technologies have allowed the integration of sensor systems into miniature multifunc-
tional configurations for the detection of factors important for plants, such as oxygen, pH
(Guice et al. 2005; McNaughton et al. 2005), potassium (Cosofret et al. 1995), iron
(Mlika et al. 1997), phosphate (Engblom 1998), and nitrate (Knoll et al. 1994; Barker et
al. 1998). Although these devices are small and can even accommodate multiple sensor
types, they are far from nanoscale devices and little is known regarding their long-term
operation and functionality.
9.7 Plan(t)s for space exploration
Envisage a scenario where selected plant species would be genetically engineered and re-
motely controlled to provide clean air, potable water, and food while at the same time act-
ing as a pharmaceutical factory and source of raw materials. Specifically engineered and
controlled species would be integrated into a cohesive system of sensor-laden, intelli-
gently controlled structures (greenhouses) to provide for immediate life support needs
(air, water, food) while also supplying the necessities and enhancers for long-term pres-
ence (clothing, shelter, pharmaceuticals, nutraceuticals, materials, fiber, flavoring, per-
fumes, soaps). In addition to providing life support requirements, plants are fundamental
for the maintenance of the psychological well-being of a crew, particularly on long-term
missions or permanent settlements.
The concept is graphically shown in Figure 9.1 (see also Color Section). Remote in-
structions, capable of traveling small or great distances (such as radio signals), are gen-
erated and sent to the primary receiver. The primary receiver is a physical device (such
as an antenna) located in close proximity to the target plants. The primary receiver
processes the incoming instructions and generates a secondary signal to which the plants
have been engineered and programmed to respond (such as chemical signals, low-fluence
infrared radiation, or other novel electromagnetic wavelengths).
The secondary signal is perceived by the plant via existing natural components (such
as organelles like plastids or pigments such as phytochrome) or via a yet-to-be-designed
component we call a “perceptosome.” We envision perceptosomes as rationally designed,
bionanotechnologically derived units within the plants. We anticipate they would be
based on peroxisomes—vesicles with highly specialized functions that are designed for
post-translational import of signal-tagged proteins synthesized in the cytoplasm.
Different perceptosomes would have different receptors for import sequences, and genes
would be modified so that the required protein (pigment) had the requisite import mole-
cule attached. Thus, proteins normally located in the cytoplasm or other organelles could
be modified to make perceptosomes unique for particular purposes. These percepto-
somes would be stimulated by the secondary signal to activate a cascade of intercellular
or systemic signaling pathways. The systemic signals would take chemical, physical, or
electrical form and would in turn stimulate gene activation in appropriate target tissues.
This would result in the initiation of programmed functions such as increased photosyn-
thetic rate, specific secondary product biosynthesis, or induction of flowering.
All the steps in this process would be integrated into a sensor-rich, robotically en-
hanced, and intelligently controlled monitoring and feedback control system. Ultimately,