Low-amplitude, high-frequency electromagnetic field exposure causes delayed and reduced growth in <em>Rosa hybrida</em>

International audienceIt is now accepted that plants perceive high-frequency electromagnetic field (HF-EMF). We wondered if the HF-EMF signal is integrated further in planta as a chain of reactions leading to a modification of plant growth. We exposed whole small ligneous plants (rose bush) whose growth could be studied for several weeks. We performed exposures at two different development stages (rooted cuttings bearing an axillary bud and 5-leaf stage plants), using two high frequency (900 MHz) field amplitudes (5 and 200 V m(-1)). We achieved a tight control on the experimental conditions using a state-of-the-art stimulation device (Mode Stirred Reverberation Chamber) and specialized culture-chambers. After the exposure, we followed the shoot growth for over a one-month period. We observed no growth modification whatsoever exposure was performed on the 5-leaf stage plants. When the exposure was performed on the rooted cuttings, no growth modification was observed on Axis I (produced from the elongation of the axillary bud). Likewise, no significant modification was noted on Axis II produced at the base of Axis I, that came from pre-formed secondary axillary buds. In contrast, Axis II produced at the top of Axis I, that came from post-formed secondary buds consistently displayed a delayed and significant reduced growth (45%). The measurements of plant energy uptake from HF-EMF in this exposure condition (SAR of 7.2 10(-4) W kg(-1)) indicated that this biological response is likely not due to thermal effect. These results suggest that exposure to electromagnetic field only affected development of post-formed organs

Distributions of firing rates (top row) and latencies (bottom row) at single pheromone doses are dose-dependent.

<p>(<b>A</b>) Comparison in ORNs of raw firing rates <i>F</i>_raw (not corrected from control stimulations) for control stimulations (green) and for pheromone doses −1, 0, 1, 2, 3, 4 log ng (blue, from left to right). <i>F</i>_raw at <i>C</i> = −1 log ng not significantly different from control (Kolmogorov-Smirnov test, <i>p</i> = 0.43). (<b>B</b>) Comparison in ORNs of latencies <i>L</i> for same stimuli and doses (from right to left) as in (A). (<b>C</b>) Comparison in PNs of firing rates <i>F</i>_raw for control stimulations (green) and for pheromone doses −3, −2, −1, 0, 1 log ng (red), same representation as in (A). <i>F</i>_raw at <i>C</i> = −3 log ng not significantly different from control (Kolmogorov-Smirnov test, <i>p</i> = 0.43) but significantly different from <i>F</i>_raw at <i>C</i> = −2 (<i>p</i><10⁻⁴). (<b>D</b>) Comparison in PNs of latencies <i>L</i> for same stimuli and doses as in (C). (<b>E, G</b>) Comparison of firing rates <i>F</i> (corrected from control stimulation) in ORNs (blue) and PNs (red) at the same doses −1, 0 (in E) and 1 log ng (in G). For <i>C</i>≤1, the mean firing firing rates of ORNs is smaller than that of PNs. (<b>F–H</b>) Comparison of latencies, same representation as in (E, G). At all doses, the mean firing latency of ORNs is larger than that of PNs. At <i>C</i>≥1, the shortest ORN latencies become almost as short as the shortest PN latencies.</p

Latencies are linear functions of pheromone dose with different parameter values in each neuron.

<p>(<b>A</b>) Measured latency <i>L</i> (dots) of 3 ORNs fitted to decreasing lines (eq. <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003975#pcbi.1003975.e008" target="_blank">8</a>; solid curve) showing minimum latency <i>L</i>_m and maximum latency <i>L</i>_M at threshold <i>C</i>₀ given from <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003975#pcbi-1003975-g006" target="_blank">Fig. 6A</a>. (<b>B</b>) All (<i>N</i> = 38) fitted ORN dose-latency curves. (<b>C</b>) Three examples of PN latency curves. (<b>D</b>) All (<i>N</i> = 44) fitted PN dose-latency curves. (<b>E</b>) Maximum latencies <i>L</i>_M at threshold dose <i>C</i>₀ fitted to lognormal CDFs; same <i>N</i>'s as in (B, D) and representation as in <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003975#pcbi-1003975-g006" target="_blank">Fig. 6E</a>. (<b>F</b>) Minimum latencies <i>L</i>_m fitted to normal CDFs; same <i>N</i> and representation as in (E). A few zero latencies arise in PNs from variability on pheromone transport time <i>T</i>_t.</p

Ca²⁺ imaging shows that each pheromone component activates a single glomerulus in the MGC.

<p>(<b>A</b>) The main pheromone component activates the cumulus only. (<b>B, C</b>) The two secondary components activate two neighboring glomeruli. (<b>D</b>) The blend of the 3 components in the behaviorally most efficient ratio 4∶1∶4 activates the whole MGC. Outlines of antennal lobe (AL), antennal nerve (AN) and the 3 main subdivisions of MGC are shown.</p

Firing rates are Hill functions of dose with different parameter values in each neuron.

<p>(<b>A</b>) Measured firing rate <i>F</i> (dots) of 3 ORNs fitted to Hill functions (eq. <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003975#pcbi.1003975.e004" target="_blank">4</a>; solid curves) showing parameters <i>F</i>_M and <i>C</i>_1/2 and characteristic <i>C</i>₀ and <i>C</i>_s for <i>F</i>₀  =  5 AP/s. (<b>B</b>) All (<i>N</i>  =  38) Hill curves fitted to ORNs. (<b>C</b>) Hill curves of 3 PNs. (<b>D</b>) All (<i>N</i>  =  37) PN curves successfully fitted to Hill functions. (<b>E</b>) Distribution of maximum firing rates <i>F</i>_M in the ORN (blue, <i>N</i> = 38) and PN (red, <i>N</i> = 37) populations. Each empirical CDF (staircase) with its fitted normal CDF (dotted curve) and corresponding PDF (dashed curve). (<b>F</b>) Distributions of dynamic ranges <i>ΔC</i> (related to <i>n</i>), same <i>N</i> and representation as in (E) except fitted distribution is lognormal for ORNs.</p