Researchers Discover Why Plants Wither

In stressful situations such as lack of water, plants cannot remove the harmful byproducts of photosynthesis, withering and dying as a result.

AsianScientist (Apr. 29, 2016) – Researchers in Japan have shown that harmful reactive oxygen species (ROS) created during plant photosynthesis are the cause of withering. Their findings, published in Plant Physiology, could help to ensure stable food supplies by cultivating plants that can withstand global warming and other environmental stresses.

The majority of plants depend on photosynthesis as an essential energy source. However, when the light energy necessary for photosynthesis is absorbed in excess, harmful ROS are produced. In most cases plants use enzymes to deal with these ROS.

If plants are exposed to environmental stresses such as lack of water or excess minerals, their ability to photosynthesize is reduced; the ROS removal mechanism cannot keep up with the ROS produced from excess light energy; and plants wither and die. Researchers already knew that ROS are produced within chloroplasts in plant cells, but the exact location and the mechanisms behind this were unclear.

To explore this problem further, the research team, led by Associate Professor Miyake Chikahiro and PhD student Takagi Daisuke from the Kobe University Graduate School of Agricultural Science, extracted chloroplasts and thylakoid membranes from leaves and then exposed them to excess light using repetitive short-pulse illumination.

Findings revealed that a protein known as P700, which absorbs light energy within photosystem I, stopped functioning as a result of exposure to excess light. Photosystem I is a protein complex in thylakoid membranes that plays a major role in plant photosynthesis.

They researchers observed that three types of reactive oxygen species were produced: superoxide radicals, hydroxyl radicals and singlet oxygen. They further confirmed that by limiting the flow of electrons to photosystem I, the production of reactive oxygen species was suppressed.

Due to factors such as global warming, Earth’s natural environment is becoming increasingly inhospitable to plant life.

“By revealing the mechanism for the production of ROS and part of its regulatory mechanism, there are future possibilities for ensuring a stable food supply despite global warming,” said Miyake.

“The next step is to reveal the regulatory mechanism for ROS on a molecular level.”

The article can be found at: Takagi et al. (2016) Superoxide and Singlet Oxygen Produced Within the Thylakoid Membranes Both Cause Photosystem I Photoinhibition.


Source: Kobe University.
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