PARENT SESSION
Posters P4Aa Chlorophyll and bilin based antenna systems. Abstracts (239-271)

Zn-Chl a is accumulated functionally in Chlorella heterotrophycally grown in the dark with an excessive amount of Zn²⁺. Isamu Ikegami^*,1, Aki Nemoto¹, Kohki Sakashita¹, ¹ Faculty of Pharmaceutical Sciences, Sagamiko, Kanagawa, Japan

ABSTRACT- Autotrophycally grown Chlorella does not survive in the presence of 0.5-1.0 mmol/L of Zn²⁺. However, Chlorella, when heterotrophically grown in the dark with 10-30 mmol/L of Zn²⁺, starts to proliferate after the long lag phase, e.g., after about one month with 15 mmol/L of Zn²⁺. The lag period depends on the amounts of Zn²⁺; the longer, the higher is the concentration of Zn²⁺. Once the growth starts, the growth rate is almost the same as that of the cells grown in the normal cultivation media. We found that Zn-Chl a is accumulated in Chlorella grown in the presence of more than 15 mmol/L of Zn²⁺. (1) At the early log phase, Pheophytin a was present with an amount larger than Chl a, probably due to the inhibitory effects of Zn²⁺ on Mg-chelatase. (2) At the late log phase, Chl a becomes dominant, and Zn-Chl a appears. (3) At the stationary phase, Zn-Chl a is gradually accumulated, reaching finally to about 20% of the total Chl a. (4) Low-temperature fluorescence of Chl a shows that F685 was dominant at the early log phase, while its yield markedly decreased at the stationary phase. Thereafter, F725 appeared and became dominant at the late stationary phase. (5) Although P700 was hardly detected at the early log phase, its formation preceded that of antenna at the early stationary phase, resulting in the low Chl a/P700 ratio of about 100. The ratio reached about 250 at the late stationary phase. (6) These results suggest that Chl a is not properly incorporated into the membranes during the period of cell (and chloroplast) division. At the stationary phase, Chl a, together with Zn-Chl a that could be chemically synthesized via Pheo a, is functionally incorporated into Chl-proteins.

KEY WORDS: Zinc-Chlorophyll a, Chlorella, Chlorophyll a, low temperature fluorescence