Aluminium modulation of the photosynthetic carbon reduction cycle in Zea mays |
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Authors: | FC Lidon JC Ramalho and MG Barreiro |
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Institution: | (1) Plant Biology Unit, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2825 Monte da Caparica, Portugal;(2) o Cientifica Tropical-CEPTA, Instituto de Investigaçã, Portugal;(3) Portugal Plant Physiology Department, Estação Agronómica Nacional, Quinta do Marquês, Tapada da Ajuda, Apartado 3014, 1301 Lisboa Codex, 2780 Oeiras, Portugal |
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Abstract: | Two-weeks-old maize (Zea mays L. cv. XL-72.3) plants were submitted to Al concentrations of 0-81 g m-3 for 20 d, after which the A1 concentration-dependent effects on CO2 uptake by the mesophyll tissue and subsequent CO2 assimilation in the photosynthetic carbon reduction cycle of bundle sheath cells were investigated. The net photosynthetic rate (PN) and stomatal conductance (gs) increased continuously up to 27 g m-3 Al, whereas the intercellular CO2 concentration showed minimum values with the 27 g m-3 Al treatment. Moreover, the starch and saccharide concentrations, and fructose-1,6-bisphosphatase did not change significantly with increasing Al concentrations. The photosynthetic electron transport rates along with photosystems 2 and 1 started falling from 9 g m-3 Al onwards, while thylakoid acyl lipid composition did not show a clear pattern. With the Al concentration at 81 g m-3, NADP-malate dehydrogenase activity decreased to minimum values, whereas the opposite occurred with those of pyruvate dikinase, NADP-malic enzyme, and phosphoenolpyruvate carboxylase. Thus in vivo Al concentrations modulate the photosynthetic reduction cycle, possibly by interacting with the carbon flow rate exported to the cytosol. Although the inhibition of NADP-malate dehydrogenase activity might limit pyruvate dikinase, NADP-malic enzyme, and phosphoenolpyruvate carboxylase activities, in vivo the balance between phosphoenolpyruvate production and its carboxylation remains unaffected. |
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Keywords: | Al fructose-1 6-bisphosphatase intercellular CO2 concentration maize NADP-malate dehydrogenase net photosynthetic rate photosystems 1 and 2 saccharides stomatal conductance |
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