Super veg
Find out more about the food you eat.
To help plant breeders improve the potatoes and tomatoes we eat we need to understand the background to the qualities (e.g. flavour) we are interested in. Below are some of the qualities investigated by EU-SOL and how genes can affect them.
Processes and taste
The amount and type of sugar and acid in a tomato and hence its overall taste is dependant on a number of processes that occur during the growth and ripening of a tomato. Here we will look at how these processes affect the sugar content of the tomato.
Tomato growth
During the second stage of development a tomato is flooded with acids and sugars, expanding to up to 10 times its original size. This is the stuff that makes it attractive for animals to eat.
Most of sugar in a tomato has come from the leaves where it is made in a process called photosynthesis. In this process sugar is made from water and carbon dioxide by using energy from the sun. Oxygen is released as a by product. Sugar is a source of energy, used in both plants and animals; the presence of sugar in a tomato makes it attractive for animals to eat.
The transport of sugar from the leaves to a tomato occurs along the phloem – a tube that runs along the stem and branches of a plant. Enzymes in the tomato convert the glucose coming out of the phloem into other compounds and so maintain a glucose gradient into the tomato fruit. This gradient makes means that glucose will keep flowing from the leaves along the phloem to the fruit.
Tomato ripening
Not only the amount but also the type of sugar in the tomato will affect its taste. In a green tomato the ratio of sucrose to fructose is 3:1 but as the tomato ripens some of that sucrose is converted into fructose until the amount of each is roughly equal. As fructose is sweeter than sucrose this corresponds with an increase in the tomato’s overall sweetness. This conversion of glucose to fructose is controlled by a specific enzyme called Invertase.
