& opinion


Sussex biologists are growing tequila plants in their laboratory greenhouses. Have scientists at the University of Sussex become fed up with paying taxes on their favourite tipple and resorted to making their own? Sally Ainsworth went in search of the truth.

A little crop of Mexican agave is flourishing thousands of miles from home in the dismal Sussex winter. The fermented sugars of Agave tequilana form the basis of such favourites as the Margarita, Tequila Sunrise and ‘old faithful’ Tequila Slammer, underpinning some of our most memorable (or least memorable) nights on the town!

Green-fingered DPhil student Ivan Saldana Oyarzabal has imported eighteen tequila plants from his native Mexico for two main reasons (sadly, neither have anything to do with tequila!) Here comes the science bit:

First, the way that agaves photosynthesise (using the sun’s energy to make carbohydrate from carbon dioxide and water) is different to that of the majority of plants. Interestingly, agaves have evolved an adaptation to this process in that they open their stomata at night to gather CO2 and, instead of using it right away, store it overnight until the sun comes up and the stomata close. During the day, agaves effectively ‘hold their breath’ while they use sunlight energy to turn the stored carbon into carbohydrate.

The name given to this method of photosynthesis is CAM (Crassulacean Acid Metabolism), and it is frequently associated with plants in hot, arid regions where water conservation is of utmost importance (cacti also photosynthesise in this way).

The second reason that Ivan is researching tequila plants is that they use interesting carbohydrates to store their energy reserves. The usual products of photosynthesis in plants are starch and sucrose, but in agaves the carbohydrates are made up of chains of fructose, called fructans. Apart from being the sugar that (when fermented) makes tequila, fructans are fascinating in their own right. The human metabolism is unable to digest fructans, and thus they are safe sweeteners for diabetics and are used widely in the food industry as low-calorie replacements for fat and sugar. In addition, they are heralded as ‘prebiotic’, as they act to promote the growth of healthy bacteria in the gut. A downside of this is flatulence, Jerusalem artichokes are particularly high in fructans, and if you’ve ever sampled a Jerusalem one, you’ll know what I’m saying!

The agave is the only plant to combine both CAM photosynthesis and fructan storage, and Ivan’s research here at Sussex University is the first to explore how the two are connected.

So, it seems that the BIOLS won’t be your first port of call when shopping for your next houseparty. Instead, Ivan Saldana Oyarzabal is investigating the link between a photosynthetic adaptation in plants and the exciting carbohydrate that they make. At least, that’s his story.