Agriculture Reference
In-Depth Information
Atriplex nummularia
can achieve biomass yield of 20 to 30 t ha
-1
year
-1
and have been shown
to accumulate up to 40% NaCl in their dry matter. Recent studies suggest that halophytes may
be useful for phytoremediation of heavy metal contaminated salty soils (Glenn
et al.
1999;
Williams
et al.
1994; Jordan
et al.
2002, López-Chuken and Young, 2005; Ghnaya
et al.
2005).
Furthermore, heavy metals limit plants' growth and decrease its development rate by
affecting various aspects of plant physiology. They restrict photosynthesis, decrease
chlorophyll content, as well as induce oxidative damages (Olmos
et al.
2003; Ederli
et al.
2004; Chaoui and Ferjani, 2005). Alteration of the plant water status has been reported in
some studies (Barcelo and Poschenrieder, 1990; Perfus-Barbeoch
et al.
2002). Mineral
disturbances induced by the interaction of heavy metals with essential macro and
microelements are important causes of toxicity in plants (Larbi
et al.
2002, Kim
et al.
2003,
Ederli
et al.
2004, Ghnaya
et al.
2005). Thus, the reduction of the growth observed in plants
subjected to heavy metals often corresponds to the resultant of several parameters related to
direct action (toxic effect linked to an accumulation of heavy metals in tissues) and/or to
indirect effect (limitation of mineral and water nutrition's).
However, little is known about the implication of each of these two components in the
growth limitation. The split root system, ensuring a load of the shoots with heavy metals and
an appropriate nutrient supply, constitutes an adequate method to determine the implication of
the nutritional disturbance in the growth-decrease under heavy metal treatment.
In a previous study, we showed that shoot-Cd
2+
concentration varied between 350 and
700 µg/gDW in both species when cultivated in the presence of Cd
2+
(Ghnaya
et al.
2005).
However, this accumulation was accompanied with a growth reduction and mineral nutrition
(K, Ca and Fe) disturbances. The present study aimed at determining whether heavy metals
(Cd and Ni) limit
S. portulacastrum
and
M. crystallinum
growth through impairment of some
essentials nutrients acquisition (Ca
2+
, K
+
and Fe), or through a toxic effect linked to an
excessive metal accumulation in shoots. Thus we conducted a split-root experiment to
separate the two factors.
M
ATERIALS AND
M
ETHODS
Plant Material and Growth Parameters
Sesuvium portulacastrum
L.
(Aizoaceae), a dicotyledonous halophyte commonly known
as sea purslane, was propagated by cutting. Three cm long-stem segments with one node and
two opposite leaves were taken from mother plants growing under natural condition, in a
mixture of sandy soil and organic matter, and irrigated with tap water. They were disinfected
for 5 minutes in saturated calcium hypochlorite solution, and rinsed abundantly with distilled
water. They were then placed for 7 days in an aerated Hewitt (1966) solution diluted 10 times,
supplemented with 4.5 µM Fe EDTA (Jacobson, 1951) and micronutrients (Arnon and
Hoagland 1940). Rhizogenesis took place after one week. Seedlings of
Mesembryanthemum
crystallinum
L. (dicotyledonous halophyte from the Aizoaceae family, commonly known as
common ice plant) were obtained by germination. The seeds were collected from Thina (Sfax,
300 km south of Tunis), sterilised by dipping them into a 10 % H
2
O
2
solution during 20 min.
