Abstrakt

Photosynthetic Performance in Relation to Nitrogen Limitation-Induced Starch Production in a Marine Green Microalga Tetraselmis subcordiformis

Changhong Yao, Yadong Chu, Yinghui Liu and Xupeng Cao

Microalgal starch is considered to be an alternative to the crop-based starch with variety of applications. Nitrogen limitation is an effective method to trigger starch accumulation in microalgae. The relationship between starch accumulation and photosynthetic performance of microalgae have to be disclosed to balance the inconsistency between starch accumulation and lose of photosynthetic activity under nitrogen limitation. This study aimed to investigate the photosynthetic performance in relation to nitrogen limitation-induced starch production in a marine green microalga Tetraselmis subcordiformis. The highest starch productivity of of 0.50 g L^-1 d^-1 and starch content of 60.5% DW were both obtained in the culture with medium initial nitrate concentration of 1.0 mM on Day 2. Along with the moderate decline of maximum quantum efficiency of photosystem II (F_vF_m) and photosystem II operating efficiency (Φ_PSΙΙ) therein, it was evidenced that moderate stress condition was preferable for maximal starch production. Much less increase of Chl a/b ratio, an indicator of decreased antenna size, was found in the culture with less initial nitrate and more starch accumulation, suggesting that photoinhibition should be inherently a prerequisite for starch production in T. subcordiformis. The more prominent increase of non-photochemical quenching (NPQ) was accompanied by the stronger starch accumulation ability, indicating that the maintenance of photoprotective function via heat dissipation and Cyclic Electron Flow (CEF) around photosystem I (PS I) could also be of importance for the starch accumulation in T. subcordiformis.