Laboratory Four
An investigation of biochemical changes to tomato
fruit when it ripens
Introduction
According to an old country song by John Denver, the only two things money
can't buy are true love and homegrown tomatoes (I am being honest here, feel free
to check out the following link on “youtube” if you don’t believe me:
). Oh, and
PLEASE, do NOT come
to me and ask who John Denver is!!!!! Shame on YOU if you don’t know!!!!!!!!
Anyway
, the tomato has become a model system for the study of fruit
ripening and, more particularly, the changes that bring about fruit softening. In
this fruit, despite some results implicating the hemicellulosic and cellulosic cell wall
fractions in fruit softening, the most recent work in the area has focused on the
pectic fractions. In particular, there has been much interest in the polyuronide-
solubilizing enzyme, polygalacturonase. Its activity rises dramatically during
ripening, and a close correlation between polygalacturonase and pericarp softening
has been demonstrated in a range of tomato cultivars.
Naturally, tomatoes unevenly ripen, showing darker green patches when
unripe and variable redness when ripe -- traits that still show up in garden-variety
and heirloom breeds. However, in the late 1920s, commercial breeders stumbled
across a natural mutation that caused tomatoes to ripen uniformly -- from an even
shade of light green to an even shade of red. This "uniform ripening" mutation has
become indispensable to the $2 billion a year U.S. commercial tomato market,
showing up in almost all tomatoes produced for grocery stores. The uniform redness
makes it ideal for groceries, where customers expect evenly colored, red fruit.
An important fact to remember:
Whilst leaves are the primary
photosynthesis factories in a plant, developing tomato fruit can contribute up
to 20 percent of their own photosynthesis, yielding high sugar and nutrient
levels in fully ripe
fruit.
The uniform ripening mutation, which commercial
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