Bhoopander Giri

Arbuscular mycorrhizal fungi in alleviation of salt stress: a review

BACKGROUND Salt stress has become a major threat to plant growth and productivity. Arbuscular mycorrhizal fungi colonize plant root systems and modulate plant growth in various ways. SCOPE This review addresses the significance of arbuscular mycorrhiza in alleviation of salt stress and their beneficial effects on plant growth and productivity. It also focuses on recent progress in unravelling biochemical, physiological and molecular mechanisms in mycorrhizal plants to alleviate salt stress. CONCLUSIONS The role of arbuscular mycorrhizal fungi in alleviating salt stress is well documented. This paper reviews the mechanisms arbuscular mycorrhizal fungi employ to enhance the salt tolerance of host plants such as enhanced nutrient acquisition (P, N, Mg and Ca), maintenance of the K(+) : Na(+) ratio, biochemical changes (accumulation of proline, betaines, polyamines, carbohydrates and antioxidants), physiological changes (photosynthetic efficiency, relative permeability, water status, abscissic acid accumulation, nodulation and nitrogen fixation), molecular changes (the expression of genes: PIP, Na(+)/H(+) antiporters, Lsnced, Lslea and LsP5CS) and ultra-structural changes. Theis review identifies certain lesser explored areas such as molecular and ultra-structural changes where further research is needed for better understanding of symbiosis with reference to salt stress for optimum usage of this technology in the field on a large scale. This review paper gives useful benchmark information for the development and prioritization of future research programmes.

Purification strategies for microbial lipases

Microbial lipases today occupy a place of prominence among biocatalysts owing to their ability to catalyze a wide variety of reactions in aqueous and non-aqueous media. The chemo-, regio- and enantio-specific behaviour of these enzymes has caused tremendous interest among scientists and industrialists. Lipases from a large number of bacterial, fungal and a few plant and animal sources have been purified to homogeneity. This has enabled their successful sequence determination and their three-dimensional structure leading to a better understanding of their unique structure-function relationships during various hydrolytic and synthetic reactions. This article presents a critical review of different strategies which have been employed for the purification of bacterial, yeast and fungal lipases. Since protein purification is normally done in a series of sequential steps involving a combination of different techniques, the effect of sequence of steps and the number of times each step is used is analyzed. This will prove to be of immense help while planning lipase purification. Novel purification technologies now available in this field are also reviewed.

Mycorrhizal inoculant alleviates salt stress in Sesbania aegyptiaca and Sesbania grandiflora under field conditions: evidence for reduced sodium and improved magnesium uptake

A field experiment was conducted to examine the effect of the arbuscular mycorrhizal fungus Glomus macrocarpum and salinity on growth of Sesbania aegyptiaca and S. grandiflora. In the salt-stressed soil, mycorrhizal root colonisation and sporulation was significantly higher in AM-inoculated than in uninoculated plants. Mycorrhizal seedlings had significantly higher root and shoot dry biomass production than non-mycorrhizal seedlings grown in saline soil. The content of chlorophyll was greater in the leaves of mycorrhiza-inoculated as compared to uninoculated seedlings. The number of nodules was significantly higher in mycorrhizal than non-mycorrhizal plants. Mycorrhizal seedling tissue had significantly increased concentrations of P, N and Mg but lower Na concentration than non-mycorrhizal seedlings. Under salinity stress conditions both Sesbania sp. showed a high degree of dependence on mycorrhizae, increasing with the age of the plants. The reduction in Na uptake together with a concomitant increase in P, N and Mg absorption and high chlorophyll content in mycorrhizal plants may be important salt-alleviating mechanisms for plants growing in saline soil.

Glomus macrocarpum: a potential bioinoculant to improve essential oil quality and concentration in Dill (Anethum graveolens L.) and Carum (Trachyspermum ammi (Linn.) Sprague)

The effects of application of two arbuscular mycorrhizal (AM) fungi Glomus macrocarpum and G. fasciculatum on shoot biomass and concentration of essential oil in Anethum graveolens L. and Trachyspermum ammi (Linn.) Sprague fruits were evaluated. Results revealed significant variation in effectiveness of the two AM fungal species. AM fungal inoculation in general improved the growth of the plants. On mycorrhization, the concentration of essential oil increased up to 90% in dill and 72% in carum over their respective controls. Glomus macrocarpum was more effective than G. fasciculatum in enhancing the oil concentration. The constituents of the essential oils were characterized by gas liquid chromatography. The levels of limonene and carvone were enhanced in essential oil obtained from G. macrocarpum-inoculated dill plants, while G. fasciculatum inoculation resulted in a higher level of thymol in carum.

Arbuscular Mycorrhiza: Approaches for Abiotic Stress Tolerance in Crop Plants for Sustainable Agriculture

Soil stresses such as salinity, drought, and heavy metals are major hindrances to crop productivity as these can significantly decrease plant growth and production. Colonization with arbuscular mycorrhizal fungi (AMF) can enhance plant tolerance to these stresses. Arbuscular mycorrhizal associates are integral, functioning parts of plant roots and can significantly increase plant growth and production due to the formation of extensive hyphal network and production of biochemicals like glomalin. This chapter provides an overview of mechanisms evolved by AMF to help plants survive in these stressful conditions. These mechanisms include enhanced growth, prevention of nutrient deficiency and ion toxicity, osmotic adjustment, enhancing the activities of antioxidants and prevention of oxidative damage, improving photosynthesis, and water status. In addition, stress avoidance strategies include exclusion of toxic ions, restriction of entry of toxic ions and immobilization of heavy metals in soil or plant roots.

Preinoculation with Arbuscular Mycorrhizae Helps Acacia auriculiformis Grow in Degraded Indian Wasteland Soil

Abstract The effect of inoculation of two arbuscular mycorrhizal fungi, Glomus fasciculatum, and G. macrocarpum, alone and in combination, on establishment and growth of Acacia auriculiformis in a wasteland soil was studied under nursery and field conditions. Under nursery conditions, mycorrhiza-colonized seedlings showed significantly higher root shoot dry weights and higher concentrations of phosphorus (P), potassium (K), zinc (Zn), copper (Cu), iron (Fe), and sodium (Na) in shoots of mycorrhizal than nonmycorrhizal seedlings. However, concentration of calcium (Ca) was unchanged. Acacia auriculiformis exhibited a maximal mycorrhizal dependency of 79.6% on dual inoculation. Mycorrhizal dependency differed with AM fungal isolates and age of the plant. Under field conditions, AM colonization of A. auriculiformis enhanced tree survival rates (85%) after transplantation. Arbuscular mycorrhiza-colonized plants showed significant increase in height, biomass production, and girth as compared to nonmycorrhizal plants. In general, all growth parameters were higher on dual inoculation of G. fasciculatum and G. macrocarpum as compared to uninoculated plants under both nursery and field conditions.

VA Mycorrhizal Techniques / VAM Technology in Establishment of Plants under Salinity Stress Conditions

This chapter give a brief account about salt stress and its effect on plant growth, nutrition and on distribution, type and number of VAM fungi. VAM help in establishment of plants under salinity stress. Techniques to assess soil and plant activity has also been given.

Soil Factors in Relation to Distribution and Occurrence of Vesicular Arbuscular Mycorrhiza

The role of vesicular-arbuscular mycorrhizal fungi in yie,u augmentation of crop is well established yet little is understood about their growth, biology and ecology. These fungi form a symbiotic relationship with plant roots, and the fungal symbiont becomes a major interface or connection between soil and plants, therefore studies on mycorrhizal systems need to consider soil as well as plants and fungi. Soil proporties can affect spore germination, colonization of host roots and ability of the VAM fungi to influence the growth and physiology of the host plant. A high degree of edaphic specificity in indigenous asemblages of VAM fungi from contiguous soil has been observed. Soil physico-chemical characteristics viz. soil moisture, soil tempterature, soil pH, soil texture, nutrient levels alter the occurrence, distribution, and effectiveness of VA mycorrhizae.

Arbuscular Mycorrhizal Fungi and Tolerance of Salt Stress in Plants

Soil salinity has become a serious land degradation problem and is increasing steadily in many parts of the world, particularly in arid and semiarid areas. Increased salinization of arable land is expected to have devastating global effects and would lead to 30% land loss within the next 25 years and up to 50% by the middle of the twenty-first century. Plants growing in saline conditions generally last to three distinct stresses, ionic, osmotic, and oxidative. The toxic effects of specific ions such as Na+ and Cl−, prevalent in saline soils, disrupt the structure of enzymes and other macromolecules, damage cell organelles, disrupt general metabolic activities, inhibit protein synthesis, and induce ion deficiency. Plants exposed to low water potential face the problem of physiological drought condition. Moreover, salinity creates nutrient imbalance in the plant due to decreased and differential uptake of nutrients and/or their translocation to the shoot and leaf tissues, rendering the plants weak and unproductive. Arbuscular mycorrhizal fungi (AMF) are ubiquitous soil microorganisms that build up symbiotic associations with the majority of higher plants, establish a direct physical link between soil and plant roots, constitute an integral component of the natural ecosystems, and predominantly exist in the saline environment. The extraradical hyphae of AMF run several meters away from the depletion zone, increase root surface area and facilitate nutrient absorption by the plant. Indeed, AMF improve physiological processes and general metabolic activities of the plant and help in the mitigation of physiological drought, which is often imposed under saline conditions. Therefore, the application of AMF could offer a cheaper and cost-effective alternative to counteract the problem of salinity. In this review chapter, we have discussed the factors influencing soil salinization and possible approaches to overcome the problem of salinity stress. The underlying physiological, biochemical and molecular mechanisms by which mycorrhizal plants could improve salt tolerance has also been described.

Arbuscular Mycorrhizal Fungi: Green Approach/Technology for Sustainable Agriculture and Environment

To feed the growing population, global food production needs to be doubled by 2050. The fertilizers cost have increased several folds in the last few years, which necessitates agrarian community to be less reliable on chemicals to grow and protect their crops. Moreover, dependency on chemical fertilizers and pesticides has led to the deterioration of human health, disruption of ecosystem functioning and degradation of our environment. To overcome these problems, there is a need to explore and exploit the beneficial plant–soil microbe interactions to meet the food demand without affecting the relationship between the man and his environment. Arbuscular mycorrhizal fungi (AMF) are known to form symbiotic association with the roots of more than 90% of the terrestrial plants. They serve as biofertilizer and enhance the plant growth by accelerating nutrient uptake, particularly of inaccessible nutrients like phosphorus and nitrogen from the soil. Beside mineral nutrition, AMF also maintain the root hydraulic conductivity, increase the plant net photosynthetic capacity, improve stomatal conductance. The multifunctional extraradical hyphae of the fungus provide numerous ecological advantages like maintaining the soil health by influencing the beneficial microbes, aggregating soil particle and preventing soil erosion, conferring resistance to various stresses, enhance ecosystem productivity, bioremediation of degraded land, serving as soil carbon sink. In this chapter we attempt to discuss different role played by AMF, which make them potential tool for sustainable agriculture and environment. It is tempting to state that AMF served for 3E’s i.e. eco-friendly, economic and enhanced yield.