Abstract

Salt toxicity is one of the major problems in modern agriculture. Plants can employ silicon as a protective agent against stresses and the mechanisms of this process remain unknown. Two Egyptian clover (Trifolium alexandrinum) cultivars differing in salinity tolerance were used (Helaly, salt sensitive and Sarw1, salt tolerant). They were grown in pots filled with normal and saline soil (2000 and 3000 ppm) in the absence or presence of diatomites (0, 1.5, 3 and 4.5 g/kg soil). Results indicated that diatomite significantly offset the negative impacts of salinity and increased tolerance of sensitive cultivar of clover (Helaly) to salinity stress. Salinity decreased markedly all measured growth parameters (plant height and fresh and dry weight of fodder/pot), photosynthetic rate , the percentage of relative water content (%RWC), percentage  of membrane stability index (%MSI), total photosynthetic pigment, and the contents of each of magnesium (Mg), potassium (K), phosphorus (P), and calcium (C) while it increased the levels of both amino acids, proline and sodium (Na) in both  T. alexandrinum cultivars, however the effect was more profound on the sensitive line. Addition of diatomite at an upgraded rates solely or combined with both concentrations of NaCl significantly increased the above measured growth parameters, photosynthesis, %RWC, %MSI, total pigment and the accumulation of each of Mg, K, P and Ca. Moreover, it synergistically increased the content of total amino acids while, on the other hand, reduced the contents of proline and Na. Notably, the impact of diatomite in mitigating the deteriorative effect of salinity was clearly manifested more in sensitive lines of clover than in tolerant ones and under the higher dose of salinity (3000 ppm) as compared to the lower dose (2000 ppm). Moreover, diatomite fertilization either alone or interacting with salinity induced two distinctive protein electrophoratic bands (233 and 25 KD) which were absent in either the control or salinity stressed cultivars. In this respect, diatomite was most effective at 3 g/kg on Helaly and 4.5 g/kg on Sarw1 imposed to the higher dose of salinity (3000 ppm). Diatomite application either alone or combined with salinity induced several distinguished amplified DNA fragments in both clover cultivars using PCR- RAPD analysis , although the number of induced polymorphic DNA fragments were more in Helaly than in Sarw1. These results indicate that diatomite recovered and improved the morphologic, metabolic and biochemical status of both cultivars under salinity stress and especially the sensitive line (Helaly).

Key words: Diatomite, growth, proline, aminoacids, membrane stability index, relative water content, minerals, protein electrophorasis and RAPD-(DNA).

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