Author: Meera Maniar
Artist: Meera Maniar
Editor: Altay Shaw
As mankind continues to strive towards the stars, there will come a point where we will be considering the colonisation of interstellar planets and systems. This involves the creation of an entirely novel environment around us to shield us from the unforgiving nature of space. We are fragile beings; without air, we suffocate. Without water, we die of thirst. And without food, we will starve. Packaging is completely unsustainable. Packaging mountains of food to send with the astronauts on every mission is completely unsustainable. It is costly economically and in terms of the extra weight it places on the spacecraft and is only designed as a short-term plan.
As a result, plants are beginning to garner attention as crucial components to deep space travel. They are considered key organisms in Bioregenerative Life Support Systems – with the aim of supporting astronaut life in long-term missions. Aside from sustaining humans, farming in space can also carry mental benefits through crew cooperation.
That being said, space is a hostile environment – ionising gamma radiation can penetrate through the thickest of materials, scorching coronal mass ejections will incinerate anything in their path, and zero gravity is known to cause drastic physiological changes. The two main constraints plants will have to deal with are microgravity and gamma radiation, due to their ability to alter gene expression, signalling, and cell differentiation. Despite this, plants have successfully completed their entire life cycle in space conditions.
There is a subtle difference between zero gravity and microgravity – microgravity is the condition of very low gravity in an environment yet a gravity that still exists. It has been found that while microgravity has no effect on cell proliferation in plants grown in space, it does significantly influence their physiology (De Micco et al.) . When growing the model organism Arabidopsis thaliana, the cell cycle was being sped up due to the downregulation of genes that facilitate the transition from the G1 (growth phase) to the S phase (stage of DNA replication). Furthermore, researchers noted a considerable downregulation in genes controlling the creation of ribosomes and an increase in chromatin condensation. Ultimately, microgravity allows for the completion of the entire plant life cycle, albeit with diminished embryo quality and delayed development.
Gamma radiation brings about much more varied and intriguing effects in plants. Plant breeders commonly use this technique to modify gene expression and physical characteristics in plants, thereby increasing their productivity. Gamma radiation has what is called a hormetic effect – changes only until a certain threshold will benefit the organism. If the dose of radiation increases beyond that point, it will begin harming the plant. Increasing the dosage to over 300 Gy began to block mitosis. Positive correlations have been found between gamma radiation doses and germination levels, root-shoot length, and the number of seeds per plant. An increase of 18-32% of root length was reported in Triticum aestivum when treated with 20 Gy gamma radiations (Katiyar et al.).. Another extraordinary property of gamma rays is their ability to confer stressor resistance to plants. Plants were made more tolerant to heavy metals by gamma radiation through increased chloroplast size and a rise in chlorophyll content. Furthermore, gamma ray induced elevation in the levels of metal ion transporters AtPDR12 and 8 was observed, conferring some metal resistance.
Similar effects were seen in salinity, drought resistance, and heat. Due to their high energy, gamma rays cause point mutations (single base changes) in an estimated 1 in around 6 million bases. In the case of salinity, gamma ray irradiation can improve plant defence systems by increasing transcription levels of the salt overly sensitive (SOS) genes – a set of genes that detect and mediate the levels of sodium ions that can pass in and out of vascular plant tissue. Increases in the activities of antioxidant enzymes and molecules both battle droughts and extreme heat by decreasing the amount of ROS (reactive oxygen species) in the tissue, which prevents the breakdown of crucial macromolecules such as DNA and membrane phospholipids.
It will be generations until we can colonise space en masse. Before we can begin looking towards the stars, we need to take care of the Earth. Higher temperatures, altered currents and increased salinity are all outcomes of climate change, cumulatively responsible for 70% of losses in major grains such as rice and wheat. Not only do they stress the plants, they also bring about health conditions in those who consume them. Gamma radiation exposure is essential for crop productivity enhancement, especially in response to a changing planet. These explorations are not only relevant to our distant future, but they may just be the very breakthroughs that change our fate.
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