Abstract:
© 2020 SAAB The desiccation tolerant (DT) fern species Crepidomanes inopinatum and Loxogramme abyssinica often grow together in the understory of KwaZulu-Natal Afromontane forests. Crepidomanes inopinatum is a “filmy” fern that dries rapidly because it lacks a cuticle; by contrast L. abyssinica possesses a cuticle, and therefore dries slowly. It was predicted that because C. inopinatum dries quickly, this species would have little time available to induce DT mechanisms, and therefore mainly relies on constitutive mechanisms. By comparison, the slow-drying L. abyssinica has time to put DT mechanism in place, and therefore may depend more on inducible mechanisms. Here we tested whether a drying-rehydration cycle induces two mechanisms often suggested to contribute DT, specifically increases in the activity of two reactive oxygen species (ROS) scavenging enzymes and the concentration of soluble sugars. Measurement of chlorophyll fluorescence parameters showed that both species recover rapidly during rehydration after desiccation, confirming that both are genuinely poikilohydric. In both species slow desiccation increased the activity of the ROS scavenging enzyme superoxide dismutase (SOD), and the concentrations of soluble sugars. Desiccation had little effect on the activity of the (ROS) scavenging enzyme peroxidases (POX) in either species, suggesting that maintenance of POX activity is a constitutive DT mechanism. However, the main difference between the two species was that de-acclimation occurred in the filmy fern; moist storage under cool dim light for a week reduced DT. By contrast, in the fern with a cuticle no de-acclimation occurred. However, overall, results suggest that counter to our original hypothesis, inducible DT mechanisms occur even in filmy ferns that desiccate rapidly.
