Pyridine nucleotides and redox charges during germination of non-dormant and dormant caryopses of Avena sativa L.

In order to investigate the possible biochemical mechanisms involved in tri ggering the early steps of germination, reduced and oxidized pyridine nucle otides (PN) were analysed and compared in embryos separated from endosperms during the imbibition of non-dormant and dormant caryopses of Avena sativa L. (var. Noire de Moyencourt). Experiments were conducted at the restricti ve temperature of 30 degrees C, and PN contents were also determined after imbibition for Gh in the presence of either sodium azide (NaN3), gibberelli n (GA(3)), or ethanol, all compounds known to stimulate the germination of dormant seeds. The main differences detected were: a quick rise in the cata bolic redox charge (CRC = NADH/[NADH+NAD(+)]) in the embryos of non-dormant caryopses during the sensu stricto germination phase, followed by an incre ase in all contents of cofactors in the growing embryos. Since comparable o bservations could be done in embryos of dormant caryopses after addition of either NaN3 or ethanol, this increase of the CRC, probably due to an activ ation of glycolysis, could initiate germination. The effect of GA(3), found to be very different, is discussed. In addition, stimulation of the pentos e phosphate pathway through the synthesis of NADP(+) by NAD(+) kinase (E.C. 2.7.1.23) appears to be essential for the growth of the seedlings. In the embryos of dormant caryopses, the lack of rise of CRC and the subsequent we ak synthesis of PN could be one of the limiting factors for germination.