THE EFFECT OF MYCORRHIZA GROWTH AND EXPRESSION OF SOME GENES IN BARLEY

Abstract

Barley is one of the most important crops for food consumption. Soil fertilization using minerals and chemical compounds are not safe for human health beside beingas expensive. Therefore, It is important to find suitable alternatives. The arbuscular mycorrhiza (AM) is characterized by the formation of arbuscules (sometimes vesicles). The fungus occupies various proportions of the volume of host cells but is separated from the cell cytoplasm by the elaboration of the host plasma membrane forming a fungal membrane and an apoplectic compartment between the fungus and host cytoplasm. Mycorrhiza changes whatever source of phosphorus into phosphoric acid which acidifies the rhizosphere and thus increases the availability of elements for plants uptake. The increase of the availability of elements specially, calcium which plays the main role in cell signaling which could lead to switch on or accelerate the function of several genes such as protein kinases and other genes related with photosynthesis and eventially, affect the plant growth. Inoculation with mycorrhiza increased all plant growth variables such as number of leaves, stem fresh and dry weights and root dry weight Shockley et al. (2004). Gahoonia and Nielsen (2004) reported that the inoculation with mycorrhiza enhanced the release of organic acids and higher acid phosphatase activity in the rhizosphere which may be useful for increasing phosphorus acquisition from inorganic and organic phosphorus pools to the plant. Al-Karaki et al. (2004) found that biomass and grain yields were higher in mycorrhizal than non-mycorrhizal plants. Wu et al. (2005) reported biofertilizer as an alternative to chemical one to increase soil fertility and crop production.
Glassop et al. (2005) reported that a very large number of plant species are capable of forming symbiotic associations with arbuscular mycorrhizal (AM) fungi. Moreover, they reported that a large number of phosphate (P) transporters have been identified in plants; tissue expression patterns and kinetic information supports the roles of some of these in the direct root uptake pathways. Chen et al. (2007) indicated that the beneficial impacts of mycorrhizal colonization on plant growth could be largely explained by improved P nutrition. On the other hand, Baltruschat et al. (2008) found that the root endophytic basidiomycete Piriformospora indica increase the tolerance against abiotic stress as in many plants.
Gryndler et al. (2009) concluded that mycelia of AM fungi are influenced by organic matter decomposition via release of the compounds during the decomposition process and also by secondary metabolites produced by microorganisms involved in organic matter decomposition. Araim et al. (2009) reported that AM colonization significantly increased the mass of shoots and roots and the concentrations of proteins and most of the phenolics in the roots. Hence, the selected trait of mycorrhiza could play an important role in optimizing the growth of E. purpurea by inducing the production of secondary phytomedicinal metabolites.
The impact of mycorrhizaon gene expression has been addressed by some recent studies, Hause et al. (2002) reported that colonization of barley (Hordeum vulgare Cv. Salome) roots by an arbuscular mycorrhizal fungus, led to elevated levels of endogenous jasmonic acid (JA) and its amino acid conjugate JA-isoleucine, whereas the level of the JA precursor remained constant. The rise in jasmonate was accompanied by the expression of genes coding for an enzyme of JA biosynthesis. Delp et al. (2003) performed relative quantitative RT-PCR and western blotting to investigate the expression of three genes with potentially regulatory functions from the arbuscular mycorrhizal fungus Glomus intraradices in symbiosis with barley.
Weidmann et al. (2004) identified 29 plant genes which were upregulated in response to Medicago truncatula root inoculation with mycorrhiza. Twenty-two protein spots, 14 upregulated and 8 downregulated were found changed in mycorrhiza inoculated plants as compared with the non inoculated ones by Liang et al. (2007). Abo Doma et al. (2008) indicated that the treatment with mycorrhiza significantly increased plant growth in two cultivars of wheat using different yield related traits. Moreover, transcriptome analysis using real timereverse transcriptase indicated that mycorrhiza treatment resulted in an increase in the gene expression of proline 5 carboxilate synthetase (P5CS) on the transcription level. Roldán et al. (2008) indicated that differential gene expression for genes conferring superoxide dismutase and peroxidases were recorded between mycorrhizal and non-mycorrhizal shoots of juniperus oxycedrus seedling.
This investigation aimed to: 1- study the effect of barley root inoculation with mycorrhiza on some plant traits and 2-determine the changes in gene expression of the genes conferring calcium dependent protein kinases (CDPKs), phosphoenol pyrovate carboxylases (PEPCs) and proline-5 carboxylate synthetase (P-5CS) in barley plants in response to their inoculation with mycorrhiza at the molecular level as quantified using RT-PCR.