Effects of epiphytic diatom Licmophora paradoxa on photosynthesis, malondialdehyde content and antioxidant enzymes activities of Pyropia yezoensis

This study investigated the effects of epiphytic diatom Licmophora paradoxa on the physiological activities of Pyropia yezoensis, including photosynthesis, malondialdehyde (MDA) content and antioxidant enzymes activities. The photosynthetic activity was measured using chlorophyll fluorescence technology. Physiological indexes, such as chlorophyll-a, MDA content, antioxidant enzymes superoxide dismutase (SOD), and catalase (CAT) were determined by spectrophotometry. The results showed that photosynthetic parameters, the maximum quantum efficiency of PSII (F_v/F_m), the maximum electron transport rate (rETR_max), the minimum saturating irradiance (E_k) and Chl-a content decreased in P. yezoensis, which had been previously attached by the diatom L. paradoxa. On the other hand, physiological indexes of the resistance mechanism, such as MDA content, SOD and CAT antioxidant enzymes activities were significantly increased in the host P. yezoensis. It is concluded that epiphytic diatoms created adverse effects on the photosynthesis of P. yezoensis, and stimulated the physiological responses of P. yezoensis to epiphytes. This study is beneficial/ helpful to better understand the relationship between epiphytic microalgae and host macroalgae.