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Can plants respond to root exudates from touched neighbours?

Abstract

In nature, plants exposed to touch by several means e.g. leaves touching with neighbours, passing animals, etc., which stimulates the plant and alters its behaviour. In this study, we have investigated the interactions between touched plants and their untouched neighbours through root exudates. We hypothesised that plants are able to detect signals from the root exudates of their touched neighbours, and as a response, they will change their own biomass allocation pattern. Two experiments were conducted (transferring and sharing) experiments. In the transferring experiment, touched maize plants were hydroponically grown in half-strength Hoagland solution, afterward these plants were replaced with three weeks younger untouched plants. The latter were exposed to root exudates from the former touched plants. In this set up, the control was plants were exposed to root exudates from the former untouched plants. In the sharing experiment, both touched and untouched “exposed” plants of the same age were grown together, sharing the same nutrient solution. The control in this case was plants sharing the same nutrient solution with untouched plants. Root exudates were the only means of interactions between treatments, and the other means (e.g. volatile organic compounds) were prevented. Plants transferred to the nutrient solution of previously touched plants allocated more biomass to leaves and stems, and reduced their allocation to roots when compared with the control. By contrast, plants that shared root environment with touched neighbours produced more total dry weight, stem dry weight, root dry weight and lateral roots when compared to plants sharing this environment with untouched plants. This study validates the ability of the untouched plants to perceive and respond to signals emitted by root exudates of the touched neighbour. DOI: 10.13140/RG.2.1.5145.2244
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Can plants respond to root exudates of touched
neighbours?
Ali Elhakeem1,2, Niels Anten2 & Velemir Ninkovic1
1 Swedish University of Agricultural Sciences, Department of Crop Production Ecology, Ulls väg 16, Box 7043, 750 07 Uppsala, Sweden.
2 Wageningen University, Centre for Crop Systems Analysis, PO Box 430, 6700 AK, Wageningen, the Netherlands.
Introduction
In nature, plants live together in communities composed of one or
more species, and they incessantly communicate through a various
mechanisms (e.g. Volatile organic compounds, light cues and root
exudates) to interact with their neighboring plants. Leaves touching
between undamaged neighboring plants considered as the most
common daily base mechanical stimuli to which an individual plant has
to respond.
The ecological significance of plants interaction through root exudates
as a response to mechanical stimuli has not been yet investigated.
Conclusions
Through root exudate interaction, plants can acclimate and respond to
the physiological and morphological statues of their mechanically
stimulated (Touched) neighbors from the same genotype.
Objectives
Methods
Treated maize plants (T) growing in Hoagland solution were
brushed for 1 min over a period of 7 days, and then replaced with
new plants (Et) to be exposed for 6 days to the former growing
solution. Controls were plants (Ec) that transferred and exposed to
the growing solution of the untreated ones (C).
Et Ec
… . .. . .. . ..
. . .. … … . .. . .. . ..
. . .. …
Treated maize plants (T) shared the same growing solution with
untouched neighbouring plants (E). Control was untouched
plants (C) shared the same solution
Results
a
b b
20
30
40
50
Touched Exposed Control
Leaf mass fraction (%)
a
b
a
0.02
0.04
0.06
Touched Exposed Control
Stem dry weight (gm)
a b
a
0.05
0.1
0.15
0.2
Touched Exposed Control
Total dry weight (gm)
a
b
ab
0.02
0.04
0.06
Touched Exposed Control
Root dry weight (gm)
0.3
0.35
0.4
Et Ec
*
0.4
0.425
0.45
Et Ec
*
0.15
0.2
0.25
0.3
Et Ec
*
0
1
2
3
Et Ec
*
Stem mass fraction (%)
Leaf mass fraction (%)
Shoot-Root ratio
Root mass fraction (%)
References
Braam J (2005) In touch: plant responses to mechanical stimuli. New Phytol 165:373389.
Markovic D., Glinwood R., Olsson U. and Ninkovic V. (2014). Plant response to touch affects the
behaviour of aphids and ladybirds. Arthropod-Plant Interactions, 8: 171 181.
Ninkovic V. (2003). Volatile communication between barley plants affects biomass allocation.
Experimental Botany, 54 (389): 1931 1939.
Center of Crop System Analysis
P.O. Box 430, 6700 AB Wageningen
Contact: ali.elhakeem@wur.nl
T + 31 (0)317 48 53 15, M +31 (0)6 17 68 71 60
www.csa.wur.nl
Department of Crop Production Ecology
P.O. Box 7043, 750 07 Uppsala, Sweden
Contact: velemir.ninkovic@slu.se,
T + 46 (0) 18 67 25 41, M +46 (0) 73 984 22 33
www.slu.se/ecology/velemirninkovic
To Investigate the morphological
changes of the exposed neighbor
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Article
Full-text available
Touching between leaves of the same plant and/or by neighbouring plants is one of the most common mechanical stimuli to which an individual plant has to respond on a daily basis. The possible ecological implications of a plant’s response to touch on plant–insect interactions have not been explicitly investigated. We examined whether plant response to 1 min daily touchingover a period of 6 days affects host plant acceptance by the bird cherry-oat aphid Rhopalosiphum padi L. on maize and by the black bean aphid Aphis fabae Scop. on bean, as well as olfactory preference of an aphid predator, seven-spotted ladybird Coccinella septempunctata L. Maize plants responded to touch with significant reduction in plant height, total plant biomass, leaf weight, leaf surface, shoot/root ratio and specific leaf area (SLA), while bean plants responded with reduced stem height and reduced SLA. Both aphid species showed significantly reduced acceptance of touched plants compared with untouched plants. The two aphid species and male and female ladybirds preferred volatiles from untouched plants over those from touched plants. Volatiles in the headspace of touched and untouched plants were collected and identified. Stepwise discriminant analyses identified (E)-nerolidol and (E)-bcaryophyllene in maize and 6-methyl-5-hepten-2-one and an unidentified sesquiterpene in bean as the best discriminating compounds in the volatile profiles of touched plants. Our study suggests that touch-induced changes in plants can potentially affect host plant selection by aphids and habitat searching by ladybirds. Thus, touch-induced changes in plants may have significant effects at higher trophic levels.
Article
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Patterns of biomass allocation between different plant organs have often been used to explain the response of plants to variations in resource availability. This paper reports how aerial allelopathy (plant–plant communication) affects biomass allocation, that is the trade‐off between root, stem and leaves, and also relative growth rate (RGR, increase in biomass per unit biomass per unit of time, mg g–1 d–1) and its components. Based on previous experiments, communication between two barley (Hordeum vulgare L.) cultivars (Alva and Kara) was used for the present study. Kara exposed to volatiles from Alva allocated significantly more biomass to roots compared with Kara exposed to volatiles from Kara or to clean air. There was no significant difference between plants of Kara exposed to volatiles from Kara and those exposed to clean air. Changes in total dry weight (TDW), RGR and unit leaf rate (ULR, increase in biomass per unit time and leaf area, kg m–2 d–1) were not significantly affected by plant–plant communication. However, there was a significant increase in specific leaf area (SLA, leaf area per leaf dry weight, m2 kg–1) in Kara when exposed to volatiles from Alva. The results show that aerial plant–plant communication does not affect total biomass production but does significantly affect biomass allocation in individual plants. There may be differences in the volatile profiles of Kara and Alva that induce increased biomass allocation to roots in the Kara plants exposed to volatiles from Alva.
Article
Summary 1 Acknowledgements 14 References 14 Perception and response to mechanical stimuli are likely essential at the cellular and organismal levels. Elaborate and impressive touch responses of plants capture the imagination as such behaviors are unexpected in otherwise often quiescent creatures. Touch responses can turn plants into aggressors against animals, trapping and devouring them, and enable flowers to be active in ensuring crosspollination and shoots to climb to sunlit heights. Morphogenesis is also influenced by mechanical perturbations, including both dynamic environmental stimuli, such as wind, and constant forces, such as gravity. Even individual cells must sense turgor and wall integrity, and subcellular organelles can translocate in response to mechanical perturbations. Signaling molecules and hormones, including intracellular calcium, reactive oxygen species, octadecanoids and ethylene, have been implicated in touch responses. Remarkably, touch-induced gene expression is widespread; more than 2.5% of Arabidopsis genes are rapidly up-regulated in touch-stimulated plants. Many of these genes encode calcium-binding, cell wall modifying, defense, transcription factor and kinase proteins. With these genes as tools, molecular genetic methods may enable elucidation of mechanisms of touch perception, signal transduction and response regulation.
Box 430, 6700 AB Wageningen Contact: ali.elhakeem@wur.nl T + 31 (0)317 48 53 15, M +31 (0)6 17 68 71 60 www
  • Crop Center
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Center of Crop System Analysis P.O. Box 430, 6700 AB Wageningen Contact: ali.elhakeem@wur.nl T + 31 (0)317 48 53 15, M +31 (0)6 17 68 71 60 www.csa.wur.nl Department of Crop Production Ecology P.O. Box 7043, 750 07 Uppsala, Sweden Contact: velemir.ninkovic@slu.se, T + 46 (0) 18 67 25 41, M +46 (0) 73 984 22 33 www.slu.se/ecology/velemirninkovic