Investigating physiological and biochemical

particularly legumes, such as Trifolium (
Winter, 1982
; 
Rogers et al., 1997
), Medicago 
(
Sibole et al., 2003
), Glycine (
Luo et al., 2005
), and Lotus (
Teakle et al., 2007
), and 
woody perennials, for example, Citrus and Vitis (
Romero-Aranda et al., 1998
; 
Moya 
et al., 2003
). Severe leaf chlorosis and depression of photosynthesis were found for 
red kidney bean (Phaseolus vulgaris) (
Hajrasuliha, 1980
), and high concentrations of 
Cl
-
led to a decrease in the growth rate. Previous investigations on soybean (Glycine 
max L.) clearly indicated a sensitivity of this species to high concentrations of Cl
-
(
Lauchli and Wieneke, 1979
; 
Parker et al., 1983
). Based on analysis of a number of 
field trials of wheat and chickpea crops, 
Dang et al. (2008) 
concluded that the Cl
-
concentration in the soil was more important in reducing growth and yield than Na
+
. 
They found that Cl
-
concentration in the youngest mature leaf of bread wheat, durum 
wheat, and chickpea varied much more with increasing levels of subsoil salinity than 
with Na
+
concentration (
Dang et al., 2006
), suggesting that Cl
- 
toxicity was relatively 
more important to growth than Na
+
toxicity. Tavakkoli et al. (2010) reported that 
exposure to high concentrations of Cl
–
is a major cause of losses in yield due to soil 
salinity in faba bean. 
Mechanisms for keeping cytoplasmic concentrations of Na
+
and Cl
-
below toxic 

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36 
levels are mainly of two types: the mechanisms which minimize salt entry in the root 
and its transport through the plant, and other mechanisms reduce the salt buildup in 
the cytoplasm by sequestration in vacuoles. In fact, most of the plants exclude nearly 
98% of the solutes in the soil solution and transport only about 2% solutes to the 
shoots via xylem. This high degree of exclusion is achieved through (i) tightly 
controlled uptake from the soil because the epidermis of the roots forming a virtual 
‘barrier’ to the salt entry into the roots (Lauchli et al., 2008) and (ii) regulated 
movement in the xylem by controlled loading of Cl
-
into the xylem (Tregeagle et al., 
2010) or (iii) by retrieval of Na
+
as it moves in the transpiration stream to the leaves 
(James et al., 2006).
The unidirectional Na
+
uptake is all the same and does not differ between salt 
sensitive and salt tolerant genotypes in most species. But salt tolerant genotypes have 
the ability to more actively exclude Na
+
via plasma membrane Na
+
/H
+
antiporters. In 
barley, salt tolerant varieties loaded much higher amounts of Na
+
into the xylem 
compared with sensitive genotypes (Shabala et al., 2010), for more osmotic 
adjustment in the shoot (Shalaba and Mackay, 2011). The most obvious physiological 
hallmark’ distinguishing halophytes from glycophytes is their ability to select K
+
from 
a mixture dominated by Na
+
and yet accumulate sufficient Na
+
for the osmotic 
adjustment. At the whole-plant level, the selectivity between K
+
and Na
+
(S
K/Na
) in 
halophytes is within the range of 100-200, even at external salinities exceeding sea 
water levels. Thus, it appears that there is nothing really unique to halophytes that is 
not present in glycophytes; the major difference is that the halophytes control these 
mechanisms more efficiently than glycophytes (Shalaba and Mackay, 2011).