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2020-10-18

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Relevant for: Environment | Topic: Environmental Degradation - GHGs, Ozone Depletion and Climate Change

Alarm call: Scientists warn higher temperatures during the ‘growing season’ in the tropics and sub-tropic regions will greatly affect crop productivity.   | Photo Credit: banjongseal324

Between the year 1870 (the first industrial revolution) and today, the global temperature has risen by almost 2 degrees Celsius. This has come about due to more fossil burning (oil, natural gas, coal), which has also increased the carbon dioxide (abbreviated as CO2) levels from 280 ppm to 400 ppm. This heating has caused glaciers (and snow capping mountains) to melt and the sea level to rise. Daniel Glick, in the October 2 issue of National Geographic Magazine warns that the glaciers in Garhwal, Uttarakhand may virtually disappear by 2035!

The rise in CO2 levels has also acidified the ocean, leading to weakening the shells and skeletons of animals living in the sea, climate.org. On land, the rise in CO2 levels has both positive and negative effects. This being a ‘Green House Gas’, it traps the Sun’s heat from the atmosphere and warms the temperature, aids in the photosynthesis of plants, making them grow more, but at the same time restricts the plant’s ability to absorb nitrogen, thus restricting crop growth, phys.org.

How will this CO2 level heating affect food security in the coming years? D.S. Battisti and R.L. Naylor warned of this in 2009 in their paper in Science: “Historical warnings of future food insecurity with unprecedented seasonal heat” <DOI: 10.1126/science.1164363>. They warned that such higher temperatures during the ‘growing season’ in the tropics and sub-tropic regions (India and our neighbours, Saharan and Sub-Saharan Africa and parts of South America) will greatly affect crop productivity, and that this would be the ‘norm’. Given this double whammy of affecting ocean life and food security, it is unpardonable for Donald Trump, president of the US, and Jair Bolsonaro, president of Brazil, to promote industry at the cost of climate change.

How do global rise in temperature and CO2 level affect plant growth and yield? Do they promote higher yields or do they also lead to stress in the metabolism, generating some negative effects? Can we do some laboratory experiments on a model plant and see what happens at today’s (normal) temperature and a ‘future’ higher one; likewise at today’s CO2 and a ‘future’ higher level? J. Yu and his colleagues did try such experiments in 2017 in their paper: “Metatabolic pathways involved in CO2 enhanced heat tolerance in Bermuda grass” in the journal Frontiers in Plant Science https://doi.org/10.3389/fpls.2017.01506.They found that there was improved heat tolerance, and suppressed heat-induced damages. These are interesting results, but on a grass which is good for animals such as rabbits and cattle, and not for humans who do not have ruminant stomachs, nor teeth that grow upon usage as they do.

While grasses are what botanists call C4 plants, food grains (our staple food) are C3 and the way photosynthesis is done is somewhat different. It would thus be useful if such experiments are done on beans and legumes such as chana, chickpeas and similar grains (called ‘plant meat’).

It is towards this that a group from the Hyderabad Centre of the international agency ICRISAT (International Crops Research Institute for the Semi-Arid Tropics) decided to look at how two kinds of chickpea (the desi chana dal or the Bengal gram and the Kabuli chana (originally from Afghanistan) behave under different CO2 levels (current level of 380 ppm, and two higher levels (550 and 700 ppms). The plants were sown under these conditions, and harvested during the vegetative and reproductive stages (15 days and 30 days) post germination. The results of this study titled: ‘Molecular and physiological alterations in Chickpea under elevated CO2 concentrations’, by Paramita Palit et al in Plant and Cell Physiology 61(8):1449-1463 (2020) doi:10.1093/pcp/pcaa007, available online at https://academic.oup/pcp.

Since the whole genome sequence of the chickpea was earlier published by this group (Varshney et al, Nature Biotechnology 31,240-246, 2013 https://doi.org/10.1038/nbt.2491, they could identify as many as 138 metabolic pathways, mainly involved in sugar/starch metabolism, chlorophyll and secondary metabolite biosynthesis, and could get to decipher the pathways that lead to how high CO2 levels modify the growth of the chickpea plants. They found a noted increase in the root and shoot (plant height) lengths. Also the number of nodules in the roots (where nitrogen-fixing bacteria live) changed at high CO2 levels. Note that decrease in chlorophyll synthesis hastens leaves turning yellow and plant ageing (senescence).

Interestingly, the group found that desi chana and kabuli chana responded differently at high CO2 levels. This needs to be explored further.

Now, given the details of the 138 metabolic pathways identified, one can look deeper into how we can use molecules or agents that can promote or inhibit specific pathways through which growth and yields can be increased, and also the type of legumes that will best suit local conditions. Now that Nobelists J. Doudna and E. Charpentier have shown us how to edit genes, perhaps the time has come to do this too on specific local legumes!

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