HARNESSING HEAT STRESS IN VEGETABLE CROPS TOWARDS MITIGATING IMPACTS OF CLIMATE CHANGE - Climate Dynamics in Horticultural Science - page 175

them. Due to high soil temperature, germination may be hampered leading
to inadequate plant emergence and establishment, which can limit the pro-
ductivity of several warm-season vegetables such as okra, tomato, brinjal
and cucurbits. In such cases, deep placement can be done to overcome the
problem. In temperate or subtropical climatic zones having seasonal varia-
tions in temperature, sowing date can be varied so that the crop can escape
high temperature stress during the subsequent sensitive stages of crop de-
velopment. Intense direct solar radiation and high temperature can cause
damage to fruits as may be seen in tomato where sunscald is observed due
to high temperature. Shading of the fruits by foliage can be the avoidance
mechanism to this problem (Hall, 2011).
10.3.2 TOLERANCE MECHANISMS
Heat tolerance is generally defined as the ability of the plant to grow and
produce economic yield under high temperature conditions. It is a highly
specific trait and may vary significantly among closely related species,
even different organs and tissues of the same plant. Plants have evolved
various mechanisms for thriving under higher prevailing temperatures.
These include short-term avoidance/acclimation mechanism or long-term
evolutionary adaptations. Some major tolerance mechanisms are ion trans-
porters, late embryogenesis abundant (LEA) proteins, osmoprotectants,
antioxidant defense, and factors involved in signaling cascades and tran-
scriptional control and these are essentially significant to counter act the
stress effects (Rodríguez et al., 2005; Wang et al., 2004).
Leaf orientation, transpirational cooling and changes in membrane
lipid composition are more important short-term response against heat
stress (Radin et al., 1994, Rodríguez et al., 2005). Smaller yield losses due
to early maturation in summer shows possible involvement of an escape
mechanism in heat stress tolerance (Adams et al., 2001). Different tissues
in plants show variations in terms of developmental complexity, exposure
and responses towards the prevailing or applied stress types (Queitsch et
al., 2000). The stress responsive mechanism is established by an initial
stress signal that may be in the form of ionic and osmotic effector changes
in the membrane fluidity. This helps to reestablish homeostasis and to pro-
tect and repair damaged proteins and membranes (Vinocur et al., 2005).