Agriculture Reference
In-Depth Information
et al., 1997; Young et al., 2004). Impairment of pollen and anther develop-
ment by elevated temperatures is another important factor contributing to
decreased fruit set in many crops at moderate to- high temperatures (Peet
et al., 1998; Sato et al., 2006). The stage of pod filling in case of legumes
is also very critical. High temperature during this period hampers yield
and quality of the crop.
Thus, for vegetable production under high temperatures, it is important
to know the developmental stages and plant processes that are most sensi-
tive to heat stress, as well as whether high day or high night temperatures
are more injurious. Such insights are important in determining heat-toler-
ance potential of crop plants.
10.4.4 PHYSIOLOGICAL REACTIONS
10.4.4.1
WATERS RELATIONS
Plant water status is the most important variable under changing ambient
temperatures (Mazorra et al., 2002). Generally, plants tend to maintain
stable tissue water status irrespective of temperature when adequate mois-
ture is present. High temperatures, however, severely impair this tendency
when water is limiting (Machado and Paulsen, 2001). Under field condi-
tions, frequent association of high temperature stress with reduced water
availability has been observed (Simoes-Araujo et al., 2003). In tomato
heat stress disturbs the leaf water relations and root hydraulic conductiv-
ity (Morales et al., 2003). During daytime enhanced transpiration induces
water deficiency in plants, leading to a decrease in water potential and
hence altering many physiological processes (Tsukaguchi et al., 2003).
High temperatures seem to cause water loss in plants more during daytime
than nighttime.
10.4.4.2
COMPATIBLE OSMOLYTES ACCUMULATION
Accumulation of certain organic compounds of low molecular mass,
known as compatible osmolytesis one of the key adaptive mechanisms in
many plants grown under abiotic stresses, including salinity, water defi-
cit and extreme temperatures (Hare et al., 1998; Sakamoto and Murata,
2002). Under stress conditions, different plant species may accumulate a
