Acclimation and adaptation of plants to different environmental abiotic stresses - Climate Change Effect on Crop Productivity - page 332

14.2 types of plant stress
Agriculture and climate changes are interrelated processes.
One may result in the other. Climate change induces many bio-
chemical, molecular and physiological changes and responses
that influence various cellular and whole-plant processes that
affect crop yield and quality. Abiotic stresses, such as drought,
salinity, extreme temperatures, chemical toxicity and oxidative
stress, are serious threats to agriculture and the natural status of
the environment. Abiotic stress is the primary cause of crop loss
worldwide, reducing average yields for most major crop plants
by more than 50% (Bray et al. 2000). Drought, salinity, extreme
temperatures and oxidative stress are often interconnected, and
may induce similar cellular damage. For example, drought and/
or salinisation are manifested primarily as osmotic stress, result-
ing in the disruption of homeostasis and ion distribution in the
cell (Zhu 2001). Oxidative stress, which frequently accompanies
high temperature, salinity or drought stress, may cause denatur-
ation of functional and structural proteins (Smirnoff 1998).
The complex plant response to abiotic stress, which involves
many genes and biochemical-molecular mechanisms, is sche-
matically represented in Figure 14.2. The ongoing elucidation
of the molecular control mechanisms of abiotic stress tolerance,
which may result in the use of molecular tools for engineer-
ing more tolerant plants, is based on the expression of specific
stress-related genes. These can be divided into three sets of cat-
egories as follows:
First categories : These categories are involved in signalling
cascades and in transcriptional control, such as MyC, MAP
kinase and SOS kinase (Zhu 2001), phospholipases (Frank
et al. 2000) and transcriptional factors such as HSF, and the
CBF/DREB and ABF/ABAE families (Choi et al. 2000).
Secondary categories : These categories are directly involved
in the protection of membranes and proteins, such as
heat-shock proteins (HSPs) and chaperones, and late
embryogenesis abundant (LEA) proteins (Thomashow
1999; Bray et al. 2000).
Third categories : These categories are involved in water
and ion uptake and transport such as aquaporins and ion
transporters (Blumwald 2000).
To maintain growth and productivity, plants must adapt to
stress conditions and exercise-specific tolerance mechanisms.
Plant modification for enhanced tolerance is mostly based on