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Plant Soil (2009) 316:217226 DOI 10.1007/s11104-008-9772-4
REGULAR ARTICLE
Manganese requirement for optimum photosynthesis and growth in NAD-malic enzyme C-4 species
Maru Kipleting Kering & Krystyna Lukaszewska &
Dale G. Blevins
Received: 21 July 2008 /Accepted: 2 September 2008 / Published online: 20 September 2008 # Springer Science + Business Media B.V. 2008
Abstract Despite the evidence for a critical role of Mn in malate decarboxylation and CO2 release for carbon fixation reactions in C-4 plants, there is a lack of information on their Mn requirement. The objective of this study was to establish Mn levels needed for optimum growth and photosynthesis of four agriculturally important C-4 species, NAD-ME C-4 pearl millet and purple amaranth, and NADP-ME C-4 corn and sorghum, as compared to two C-3 species, wheat and squash. Plants were grown hydroponically in a complete nutrient solution with Mn concentrations ranging from 0 to 100 M. We report that under these conditions, C-3 and NADP-ME C-4 plants reached their maximum biomass production with 25 M Mn, the concentration commonly used in plant nutrient media. In contrast, Mn concentrations supporting maximum performance of NAD-ME C-4 plants were up to 20-fold higher and ranged between 50 and 100 M. Although leaf tissue Mn concentrations increased in parallel with Mn nutrition in all plants, the higher leaf Mn had no effect on NADP-ME C-4 or C-3 plants, but it caused a large, up to 100%, increase in net photosynthetic rate in NAD-
ME C-4 species. The highest photosynthetic rates across the spectrum of photon flux density were recorded for C-3 and NADP-ME C-4 plants receiving 25 M Mn, and for NAD-ME C-4 species millet and amaranth supplied with 50 or 100 M Mn, respectively. Squash (C-3) plants were the most sensitive to Mn and their photosynthetic rate was severely depressed with more than 10 M Mn. The increase in photosynthetic rates of NAD-ME C-4 species occurred without an increase in stomatal conductance, eliminating CO2 uptake as the main cause. We propose that the higher photosynthetic rates in NAD-ME C-4 species supplied with higher Mn were a result of increased activation of the Mn-dependent NAD-ME in bundle sheath cells, producing greater CO2 supply for Calvin cycle reactions. This is, to our knowledge, the first report on a...