The ascorbate system in recalcitrant and orthodox seeds

Recalcitrant seeds of Ginkgo biloba L,, Quercus cer I is L,, Aesculus hippo castanum L, and Cycas revoluta Thunb, are shed bgl the plant at a high mois ture content, contain a large amount of ascorbic acid (ASA) and maintain hi gh ascorbate (ASC) peroxidase (EC 1.11.1.11) activity. Three proteins showi ng ASC peroxidase activity are present in G, biloba seeds. Conversely, dry orthodox seeds (Vicia faba L,, Avena sativa L,, Pinus pinea L.) are complet ely devoid of ASA and ASC peroxidase. Experimentally induced rapid variatio ns of the mater Iel el in both recalcitrant and orthodox seeds do not affec t the ASC peroxidase; slow dehydration affects the ASC peroxidase activity moderately in recalcitrant seeds, but provokes a complete loss of germinabi lity. Another peculiar difference between orthodox and recalcitrant seeds c oncerns the ascorbate recycling enzymes, ascorbate free radical (AFR) reduc tase (EC 1.6.5.4) and dehydroascorbate (DHA) reductase (EC 1.8.5.1), The DH A reduction capability is lo in recalcitrant seeds, but is high in the orth odox ones. In contrast, AFR reductase activity is high in recalcitrant seed s and low in the orthodox ones. Data reported here concerning the ASC syste m appear to contribute to better understanding the recalcitrance. The prese nce of three different proteins showing ASC peroxidase activity in the arch aic seed-bearing plant G. biloba and its involvement in the spermatophyte e volution is discussed.