Following treatment with 5-aminolevulinic acid the activity of iS-adenosyl-L- methionineimagnesium protoporphyrin IX methyltransferase (EC 2.1.1.11) in wheat leaves decreased, whereas monomethyl ester magnesium protoporphyrin IX and protochlorophyllide accumulated. The inactivation of the enzyme was the result of a cessation of the enzyme-product complex dissociation because of the limited number of porphyrin-binding sites on the structural carrier.
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.].