End-of-Day Light Control of Growth and Pigmentation in the Red Alga Porphyra umbilicalis (L.) Kützing

Abstract

Abstract The effects of end-of-day light pulses on thallus expansion, cell size, pigmentation and intracellular accumulation of C and N in the red alga Porphyra umbilicalis were analysed. Red (R) light pulses applied at the end of 12 h white light photoperiod for 14 d stimulated thallus expansion and produced an increase in cell size. Growth rate was higher after red (R) than after blue (B) light pulses. Red or blue light affect thallus expansion, but not the thallus weight, and was partially reversed by far-red (FR) light pulses. Red light pulses promoted chlorophyll a accumulation whereas B light pulses stimulated the accumulation of phycoerythrin, phycocyanin and soluble protein. The effects of R or B light pulses on pigmentation were partially reversed by FR light, except for phycocyanin. Intracellular C content was similar under both R and B light treatments and higher than after FR light pulses and non-irradiated control. However, intracellular N content was higher after end-of-day R than after end-of-day B light pulses. Total absorptance (400-760 nm) of the thalli was higher after B than R light pulses. However, the ratio of total absorptance and concentration of total pigments (chlorophyll and biliproteins), used as index of light absorp­ tion efficiency, was higher after R than after end-of-day B light pulses. The efficiency of light absorption decreased after the application of FR light pulses. These observations explain the higher growth rate, in terms of thallus expansion, after R than after B end-of-day light pulses and FR treatments. The possible action of phytochrome and a B light photoreceptor in the control of growth and pigmentation in Porphyra umbilicalis is suggested.