UV-A Inhibition of Alternative Respiration in Pea Leaves and a Unicellular Green Alga Chlamydomonas reinhardtii

Total respiration (v_T) increased after exposure to UV, but a decrease in the capacity of SHAM-sensitive-alternative respiration (V_ait) was accompanied by an increase in residual respiration (v_res). The capacity for CN sensitive-cytochrome c respiration (V_Cyt) was not inhibited by UV-A. After 4 h of irradiation of high-CO₂-grown cells of Chlamydomonas reinhardtii with UV-A (2 μW. cm⁻²) in the presence of white light (300μE.m⁻²s⁻¹), the capacity of V_alt was reduced from 10 to 4 μmol O₂ mg⁻¹Chl.h⁻¹ a 60% reduction. After a similar exposure to UV-A, the capacity of V_alt in pea leaves was reduced from 13 to 5 μmol O_2-g ⁻¹ fr wt.h⁻¹ Exposure to UV-C was not inhibitory, but UV-B caused up to 25% inhibition of the V_alt. Twenty to 48 h after exposure to UV-A radiation, the capacity of alternative respiration had recovered. UV-A inhibition of the alternative respiration was consistent with UV-A absorption by quinones, except that UV-A did not inhibit the cyt c pathway of electron transport that also involves the ubiquinones.