Chemistry Reference
In-Depth Information
water and solute potentials (Table 3). In halophytes, this mechanism involves physiological
and biochemical adaptations for maintaining protoplasmic viability as cells accumulate
inorganic ions mainly Na
+
, Cl
-
, followed by Ca
2+
, K
+
and Mg
2+
,
and other organic solutes to
achieve osmotic adjustment [41, 46, 54]. However, these ions may be sequestered in vacuoles
leaving relatively low ions in the cytoplasm. Some authors [55] reported in their review that
crops including cereals tolerate NaCl by excluding Na
+
from the transpiration stream as well
as sequestration of Na
+
and Cl
-
in the vacuoles of root and leaf cells, and promote other
physiological processes like faster growth rates and longer duration by maintaining high
concentrations in K
+
despite the osmotic stress of the salt outside the roots [28, 56]. Organic
solutes like glycinebetaine, proline, sugars, polyols etc., may accumulate in the cytoplasm to
achieve osmotic balance inside the cells, and therefore play a pivotal role in plant cytoplasmic
osmotic adjustment. Thus, salt tolerance in these plants can be attributed mainly to the fact that
these plants accumulate low-molecular-mass organic compounds (compatible solutes) [57-60].
Salt stress of growth
medium
(NaCl, molm
-3
)
Osmotic potential of growth
medium
(Ψ
s
, MPa)
Roots Leaves
Cajeme Yecora Cajeme Yecora
0
-0.05
-0.50
-0.49
-0.92
-0.98
50
-0.25
-0.62
-0.62
-1.17
-1.27
100
-0.44
-0.72
-0.69
-1.46
-1.51
150
-0.61
-0.80
-0.74
-1.85
-1.86
Table 3.
Osmotic adjustment (MPa) in two Mexican wheat cultivars exposed to salt stress [22].
These solutes, as non-toxic cytoplasmic osmotica, that play major roles in the physiology
and biochemistry of plant cells and have contributed in the process of osmotic adjustment,
maintaining turgor and hydration of cellular microstructures, as sources of some carbon and
nitrogen skeletons, and osmoprotectants [61, 62].
As osmoprotectants, these compounds
tend to be excluded from the hydration sphere of proteins and stabilizing the folded protein
structure [63-65], maintaining plasma membranes, protecting the transcriptional and
translational machineries and intervening in the process of refolding of enzymes as
molecular chaperones [66, 67]. Moreover, compatible compounds like proline and
glycinebetaine
can induce the expression of certain stress-responsive genes, including those
for enzymes that scavenge reactive oxygen species [68].
4. Microorganisms associated with wild plants
Higher plants are normally colonized by microorganisms, which include bacteria, fungi,
algae or protozoa. Microorganisms interact with plants because plants offer a wide diversity
of habitats including the (a) phyllosphere (aerial plant part), (b) rhizosphere (zone of
influence of the root system), and (c) endosphere (internal transport system). Interactions of
epiphytes, rhizophytes or endophytes may be detrimental or beneficial for either the
microorganism or the plant, and may be classified as neutralism, commensalism, synergism,
mutualism, amensalism, competition or parasitism [69]. Symbiosis is a relationship that both
