Agriculture Reference
In-Depth Information
necessary to adjust the water application rate based on crop ET. Stomata
regulated reduction in transpiration is a common response of plants to
drought stress which also provides an opportunity to increase plant water-
use efficiency. Bahadur et al. (2010) reported that mild or severe water
stress in tomato significantly reduces the transpiration rate and increase
the leaf temperature.
9.3.6 CELL MEMBRANE STABILITY (CMS)
A major impact of plant environmental stress is cellular membrane modi-
fication, which results in its perturbed function or total dysfunction. The
cellular membrane dysfunction due to stress is well expressed in increased
permeability and leakage of ions, which can be readily measured by the ef-
flux of electrolytes, andmay be used as a tolerance index for drought stress
(Sayar et al., 2008; Yang et al., 2008). The degree of cell membrane injury
caused by stress can be assessed using this technique. Electric conductivi-
ty of solution containing the electrolytes leaking from leaf segment is used
to assess the degree of drought tolerance. The tolerant genotypes show
less electrolyte leakage due to maintenance of integrity of cell membrane.
9.3.7 RELATIVE WATER CONTENT (RWC)
The relative water content (RWC) of a tissue is the fraction of turgid
weight that is remaining in the tissue. Tissue watercontent can vary greatly
among organs, developmental stages, seasons, habitats, and species. How-
ever, a relative degree of tissue hydration can be calculated by comparing
the current hydration of a tissue to its maximum potential hydration. RWC
represents a useful indicator of the state of water balance of a plant, essen-
tially because it expresses the absolute amount of water, which the plant
requires to reach artificial full saturation. This method has gained favor
over LWP as a very relevant physiological measure of plant water deficit.
Its advantage is that it accounts for the effect of OA in affecting plant
water status. Two plants with the same LWP can have different RWC if
they differ for OA. Drought stress results in decreased RWC (e.g., Fu and
Huang, 2001; Shaw et al., 2002). Bahadur et al. (2009 and 2010) noticed
significant reduction in leaf RWC in okra and tomato, respectively with
