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  • Author or Editor: A. Tammam x
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Soil salinity is a major constraint to food production because it limits crop yield and restricts the use of land previously uncultivated. Breeding for tolerance to salinity in crops has usually been limited by the lack of reliable traits for selection. The mechanism of salt tolerance in two cotton ( Gossypium barbadens L.) cultivars (Giza 70 and Giza 88) and their responses to shoot spraying with 200 ppm m −3 IBA were studied.Treatment with IBA not only improved the growth of salt-affected Giza 70, but also increased the growth of this cultivar up to −2.7 MPa and reduced the inhibitory effect of salinity on photosynthetic pigments.This was accompanied by differences in the accumulation of sucrose and total soluble sugars and in the total available carbohydrate and protein contents. IBA ameliorated the inhibitory effect of salinity on growth, increased the carbohydrate and protein contents of both cotton cultivars and markedly retarded the accumulation of proline and glycine betaine. It resulted in the reduction of Na + accumulation in Giza 70, while in Giza 88 it enhanced the absorption and translocation of K + , resulting in higher K + /Na + ratios in the shoots. There were pronounced differences in the electrophoretic patterns of the proteins in both cultivars under salt stress and IBA treatment.

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The leaf area, fresh and dry matter, and water content in the roots and shoots of broad bean were significantly reduced with a rise in salinity. The protein components in the roots and shoots decreased in response to salinity, whereas the proline content significantly increased. The sodium content in both roots and shoots increased with increasing salinity, whereas potassium and calcium decreased. Salinity induced an increase in total amino acids and ammonia. Spraying with salicylic acid (SA) increased the three growth parameters, stimulated the synthesis of protein at all salinities, retarded the accumulation of proline, retarded the accumulation of Na+ and increased the content of K+ and Ca2+. The total content of amino acids was about 1.6-fold the untreated control and there was a drastic increase in the content of threonine and serine. The electrophoretic pattern of SA-treated seedlings showed 21 polypeptides compared to 12 in the salt-treated ones. Salinity plus SA resulted in the disappearance of 4 polypeptides. In addition, two peptides with molecular masses of 99 and 102 kDa appeared in the gel in both NaCl-treated seedlings and NaCl+SA-treated seedlings.

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The mechanisms by which Azolla caroliniana respond to salt stress in absence and presence of nitrate is investigated. Screening of amino acid and differential display is used to compare overall differences in gene expression between salinity-stressed and unstressed Azolla caroliniana by quantitative reverse transcriptase polymerase chain reaction (RT-PC R). Results showed that under saline conditions, aspartic acid, glutamic acid, alanine and leucine were the amino acids found to be abundant in Azolla caroliniana, accounting for 11.26%, 8.66%, 9.43%, and 12.36%, respectively. Following salinity stress, a decrease in free glutamate concomitant with a parallel decrease in free proline was indeed evident. Interaction between nitrate and salinity stress increased proline content significantly. By screening a cDNA library, we have identified protein products by homology with known proteins. The RNA transcripts encoding protein influencing secondary metabolites and vacuolar Na+/H+ antiporter that facilitate the transport system. The databasematched under interaction of nitrate and 50 mM NaCl were associated with wall biosynthesis, disease resistance, metabolite transport and protein regulator, other gene for metabolism of steroids and secondary transport. Results obtained from this research could represent a key step in understanding the molecular mechanism of salt tolerance of Azolla caroliniana in the presence and absence of nitrate.

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The effect of aluminium was investigated on the seedlings pre-treated by two concentrations of boron 4 μM or 32 μM grown in water culture using a concentration of 500 μM Al for 3 days. Semithin and ultrathin sections of the apical region of the roots and transmission electron microscopy micrographs were analysed of fourteen-day-old Al-tolerant (‘Sakha 93’) cultivar of Triticum aestivum. Results showed that the amelioration effect of boron treatment was pronounced at 32 μM B level. Rigidity of cell wall and plasma membrane in the wheat root apex cells (Zone of root hairs) could result from the formation of bonds of ions of the toxicant with components within their structures and appears as dark precipitants in cross sections. Cross sections of the apical region of the control plant roots showed well-developed normal anatomical structure and cell ultrastructure typical for those of root regions. Slight alterations under the influence of aluminium or boron alone or both of them and the role exhibited by boron in ameliorating of aluminium toxicity were observed. In spite of these alterations, the seedlings keep grown in face of Al-stress. The obtained results proved the high resistance of the studied ‘Sakha 93’ cultivar to aluminium stress. Aluminium detoxification coincides with increased Ca2+ content in the root apex to cope with alleviation of Al-stress; boron may have a role in this concern. Possible Al-toxicity and -tolerance, as well as boron alleviation of toxicant stress in this tolerant cultivar was briefly discussed.

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