Physiology and Molecular Biology of Stress ... - KHAM PHA MOI

Water Stress
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2.3. The First Sacrifice in Drought
Plants experience a huge difference in light intensity, from that of full sunlight in the
daytime to dark at night. Light of high intensity is very damaging to plants under
drought conditions, even in the presence of drought tolerance systems. To determine
the first drought-induced injury that occurs in plants before complete collapse, Flexas
and Medrano (2002) reviewed the literature in an attempt to correlate the biochemical
events during drought stress with the physiological parameters (Figure 1). They noticed
that the decreases in some biochemical activities corresponded fairly well to
decreases in stromatal conductance, but not to decreases in relative water content or
mesophyll water potential, during progressing drought. The first biochemical step
impaired during drought is ATP synthesis. RuBP regeneration, which is related to this,
is also susceptible to mild drought stress. Down-regulation of electron transport occurs
under more severe drought conditions, before irreversible PSII damage.
Figure 1. Susceptibilities of physiological and metabolic events to drought stress.
This figure was adapted from Flexas and Medrano (2002). It shows the degree
of stomatal conductance that occurs with each event shown under various drought
levels and percentage of the study in which the decrease of the event in question
occurred. ATP synthesis was the most susceptible to drought stress
3. COMPATIBLE SOLUTES AND DROUGHT STRESS
A wide variety of organisms synthesize and accumulate small molecule compounds
known as compatible solutes (osmolytes or osmoprotectants) in their cells as a way of