Pyridine nucleotide charge reduces photosynthesis under short-term oxygen deficiency.
Zude-Sasse M., Hartmond U., Ebert G., Lüdders P.
Author Affiliation: Institute of Agricultural Engineering Bornim e.V., Max-Eyth-Allee 100, 14469 Potsdam-Bornim, Germany.
Journal of the American Society for Horticultural Science 126 : 703-709
Abstract : Soil flooding reduces partial pressure of oxygen (pO2) in the root zone and often results in a reduction in photosynthesis and growth. In greenhouse studies, rooted stem cuttings of the mango (Mangifera indica) rootstock selection 13/1 were exposed to anoxia by saturating the root zone with N2 for up to 52 h. Reduced pO2 in the root zone affected the energy status of the roots and particularly enhanced the phosphorylated and non-phosphorylated pyridine nucleotide charges - the ratio of reduced nicotinamide adenine dinucleotides (NAD(P)H) to total nicotinamide adenine dinucleotide content (oxidized NAD(P)+ plus NAD(P)H) - that drive the redox reaction rates in cell metabolism. Also, the pyridine nucleotide charges in leaves were enhanced, while the photosynthetic rate decreased following reduction in pO2 in the root zone. During up to 4 h of reduced pO2, the ratio of internal CO2 concentration in the mesophyll to ambient CO2 concentration was unchanged. This implies a non-stomatal influence on photosynthesis. In addition, light saturation of photosystem II occurred at lower irradiance (470 µmol m-2 s-1) resulting in reduced maximum photochemical efficiency below that of the high pO2 controls. After 28 h of reduced pO2, NAD(P) charges in the leaves returned to normal, diminishing its potential effect on net photosynthetic rate.