Once scientists understood the various roles of plant growth regulators, they began
finding ways to manipulate them to alter plant growth. We also do this in our gardens. For
example, every time we prune our mum seedlings or rotate our windowsill plants, we are
manipulating auxin levels. And of course we do this directly when we use a rooting powder.
Gibberellins are used by commercial growers to
increase the size of seedless grapes, make celery stalks larger and crisper, and induce
germination in dormant seeds. Gibberellins are even used in the brewing industry, to
promote uniform seed germination during the malting process.
Ethylene gas is widely used to influence the ripening of
many commercial fruits such as apples, tomatoes, and grapes. It is also used to facilitate
harvesting in a number of commercial crops, because it promotes abscission of the fruits.
And it is used in modern food storage facilities and during transportation to allow for
worldwide distribution of perishable crops.
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Apples in February?
How is it that the apples I store in my basement, or even my refrigerator,
become over-ripe and mushy after several weeks (or at most a few months), but I can
purchase crisp, locally-grown apples almost year round? How do they store
them from September to June?
Apples slated for long-term storage are loaded into special "controlled
atmosphere," or CA, storage rooms. These are large, airtight rooms in which
relative levels of oxygen, carbon dioxide and other gases can be regulated. Apples are
usually stored at about 3% oxygen, and up to 5% carbon dioxide. For comparison, ordinary
air contains about 21% oxygen and .03% carbon dioxide.
The lower level of oxygen and higher level of carbon dioxide slow respiration in
the stored apples, in turn slowing down the ripening process. (Apples continue to respire
even after they're picked.) Also, the high levels of carbon dioxide inhibit the action of
ethylene, slowing ripening. |
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