Photosynthtic Inhibition on the Microalga Dunaliella sallina (Chlorophyta) by the Dried Macroalga Gracilaria lemaneiformis (Rhodophyta)

The effects of the dried macro alga, Gracilaria lemaneiformis (Rhodophyta), on photosynthesis of a highly stress-resistant micro alga, Dunaliella sallina, were studied. D. sallina was cultured with dried G. lemaneiformis under controlled laboratory conditions. Photosynthetic oxygen evolution was measured and the chlorophyll a (Chl a) fluorescence transient O-J-I-P curve coupled with its specific parameters was established. In vivo, the Chl a fluorescence transients were recorded at high time resolution and analyzed via the JIP-test to evaluate photo system II activity. A clear dose-relevant relationship was estabished between the dried biomass of G. lemaneiformis and its inhibitory effect on D. sallina. A decrease in the light-saturated maximum photosynthetic oxygen evolution rate (P_max) was observed, which was also time-relevant. Also an O-J-I-P curve along with its specific parameters were reduced. The dark respiration rate (R_d) showed a reverse pattern. The main photosynthetic inhibitory targets of the macro alga on the micro alga, based on the JIP-test and the amount of oxygen evolution, can be expressed as the number decrease of active reaction centers, the blocking of the electron transport chain, and the damage to the oxygen-evolving complex. The results of this study indicate that dried fragments of G. lemaneiformis effectively inhibit photosynthesis in D. sallina and could thus be potential candidates in controlling and mitigating harmful algal blooms.