Alleviation of salt-induced ionic, osmotic and oxidative stresses inCajanus cajannodules by AM inoculation

Abstract

Legume-Rhizobium symbiotic nitrogen (N 2 ) fixation plays a critical role in sustainable nitrogen management in agriculture. The nitrogen fixed by the root nodules not only affects the nitrogen cycle of nature, but is also of great economic importance. A number of physiological and biochemical processes in the nodules are affected by salt stress. The objective of this study was to evaluate the role of arbuscular mycorrhiza (AM) in moderating toxic effects of salt stress on nodular metabolism in Cajanus cajan (L.) Millspaugh (pigeonpea) cv. Manak. Exposure of plants to salinity stress (4, 6 and 8 dSm 71 ) caused ionic imbalance, which resulted in increased Na þ and reduced K þ and Ca 2þ contents in the nodules. Salinity induced increased synthesis and accumulation of proline and glycine betaine. Salt stress significantly increased the antioxidant enzyme activities in the nodules of all plants. Nodular growth suffered remarkably and a marked decline in nodule biomass was observed under salt stress. Leghemoglobin content and acetylene reduction activity (ARA) also declined under saline conditions. AM could significantly improve nodule dry mass, leghemoglobin content and nitrogenase activity, and phosphorus content under salt stress. Activities of antioxidant enzymes increased markedly in nodules of mycorrhizal-stressed plants. This study suggested a correlation between improved functional efficiency of nodules and higher osmolyte accumulation and enhanced antioxidant enzyme activities of AM plants under stressed conditions relative to the nodules of uninoculated plants.

Arbuscular mycorrhizal symbiosis and alleviation of salinity stress

“…These are not merely non-toxic cellular osmolytes but they can also stabilize the structures and activities of protein complexes and maintain the integrity of membrane against the damaging effects of excessive salt (Gorham ,1995). It was found that at higher salinity levels the glycine betaine content of AM treated pigeon-pea plants was about 2-fold greater than that of non-AM plants ( Manchanda and Garg, 2011). Enzymes activity: There is accumulating evidence that production of reactive oxygen species (ROS) is a major damaging fac-tor in plants exposed to different environmental stresses, including salinit.…”

“…Peroxidase (POX) and catalase (CAT) are involved in the defense mechanisms of plants in response to pathogens either by their participa-tion in cell wall reinforcement, or by their antioxidant role in the oxidative stress generated during plant pathogen interaction (Mehdy, 1994). Manchanda and Garg (2011) reported that low and moderate salinity further increased the antioxidant enzymes activity in the nodules of mycorrhizal-stressed Cajanus cajan plants. Soybean plants inoculated with salt pretreated mycorrhizal fungi showed salt adaptation through increased SOD and POX activity in shoots, to those inoculated with the nonpretreated fungi (Ghorbanali et al, 2004).…”

Properties of the halophyte microbiome and their implications for plant salt tolerance

“…Osmoregulation can be also achieved with betaines and with sugars. Both are increased in mycorrhizal plants and were suggested as being involved in salt tolerance (Porcel and Ruiz-Lozano 2004;Manchanda and Garg 2011).…”

Effect of Zinc and Bio Fertilizers on Antioxidant Enzymes Activity, Chlorophyll Content, Soluble Sugars and Proline in Triticale Under Salinity Condition

“…Mycorrhiza is a symbiotic association between plant roots and fungi. Arbuscular mycorrhizal fungi promote salinity tolerance by utilizing various mechanisms such as accumulation of compatible solutes and production of higher antioxidant enzymes (Manchanda and Garg, 2011). Mycorrhizal fungi increase the sugar content of the host plant by hydrolysis of starch to sugars and preventing structural changes in soluble protein .…”