Feeding caterpillars make leaves shine

June 4, 2015, Max Planck Society
The image shows the amounts of light accumulated over a period of 30 minutes, highlighting the changing calcium concentrations. These are represented by a color code (blue=low, red=high). The arrow points to an area where a cotton leafworm (Spodoptera littoralis) and two Arabidopsis thaliana leaves are located in a small cage. Credit: Victoria Kiep / Martin Luther University, Halle-Wittenberg; Jyothilakshmi Vadassery / Max Planck Institute for Chemical Ecology

When a plant is attacked by herbivores, this triggers a number of physiological responses in the plant. Calcium ions are important messengers for the processing of wound signals in plant cells. They regulate signal transduction and indirectly control plant defense mechanisms. Scientists of the Max Planck Institute for Chemical Ecology in Jena and the Institute of Agricultural and Nutritional Science of the Martin Luther University in Halle-Wittenberg, Germany, have now succeeded in visualizing the immediate wound or herbivory responses in plants. They used Arabidopsis thaliana (thale cress) plants that produce a special protein which breaks down after the binding of calcium ions and emits free energy in the form of light. The amount of light corresponds to the calcium concentrations in the cells of the respective leaf areas. By using a highly sensitive camera system the researchers could track the calcium flow in the plants. Visualization revealed that calcium signals occur systemically and wander from attacked to neighboring leaves within a short period of time, and ultimately put the whole plant into a state of defense readiness.

Calcium is a universal intracellular messenger. In plants, many physiological processes are mediated by ions, especially responses to abiotic and biotic stresses, such as feeding caterpillars. These trigger the activation of a number of defense mechanisms. If a leaf is attacked by an insect, the wound signal which emanates from the affected leaf is transmitted to other, unattacked leaves. In order to visualize this signal, the scientists performed experiments with transgenic Arabidopsis plants which were genetically modified to express a protein in the cytosol, the liquid inside the cells, which breaks down and releases light energy after it has bound calcium ions. The emitted light energy correlates with the respective concentrations of . In this way, intracellular changes of can be determined directly. Moreover, these processes can be made visible in the plants by applying a highly sensitive camera system which uses charge-coupled devices (CCD). "It is very impressive to see how every bite of a caterpillar makes certain leaf areas shine. The immediate reaction of the plants is clearly visible," says Victoria Kiep, who carried out most of the experimental work together with Jyothilakshmi Vadassery.

Spodoptera littoralis larva feeding on a Arabidopsis thaliana (thale cress) plant. Credit: Sandra Scholz and Monika Heyer / Max Planck Institute for Chemical Ecology

It was very important for the researchers to show that the calcium signal is a systemic process, rather than a local one, as it wanders from the attacked leaf to neighboring leaves within a few minutes to trigger the subsequent defense responses. "We succeeded in visualizing the dynamic signal processing of intracellular calcium as a secondary messenger which is elicited by insect feeding and transmitted systemically to unattacked areas of the plant," Axel Mithöfer, the leader of the project group "Physiology of Plant Defense" in the Department of Bioorganic Chemistry, summarizes the results of the study.

How calcium signals are elicited in different and separate areas of plants is not yet fully understood. However, the scientists speculate that electric signals which are transmitted via the vascular system of plants, so-called vascular bundles, play an important role. There are no important differences between calcium signals which are elicited by mechanical wounding and those which are triggered by feeding caterpillars. Surprisingly, the application of larval oral secretions inhibited the transduction of calcium signals to neighboring leaves in the experiment. Of general importance for systemic calcium signaling is the wounding of the vascular system of the leaf, which is also responsible for the internal transport of water and nutrients in the plant.

Feeding caterpillars make leaves shine
Calcium concentrations in the same 30 minutes period, however, divided into subsequent 5 minute intervals. The temporal sequence of the larval feeding on the first (below, 0-15 min), then on the second (above, 15-30 min) leaf is clearly visible, as is the appearance of systemic signals in the neighboring leaves. Credit: Victoria Kiep, Martin Luther University, Halle-Wittenberg; Jyothilakshmi Vadassery, MPI Chem. Ecol.

Further experiments are planned in order to find out which kind of wounding triggers the systemic calcium signal, for example, whether a similar wound response is elicited by aphids and spider mites, as these insects puncture the plant tissue to suck the plant sap and damage the tissue only slightly. The scientists would like to investigate how is achieved in grasses whose vascular bundles are structured differently in comparison to Arabidopsis which belongs to the Brassicaceae family. They are also interested in determining the operating distance of calcium signals in general and would like to answer the question whether the signals can be transmitted to the plant roots.

This study demonstrates that calcium signals, which are necessary for eliciting plant defense responses, and their spatial and temporal expansion can be visualized. Moreover, the scientists showed that can be studied directly in intact plants in different physiological and ecological contexts, which helps to better understand its role as a secondary messenger in . [AO/AM]

Explore further: Blossom end rot: Transport protein identified

More information: Kiep, V., Vadassery, J., Lattke, J., Maaß, J.-P., Boland, W., Peiter, E., Mithöfer, A. (2015). Systemic cytosolic Ca2+ elevation is activated upon wounding and herbivory in Arabidopsis. New Phytologist. DOI: 10.1111/nph.13493

Related Stories

Blossom end rot: Transport protein identified

November 23, 2011

Poor calcium distribution in agricultural crops causes substantial loss of income every year. Now a Korean-Swiss research team under the co-leadership of plant physiologists at the University of Zurich identified a protein ...

Abscisic acid treatments can prevent tomato blossom-end rot

January 14, 2015

Plants are subjected to numerous environmental stresses—drought, extreme temperatures, and excess light can all affect plant growth and quality. Looking for methods to improve the quality of tomato plants, researchers at ...

Novel electric signals in plants

March 9, 2009

Using ion-selective micro-electrodes electrical signals in plants moving from leaf to leaf could be measured. The speed of the signals spreading as voltage changes over cell membranes ranged from 5 to 10 cm per minute. The ...

Spying on plant communication with tiny bugs

April 23, 2014

Internal communications in plants share striking similarities with those in animals, new research reveals. With the help of tiny insects, scientists were able to tap into this communication system. Their results reveal the ...

How plants manage calcium may reduce effects of acid rain

March 9, 2007

A new understanding of how plants manage their internal calcium levels could lead to modifying plants to avoid damage from acid rain. The pollutant disrupts calcium balance in plants by leaching significant amounts of the ...

Recommended for you

Genome duplication drives evolution of species

September 25, 2018

Many wild and cultivated plants arise through the combination of two species. The genome of these so-called polyploid species often consists of a quadruple set of chromosomes—a double set for each parental species—and ...

Some female termites can reproduce without males

September 24, 2018

Populations of the termite species Glyptotermes nakajimai can form successful, reproducing colonies in absence of males, according to a study published in the open access journal BMC Biology.

Photosynthesis discovery could help next-gen biotechnologies

September 24, 2018

Researchers from The University of Queensland (UQ) and the University of Münster (WWU) have purified and visualized the 'Cyclic Electron Flow' (CEF) supercomplex, a critical part of the photosynthetic machinery in all plants, ...

How fruits got their eye-catching colors

September 24, 2018

Red plums. Green melons. Purple figs. Ripe fruits come in an array of greens, yellows, oranges, browns, reds and purples. Scientists say they have new evidence that plants owe their rainbow of fruit colors to the different ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.