Maximum Yield Australia/New Zealand March/April 2019 | Page 56
o n c e
inside the roots or root cells, water
and dissolved nutrients travel through
different root pathways in one of two
ways — either symplastic movement
or apoplastic movement.”
Behind the root cap is the cortex, which makes up the
bulk of the rest of the root. The cortex is loosely packed
with cells and empty space, both of which store water and
allow it to flow into the xylem vessels, sending water and
dissolved nutrients to the above-ground shoot systems.
Roots lack openings such as the stomata found in leaves.
Rather, roots are covered in thin-walled cells, known
as parenchyma cells, which act as a water-absorbing
membrane. These are primarily found in the cortex of the
root. This entire outer wall of the cortex is known as the
epiblema and the main conduit for this transport at the
centre of the cortex is known as the endodermis. Unlike
the rest of the cortex, the cells in the endodermis are more
tightly arranged so water does not escape back into the
cortex but can be sent on its merry way upwards through
passage cells. However, this does not happen until the
water and nutrients have passed the root system’s smell
test. To that end, the endodermis is a plant guardian. If
the plant has inadvertently absorbed any toxic material,
the endodermis filters it out and rejects it. A waxy
barrier known as the Casparian strip is the gatekeeper
at play here. Proteins within the cells allow for the good
compounds and molecules to pass, while toxins are
weeded out and removed.
Root hairs are an extension of the endodermis. These fine,
long, and narrow projections grow out from mature roots,
helping increase a root system’s ability to absorb moisture
and nutrients by increasing the root system’s surface
area, which increases contact between roots and soil.
The stele, pericycle, conjunctive tissue, and vascu-
lar bundles round out some of the lineup that make
up the typical root. If you really, really want to know
more about the intricate functions of roots, or have a
severe case of insomnia, look up “histogen theory” and/
or “Quiescent Center.” For our purposes here, these
go way beyond the realm of useful knowledge for the
layman horticulturist, this author included.
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Maximum Yield
The Secret World of Roots
Root systems are a network of connected botanical append-
ages whose entire mass can sometimes dwarf the above-
ground portion of the plant it is supporting. It takes a lot of
work behind the scenes to feed and care for all the flowers,
fruits, and leaves getting most of the accolades. They don’t,
however, work alone. The root (mostly below ground) and
shoot (mostly above ground) systems work in unison in a
positive feedback loop. Though an oversimplification of the
process, it’s safe to say the photosynthesis work the leaves
and greens do sends nutrients below to the root system, which
is then able to expand and grow, sending more food and water
upward so more leaves can be produced. Then more photosyn-
thesis can occur, and more roots can develop and so on.
Roots are constantly attracting and transporting water and
dissolved nutrients from the medium they are in. Deep down
in the root cells, a pressure builds. This root pressure creates
a siphon-like action which forces water and nutrients up into
the above-ground portions of the plant while water and nutri-
ents from the surrounding soil are drawn into the root. This
is due to the higher concentration of nutrients and minerals
inside the root cells than in the soil environment around the
root system. In addition to this force, moisture from the soil
is continually being absorbed into the roots by the negative
water potential within the root cells.
Symplastic vs Apoplastic Movement
of Water and Nutrients in Roots
Once inside the roots or root cells, water and dissolved
nutrients travel through different root pathways in one of
two ways — either symplastic movement or apoplastic
movement. Most water and nutrients move through the roots
via apoplastic movement. When this happens, water does
not actually enter the cells, but travels through the passages
between cells. Think of this as a hallway connecting
bedrooms. This is easier than travelling by symplasticity.