Question

Why plants store fructose in fruits instead of glucose?

Answer 1

Simply, Fructose is also a synthesis product of photosynthesis. In the latter part of the Calvin cycle the enzymes aldolase and fructose-1,6-bisphosphatase convert a G3P and a DHAP into fructose 6-phosphate (6C).

Typically fructose and glucose will be combined to form sucrose at the site of photosynthesis, this is one of the main transport sugars in many plants. Sucrose will then be exported to other 'sink' tissues such as fruits or tubers etc... When it the sucrose at a destination tissue it will then be converted back to glucose and fructose by an enzyme such as invertase and stored (or used).

Many fruits are a good source of sucrose or fructose because as the fruits ripen they accumulate fructose and/or sucrose in order to make the fruits attractive to eat to the plant's primary seed . When the fruits ripen the plant begins to preferentially move sucrose from the sites to photosynthesis to the fruits.