You are here
In this series, we detail on how ‘abused’ antibiotics are helping superbugs and why we tend to so
“We are giving antibiotics to more than 75% of patients. Even for the common cold, we prescribe two tablets of Septran [co-trimoxazole]”
This is not a confession of a doctor or a surgeon, but of a self-taught rural pharmacist! While his intentions to cure the ill may be good, does he/she know what that translates to? Turns out, THEY HAVE NO IDEA!
The discovery of antibiotics, their ubiquitousness, and the ease of accessibility has transformed healthcare. Fatal diseases like pneumonia and typhoid can now be cured, and surgeries can be performed without any risk of infections. And the epicenter of this transformation was the healthcare sector. Pharmaceutical industries became the producers of these magic pills called antibiotics and doctors – armed with their knowledge and expertise – became their guardians, and pharmacists the helpers. We, the people, owing to our trust in the healthcare system, became the proud consumers.
But, over the years, the roles have mixed up, and that has worked in favor of superbugs. Superbugs are certain bacteria that have defied antibiotics, developed resistance to them and are now threatening our existence. Now, we have superbugs resistant to tuberculosis, influenza and a host of other diseases. The problem is so severe that the World Health Organization has put out a list of superbugs, urging researchers to come up with better antibiotics against these malefactors.
“Not getting the right drugs for the right duration is one of the leading causes of Anti-microbial resistance (AMR)”, says Prof. Joy Sarojini Michael of the Christian Medical College (CMC), Vellore. “This mainly happens due to the wrong prescription by doctors/quacks as a result of their lack of knowledge”, she adds.
If the prescription by doctors is questionable, can we really trust the prescription by a pharmacist? Or self-medication?
Antibiotics caught in the game of perceptions
The fact that pharmacists are turning into doctors and prescribing antibiotics for health issues like the common cold, are concerning for many reasons. Firstly, they are not entitled to prescribe antibiotics, or for that matter, any drug! Secondly, antibiotics do not cure a common cold, since it is caused by a virus, and should be treated by antivirals, not antibiotics. Thirdly, they may have no clue about the medical history of the infected person and might prescribe an antibiotic that might be allergic. If so, then why do people approach pharmacists for drug-prescription in the first place?
Perceptions of people in the healthcare sector-- doctors, patients, pharmacists -- form the driving force behind the rise of superbugs in India.
In a study, researchers at CMC Vellore studied the perceptions of people, pharmacists and doctors in the Vellore region to better understand the causes behind the misuse of antibiotics. It was a group discussion based qualitative study conducted in 2013. The researchers found that people’s financial status and accessibility to doctors were major determinants of people visiting doctors. “To see a doctor, we take leave from work and stand in a queue. Finally, the doctor will prescribe, possibly the same drug as the pharmacist. So, we go to pharmacy shop instead to get it quicker”, remarked one of the participants in the discussion who hailed from Vellore.
There is no cheer in the rural areas of the country either. With healthcare services already in the dismal state, people opt to take self-medication. “For dysentery, we have separate native treatment. Allopathic medicines have side effects”, they perceive, as told by one who participated in the survey. When enquired about the knowledge of antibiotics and antibiotics resistance, most people knew which antibiotics cured which symptoms, but had little idea of what antibiotics resistance meant.
If you thought the pharmacists and doctors, who are well aware of the repercussions of misuse/overuse of antibiotics, were any responsible, you could not be farther from the truth! In the study, one doctor is said to have admitted, “If we ask for investigations on the first day, the patient never turns up again! So, instead, we immediately give antibiotics and watch for two days. Nobody bothers about diagnosis, only symptom relief.”
The pharma companies are compliant in this ploy too. “Reputed pharma companies offer complementaries for prescribing their drugs. If you prescribe more, they offer air-conditioned car or free tickets... Of late, we are forced to try new antibiotics”, confessed another doctor.
The pharmacists have a different motivation to sell antibiotics without prescription, to prescribe antibiotics, or to even change prescriptions. One pharmacist, interviewed for the study, confessed – “Nobody likes to lose business. We give whatever the customers ask. Competition, the location of shops, license issues...everything has become commercialized.”
Though there are different perceptions about the use of antibiotics, there is one overarching commonality – the antibiotics prescription depends more on sociological factors like quick recovery, patient satisfaction, and commercial incentives rather than biological factors like proper diagnosis and cure.
Added to this is the fact that the Indian market offers more than 10,000 antibiotics formulations; while the National List of Essential Medicines – containing medicines that satisfy the priority healthcare needs of the majority of the population – contains only 21 antibiotics and two antibiotics combinations. This disparity itself points to a vast misuse of antibiotics.
“We need to be proactive. Already we are behind and the bacteria are developing new ways of surviving”, cautions Prof. Sujith J. Chandy, the lead author of the above-mentioned study and a professor at CMC Vellore. “The problem is that AMR is a multifactorial problem and therefore the solution is complex, and interventions have to be at all levels and including all stakeholders. Some of the factors are difficult to change, but some are slightly easier. For our part, we need to promote health education, hygiene practices, and antibiotic use by using them in the right dose, right duration, right frequency”, he adds.
Until scientists develop better alternatives to current antibiotics, and the government strengthens regulation on its usage, the best we can do is to advocate the judicious use of antibiotics – the right dose, the right duration, and the right frequency go a long way to keep these superbugs at bay. After all, as responsible citizens, we also have a responsibility towards our country, don’t we?
In a step that could ease some tension about India's Neutrino Observatory, the Indian National Science Academy (INSA), the National Academy of Sciences (NAS) and Indian Academy of Sciences (IAS) have issued a joint statement supporting the India-based neutrino observatory to be set up in Bodi West Hills in Theni district of Tamil Nadu.
The India-based Neutrino Observatory (INO) is a multi-institutional collaboration to build a world-class underground laboratory to study high energy and nuclear physics. The primary goal of the laboratory is to study neutrinos—fundamental particles with almost no mass that are produced either by radioactivity in the atmosphere, or by the Sun, or by high energy particles coming from space. The laboratory will consist of a large cavern longer but narrower than an average football pitch, and several smaller caverns. These are accessed by a 2100 m long and 7.5 m wide tunnel. The laboratory will also house one of the world’s most massive magnetised iron plates weighing a whopping 50,000 tons!
However, the rosy dream of INO being a full-fledged, underground science laboratory for studies in physics, biology, geology and hydrology has run into obstacles since its inception in 2002. The project faced initial setbacks when the first chosen location in Singara near Nilgiri Hills, Tamil Nadu faced immense protest from environmental groups, due to a perceived threat to Mudumalai Tiger Reserve. It was then shifted to Bodi West Hills in Theni, where the project again raised many environmental concerns, again due to its proximity to Mathikettan Shola National Park in Kerala. In a whiff of relief, the Ministry of Environment, Forest and Climate Change, Government of India, finally provided the clearance for the project to go ahead as a special case, after obtaining the necessary permissions from the State Pollution Control Board and forest clearances, on 26th March 2018.
The INO project is of the nation's largest scientific project yet, where nearly 100 scientists, from 25 research institutes and universities across the country, would be collaborating to create new waves in particle physics with their research. In their statement, the three premier academies also highlighted the same, affirming their support to INO. “The Science Academies of India are strongly supportive of the establishment of such an experimental facility for its intrinsic scientific value”, reads the statement.
The statement also appealed to the nation to support the collaborative effort—“The science academies hereby appeal to people of the district, state, and country to support this educational and research project wholeheartedly. A successful INO experiment will be a major technological and scientific national achievement.”
A new study by scientists from Indian Institute of Science (IISc) has shown that hues of different colours generate large gamma oscillation in the primary visual cortex, the region of the brain that processes visual information. Reddish hues were seen to cause the strongest oscillations.
While monitoring the electrical activity of a brain, gamma oscillations or oscillation of neurons at frequency range around 30 to 80 hertz, are known to be a prominent signature of sensory stimulation, like seeing, touching and hearing. These oscillations are influenced by the properties of the stimulus and behavioural state. Gamma oscillations also play a purported role in natural vision, evidence for which is still lacking, and in cognitive functions, like paying attention.
Although gamma oscillations generated by the visual senses have been studied before, these studies were conducted using light from an achromatic (colourless) lens. In their new study, the scientists wanted to understand the response of the gamma oscillations, when different colours are presented in the field of view.
Tests conducted on monkeys have shown a dependence of the gamma oscillations to properties of the colour, like hue and saturation. Three adult female monkeys were shown flashing colours of different hue, saturation and luminance, while the gamma oscillations were recorded using probes implanted surgically.
“We show that gamma oscillations of extremely high magnitude (peak increase of ∼300-fold in some cases), far exceeding the gamma generated by optimally tuned achromatic gratings, are induced… by full-field color stimuli of different hues” say the authors about the result of the study.
They also noted that the gamma oscillations the strongest oscillations were recorded for long-wavelengths or reddish hues. The oscillations depended by the purity of the hue and increased with hue saturation. Interestingly, the luminance, or the intensity or brightness of the light did not appear to influence the oscillations. They also noted a strong correlation between L and M cone cell (types of photoreceptor cells in the eye) contrast produced by the stimuli. This, the author suggest gamma oscillations could be a marker of the specific mechanisms underlying this L-M cone contrast.
“These findings provide insights into the generation of gamma oscillations, as well as the processing of color along the visual pathway” say the authors about the importance of their work.
India is infamously called the ‘diabetes capital of the world’. With over 40 million diabetics in the country, we have a distinction of having the highest number of diabetics for any country. This has huge implications on the country’s healthcare, forcing doctors, scientists and citizens to work together to manage and remediate this condition. Now, researchers at the Indian Institute of Technology Bombay (IIT Bombay) have some sweet news for diabetics. They have developed a polymer based bioartificial pancreas that can be implanted inside the body, thus helping in managing diabetes.
Diabetes mellitus is a chronic metabolic disorder in which sugar levels in the blood are very high for a prolonged period. In a healthy person, the body breaks up the carbohydrates in the food, into glucose, which supplies energy. This is done with the help of a hormone called insulin, produced in the pancreas. However, in a diabetic, the body either does not make enough insulin (Type 1 diabetes), or cannot use the insulin it produces (Type 2 diabetes). In some cases, it could be a combination of both.
To treat Type 1 diabetes, a condition affecting three out of 100,000 children of 0–14 years, doctors recommend the use of insulin injections, insulin pumps, or transplantation of either the whole pancreas or islet cells — part of the pancreas that produces insulin. Recently, there has been considerable progress in developing bioartificial pancreas with islet cells which mimic the function of a natural pancreas. However, a persistent roadblock has been the issue of biocompatibility — the body treats the bioartificial pancreas as a ‘foreign’ object, triggering the immune system’s response, which can degrade the function of the artificial pancreas.
In this study, the researchers have developed a bioartificial pancreas using polymer based hollow fibre membrane that is biocompatible and can also grow and sustain insulin producing cells on it. “A hollow fibre membrane is a narrow tube about 1 mm in diameter with pores in the wall ”, explains Prof. Jayesh Bellare from IIT Bombay, who led the study. “When liquid is passed through the tube (also called lumen), the wall selectively retains certain constituents and allows others to pass through”, he says, adding that this sort of ‘selective separation’ is used in many processes, including dialysis.
The researchers made these patented hollow fibre membranes using a polymer called polysulfone, which is known for its toughness and stability, with an additive compound called TPGS (d-α-Tocopheryl polyethylene glycol 1000 succinate). “The advantage of our hollow fibre membrane is that it supports the cells to grow by mimicking the extracellular matrix in which the cells naturally grow, and simultaneously, allows insulin to reach the patient while preventing an immune reaction from cells if they are of foreign origin”, remarks Prof. Bellare.
The inner side of the hollow fibre membranes developed by the researchers has pores in the nanometer range and is responsible for the selective separation of insulin. The rest of the membrane is more porous and has bigger pores which provide support. The researchers made the bio-artificial pancreas by placing together one or more hollow fibres to form a small bioreactor — a container-like structure where insulin is produced.
The researchers have tested their device with both human stem cells derived from umbilical cord, as well as islet cells from pig pancreas. “For the first time ever, we have successfully encapsulated human stem cells and porcine cells in our novel and patented material derived hollow fibre membrane”, says Prof. Bellare. The researchers then implanted these devices into diabetic mice for 30 days and found that these implants caused no abnormalities to other organs. In addition, the immune cells of the mice did not attack the implants, and blood vessels were also seen growing on the cells of the implants.
The research could improve the quality of life for more than 542,000 children in the world living with Type 1 diabetes. So how far are we from seeing this bioartificial pancreas in action? “Although there is a long way to go for making islet transplantation a cure for diabetes, but with the right material and cell type, this can become a reality”, says Prof. Bellare. As a next step, the researchers plan to continue studying the how the new device behaves in large animals. “Much more will be needed to bring this in human trial; the basic technology has been demonstrated in our work”, he concludes.
Researchers at IIT Bombay propose an easy method to extract nutrient rich oil, protein and fibre from pomegranate seeds.
We all enjoy a healthy, tasty and refreshing glass of pomegranate juice. Some of us prefer the juice over eating the arils as we may not like biting into the tasteless seeds. But do you know that the seeds are a source of a very healthy oil? In a study, Prof. Amit Arora and his team from the Indian Institute of Technology Bombay have proposed a new cost-effective, zero-waste method of extracting oil from pomegranate seeds, which also yields high-quality protein and dietary fibres.
India is the world’s largest producer of pomegranates, with a yield of 2.3 million tons in 2016 alone. With the increasing consumption of pomegranate juice, there has been an explosive increase in its waste products—the seeds—constituting about 10% of the total weight. While the oil extracted from the seeds has high medicinal value due to its anti-cancer, anti-oxidant and anti-diabetic properties, the byproducts obtained during extraction are are also rich in protein and dietary fibres.
“Considering the quality of oil and protein in pomegranate seeds, it can very well replace flax seeds. It is very similar to chia seeds in properties. It can be considered as a replacement in gaining many functional properties”, says Prof. Arora, talking about how pomegranate seeds fare against the well-known chia seeds and flax seeds.
While there have been earlier attempts to extract oil from pomegranate seeds, they could extract oil only partially, and the rest of the produce had to be discarded. The commonly-used cold-press technique, where a hydraulic press is used to squeeze out the oil, can only extract 40-50% of the oil, and is energy consuming. A popular extraction process uses organic chemicals like hexane which could lead to environmental contamination and health hazards and hence, requires a lot of care in handling and disposing of the chemicals. This increases the costs for construction and operation. A few other methods that involve high temperature and mechanical pressure not only decrease the quality of oil but also degrade the proteins, thus reducing the nutritional and economic value of the oil. Other methods of extraction, including some that use ultrasound and microwave, are sophisticated and expensive, even though they yield 95-99% of the oil.
In this study, Prof. Amit Arora and his team have tried to address these shortcomings with a new approach. They have proposed a one-pot oil-extraction method that is not only environment-friendly but can also extract a highly nutritious oil. The method is fairly simple and can also be used for small quantities of seeds, say the researchers.
In the proposed method, pomegranate seeds are dried, powdered and added to sodium phosphate and incubated for 10 minutes at 45oC. This is then mixed with an enzyme called protease that breaks down the outer covering of the seeds, releasing the oil. The seed-enzyme mixture is shaken continuously for 4 to 16 hours and then centrifuged for 20 minutes. After this, clear layers of pure oil, proteins and fibres are formed, which can then be extracted.
The researchers, after several trials of extraction with different concentrations of protease, found an optimum quantity to mix with the seeds, which could completely extract all the oil, proteins and fibres in 14 hours. They obtained a maximum yield of 98% for the oil and 93% for the proteins. The resulting products were of a higher quality than those obtained from other methods.
The researchers believe this study could help bring out some interesting uses and applications of pomegranate oil, including those in medical and cosmetics industry. Since the research was conducted on a small-scale, the feasibility of industrial-sized extraction units is yet to be studied. “So far, no adverse effects of the pomegranate seed oil have been reported. The oil tends to become rancid if kept for a long time. Studies on its shelf life and stability in food formulation need to be explored”, says Prof. Arora on the prospects of the research.
Researchers from ICMR-National Institute for Research in Reproductive Health, Bombay, College of Pharmacy, and Indian Institute of Technology Bombay in Mumbai used popular online algorithms and molecular dynamics, to design an effective antimicrobial peptide.
Antimicrobial peptides (AMPs) are a host of biological molecules part of the innate immune system found in almost all the classes of life. Unlike conventional antimicrobial drugs, like antibiotics, AMPs exhibit a broad spectrum of antimicrobial activity, attacking multiple cellular targets. This makes it particularly difficult for a pathogen to evolve resistance against AMPs. This has made AMPs a target of a host of studies with digital tools like machine learning algorithms employed, to classify and design more AMPs, with natural AMPs as template.
For their study, the researchers screened through a library of peptides, with DNA similarity to known AMPs—Myeloid Antimicrobial Peptide (MAP) family. MAPs exhibit a broad spectrum of antibacterial, antifungal, anticancer, and antiviral activity, and thus were chosen as the template. Next, around 1000 random peptides were designed, by making small changes to the template molecule. After screening the 1000 peptides using CD-HIT webserver, 935 of them with <85% identity of the template were selected for further studies.
The researchers then used popular online algorithms like AntiBp2, ADAM, CAMPR3, and iAMP-2L were used to predict the antimicrobial activity of the 935 peptides. “Seven of the 935 peptides had prediction scores greater than that of the known antimicrobial peptide BMAP-28(1–18)” say the authors of the study. Next, three samples out of the seven peptides were chosen at random for further studies. The three samples were tested for their antimicrobial activity against Gram-positive Staphylococcus aureus and Gram negative E-coli. Two out of the three were seen to have excellent antimicrobial activity against these pathogen.
Interestingly, the researchers noticed a switch in the activity of one of the designed AMPs, due a single residue mutation. This suggests that single residue change could have a drastic effect on the potency of AMPs. The authors suggest using molecular dynamics simulations to make such single residue changes to amplify the potency of AMPs
The study shows, although online prediction algorithms could help with designing newer AMPs, for an effective outcome, the algorithms have to be used along with molecular dynamics guided rational design for an effective outcome.
Yesterday, the Indian Meteorological Department predicted this year’s monsoon to be normal. But wait, we are still in the early summer months, right? How did they do that well ahead in time for our farmers to sow their seeds and plan their irrigation resources and for civic authorities to plan the distribution of water for domestic and industrial uses? With much of our country relying on monsoon, perfecting the art of predicting it right is necessary. Scientists have now perfected the art, thanks to a study published in Nature’s Scientific Reports, where the arrival of monsoon could be predicted as early as three months in advance!
Until now, the Indian Meteorological Department (IMD) was able to predict the arrival or onset of monsoon about fifteen days in advance. However, this is too less a time for farmers to completely plan their agricultural activities or water resources. That’s why researchers from Indian Institute of Tropical Meteorology (IITM) started thinking about the best way to crack this problem and have now devised a method to predict the arrival of monsoon a season in advance.
The arrival of monsoon is not a silent affair. Large scale changes occur in the atmosphere over the Arabian Sea, the Indian peninsula and the Indian Ocean before monsoon arrives in Kerala. Meteorologists study these changes, including rainfall, wind and radiations in the atmosphere, that occur only a few weeks earlier, to make predictions.
“Most of the present dynamical prediction system has the limitation of predicting monsoon onset date only 2-3 weeks in advance. The primary motive of our study was to show the possibility of using a global seasonal forecasting model (CFS v.2) to predict early or delayed onset from the large-scale atmosphere-ocean conditions during February itself”, said Mr. Maheswar Pradhan, a scientist at IITM and an author of the study.
The Indian monsoons depend not only on atmospheric changes, but also on global climatic phenomenon like the El Nino Southern Oscillations (ENSO), Indian Ocean Dipole (IOD), North Atlantic Oscillation (NAO) as well as Pacific Decadal Oscillations. These are patterns of climate variation which repeat after relatively long time periods. The researchers have used global circulation models (GCMs)--computer-based climate models used for weather forecasting—to capture these global weather patterns and make early predictions of monsoon.
Interestingly, when the monsoon arrives in Kerala, the temperature over the Indian peninsula becomes more than the temperature over the Indian Ocean. During other times, the temperature over Indian peninsula is lesser than the temperature over the ocean. The researchers used this phenomenon, called temperature inversion, in their models for monsoon prediction.
For this study, the researchers used data from the United State’s National Center for Atmospheric Research (NCAR) and the National Centers for Environmental Prediction (NCEP) and predicted the monsoon onset date for a period of 26 years (from 1982 to 2008). They then compared their predictions with the actual IMD data for the same period on the arrival of monsoon.
The results showed that the mean onset date predicted by the study was 30th May, whereas the mean date as per data from IMD was 2nd June. More interestingly, the new model could predict the variation in the arrival of monsoon with considerable accuracy. “It is found that the model prediction has a good has a hit rate of 60-70% for early and delayed onset. In other words, out of 10 early or delay years, 6-7 are captured correctly”, said Mr. Pradhan. They also observed that global sea surface temperatures have a considerable influence on the arrival of monsoon in India; higher sea surface temperatures over Pacific and Indian Ocean caused delays.
The researchers are now working towards improving this model by adding a few more parameters that can help in improving the accuracy of the model. “In the current setup (models), monsoon onset variability is largely controlled by EL-Nino & Southern Oscillation. We need to identify more parameters that influence monsoon and improve the simulation of these drivers in order to further improve the prediction skill”, remarks Mr. Pradhan, talking about the future plans.
Editors Note: An earlier version of the article was inadvertently published. The error is regretted.
A team of scientists from Rice University, Texas, USA, Indian Institute of Science (IISc), Bengaluru, Bruker Nano Surfaces, Minnesota, USA and Indian Institute of Technology Gandhinagar, Gujarat have developed a new way to exfoliate a 2 dimensional metal sheet, few layers o even up to a single layer of atoms thick. The novel method, the scientists claim, could be used to make metal sheets of low-melting pure metals and alloys.
2 dimensional materials, ever since the first layer of carbon atoms—called graphene, was first created in 2004, has captivated scientists. They are materials made of a single layer of atoms or molecules. From enabling faster and more efficient electronics to revealing new physics, 2 dimensional materials have been studied extensively over the last decade. Their electrical and mechanical properties have also been exploited to engineer many of the modern gadgets. While 2 D sheets of many elements and compounds have been produced over the years, pure-metallic layered 2D sheets were rare.
For their experiment, the scientists used a combination of theoretical and experimental evidence to demonstrate a new, simple, low cost and effective method to exfoliate 2D sheets of low-melting pure metal and alloy on to substrates made of semiconductors or other materials. For their demonstration, the scientists chose Gallium, an elemental metal with a very low melting point temperature of around 29 degree Celsius. 2D sheets made of a single layer or a few atoms thick layer of gallium is called gallenene.
Capitalizing on the weak interface between the solid and molten phases of the gallium metal, the scientists used solid-melt interface exfoliation method, to extract just a layer of the liquid metal. The metal is exfoliated on to a substrate made of silicon. The sheet thus formed was found to stable. Further experimentation on the gallenene sheets using phonons or sound waves showed that the atomic arrangements of the sheet and thus its stability could be controlled using bulk gallium suitable lattice parameters or crystal structure.
Interestingly, when a 2D sheet of gallenene interacts with other 2D semiconductors, it induces semiconductor to metal transition in the latter. The scientists claim this property can be utilized, “paving the way for using gallenene as promising metallic contacts in 2D devices”. According to the authors “Our findings suggest that gallenene provides excellent opportunities to explore its applications as a 2D metal in plasmonics, sensors, and electrical contacts.”
The solid-melt interface exfoliation method developed, however, could be used for more than just metal. Talking about the versatility of the new method, the authors claim “our easily scalable and simple technique allowed us to exfoliate different substrates, which can be used for a variety of applications.”
The summer is here, and the newspapers are already flashing headlines on how hot this summer could be. While we humans may turn on the air coolers, what would the thousands of animals and plants do? It turns out, some trees have unique tricks up their leaves, quite literally! A new study by researchers from the Indian Institute of Science Education and Research (IISER), Pune, and Oak Ridge National Laboratory, USA, shows how tropical trees deal with the heat and the adaptations in their leaves that help them survive in extreme heat conditions.
Increased heat intensity, reduced water availability and frequent droughts are some of the extreme events that can trigger a plant’s cellular stress—a range of molecular changes in the cells. It results in reduced photosynthesis and subsequent death. Studies in the past have shown that the thermal tolerance for leaf functions like photosynthesis varies inversely with latitude. Thus, tropical plants have a higher thermal tolerance as compared to other plants.
However, the relationship between thermal tolerance and the temperature of the plant’s habitat is not linear. For an increase of 20⁰ C habitat temperature, the thermal tolerance increases by only 8⁰ C. This weak relationship, coupled with significant thermotolerance variations (10-20 ⁰C) observed between species within a region, suggest that the besides the habitat,leaf temperature tolerance could have other factors influencing them.
One such factor could be the leaf structure and its form. To test this, the researchers looked at the role of leaf traits like the area of the leaf, the ratio of leaf dry weight to single-sided leaf area (leaf mass area) and the ratio of leaf dry weight to wet weight, in regulating leaf temperature.
The researchers studied saplings of 12 species grown in a seasonally dry tropical region in Maharashtra with a controlled environment that could manipulate light, water and temperature. A previous related study by the authors had looked at the thermotolerance in tropical tree species in an open environment. In this study, published in the journal AoB Plants, the researchers have examined the photosynthesis rates in a controlled environment.
Plants perform photosynthesis using chlorophyll pigments in their leaves. Chlorophyll fluorescence is a phenomenon that occurs when the light is re-emitted by chlorophyll pigments and is used as an indicator of the rate of photosynthesis. The variations of fluorescence with temperature indicate the photosynthetic thermotolerance and are widely used to understand plant sensitivity to extreme temperatures.
The study investigated leaf thermotolerance across the 12 species by quantifying the temperature at which there was a 50% decrease in photosynthesis. It also looked at the relationship of thermotolerance with leaf traits and photosynthetic rates. To study the relationship between thermotolerance and drought tolerance among species, the researchers subjected the saplings to drought and well-watered conditions.
The study found that thermotolerance varied widely between species from 44.5⁰C to 48.1⁰C—a significant finding because these upper limits are close to the maximum temperatures of their habitats and hence indicate a risk from further temperature increase. The researchers observed that drought increased the thermal tolerance of the leaves, which was positively related to the leaf mass area and negatively associated with photosynthetic rates. Hence, species with higher photosynthesis rates and lower leaf mass area are less thermotolerant and more vulnerable to increased temperatures. The study also found that evergreen species that have a more significant leaf mass area, thicker leaves and longer lifespans were more thermotolerant than deciduous species. This finding assumes significance as it may lead to future species composition favouring evergreen species with high leaf mass area and low photosynthesis rates.
The findings reveal how plants could respond in the wake of global warming, which may not be random but influenced by functional attributes. “Similar studies in dry sub-tropical forests elsewhere found a positive relationship between thermotolerance with leaf longevity but not with leaf mass area. This indicates that these relationships may not be universal, but dependent on environments”, say the researchers, stressing the need for more such studies from diverse environments to understand how different plants may respond to climate change.