Photosynthesis response to triacontanol correlates with increased dynamics of mesophyll protoplast and chloroplast membranes

The effects of a long chain aliphatic alcohol 1-triacontanol (TRIA) on the photosynthesis and membrane properties of mesophyll protoplasts and chloroplasts isolated from pea leaves were studied. In vitro treatments of isolated protoplasts caused a large enhancement (166% ) of the CO2-fixation rate after 60 min of TRIA (10^-6 M) application as compared to the control. An enhanced photosynthetic response was observed in in vitro treated leaf pieces. Application of octacosanol (OCTA) under the same experimental conditions did not result in any stimulating effects. In vivo treatments of pea seedlings also resulted in a significant increase of the net CO2 uptake to 109% and 119% in 10^-8 M and 10^-6 M TRIA-treated plants respectively. It was demonstrated that the incubation of both protoplasts and chloroplasts with TRIA resulted in a rise of the excimer/monomer (I_E/I_M ) ratio of pyrene (Py) fluorescence, thus indicating remarkable fluidization and/or disordering of the lipid matrix of their membranes. This effect depended on the incubation time and became evident at very low concentrations of TRIA (0.3 M). The increase of membrane fluidity was accompanied by TRIA-induced alterations in the dielectric environment in the membrane regions where Py molecules are situated. The results are discussed in terms of specific concentration dependent TRIA-induced alterations of the dynamic properties of protoplast and chloroplast membranes and their possible involvement in the initiation of the integral physiological response to exogenous application of TRIA.