Agriculture Reference
In-Depth Information
Drought
Early
Perception and signalling
Increase ABA
Decreased water content
Decreased transpiration
Hormones and secondary
messenger systems
Kinases and
other enzymes
Intermediate
Cell wall adjustment
No osmotic adjustment
Responses
Late
Establishment of homeostasis
Reduced growth
Energy saving
Acclimation
Figure 12.2 Physiological and biochemical responses to moderate drought.
mechanism. In order to escape from the physical stress,
legumes tend to bring about changes that ensure the
completion of their life cycle before extreme drought
conditions set in. In contrast, drought avoidance
involves the retention of water within the plant body to
ensure that the plant is not dehydrated. Selection of the
appropriate mechanism depends on the speed at which
morphological and physiological changes occur.
Increased water retention is carried out by changes in
root morphology to help absorb more water from the
soil, by decreasing the stomatal and cuticular conduc-
tance, and by decreasing transpiration. Moreover, the
expansin genes are upregulated to help in expansion of
cells (Hayashi et al., 2012). This improves the capacity of
the plant cell to retain water. Other changes include
alterations in leaf water potential, and changes in chlo-
rophyll content and the root-to-shoot ratio, all of which
synergistically contribute to increasing the water reten-
tion in legumes.
The genetic elements upregulated in response to
drought influence a number of biochemical processes to
Table 12.2 Signalling cascade and effector elements activated
in response to environmental stress factors.
Salt stress
Drought stress
Cold stress
Presentation
Osmotic stress/
sodium toxicity
Osmotic stress
Decreased
functionality
Secondary
messenger
system
Phosphatidic acid,
abscisic acid,
calcium, hydrogen
peroxide
Phosphatidic
acid, abscisic
acid, calcium,
hydrogen
peroxide
Calcium,
hydrogen
peroxide
Kinases
AtSK, SnRK, CBL,
CDPK, MAPK, SOS
SnRK
CBL, CDPK,
MAPK, SnRK
Response
Stress responsive
gene expression,
antiporter
activation
Decreased
transpiration
Membrane
stabilization
Abbreviations: AtSK, Arabidopsis Shaggy/GSK3-like kinases; CBL,
calcineurin B-like; CDPK, calcium-dependent protein kinases; MAPK,
mitogen-activated protein kinases; SnRK, sucrose non-fermenting-
1-related kinases; SOS, salt overly sensitive.
 
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