Agriculture Reference
In-Depth Information
Cytokinins occur naturally and are manufactured. Most of the cytokinins are
derivatives of adenine.
Cytokinins also delay senescence and hence can be used to prolong the
shelf life of fresh vegetable and cut flowers and to promote seed germination.
Cytokinins appear to be involved with transfer RNA (t-RNA) and, therefore,
they possibly play a role in regulating the incorporation of specific amino
acids into proteins.
Toxicity
Some formulations may cause severe reversible eye irritation and have a
signal word, “Warning,” on the label (ProShear). See
Table 5.28
for a listing
of commercial products.
4.
Ethylene and Ethylene Generators
In contrast to complex auxins, gibberellins, and cytokinins, ethylene is a
simple gaseous compound. In 1932, it was discovered that ethylene would
promote flowering in pineapples. The subsequent discovery of the role of
ethylene in fruit ripening has been of considerable commercial importance in
the banana and citrus industries.
Mode of Action
Ethylene appears to influence the enzymes of the physiological state of
the absorbing tissue. Ethylene may serve as a trigger, or be induced by aux-
ins, or act as a synergist resulting in a chain of biochemical and/or physio-
logical events such as the ripening of bananas or the prevention of the open-
ing of flower buds of carnations and fruit trees.
Ethephon, introduced in 1967, is an ethylene generator. It generates eth-
ylene when added to solutions with a pH >4, which are then sprayed onto fruit
trees to promote ripening. Another active ingredient, 2-chloroethylmethyl-
bis(benzoxy) silane, was introduced by Ciba-Geigy in 1972. Like ethepon,
this silane decomposes in the presence of water to release ethylene. This
compound is used as a chemical abscission or as a thinning agent in apples,
peaches, oranges, and other fruits.
The exact mode of action of ethylene is unclear but probably involves the
binding of the molecule to a specific receptor.
Toxicity
The products Cerone and Prep are classified in the Toxic Category I be-
cause of the potential of severe irreversible eye damage. They are labeled with
the signal word “Danger.” The product Ethrel is labeled with the signal word
“Warning” because it can cause severe reversible eye irritation, whereas, the
product Florel has a formulation which is labeled with the word “Caution.”
See
Table 5.28
for listing commercial products.
