138
Subtle Agroecologies
parasites 6 such as powdery mildew and rust, in which redox potential and pH measurements in
leaf sap were the main observations. He developed a simple and quick method for redox measurements in the tissue of detached leaves and formulated a hypothesis for why the biophysical
status of a plant plays such an important role in resistance, and plant physiology in general. He
found that the principle of resistance lies in the ability of the parasite to gain the energy from the
host cell. The parasite uses the terminal oxidase of the host plasmalemma (the plasma membrane
of the cell wall) as its energy source.
Plant roots generate electric currents and associated electric felds as a consequence of electrogenic ion transport at the root surface. van West et al. (2002) demonstrated that swimming zoospores
of oomycete plant pathogens 7 to plant roots are partly attracted by electrotaxis (the movement of an
organism in an electric feld) in natural root-generated electric felds. The zones of accumulation of
anode- or cathode-seeking zoospores adjacent to intact and wounded root surfaces correlated with
their in vitro electrotactic behaviour (either attracted to the anode or the cathode). Manipulation of
the root electric feld was refected in changes in the pattern of zoospore accumulation, and imposed
focal electric felds were capable of overriding endogenous signals at the root surface. Data suggested that electrical signals from a potential difference (voltage) between root and rhizosphere/
rhizoplane can augment or override chemical cues in mediating short-range tactic responses of
oomycete zoospores at root surfaces. These fndings may help in the future to better assess risks for
infection of root-borne diseases.
Akay and Kara (2006) investigated quality parameters that can be measured by different methods. One of them is Vincent’s bioelectronic method (BEV). The P-value is measured in sap pressed
from fruits or vegetables. It is based on three factors: pH (acidity), rH (redox potential) and R
(resistivity). The P-value integrates the three parameters to a parameter of quality and is calculated
as [30 × (rH − 2pH)]2/R (Hoffmann, 1991), which is expressed in microwatts (μW).
These electrochemical parameters can tell us something about the production conditions and the
effects on humans after consumption. Products with low P-value are supposed to be health promoting. Good foods give us more power than bad ones and are good for our health. Life processes in
plants and animals can be described as chains of electrochemical or redox reactions. The P-value is
used in the areas of environment, human medicine and food research. Food with low redox values
provides many electrons that counteract free radicals (in other words have an anti-oxidising effect)
and hence contribute to health. Good examples of these ‘curing foods’ are beetroot, (organic) carrots and fermented cabbage.
Hoffmann et al. (2007) worked on electrochemical quality assessment, using the redox potential
(rH in mV), resistivity (ohm) and pH of a liquifed, homogenised sample. In his book, Hoffmann
explained the relationship between redox value and entropy: a lower redox potential coincides with
lower entropy, which means less chaos or more organised tissue.
Northolt et al. (2004) investigated the usefulness of electrical parameters to assess carrot quality
and the development of the inner quality concept and concluded that these measurements can be
valuable. Their report presents a comprehensive explanation of the meaning of the different parameters, as provided in Box 12.1.
EFFECTS OF APPLIED, EXTERNAL, ELECTRICAL (ELECTROMAGNETIC)
FACTORS ON PLANTS AND THEIR MICROBIOMES
This section explores a number of experiments aiming to infuence plant growth to the beneft of the
grower/farmer. Although this work started in the beginning of the twentieth century, to the author’s
6 An obligate parasite is a parasitic organism that cannot complete its life cycle without exploiting a suitable host. If an
obligate parasite cannot exploit a host, it will fail to reproduce.
7 Oomycetes, also known as ‘water moulds’, are a group of several 100 organisms that include some of the most devastating
plant pathogens. The diseases they cause include seedling blight, damping-off, root rot, foliar blight and downy mildew.
Subtle Agroecologies
parasites 6 such as powdery mildew and rust, in which redox potential and pH measurements in
leaf sap were the main observations. He developed a simple and quick method for redox measurements in the tissue of detached leaves and formulated a hypothesis for why the biophysical
status of a plant plays such an important role in resistance, and plant physiology in general. He
found that the principle of resistance lies in the ability of the parasite to gain the energy from the
host cell. The parasite uses the terminal oxidase of the host plasmalemma (the plasma membrane
of the cell wall) as its energy source.
Plant roots generate electric currents and associated electric felds as a consequence of electrogenic ion transport at the root surface. van West et al. (2002) demonstrated that swimming zoospores
of oomycete plant pathogens 7 to plant roots are partly attracted by electrotaxis (the movement of an
organism in an electric feld) in natural root-generated electric felds. The zones of accumulation of
anode- or cathode-seeking zoospores adjacent to intact and wounded root surfaces correlated with
their in vitro electrotactic behaviour (either attracted to the anode or the cathode). Manipulation of
the root electric feld was refected in changes in the pattern of zoospore accumulation, and imposed
focal electric felds were capable of overriding endogenous signals at the root surface. Data suggested that electrical signals from a potential difference (voltage) between root and rhizosphere/
rhizoplane can augment or override chemical cues in mediating short-range tactic responses of
oomycete zoospores at root surfaces. These fndings may help in the future to better assess risks for
infection of root-borne diseases.
Akay and Kara (2006) investigated quality parameters that can be measured by different methods. One of them is Vincent’s bioelectronic method (BEV). The P-value is measured in sap pressed
from fruits or vegetables. It is based on three factors: pH (acidity), rH (redox potential) and R
(resistivity). The P-value integrates the three parameters to a parameter of quality and is calculated
as [30 × (rH − 2pH)]2/R (Hoffmann, 1991), which is expressed in microwatts (μW).
These electrochemical parameters can tell us something about the production conditions and the
effects on humans after consumption. Products with low P-value are supposed to be health promoting. Good foods give us more power than bad ones and are good for our health. Life processes in
plants and animals can be described as chains of electrochemical or redox reactions. The P-value is
used in the areas of environment, human medicine and food research. Food with low redox values
provides many electrons that counteract free radicals (in other words have an anti-oxidising effect)
and hence contribute to health. Good examples of these ‘curing foods’ are beetroot, (organic) carrots and fermented cabbage.
Hoffmann et al. (2007) worked on electrochemical quality assessment, using the redox potential
(rH in mV), resistivity (ohm) and pH of a liquifed, homogenised sample. In his book, Hoffmann
explained the relationship between redox value and entropy: a lower redox potential coincides with
lower entropy, which means less chaos or more organised tissue.
Northolt et al. (2004) investigated the usefulness of electrical parameters to assess carrot quality
and the development of the inner quality concept and concluded that these measurements can be
valuable. Their report presents a comprehensive explanation of the meaning of the different parameters, as provided in Box 12.1.
EFFECTS OF APPLIED, EXTERNAL, ELECTRICAL (ELECTROMAGNETIC)
FACTORS ON PLANTS AND THEIR MICROBIOMES
This section explores a number of experiments aiming to infuence plant growth to the beneft of the
grower/farmer. Although this work started in the beginning of the twentieth century, to the author’s
6 An obligate parasite is a parasitic organism that cannot complete its life cycle without exploiting a suitable host. If an
obligate parasite cannot exploit a host, it will fail to reproduce.
7 Oomycetes, also known as ‘water moulds’, are a group of several 100 organisms that include some of the most devastating
plant pathogens. The diseases they cause include seedling blight, damping-off, root rot, foliar blight and downy mildew.