Changes in the content of pigments and rate of photosynthesis in Azolla microphylla Kaulf. fronds were measured during growth under solar and ultraviolet-C (UV-C) supplemented solar radiation. Maximum content of total chlorophyll (Chl) was observed on the 13th day (termination of the experiment) of treatment in both control and treated plants. The treated plants had significantly lower total Chl and carotenoid contents than the control plants during the 1st day of growth. After the 4th day of exposure to UV-C supplemented solar radiation, the Chl and carotenoids accumulation increased in treated plants, so that the pigment concentration in the treated fronds was nearer to the control values after the 13th day of treatment. Significant increase in UV absorbing pigments, anthocyanins, and flavonoids was observed at the 13th day of treatment. In spite of the roughly similar photosynthetic pigment concentration, the photosynthetic activity measured as the rate of electron transport at photosystem 2 was only 65 % of the control values after 13 d of UV-C exposure. and M. Jayakumar ... [et al.].
The effects of enhanced UV-B radiation on growth and photosynthetic activities were investigated in fronds of the aquatic fern Azolla microphylla Kaulf. The fronds were exposed to UV-B radiation intermittently once in 3 d during 12 d. Biomass and relative growth rate of UV-B treated Azolla plants and the heterocyst frequency of the UV-B treated symbiont decreased resulting in an increase in doubling time over the control. The doubling time was 3.08 d for control and 3.35 d for UV-B irradiated plants. Chl and carotenoid contents per unit fresh mass and photosystem 2 (PS2) activity also decreased under UV-B treatment. Measurements of photosynthetic activity in terms of fluorescence kinetics and PS2 mediated O2 evolution showed that the aquatic fern Azolla is sensitive to UV-B damage. and M. Jayakumar ... [et al.].