While they can photosynthesize their needs from the sun, for the most part, they still require the same general nutrients and access to water that we do. And one other critical component that they need to survive is the ability to breathe.
How To Breathe
Yes, plants breathe too, though they can hold their breath a fair bit better than animals can. When flooding occurs and plants become buried under a foot or more of water, they enter what is called a state of hypoxia. The term applies the same to us, meaning a lack of oxygen.
This leads to them activating anaerobic fermentation and continuing to convert the energy they can to keep powering their cells. This means an increase in alcohol dehydrogenase production and a reduction in the amount of energy used. Plants do their best to make their store of energy-filled carbohydrates last until they obtain access to molecular oxygen again in the air.
But this process has a severe negative side effect. An increase in dehydrogenase production also coincides with an increase in the formation of reactive oxygen species, various forms of chemical components that don’t work well with cells and their functionality. A popular form of these include the so-called “free radical” that antioxidants are said to combat. For plants, however, the form that arises is hydrogen peroxide. While small amounts of this chemical are necessary for plant metabolism, high accumulations of it from anaerobic fermentation can lead directly to cell death.
Thus, finding ways to control chemical and enzyme output under these conditions is important for protecting plants during flooding scenarios. This becomes ever more important as the effects of climate change result in unpredictable and changing flooding seasons, including expanding into areas that normally don’t have to deal with such issues.
Enzymes And Oxidases
It has been known through prior research that plant responses to hypoxia are controlled by VII Ethylene Response Factors, also known as ERF transcription factors. These help in promoting and expressing the genes that respond to such conditions, including the ones that begin the anaerobic fermentation processes. These factors also appear to regulate themselves based on O2 availability through the use of several amino acid pathways.
In a study by researchers from Oxford University and the Leibniz Institute for Plant Biochemistry, they were able to identify the particular enzymes involved in the process of stopping the hypoxia response. In many ways, plants react similarly to animals, as noted before, including in mimicking the regulatory system and the control over it by transcription factors. The levels of these factors within the cell appears to be controlled by five enzymes that are able to sense the concentration of available O2.
This family of enzymes are known as the Plant Cysteine Oxidases and they help to catalyze a reaction that stops the activation of the transcription factors and other parts of the hypoxia response. Through further chemistry testings, the scientists were able to definitively prove the relationship between molecular O2, the enzymes, and the regulation pathways. It appears that these enzymes help in breaking down the ERF transcription factors when a supply of oxygen is available, stopping the factors from activating the hypoxia response. But when oxygen becomes lacking, the enzymes are not able to function, freeing up the ERFs to do their work.
Next Up: Modification
Determining these effects are important, because this now opens up the option of manipulating the activity of these enzymes. In short, the relationship between the two isn’t very stable nor efficient. By being able to selectively turn off these enzymes by genetic modification, it could allow the breeding of plants that are able to response quicker to flooding and this efficiency will allow them to withstand being underwater longer without it stunting their growth or killing them.
The next step will be to take a model organism like Arabidopsis and apply this change, to see how that affects its tolerance to hypoxia conditions. If it works as expected, then scientists will have a new method to produce flooding-resistant plants and save harvests around the world from annual (and often worsening) floods.
Photo CCs: Pamri River near Kotra village, Udaipur, Rajasthan from Wikimedia Commons