Agriculture Reference
In-Depth Information
of the rapid metabolism dependent absorption phase were
observed at 5ºC (Sasakawa and Yamamoto 1978).
Although attention has focused largely on the consequences
of moderate and prolonged cold on plant performance, brief
unseasonal cold can also have a damaging effect on growth
and survival of the plants, may be at risk. In some regions
sudden, short cold spells may still occur during generally
warmer weather that can result in checks to growth. Rice is a
plant of tropical origin that is susceptible to damage by low
temperature below 15ºC. Cultivars of rice vary in their cold
susceptibility with japonica more cold tolerant than indica
cultivars. In seedling stage, the synthesis of several new
proteins, alternations to lipid saturation and chlorosis, where
the newly emerging leaves lack chlorophyll (Kazemitabar et
al. 2003). In many plants, chlorophyll biosynthesis in chill
(7ºC) is affected by a sharp reduction. Inhibition of chlorophyll
biosynthesis was partly due to impairment of 5-aminolevulinic
acid biosynthesis. Protochlorophyllide synthesis in chill was
inhibited because of defects in protoporphyrin IX synthesis,
Mg-chelatase and Mg-protoporphyrin IX, monoesterase cyclase
(Tewari and Tripathy 1998).
Plant mitchondria have two oxidizing pathways, the
cytochrome pathway (CP) and the alternative pathway. The latter
consists of one enzyme, the alternative oxidase (AOX). AOX is
not coupled to H
+
translocation, and therefore ATP production,
and has the potential to catalyze wasteful respiration in higher
plant mitochondria. AOX is thought to prevent production of
reactive oxygen species (ROS) in the respiratory chain, especially
under stress conditions, by helping to prevent over-reduction
of ubiquinone pool. Many abiotic stresses, including sudden
exposure to low temperature induce synthesis of AOX. The
increase in AOX capacity at low temperature is often associated
with
de novo
synthesis of AOX protein.
