the nitrate reductase activity. In another study, Renu and Goswami [7] found that NaCl decreased the to-
tal chlorophyll and carotenoid content in cotyledonary leaves of cotton. However, the carotenoid content
decreased more slowly than the chlorophyll.
Lin et al. [8] observed that with increasing NaCl concentration, the protein content in cotton
seedlings decreased while the enzyme activity and the soluble sugar content increased. These findings [8]
indicated that changes in metabolism led to synthesis of large amounts of proline and soluble sugars to
maintain the osmotic pressure. Examining a wide range of species of various genera in the family Mal-
vaceae, Gorham [10] detected the zwitterionic quaternary ammonium compound glycine betaine in all but
3 of over 100 species. In a more limited range of the species, particularly of Gossypium, glycine betaine
accumulated to concentrations sometimes in excess of 100 mM in response to water deficit or salinity
stress. In Gorham’s [10] study, glycine betaine concentrations were highest in young tissues and accu-
mulated to about 10% of the total nitrogen.
To improve salt tolerance in cotton, Shen et al. [11] grew this plant after the seeds were soaked in pa-
clobutrazol solution. They found that under salt stress the growth rate and chlorophyll, soluble sugar, and
proline contents of cotton seedlings grown from seed soaked in paclobutrazol solution were higher than
those of the controls. The results of these investigators [11] also showed a significant improvement in the
water relations of these plants. From this study [11], it was concluded that seed treatment with paclobu-
trazol can mitigate the effects of salt stress and promote salt tolerance in cotton.
According to Qadir and Shams [12], in a pot culture study, imposed salinity stress had a deleterious
effect on germination and vegetative growth with significant differences among the cotton genotypes.
Leaf area, stem thickness, and shoot and root weights decreased with increasing substrate salinity level.
Leidi and Saiz [14] studied physiological responses of two cotton cultivars previously selected on the ba-
sis of growth under salinity. They postulated that the higher tolerance was the result of several traits such
as higher Nauptake and water content. These investigators [14] also suggested that adaptation through
adequate but tightly controlled ion uptake, typical of some halophytes, along with efficient ion compart-
mentation and redistribution would result in an improved water uptake capacity under salt stress condi-
tions and lead to maintenance of higher growth rates.
Zhu and Zhang [15] studied antitranspiration and antigrowth activities of xylem sap of several plants
including maize, sunflower, cotton, and castor bean subjected to various stress treatments, such as soil
drying, flooding, and salinity. All xylem sap samples showed an increased concentration of proteins when
plants were either soil dried, salt treated, or flooded. As a result, the protein transportation flux in xylem
sap was also increased. In an experiment conducted on a salt-sensitive cultivar of cotton, Lin et al. [16]
found greater relative reductions in root length and root fresh weight than in hypocotyl length of seedlings
grown in 75 mM NaCl. This indicates that the root was more severely affected than the hypocotyl by the
salt stress.
Banks et al. [17] studied the antioxidant response of several salt-sensitive and salt-tolerant cotton cul-
tivars to salt stress during fiber development. The results of their study [17] indicated that salt treatment
reduced fiber growth in all the cultivars, except the most salt-tolerant one. Glutathione-S-transferase ac-
tivity significantly increased in all the cultivars when treated with NaCl. Regarding effects of salt stress
on enzymes in cotton plant, experiments of Fowler et al. [18] revealed increased levels of the antioxidants
peroxidase, catalase, ascorbate peroxidase, superoxide dismutase, glutathione reductase, and glutathione-
S-transferase in NaCl-stressed cotton callus and plants.
In a greenhouse experiment, Oliveira et al. [19] studied the effects of different salinity levels of irri-
gation water (0, 2000, 4000, 6000, and 8000 mg/L 70% NaCl and 30% CaCl 2 solution) on germination
and growth periods of different cotton cultivars. These investigators [19] found that salt concentrations
above 2000 mg/L decreased germination, vigor, plant height, and salt concentrations above 4000 mg/L
decreased cotton yield and dry weight. According to Kasumov et al. [21], salt stress stimulated root res-
piration by separating oxidation and phosphorylation. The antioxidant activity of roots decreased
abruptly, resulting in uncontrolled acceleration of free radical processes.
Vulkan-Levy et al. [24] carried out an experiment on the effect of water supply and salinity on Pima
cotton. These workers [24] found that an increase in water salinity caused a decrease in the seed cotton
yield and the salinity threshold increased with an increasing amount of water. Delayed fluorescence and
a decrease in intermittent amplitudes in the early stages of salt stress imposed on cotton plants were ob-
served by Ganieva et al. [25]. This phenomenon is an indication of a decrease in photosystem II (PSII)
activity. It may be related to damage to chlorophyll (Chl) in the PSII donor site and a decrease in Chl b
molecules leading to an increase in the Chl a/bratio.
682 PESSARAKLI