most genotypes, Al tended to inhibit expression of GSr and favor expression of GS1.”
t0“Maize”
Claim · model-written summary
Aluminum favored GS1 expression in root apex and elongation zone.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“in the apex (0–5 mm) and in the 6–15 mm segment of the elongation zone of most genotypes, Al tended to inhibit expression of GSr and favor expression of GS1.”
t0“Maize”
Claim · model-written summary
Aluminum did not influence leaf GOGAT and GS activities or GS isoform expression.
- Organ / stage
- leavese0
- Treatment
- Ale0
- Outcome
- GOGAT and GS activities and expression of GS isoformse0
- Direction
- did not influencee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In leaves, Al did not influence GOGAT and GS activities and expression of GS isoforms”
t0“Maize”
Claim · model-written summary
Lower leaf PEPC activity suggested lower carbon dioxide fixation.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“lower leaf PEPC activity suggests that Al intoxicated plants had lower CO2 − fixation rates.”
t0“Maize”
Claim · model-written summary
Aluminum effects appeared only after 24 hours and were similar across tolerant and sensitive genotypes.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the earliest effects observed in this investigation appeared only after 24 h of exposure to Al and were similar in both tolerant and sensitive genotypes”
t0“Maize”
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