Photocontrol of the Germination of Onoclea Spores

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Abstract
The oxygen requirements during the three phases of photoinduced germination of Onoclea sensibilis L. spores were analyzed by temporarily applying nitrogen atmosphere. The dark preinduction phase, during which the spores imbibe water and establish sensitivity to irradiation, involves an oxidative process which can be reversibly inhibited and stimulated by nitrogen and air, respectively. The induction phase of germination is characterized by a pure photochemical reaction, independent of temperature and oxygen. The postinduction phase, when the photoproduct triggers dark processes eventually leading to the protrusion of the rhizoidal or protonematal cells, involves an oxidative process which occurs within the first 10 hours of this phase. This oxidative process differs in kinetic characteristics from that in the preinduction phase. The oxidative process is inhibited by nitrogen treatment, but following nitrogen inhibition the ability of the spores to germinate can be reinstated by a long period of air intervening between the nitrogen treatment and a second irradiation. This suggests that enzymes or reactants which are needed in the postinduction process decay under anaerobic conditions and are resynthesized when the spores are transferred to air. Spores take up acetocarmine stain towards the latter part of the postinduction phase. Stain uptake is apparently succeeded very closely by cell division, and some time later by protrusion of the germling cells.