CADMIUM EXCLUSION FROM BARLEY ( Hordeum Vulgare L.): DEVELOPMENT OF PHYSIOLOGICAL AND MOLECULAR MARKERS.
Tesi di Dottorato
Data di Pubblicazione:
2014
Citazione:
CADMIUM EXCLUSION FROM BARLEY ( Hordeum Vulgare L.): DEVELOPMENT OF PHYSIOLOGICAL AND MOLECULAR MARKERS / S. Sghayar ; coordinatore: P. Bianco ; italian tutor: G. Sacchi ; tunisian tutor: C. Abdelly. UNIVERSITA' DEGLI STUDI DI MILANO, 2014 Jan 23. 24. ciclo, Anno Accademico 2011. [10.13130/sghayar-souhir_phd2014-01-23].
Abstract:
The entry into the food chain of excessive amounts of heavy metals, due to the
consumption of foodstuffs from crops grown on contaminated soils, is of increasing concern
for public health. Among heavy metals, Cd results particularly dangerous since it is easily
taken up by roots and translocated to vegetative and reproductive organs of plants without
obvious symptoms of phytotoxicity. In particular, Cd can accumulate in grains of cereals
such as rice, wheat and barley. The Codex Alimentarius Commission of the Food and
Agricultural Organization/World Health Organization set the maximum permissible concentration of Cd for human consumption at 0.1 µg g-1 for cereal grains, excluding rice (0.4 µg g-1). Among the strategies to limit the risk of introducing Cd into the human food
chain, the identification and/or constitution of plant genotypes able to exclude the metal
from the shoot or from the edible parts seems to be the most promising line of enquiry for
the future.
Among cereals, barley ranks fourth in terms of both yearly-produced amounts and
cultivated area in the world. In recent years, a correlation between presence of barley in the
diet and reduced risk of coronary heart diseases has been suggested, inducing a progressive
increase in the demand for the cereal in countries where its consumption was traditionally
limited. Although some evaluations of genotypic differences in Cd accumulation in barley
grain have been described, very little information is available about the physiological basis
of the observed variability.
Specific aims of the research were: a) to analyze six barley cultivars among the most
cultivated in Tunisia for their tolerance to relatively high Cd concentrations and ability to
limit the accumulation of the metal in shoot and grain; b) to identify the molecular and
physiological basis of the behavior of the two most divergent cultivars, i.e. the highest and
the lowest Cd accumulator, in order to develop markers useful in the selection of low-Cd
grain cultivars.
Among the six Tunisian barley cultivars, a large variability in their sensitiveness to Cd
exists. The concentrations of the metal in the roots of plants grown in hydroponic solution
in the presence of Cd did not significantly differ among the six cultivars, whereas wide
differences were apparent in the shoots, where Lemsi and Manel showed the highest and
the lowest values, respectively. Despite similar transpiration fluxes, the six barley cultivars
loaded into the xylem and translocated to the shoots different amounts of Cd. A close linear
correlation between the concentrations of the metal in the xylem sap and those measured
in the shoots was observed.
The measurements of concentration-dependent influx of Cd in the roots revealed
marked differences between Lemsi and Manel. Lemsi showed a clearer saturable
component in the low Cd concentration range; the maximum influx (Vmax) for Cd was about
threefold higher in Lemsi.
Although the Cd concentrations were not different in the roots of the two cultivars,
the amounts of phytochelatins and the ability to retain Cd were lower in Lemsi than in
Manel. The different Cd retention in roots between the two cultivars cannot be ascribed to
a differential expression of the HvHMA3 gene encoding a tonoplast-localized transporter
mediating the vacuolar sequestration of the metal. In detail, the Cd-treatments decreased
the steady state levels of HvHMA3 mRNA in the two cultivars at the same extent.
Exhaustive extraction combined with a fractionation procedure showed that in the roots of Lemsi the percentage of free non-chelated Cd ions (Cd2+), i.e. the form potentially
available for xylem loading , was twice that present in Manel
Tipologia IRIS:
Tesi di dottorato
Keywords:
barley ; cadmium ; heavy metal ; stress ; cereals
Elenco autori:
S. Sghayar
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