Plant chilling injury refers to an injury that is caused by a temperature drop to below 15°C but above the freezing point. The symptoms of chilling injury are usually a rapid wilting of the leaves and the development of water soaked patches that go on to form sunken pits due to cell collapse. Warming will lead to these damaged areas becoming brown and necrotic while continued chilling will eventually lead to the death of the plant.
Plants that live in regions where chilling is common undergo a period of hardening in the autumn that prepares them for chilling. Hardened plants do not suffer chilling injury therefore analyzing the differences between hardened and non-hardened members of the same species can yield clues to the nature of the injury. Comparison of tropical plants, which generally are incapable of hardening, to those that are chill-resistant also provides information of a similar type.
Chilling temperatures effects on plants in temperate
climateslead to a reduction or complete crop failure
due to either direct damage or delayed maturation. Even
a small drop in temperature, causing no visible damage to
chilling-sensitive plants, caused to up to 50% reduction in
their productivity (Коровин, 1969). For example, chilling
damage to young cotton plants in U.S. in 1980 resulted
in the loss of 60 million dollars. In South and South-East
Asia, high-yielding varieties of rice are not grown in areas
of more than 7 million hectares, where they may be exposed
to chilling temperatures (Wilson, 1985). Obviously,
the problem of plant resistance to chilling temperatures,
which often occur in spring and autumn in many countries,
is important for practical plant breeding.
The primary cause of chilling injury in some plants has been found to be the opening (and locking) of the leaf stomata when the permeability of the roots to water is low. Thus the leaves lose water faster than it can be replaced and they become dehydrated. Cold hardening alters the behavior of the stomata so that they close under the same conditions; the root permeability is also increased. Interestingly, drought hardening conditions the stomata similarly but the root permeability is significantly decreased, yet the plant is still able to survive chilling without leaf injury.
In other plants, the stomata behave properly at chilling temperatures and the injury is thought to be metabolic. A decrease in respiration, photosynthesis and fatty acid synthesis may all contribute to the chill-starvation of some plants. Cold hardening affects the lipid content of cell membranes and has been found to lower the optimum temperature for photosynthesis and respiration.