The structural and functional effects of electromagnetic fields on the plasma membrane of Vicia faba, the broad bean : a thesis dissertation presented in partial fulfilment of the requirements for the degree of Master of Science, Plant Biology at Massey University

Abstract

Vicia faba (broad bean) root-tip cells were exposed to electromagnetic fields at 50 and 60 Hz, square and sine waveforms and 0.1, 1, and 10 gauss. Levels of [³H]-alanine uptake and ion efflux were measured at these parameters and compared to unexposed control seedlings. The ultrastructure of cortical cells from the zone of elongation exposed to a 1 gauss, 50 hertz, squarewave field was studied under the electron microscope. In the first uptake trials alanine uptake via ATP dependant membrane carriers was stimulated by square waveform fields, but inhibited by 50 Hz fields. In the replicate trials alanine uptake was inhibited by both 50 and 60 hertz, square and sine waveform fields. The different response between trials was attributed to aging of the seeds used, owing to a six month chemical supply delay. This apparent aging of the seeds appeared to increase seedling susceptibility to modification by electromagnetic fields. The ion efflux trials saw no significant change in the pattern of ion efflux (as measured by conductivity) from exposed cells, although there was a significant decrease in hydrogen ion efflux at 0.1 and 1 gauss. A secondary inhibition effect on hydrogen ion efflux occurred with exposure to sine and square waveforms, but only in the presence of 0.1 and 1 gauss field amplitudes. The reduction in hydrogen efflux was most probably due to the inhibition of an active ATP dependent membrane carrier responsible for maintaining the transmembrane electrochemical gradient. Under the electron microscope exposed cortex cells from the zone of elongation had significantly more pinocytotic vesicles than the controls. These vesicles were believed to be involved in bulk uptake of extracellular media, which may permit exposed cells to expand more rapidly than the controls. Thus the functioning of three separate membrane transport systems were shown to be susceptible to functional modification, at least in the short term, by extremely low frequency electromagnetic fields. This introduces the potential for an enormous array of downstream effects to echo through-out the organism via signal transduction pathways.