  Plants are sensitive to thermal and electrical effects; yet the coupling of
both, known as thermoelectricity, and its quantitative measurement in vegetal
systems never were reported. We recorded the thermoelectric response of bean
sprouts under various thermal conditions and stress. The obtained experimental
data unambiguously demonstrate that a temperature difference between the roots
and the leaves of a bean sprout induces a thermoelectric voltage between these
two points. Basing our analysis of the data on the force-flux formalism of
linear response theory, we found that the strength of the vegetal equivalent to
the thermoelectric coupling is one order of magnitude larger than that in the
best thermoelectric materials. Experimental data also show the importance of
the thermal stress variation rate in the plant's electrophysiological response.
Therefore, thermoelectric effects are sufficiently important to partake in the
complex and intertwined processes of energy and matter transport within plants.
