Geoscience Reference
In-Depth Information
Expression
of stress
protein
Antioxidant
defence
Signalling
cascade and
transcriptional
control
Osmo-
protectant
Changing
leaf
orientation
Adaptation to high
temperature stress
Alternation
of membrane
lipid
compostions
Tran
spirational
cooling
Early
maturation
Leaf
rolling
FIGURe 14.6
Different adaptation mechanisms of plants to high temperature.
limit transpiration. In well-hydrated plants, intensive transpira-
tion prevents leaves from heat stress, and leaf temperature may
be 6°C or even 10-15°C lower than ambient temperature. Many
species have evolved life histories which permit them to avoid
the hottest period of the year. This can be achieved by leaf
abscission, leaving heat-resistant buds, or in desert annuals,
by completing the entire reproductive cycle during the cooler
months (Fitter and Hay 2002). Such morphological and pheno-
logical adaptations are commonly associated with biochemical
adaptations favouring net photosynthesis at HT (in particular
C4 and CAM photosynthetic pathways), although C3 plants are
also common in desert floras (Fitter and Hay 2002).
Tolerance mechanisms
Heat tolerance is generally defined
as the ability of the plant to grow and produce economic yield
under high temperature. This is a highly specific trait, and
closely related species, even different organs and tissues of the
same plant, may vary significantly in this respect. Plants have
evolved various mechanisms for thriving under higher prevailing
