the critical functions of proline is to act as an osmoprotectant against stress in plants [69–71]. At higher
levels of salinity, the proline accumulation was greater, perhaps as a last resort for plants to survive and
to avoid osmotic death.
VI. SOIL-PLANT RELATIONSHIP
All desert plants and most saline plants are totally dependent upon the availability of water in the rainy
season. This water controls their seed germination, seedling growth, and plant survival. Rainfall leaches
salts down the soil profile, as far down as the ground water, with a compensating upward movement as a
result of capillary action. Decreases in soil moisture and the intensity of evaporation lead to an increase
in soil salinity [72,73].
Halophytes studied by the authors were found to absorb salts continuously from their surrounding en-
vironment.S. baryosma, S. sesuvioides, S. fruticosa, T. triquetra, and Z. simplexcontinue to accumulate
salt in their tissues. A. lagopoides, C. cretica, and S. helvolussecrete excess salt through the entire shoot.
Fine streaks of white salt are seen on the stem and leaves throughout. On the basis of the ion analyses, Na
and Kwere among the major cations and Clamong the anions absorbed by these halophytes in large
quantities (Table 2) [74]. Considering the habit as well as the Clcontent of individual halophytes, it is
concluded that (1) the Clamounts absorbed by the leaves of Z. simplex(11–18%) and S. fruticosa
(13–19%) were nearly equal but comparatively much higher than in other species, (2) the internal Clcon-
tent of ion-accumulating species was higher than that of the two ion-secreting grass species (A. lagopoides
andS. helvolus), and (3) among the ion-accumulating species, S. baryosma(6–11%),S. sesuvioides
(3–7%), and T. triquetra(3–8%) accumulated much less Cl. Because Clis the dominant ion present in
the medium at both saline sites, it can be concluded that S. fruticosa, T. triquetra, S. baryosma, C. cretica,
andZ. simplexare well suited to these habitats, and thus they are the most salt tolerant species [75,76].
The water and salt stress on halophytes usually changes during the season. In order to survive under
these changing conditions, halophytes must also make changes in their tissue osmotic potential during the
growing season. Harward and McNulty [77] found that Naand Clconcentrations in the Salicornia
rubraplant changed from 700 mM at the start of the growing season to 2 M at the end of the growing sea-
son. The Naand Claccounted for almost 93% of the total osmotic pressure of S. rubracell sap.
568 SEN ET AL.
TABLE 1 Seasonal Variations in Proline (g/g Fresh Weight) Content in Halophytes Growing at Different
Sites (I–III)
Pachpadra (site I) Didwana (site II) Jodhpur (site III)Species Rainy Winter Summer Rainy Winter Summer Rainy Winter Summer
Aeluropus 6.2 26.6 —a 24.6 — — — — —
lagopoides
Cressa cretica 0.5 108.0 3.8 4.8 — — — — —
Salsola 0.1 7.1 5.7 — — — 0.1 7.0 2.7
baryosma
Sesuvium 2.0 — — 4.3 — — 1.8 — —
sesuvioides
Sporobolus 5.3 100.0 7.9 6.1 8.7 6.2 — — —
helvolus
Suaeda 1.4 11.9 7.0 2.7 9.9 6.6 1.9 5.8 5.0
fruticosa
Trianthema 3.4 74.7 — 3.7 14.3 — 5.2 15.6 8.2
triquetra
Zygophyllum 6.4 64.2 — — — — — — —
simplex(G)b
Z. simplex(R)c 5.7 109.9 — — — — — — —
aPlant not seen.
bGreen strain.
cRed strain.
Source:Ref. 65.