One of the characteristics distinguishing halophytes from glycophytes is their capacity to accumu-
late selectively large quantities of ions in their cells without disrupting metabolic processes [78]. Maliwal
[79] found that absorption of Na increased with increasing chloride salt concentration rather than sulfate
salinity (0.78 to 15.40 dS/m) in wheat (Triticumspp.). A number of halophytes have been analyzed for
their ionic contents [80], and the most strongly accumulated ions were Naand Clwith a few species
having relatively high sulfate and Kconcentrations. Albert and Popp [81] concluded that the Kcon-
tent was generally higher in monocotyledons, whereas the Nacontent was higher in dicotyledons. The
K/Naratio in plant tissues of Sesbania rostratawas always higher than in the substrate, indicating se-
lectivity for Kuptake, a characteristic generally considered unique to halophytes [82]. At certain con-
centrations, potassium is reported to inhibit the growth of halophytes such as Suaedaand Atriplex, while
isomotic sodium promotes growth [83]. Abbas [84], using monthly samples of Zygophyllum quatarense
populations, found that plants from a saline habitat had a higher chloride content than plants from a non-
saline habitat. Chellappan [85] determined the mineral distribution in Sesuvium portulacastrumand found
that the Nacontent increased significantly with increasing NaCl concentration. Hamada [86] and Saha
and Gupta [87] also observed an increase in Na concentration with increasing salinity in wheat and sun-
flower, respectively.
The tolerances to water and salt stress of Atriplex canescensare linked through a common mecha-
nism of Na uptake for osmotic adjustment in this species [88]. Egan and Ungar [89] observed that in
Atriplex prostrata, plant growth parameters decreased with a lowering of the medium osmotic potential,
and Ksalts were more inhibitory than Nasalts. The ion content of plant tissue generally increased with
a lowering of osmotic potential. It is suggested that halophytes such as A. triangularismay use Naas an
osmoticum to adjust the vacuolar water potential but were unable to use Kfor this function because of
a specific ion toxicity.
Ion uptake by plants was largely dependent upon their availability in the soil. When these ions fluc-
tuated in the soil by upward or downward movements, their uptake by plants was also affected. As with
soil salinity, a higher quantity of elements in plants was observed during dry periods in the Indian arid
zone [23].VII. GERMINATION ECOLOGY OF HALOPHYTESThe presence of excess salt in the soil is one of the critical factors that adversely affects seed germination
under such conditions, thereby preventing plant species from inhabiting the saline environments success-
fully [10,12,15]. Halophytes show a reduction in germination when subjected to salinities above 1% NaCl,
and increasing salt concentrations also delay germination [8]. Keiffer and Ungar [90] observed that pro-
longed exposure to saline solutions can inhibit or stimulate germination in certain species, and the result-
ing germination and recovery responses are related to the duration and intensity of their exposure to salt in
their natural habitats. Rajpurohit [21], Jhamb [22], and later Mohammed and Sen [91] carried out a detailed
study of this important aspect in the Indian desert. These investigators collected seeds from four different
sites (Pachpadra, site I; Didwana, site II; Jodhpur, site III; and Luni, site IV) and studied the effect of var-BIOLOGY AND PHYSIOLOGY OF SALINE PLANTS 569TABLE 2 Range of Ionic Content (mg/g) Accumulated by Leaves of Halophytes Growing at Different Sites
(I–III)
I II III
Species Na K Ca^2 Cl(%) Na K Ca^2 Cl(%) Na K Ca^2 Cl(%)
Aeluropus lagopoides 55–100 5–14 1–22 5.8–6.3 10 7 10 4 —a —— —
Cressa cretica 20–110 1–31 3–30 4–10 42–49 9–14 19–21 4–8 — — — —
Salsola baryosma 44–291 27–78 4–43 6–11 — — — — 37–241 8–49 2–50 1.4–2.9
Sesuvium sesuvioides 16–100 14–36 5–37 3–7 — — — — 72–106 9–21 2–20 2–3
Sporobolus helvolus 7–70 4–37 1–89 3–5 22–28 4–12 5–7 1–4 — — — —
Suaeda fruticosa 43–313 10–45 3–55 13–19 45–119 7–63 5–26 7–21 48–315 8–20 1–37 7–15
Trianthema triquetra 29–115 3–33 2–28 3–8 27–112 7–34 3–87 1–11 22–225 9–24 1–30 1.9–2.2
Z. simplex(G)b 41–91 8–35 4–65 2–8 — — — — — — — —
Z. simplex(R)c 42–105 8–15 5–52 11–18 — — — — — — — —
aPlant not seen.
bGreen strain.
cRed strain.
Source:Ref. 74.