Microwave irradiation affects gene expression in plants

Abstract

The physiological impact of nonionizing radiation has long been considered negligible. However, here we use a carefully calibrated stimulation system that mimics the characteristics (isotropy and homogeneity) of electromagnetic fields present in the environment to measure changes in a molecular marker (mRNA encoding the stress-related bZIP transcription factor), and show that low amplitude, short duration, 900 MHz EMF evokes the accumulation of this mRNA. Accumulation is rapid (peaking 5-15 min after stimulation) and strong (3.5-fold), and is similar to that evoked by mechanical stimulations.

Keywords: EMF; MSRC; bZIP; microwave; non-ionizing radiation; tomato.

Figure 1

(A) The mode stirring reverberation chamber. This is a large room with metal walls (dark lines) to exclude external EMF, an antenna (lower left) to emit tunable EMF, a rotary stirrer to make the EMF homogeneous (right side) and a plant culture chamber placed within the working volume (gray area). (B) Schematic representation of EMF types. a, non-polarized (isotropic) and homogeneous field, where the field components align in all possible directions and the field has the same amplitude at all points. b, polarized, nonhomogeneous field, where the field components align in a single direction while the amplitude varies (heterogeneity).

Figure 2

Field characteristics in the plant culture chamber. The tunable antenna was used to generate EMF of 5 Vm⁻¹ from 800–1000 MHz (A), or 893–911 MHz (B). (A) Standard deviation of amplitude for the total field (σ_xyz, bold line) and for each of the Cartesian axes (σ_x, σ_y, σ_z); dashed line: 3dB limit specified by the IEC 61000-4-21 standard. (B) Effective values measured within the nonshielded (○) and shielded (Δ) culture chamber. Dashed line: 5 V/m input signal.

Figure 3

Accumulation of LebZIP1 transcript after EMF-stimulation in the nonshielded culture chamber. Plant show either an immediate response (white bars) or a 5 min delayed response (black bars). Plants stimulated in the shielded culture chamber (gray bars). Each value is expressed relative to the nonexposed control (C) and normalized to the actin mRNA and is the average of at least 3 independent repetitions ± the standard error.