Agriculture Reference
In-Depth Information
fected, often lethally, by high temperature stress (Lobel and Asner, 2003;
Lobel and Fiend, 2007).
Heat stress is often defined as the rise in temperature beyond a thresh-
old level for a period of time sufficient to cause irreversible damage to
plant growth and development (Wahid et al., 2007). Generally heat shock
or heat stress is considered as a transient elevation in temperature, usually
10-15 °Cabove the ambient. Heat stress involves intensity (temperature in
degrees), duration, and rate of increase in temperature and the probability
and period of high temperatures occurring during the day and/or the night
determines its extent. Heat stress due to high ambient temperatures is a
serious threat to crop production worldwide (Hall, 2001).The effects of
heat stress on plant may be expressed as alterations in plant growth, devel-
opment, physiological processes, and yield (Hasanuzzaman et al., 2012a,
2013a). The tolerance mechanism of plants against this stress is by physi-
cal as well as physiological changes as well as change in their metabolism.
Plants alter their metabolism in various ways in response to heat stress,
especially by producing compatible solutes that are able to organize pro-
teins and cellular structures, maintain cell turgor by osmotic adjustment,
and modify the antioxidant system to reestablish the cellular redox balance
and homeostasis (Janska et al., 2010; Munns et al., 2008; Valliyodan et al.,
2006). At the molecular level, heat stress causes alterations in expression
of genes that are directly involved in protection from heat stress (Chin-
nusamy et al., 2007; Shinozaki et al., 2007). Genes responsible for the ex-
pression of osmoprotectants, detoxifying enzymes, transporters, and regu-
latory proteins are some worthy of mention in this context (Krasensky et
al., 2012; Semenov et al., 2009).These modification of physiological and
biochemical processes by gene expression changes gradually leads to the
development of heat tolerance in the form of acclimation, and further leads
to adaptation (Hasanuzzaman et al., 2010a; Moreno and Orellana, 2011).
Vegetables play a vital role in ensuring food and nutritional security.
However, these are highly perishable crops and their prices rise fast under
adverse climatic conditions reducing their availability, thus putting them
out of reach of the poor. The small and marginal farmers are the more
affected ones by the vagaries of climate (FAO, 2009). Most vegetables
prefer mild temperatures and are generally sensitive to environmental ex-
tremes. Hence, high temperatures and limited soil moisture are the major
causes of low yields in the tropics. Significant influence on different de-
velopment phases like vegetative growth, flowering and fruiting has been
