Atomic Gardening: A Deadly Technology Repurposed

 by Will Hartridge

Modern genetic engineering methods such as CRISPR-Cas9: a process often compared to using molecular scissors, have featured in the press frequently over the past few years and rightly so. The significance of this technique has just been demonstrated by the awarding of this year's Nobel Prize for Chemistry to Emmanuelle Charpentier and Jennifer Doudna, two key contributors to its early stages of development. However, as this topic is discussed so often in popular science media, I thought it would be interesting to shed some light onto a lesser known and older method of altering the genome of an organism to generate beneficial results: atomic gardening.

It is often overlooked that humans have been modifying nature for their own benefit for a long time. For thousands of years, farmers have created superior plants by iterating the process of choosing plants with the best characteristics and breeding them, over and over again. Selective breeding is the oldest method of altering genomes and has been considerably useful for the human race.

Although it does not technically class as genetic modification because the genes of plants are not being directly manipulated, its significance cannot be overlooked. An example of how beneficial selective breeding can be is the wild mustard plant (classification brassica oleracea), a plant which was selectively bred over centuries to produce 6 different plants, many of which are commonplace foods in our modern diets. Brussel sprouts, broccoli, cabbage, cauliflower, kale and kohlrabi (also known as German turnip) are all descendants of this exact same species.

However one of the many caveats to selective breeding is that it is a slow process because mutations are fairly rare and it has to take place over many generations. This is where atomic gardening comes in. 

In the postwar era of World War 2, atomic warfare had a bad reputation, the sheer power and devastating effects of this newfound technology had been demonstrated by the bombs dropped on Hiroshima and there was a growing public fear of imminent nuclear war during the persistent escalating of the US-Soviet arms race. On December 8th 1953, US president Eisenhower delivered a speech, where he announced a new program named “Atoms for Peace”, to the United Nations General Assembly in which he suggested that “the miraculous inventiveness of man” should be focused on finding novel and beneficial uses for the atom. One peaceful area of atomic experimentation that developed from this speech was atomic gardening: in which a radioactive isotope is allowed to irradiate a selection of crops, resulting in mutations. Most are unavailing and make the crop worse, but a select few would show favourable mutations in their phenotype (displayed characteristics). These can then be picked and selectively bred until the desired outcome is reached. This process greatly accelerates the first stage of selective breeding (waiting for mutations to change the properties of the plants). Although it was not a precise process, demonstrated by this quote from nanotechnologist Paige Johnson: "If you think of genetic modification today as slicing the genome with a scalpel, [atomic gardening was the equivalent of] hitting it with a hammer", it was still a useful technology and led to the development of many interesting plants, some of which are commercially grown and consumed to this day. See examples below.

But how does this ionising radiation emitted from radioactive sources actually change the features of plants? Firstly, certain types of radiation are called ionising because they remove electrons from atoms, resulting in free electrons and positive ions. The disruption of DNA structure caused by radiation is all because of its ionising nature and can be caused by one of two possible actions: either direct action or indirect action. In direct action, the less probable of the two, an atom that is part of the DNA structure is ionised by radiation and therefore releases a valence (outer shell) electron, and the atom becomes a free radical (an atom with an unpaired valence electron) which is highly reactive and can damage the structure of a nucleotide. In indirect action, radiation ionises water and other molecules that are present near the DNA, creating free radicals- for example the hydroxyl free radical (a hydroxide ion with one lost electron, so has a neutral charge) that again are highly reactive and cause damage to nucleotides. If even one nucleotide in the DNA sequence is damaged, it can have significant effects: due to the way DNA codes for proteins using a triplet of nucleotides to code for one amino acid, when one nucleotide is changed the whole sequence can shift (called frameshift mutation) and completely change the corresponding protein that is produced, which can result in change in a multitude of physical effects like taste, colour, structure, resistance to disease, size and much more.

This diagram demonstrates frameshift mutation

Atomic gardening existed in a few forms. So called “Gamma Gardens” were a place where atomic gardening could be put into practice on a large scale. Usually run by government laboratories, they consisted of a radiation source (usually Cobalt-60 or Caesium-137) surrounded by concentric circles of crops. After a period of irradiation, the radiation source could be lowered into a protective bunker and workers could enter and inspect and pick the plants displaying useful mutations. The plants close to the source would die immediately, and further out they would develop tumours and abnormalities. However, there is a certain distance when the radiation intensity is just right and random mutations will result in beneficial characteristics.

Images of a gamma garden

There was also a form of crowd-sourced atomic gardening that became popular and materialised in groups of enthusiasts like the UK Atomic Gardening Society which distributed irradiated seeds to its members to try and grow successful plants.

Some interesting varieties of plants produced using the larger scale methods of atomic gardening include:

• The Rio Star grapefruit featuring a dark red colour due to an increase in the plant nutrient lycopene and a high level of sweetness, which makes up around 75% of the grapefruits grown in Texas. The image on the left shows the colour of the Rio Star grapefruit compared to other varieties.

• The Todd’s Mitcham peppermint variety, a type of peppermint that is resistant to the Verticillium Wilt disease and is still used for a large fraction of the world’s mint oil and menthol production.

• The Golden Promise variety of barley that gave a very high yield per acre and made up 10% of total barley seed sales in Scotland from 1973-1984. Pictured is a Scotch whisky made using this variety of barley.

  
  
  

To conclude, although this technology is now outdated and the modern genetic engineering methods are far more accurate and advanced, it still provides an interesting insight into how an area of science that was so deadly could be repurposed in a positive way.