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

Abstract

Summary In order to investigate the possible biochemical mechanisms involved in triggering the early steps of germination, reduced and oxidized pyridine nucleotides (PN) were analysed and compared in embryos separated from endosperms during the imbibition of non-dormant and dormant caryopses of Avena sativa L. (van Noire de Moyencourt). Experiments were conducted at the restrictive temperature of 30°C, and PN contents were also determined after imbibition for 6 h in the presence of either sodium azide (NaN3), gib-berellin (GA3), or ethanol, all compounds known to stimulate the germination of dormant seeds. The main differences detected were: a quick rise in the catabolic redox charge (CRC = NADH/ [NADH+NAD+]) in the embryos of non-dormant caryopses during the sensu stricto germination phase, followed by an increase in all contents of cofactors in the growing embryos. Since comparable observations could be done in embryos of dormant caryopses after addition of either NaN3 or ethanol, this increase of the CRC, probably due to an activation of glycolysis, could initiate germination. The effect of GA3, found to be very different, is discussed. In addition, stimulation of the pentose 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 weak synthesis of PN could be one of the limiting factors for germination.