Plant neurobiology by uup

Prof K N Ganeshaiah
Coordinator, IBIN
Head, Department of Forestry and
Environment Sciences,
University of Agricultural Sciences, Bangalore -
Mention of advances in Human brain research
Written by:

What about plants?
Is there anything called ‘Neurobiology’ for Plants?
and YOU will answer at the end
Listen to me for next 45 minutes

Science is ever changing truth
DNA/Protien
as genetic
material
Human
feelings
arise from
heart
Earth
centric
theory
Atom
and
God’s
particles

Journey of Plant Neurobiology till date…

 Neurobiology: Neurobiology is the study of cells of the
nervous system and the organization of these cells into
functional circuits that process information and mediate
behavior
Nervous system may be defined as an organized
constellation of cells (neurons) specialized for the
repeated conduction of an excited state from receptor
sites or from other neurons to effectors or to other
neurons
 Plant Neurobiology: Branch of plant science deals with
signaling and behavior of plants and parts/systems
responsible for it

Events
Signal passed
Signal perception by
sensory organs
Signal transmission by
neurons and
neurotransmitters
Signal processing and
decision making
Signal to body organs to
for reaction

• How this signal perception takes place in plants?
• Do plants exhibit neurons, neurotransmitters and
brain as signal processing centers?

Do plants smell?
Do plants hear sound?
Do plants
communicate each
other?
Can plants do
mathematics
Do plants keep
memory
Do plants can see?

Crescograph
Microscope
Cameras
Isotopes
Sensors
Phytotrons
Computers and softwares

Plants smell recognize volatile compounds produced by neighboring plant as
signal for switching on their specific metabolic activity

Figure 1: Volatile Organic
Compounds (VOCs) emitted by
injured plants have a specific
ratio and concentration of
components.
(A). The danger signals emitted
by the family provide warning
that a species-specific enemy
(specialist) is nearby. In contrast,
plants that receive a VOC
message from other families
might elicit a general defense
response to prevent damage by
herbivores (generalists) attacking
various plant species
(B). By sharing common VOC
information across the plant
kingdom, plants are able to
prevent attack from a broad
range of herbivores.
(Hirokazu et al., 2012)

(A) foraging toward a
20-day-old tomato plant,
Figure 2: Seedling of Cuscuta pentagona
(Mark et al., 2006 )
(B) attaching to and beginning
to grow from stems of tomato
seedlings and
(C) close up of C..
pentagona attachment.
α-pinene, β-myrcene, and β-phellandrene

Figure 3: Behavioral response of young roots of Zea mays to a continuous 220 Hz sound
coming from left field (white arrow).

So plant respond to sound
Inference:

Figure 4: Somatic homologous recombination in UV-C- and flg22-treated plants. a, Schematic
representation of a recombination substrate used for monitoring somatic homologous
recombination (lines IC1 and IC9). GUS, b-glucuronidase gene; Hpt, hygromycin-resistance
gene. Homologous region is shown in dark blue. b, Recombination events (blue spots highlighted
by black arrows) giving a measure of homologous recombination frequency (HRF; Homologus
recombination frequency) in line IC1 after flg22 treatment. Scale bar, 1 mm; inset, £3 original
magnification. c, Somatic HRF in untreated and UV-C-treated S0 plants. Results are means ^
s.e.m. (n . 50 plants; t-test *P , 0.05). d, Somatic HRF in either untreated plants, plants treated
with flg22 A. tum., or treated with flg22. Results are means ^ s.e.m. (n . 40 plants; t-test *P ,
0.05). (Jean et al., 2006)

Figure 5: Somatic HRF in S0 plants and in the next four generations. S0 plants (line IC1)
were either untreated or UV-treated. Somatic HRF was measured in untreated S1, S2, S3
and S4 plants. Results are means ^ s.e.m. (n . 50 plants; t-test *P , 0.05 compared with the
corresponding S0 -UV generation).
(Jean et al., 2006)

Figure 6 : Somatic HRF in either self-pollinated or out crossed plants.
a) Somatic HRF in offspring of either self-pollinated untreated plants, UV-treated plants, or
plants in which one of the parents was UV-treated (n . 40 plants; t-test *P , 0.05).
b) Somatic HRF in offspring of either self-pollinated untreated plants (white bar), flg22-treated
plants (grey bars), or plants in which one of the parents was flg22-treated (hatched bars; n . 35
plants; t-test *P , 0.05).
All the results are means ^ s.e.m.
(Jean et al., 2006)

Figure 7: Somatic HRF in either self-pollinated or out crossed plants. Somatic HRF in offspring
of plants in which one parent was wild type (WT) and the other harbored the recombination
substrate (n . 40 plants; t-test *P , 0.05). White bar, both parents untreated; dark hatching, both
parents UV-treated; light hatching, one parent UV-treated.
All the results are means ^ s.e.m.
(Jean et al., 2006)

So plants do keep memory
Inference:

Figure 8: Starch content levels from experiments with unexpected variation in either starch
content at the onset of darkness or the time of onset of darkness. (A) Starch turnover in
Arabidopsis grown in 12-hr light/12-hr dark, then subject to unexpected early (8 hr, n = 6
individual rosettes, circles) normal (12 hr, n = 6, squares) or unexpected late (16 hr, n = 5,
triangles) onset of darkness. (B) Starch turnover in Arabidopsis cca1/lhy mutant grown in 12-
hr light/12-hr dark, then subject to unexpected early (9 hr, circles), or normal (12 hr, squares)
onset of darkness (n = 6–10).
(Antonio et al., 2013)

Figure 9: Starch content levels from experiments with unexpected variation in either
starch content at the onset of darkness or the time of onset of darkness.
(C) Starch turnover in Arabidopsis exposed to different daytime light levels: 90 μmol
quanta m−2 s−1 (open squares) or 50 μmol quanta m−2 s−1 (filled squares) (both n = 5,
previously all plants grown in 12-hr light/12-hr dark with 90 μmol quanta m−2 s−1).
(D) Starch turnover in Brachypodium grown in 12-hr light/12-hr dark, then subject to
unexpected early (8 hr, circles) or normal (12 hr, squares) onset of darkness (both n = 6).
Error bars are standard error of the mean throughout.

Figure 10: Chemical kinetic models capable of implementing analog arithmetic operations. (A) Pictorial summaries of
schemes for analog implementation of addition, subtraction and multiplication between the concentrations of two molecules
S and T. Square brackets indicate concentrations. (B) and (C) Schematic behavior of the stromal concentrations of S and T
molecules ([SC] and [TC] respectively), in (B) first and (C) second arithmetic division models. In the first model, the T
molecule tracks the time to expected dawn after a reset-time tr. In the second model the T molecule concentration increases
with time proportionally to 1/(expected time to dawn) between tr1 and tr2. (D) and (E) Pictorial summaries of (D) first and
(E) second analog arithmetic division models (not all reactions shown in pictures, for full details see ‘Materials and
methods’). In the reaction schemes, molecules not attached to the starch granule surface have a ‘C’ subscript. The blue disk
represents components of the starch degradation apparatus potentially activated by the S molecule in the first model, and by
the ST complex in the second model. (Antonio et al., 2013)

Figure 11. Chemical kinetic models capable of implementing analog arithmetic operations.
A. Model 1 B. Model 2 arithmetic division models to Arabidopsis

So plants can do mathematics
Inference:

Plant
Communication
Within plant
Between
plants
With
insect/microb
es
Through chemicals Through Electric signals

Figure 12: Mature leaves detect changes in CO2 concentration and elicit a stomatal response in
developing leaves. a, Leaf-cuvette experiment. Plants of Arabidopsis (Columbia, Col-0) were
grown for 4 weeks under ambient CO2 (360 p.p.m.) until leaf insertions 5 to 13 had developed.
These mature leaves were enclosed in transparent airtight cuvettes under CO2 concentrations of
either 720 or 360 p.p.m. Subsequent leaf insertions developed outside the cuvette under ambient
CO2. Plants were maintained in cuvettes for 7 to 9 days until the next five leaf insertions had
matured, the last three of which were investigated for stomatal density (no. of stomata per mm2)
and index ((no. of stomata/no. of stomata & no. of epidermal cells)2100).

Figure 13: Left → Stomatal index and density for new leaves (insertions 16 to 19) under
ambient CO2 when mature leaves (insertions 5 to 13) inside cuvettes are supplied with
increased CO2 (720 p.p.m.). Both stomatal density and index are reduced in new leaves if the
supply of CO2 is increased to the mature leaves. Right → Reverse experiment: mature leaves
inside cuvettes are under CO2 at 360 p.p.m.; external CO2 is 720 p.p.m. Stomatal density and
index increase in response to the decreased CO2 around the mature leaves.
***P*0.0005; *P*0.05; bars, s.e.m.; n4150. (Lake et al., 2001)

Figure 14: Effect on stomatal index of new leaves of reducing light incident on mature leaves by
using neutral density filters (shade) or transparent filters (full light). Stomatal index of new
leaves is reduced when mature leaves are shaded.
***P*0.0005; *P*0.05; bars, s.e.m.; n4150.
(Lake et al., 2001)

Figure 15: Schematic representation of the custom-designed experimental unit (not in scale). (a)
The seal at the base of the central cylindrical box ensured that chilli seeds arranged in a circle
around the adult plant were chemically isolated from it. (b) All seeds and adult plants within a
replicate unit were housed within 2 different sized square boxes, one inside the other, with the
air in between the two boxes removed using a vacuum pump. The whole experimental unit was
custom-made in colourless cast acrylic material (ModenGlas), which transmitted 92% of visible
light, but was opaque to ultraviolet and infrared wavelengths. (Monica et al., 2012)

Figure 16: Early growth of chilli seedlings
depends on the presence and identity of their
neighbour. (a) Seedlings growing next to a
fennel (grey solid line and triangles) are
marginally significantly taller than those
growing next to an adult chilli plant (black
solid line and squares; Pair-wise contrasts, P
= 0.07) and significantly taller than seedlings
in the empty control (black dotted line and
white diamonds; Pair-wise contrasts, P =
0.01). The observed differences in above-
ground growth among treatments (adult
fennel plant, grey solid line and triangles;
adult chilli plant, black solid line and
squares; empty control, black dotted line and
white diamonds) are amplified over time.
Only plants that emerged by day 14 are
included in these analyses (n = 32 per
treatment). Error bars indicate standard
errors. (b) Growth differences disappear
when seedlings are allowed to grow in the
absence of any adult plant after emergence (n
= 80 per treatment). Error bars indicate
standard errors.
(Monica et al., 2012)

Figure 17: Mean final root size of chilli seedlings is affected by the presence and identity of their
adult neighbours. (a) Overall, maximum root length differed significantly depending on the
neighbouring plant present in the sealed central box (n = 32 per treatment). Seedlings growing
next to adult chilli plants had significantly shorter roots than those in the empty control or
growing with the fennel (P = 0.015). (b) The presence of a neighbouring fennel during
germination and emergence caused an increase in early root development of chilli seedlings when
the communication channels are blocked, but not when unblocked (light grey bars) (F masked . F
open and Control masked; P = 0.027; n = 80 per treatment). Differences disappeared when
seedlings were allowed to grow away from a fennel plant (dark grey bars) (P = 0.94; n = 80 per
treatment). Error bars indicate standard errors. (Monica et al., 2012)

Let us watch something now….

Wait!!!
This isn’t just an animated movie,
it has something scientific

So plants can do communicate
Inference:

Some of the representatives of these subsystems are proposed for three levels of organisation of increasing complexity, cell,
organ, and organism in plants (P and Roman script) and animals (A and italic script) (Barlow, 1999; Miller and Miller, 1995).
Arrows (←and →) indicate that the process is delegated, respectively, to either a lower or higher organisational level.
Table 1: According to J.G. Miller’s Living System Theory (Miller, 1978) there are 10
subsystems out of a total of 20 subsystems which process information

Some of the representatives of these subsystems are proposed for three levels of organisation of increasing complexity, cell,
organ, and organism in plants (P and Roman script) and animals (A and italic script) (Barlow, 1999; Miller and Miller, 1995).
Arrows (←and →) indicate that the process is delegated, respectively, to either a lower or higher organisational level.

Figure 18: Vascular bundles throughout the plant body. Thin strands of vascular tissue
form networks in leaves, join into bundles in shoots, and transform into a large central
cylinder of roots which is encircled by pericycle and endodermis
Still a hypothetical view : Vascular bundles as plant neurons
Xylem: Neuron
Phloem: Axon Reasons:
 The word neuron derived from greek
language, which means vegetable fiber
Only channel throughout the plant
body which passes any information
Transmits ion to different part of plant
organs
Phloem perform functions similar to
axon as passing signals form xylem to the
tissue or cells
Neurons are cells that are specialized to receive, propagate, and transmit
electrochemical impulses.
(Baluska et al., 2009)

Cellular end poles as plant synapses
Plant synapses are stable actin-supported adhesive domains, assembled at
cellular end-poles (cross-walls) between adjacent plant cells of the same cell file, across
which auxin and other chemical signals are transported from cell to cell via F-actin-
driven and brefeldin A sensitive vesicular trafficking pathways
(Baluška et al. 2003 ; Barlow et al. 2004).

Figure 19: Possible scenario for evolution of epithelial and auxin transporting plant synapses.
Under repeated pathogen attacks and with progressive exposures of ancient terrestrial plants to
dry environments, ancient surface epithel-liketissue
(A) developed in to the contemporary epidermis and endodermis plant epithels
(B). Finally,auxin-transporting synapses evolved from epithelial synapses
(C). Red lines show synaptic cell cell adhesion domains; red crosses depict APB1; yellow balls
are recycling vesicles; and orange dots represent auxin. (Baluska and Stafeno, 2013)

Figure 20: Developmental auxin-transporting plant synapse and its role in gravisensing. (a) In
axial plant organs such as roots, cross-walls (synapses) transport auxin from cell-to- cell; the
recycling of the putative auxin efflux carrier PIN1 (blue) and the auxin influx carrier AUX1 (red)
is essential for this process. (b) Several molecules have been localized to these auxin-transporting
plant synapses. (c) Because of gravity force, the protoplast exerts a greater mechanical load on
the physical bottom of any cell in axial plant organs (indicated by the larger size of the blue
arrow). This asymmetric protoplastic load is effectively balanced by robust cell walls maintaining
tubular cell shapes.

Figure 21: Developmental auxin-transporting plant synapse and its role in gravisensing.
(c) Because of gravity force, the protoplast exerts a greater mechanical load on the physical
bottom of any cell in axial plant organs (indicated by the larger size of the blue arrow). This
asymmetric protoplastic load is effectively balanced by robust cell walls maintaining tubular cell
shapes.
(d) The absence of this protective force would result in a distortion of the protoplast shape
because of the preferential accumulation of protoplastic masses at the physical bottom.
(e) A differential mechanical load exerted on the plasma membrane domains, which constitute the
plant developmental synapse, results in a high plasma membrane tension experienced at the
physical bottom, which inevitably facilitates more exocytic events and less endocytic events at
the blue (PIN1-enriched) plasma membrane domain, whereas the opposite situation is
encountered at the red (AUX1-enriched) domain. This inherently asymmetric nature of plant
synapses, encompassing both molecular and physical aspects, results in the polar transport of
auxin along the gravity vector. (Frantisek et al., 2005)

A chemical substance which is released at the end of a nerve fibre by the
arrival of a nerve impulse and, by diffusing across the synapse or junction, effects the
transfer of the impulse to another nerve fibre, a muscle fibre, or some other structure.

Table 2: Discovery of neurotransmitters
Sources: (Kruk and Pycock 1990; Roshchina 1991, 2001; Kuklin and Conger 1995;
Oleskin 2007; Kulma and Szopa 2007)

Table 3: Level of neurotransmitters in living organisms
Sources: Fernstrom and Wurtman 1971; Kruk and Pycock 1990; Hsu et al.:1986;
Roshchina 1991, 2001; Oleskin et al. 1998; Tsavkelova et al. 2000)

Figure 22: The scheme of the evolution in the neurotransmitter (biomediator) function
(Mariela and Christina, 1997)

Table 4: The established functions of neurotransmitters in living organisms

Table 5: Processes and functions in plants modulated by acetylcholine and biogenic
monoamines

Animal/Human brain or neurons or cells produce electric signals in an
emergency

Table 6: Comparison of basic characteristics of APs, VPs, and SPs`
(Matthias et al., 2009)

Figure 23:. Techniques for measuring electrical signals in plants. (a) Extracellular recording with
four channels and a reference electrode inserted in the soil. , electrical stimulation. An AP (right)
generated by electrical stimulation appeared successively at electrodes 1, 2, 3 and 4. (b)
Intracellular measurement of the membrane potential with a microelectrode inserted into the
cytoplasm of an algal cell while the reference electrode is in contact with the artificial pond water
(APW) outside the cell. Both electrodes are filled with KCl, clamped in Ag/AgCl pellet holders
and connected to an electrometer. (Jorg and Slike, 2007)

Figure 24: Techniques for measuring electrical signals in plants. (c) Phloem potential
measurements; an aphid in feeding position with its stylet inserted into a sieve element on the
upper side of a leaf. (d) After the aphid is separated from its stylet by a laser pulse, the stylet
stump exuded sieve tube sap to which the tip of a microelectrode was attached. Cooling the
shoot evoked an AP transmitted acropetally within the phloem, while flaming of a leaf
generated a VP with different form and of long duration. t, time.
(Jorg and Slike, 2007)

Figure 25: Electrical signalling in
Mimosa pudica. (a)When the tip of a leaf
pinna is stimulated by spontaneous
cooling with ice water or mechanically
by touch, an AP is evoked and
transmitted basipetally within the rhachis
with a speed of 20–30 mm s-1. The
tertiary pulvini at the base of the leaflets
respond to the AP, causing ion and water
fluxes that lead to leaf movements. This
type of signal stops at the base of the
pinna, and no further transmission
occurrs. (b)When the leaf is stimulated
by cutting, a basipetally moving VP is
generated in the rhachis, irregular in
shape and long in duration. Its speed is
slower (5–6 mm s-1) than that of the AP;
however, it is able to pass through
secondary pulvini at the base of the
pinna and causes leaflet movements of
neighbouring pinna, and also bending of
the primary pulvinus at the base of the
petiolus.

Figure 26: Photosynthetic response of electrical signaling in poplar. (a) Experimental
arrangement of gas exchange recordings. The plant was heat stimulated for 3 s by the flame of a
lighter at the base of a mature leaf (*) to evoke a VP . (b) Typical response of JCO2 and gH2O of the
opposite, right leaf at a distance of 15 cm upon flaming of the left leaf. The arrow denotes the
instant of injury. At 180 s after stimulation, the net CO2 uptake rate (black graph) decreased
immediately and then recovered almost completely after 900 s, while the gH2O (grey graph)
remained stable.

Figure 27: Photosynthetic response of electrical signaling in poplar. (c) Spatio-temporal
changes of DF/F′m assessed by chlorophyll fluorescence imaging. The image area (length,
22 mm; width, 17 mm) covers the center of a leaf while the opposite leaf was stimulated by
flaming (*) at a distance of 15 cm similar to the set-up shown in (a). Times are given in
relation to the instant of injury (at time 0). Changes in DF/F′m took 240 s to become
apparent.A false colour shift from blue to yellow in the intervein area, equivalent to a
reduction of DF/F′m from 0.6 to about 0.2, indicates the decrease of photosynthesis. The
bar translates the false colour code into values of DF/F′m.
Jorg and Slike, 2007

Table 5: Well-documented physiological effects of electrical signals in plants
Jorg and Slike, 2007

In plants root transition zone act as brain
Each root apex is proposed to harbor brain-like units of the nervous
system of plants. The number of root apices in the plant body is high, and all
‘‘brain units’’ are interconnected via vascular strands (plant neurons) with their
polarly-transported auxin (plant neurotransmitter), to form a serial (parallel)
neuronal system of plants. (Alpi et al., 2007)

Figure 28: Anatomical basis of root and shoot apices. Anatomical organization of root (a)
and shoot (b) apices. Note very regular cell files, with cross-walls representing plant
synapses, in root apices. On the other hand, cells in shoot apices are irregularly shaped
and fail to arrange into regular cell files (Frantisek et al., 2005)

Figure 29: Sensory zones in the
root apex. There are two
clearly defined sensory zones in
the root apex: the root cap
covering the meristem and the
transition zone interpolated
between the meristem and
elongation region. Both these
sensory zones receive diverse
signals and the output is
differential switch-like onset of
rapid cell elongation, resulting in
either straight growth (when all
post mitotic cells start their rapid
cell elongation simultaneously)
or rapid turnings of the root apex.
The transition zone is flooded
with sucrose, which allows
energy demanding ‘brain-like’
information processing in cells of
the transition zone
(Frantisek et al., 2005)

Human/Animal brain
– ATP consumption: 104
molecules of ATP to
transmit 1bit of
information at a chemical
synapse
– Consumes 20% of body
oxygen
– Very well safeguarded by
skull
– Presence of otoliths to in
ear to sense gravity
Plant brain (Root tip transition
zone
– In plants ATP
consumption: Highest at
root
– Oxygen consumption:
Highest at root tansition
– Very well safeguarded by
root cap
– Presence of statoliths in
root transition zone

Biorobotics: Plantoids
Terrafarming
Nutreint sensors in soils
Diversity studies

Figure 1: A schematic view of the loop for the formulation of a formal model of a biological
system, by experimental validation.
(Barbara et al., 2010)

Now
Is there anything called as
‘Plant neurobiology’?

Gregor Johann Mendel
(1822-84)
Father of Modern Genetics!!!
• 1856: Series of breeding experiments to
study plant heredity
• First to work out the basic laws governing
the inheritance to genes
• 1866: Published detailed account of his
findings before the Brunn Natural History
• His work was not accepted by Scientific
community
• 1884: Death of Mendel
• 1900: Mendel’s work re-emerged by the
independent works of Hugo Devries,
Tschermark and Correns

 Plant neurobiology – Still an infant
 The hypotheses has to proved – Molecular genomics and
cell biology, chemical and biochemical ecology
 Needs a combined effort of plant scientists from diverse
backgrounds and from all disciplines
 Results in better understanding of crop plants
What more you want??

Plant neurobiology by uup

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