The ascorbate system in recalcitrant and orthodox seeds

Recalcitrant seeds of Ginkgo biloba L,, Quercus cer I is L,, Aesculus hippocastanum L, and Cycas revoluta Thunb, are shed bgl the plant at a high moisture content, contain a large amount of ascorbic acid (ASA) and maintain high ascorbate (ASC) peroxidase (EC 1.11.1.11) activity. Three proteins showing ASC peroxidase activity are present in G, biloba seeds. Conversely, dry orthodox seeds (Vicia faba L,, Avena sativa L,, Pinus pinea L.) are completely devoid of ASA and ASC peroxidase. Experimentally induced rapid variations of the mater Iel el in both recalcitrant and orthodox seeds do not affect the ASC peroxidase; slow dehydration affects the ASC peroxidase activity moderately in recalcitrant seeds, but provokes a complete loss of germinability. Another peculiar difference between orthodox and recalcitrant seeds concerns the ascorbate recycling enzymes, ascorbate free radical (AFR) reductase (EC 1.6.5.4) and dehydroascorbate (DHA) reductase (EC 1.8.5.1), The DHA reduction capability is lo in recalcitrant seeds, but is high in the orthodox ones. In contrast, AFR reductase activity is high in recalcitrant seeds and low in the orthodox ones. Data reported here concerning the ASC system appear to contribute to better understanding the recalcitrance. The presence of three different proteins showing ASC peroxidase activity in the archaic seed-bearing plant G. biloba and its involvement in the spermatophyte evolution is discussed