Ecophysiology of High Salinity Tolerant Plants: 40 (Tasks for Vegetation Science)

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Some specialized structures called salt glands or salt bladders are found in leaves of those plants to regulate the extra salts inside the plant body [ 43 ]. Salt glands found in Limonium axillare are composed of cells which are entirely covered by cuticle which seals the gland from the rest of the plant except for small gaps on the leaf mesophyll side, salts are deposited on the leaf surface through holes on these glands, and in mangroves Avicennia marina , salts are excreted from the upper surface of leaves [ 46 ], and the excreted solutions exceed the NaCl concentration of seawater of about 10 times [ 38 , 45 , 48 ].

Salt Bladders are found in Atriplex , which are comprised of two cells: stalk cell and bladder cell [ 20 , 49 ]. Salt glands are found also in many other halophytes like Aeluropus lagopoides , Tamarix spp. These salt glands could regulate the secretion of salts from leaves to keep their concentrations at low levels and ultimately to maintain ion homeostasis in the plant body. Salt dilution: some halophytes can dilute the accumulated ions in plant tissues to keep cytoplasmic salinity below toxic levels. These plants are considered as salt includers.

Some succulent halophytes living in Qatar include Halopeplis Fig. Halophytes having dilution mechanism are characterized by: 1 thickening in leaves, 2 elongation of cells, 3 higher elasticity of cell wall, 4 smaller relative surface areas, 5 decrease in extensive growth, and 6 high water content per unit of surface areas [ 38 , 52 ].

In addition to the ion accumulation and succulence phenomenon, shedding of old salt-saturated leaves is found in plants having dilution mechanism to avoid the damage caused by extra salt accumulation [ 53 ]. Osmoregulation or osmotic adjustment has been considered as a main secondary mechanism to tolerate salt stress. Osmotic adjustment can be defined as maintenance of positive water balance between soil environment and plant tissues, by lowering their plant.

However, these ions may be sequestered in vacuoles leaving relatively low ions in the cytoplasm. Organic solutes like glycinebetaine, proline, sugars, polyols etc. Thus, salt tolerance in these plants can be attributed mainly to the fact that these plants accumulate low-molecular-mass organic compounds compatible solutes [ 57 - 60 ]. Osmotic adjustment MPa in two Mexican wheat cultivars exposed to salt stress [ 22 ]. These solutes, as non-toxic cytoplasmic osmotica, that play major roles in the physiology and biochemistry of plant cells and have contributed in the process of osmotic adjustment, maintaining turgor and hydration of cellular microstructures, as sources of some carbon and nitrogen skeletons, and osmoprotectants [ 61 , 62 ].

As osmoprotectants, these compounds tend to be excluded from the hydration sphere of proteins and stabilizing the folded protein structure [ 63 - 65 ], maintaining plasma membranes, protecting the transcriptional and translational machineries and intervening in the process of refolding of enzymes as molecular chaperones [ 66 , 67 ]. Moreover, compatible compounds like proline and glycinebetaine can induce the expression of certain stress-responsive genes, including those for enzymes that scavenge reactive oxygen species [ 68 ].

Higher plants are normally colonized by microorganisms, which include bacteria, fungi, algae or protozoa. Microorganisms interact with plants because plants offer a wide diversity of habitats including the a phyllosphere aerial plant part , b rhizosphere zone of influence of the root system , and c endosphere internal transport system. Interactions of epiphytes, rhizophytes or endophytes may be detrimental or beneficial for either the microorganism or the plant, and may be classified as neutralism, commensalism, synergism, mutualism, amensalism, competition or parasitism [ 69 ].

Symbiosis is a relationship that both microorganisms and plants get benefits, and nitrogen fixation and mycorhizae are good examples of such relationships. The plant provides carbon materials to support the growth of microorganisms, while the latter promote plant growth by enhancing minerals uptake e. A mini review by [ 71 ], about the symbiosis relationship between desert plants and Mycorrhizae, indicated that desert ecosystems were not different from other ecosystems in the presence of mycorrhizae.

They also increase plant adaptation to abiotic stresses and some other stresses. Commensalism is another example that various chemicals are secreted from various plant parts like roots and leaves to stimulate the growth of microorganisms. Some other microorganisms can cause some diseases to plants, and this happens when the natural defense systems of the plant are ineffective. In fact, plants may limit microbial penetration by having a thick cell wall and other structural barriers like the cuticle layer that restrict infection.

Volume IV: Cash Crop Halophyte and Biodiversity Conservation

Moreover, the defense system in the plant includes the secretion of gums and some chemicals to limit the invasion of microorganisms [ 72 ]. The following are some examples of microorganisms associated with various plants from the Qatari environment and the perspectives of using these organisms to solve the outstanding problems of health, economy and food security. Qatar is home to Avicennia marina ; it is known as the grey mangrove or white mangrove trees, communities of which form several forests around Qatar shores.

These mangrove swamps are home to a wealth of life. The largest area of mangroves - and the oldest - can be found around Al Thakhira and Al Khor. Other mangrove areas in Qatar originate from fairly recent plantings by the government. Decomposers play an important role in the cycling of material and the flow of energy through an ecosystem. In the mangrove ecosystem, bacteria and fungi break down dead organic matter, such as mangrove leaves.

One teaspoon of mud from a mangrove forest is estimated to contain 10 billion bacteria. These bacteria break down the leaf litter and provide nutrients for the other organisms that live in the mangrove swamp [ 73 , 74 ]. This forms the basis of the food chain in the mangrove swamp. The nutritional value of the leaves is increased by the work of decomposers. Mangrove ecosystems are an important natural resource that should be protected.

The detritus generated by the mangroves is the base of an extensive food web that sustains numerous organisms of ecological and commercial importance. Furthermore, mangrove ecosystems provide indispensable shelter and nurturing sites for many marine organisms. The well-being of mangroves is dependent on the diverse, and largely unexplored, microbial and faunal activities that transform and recycle nutrients in the ecosystem. Conservation strategies for mangroves should consider the ecosystem as a biological entity [ 75 ].

Despite numerous studies on the biogeography, botany, zoology, ichthyology, environmental pollution, and economic impact of mangroves, little is known about the activities of microbes in mangrove waters and sediments. An effort must be made for further studies on microbial activities in mangrove ecosystems and their impact on the productivity of the ecosystem. Various types of microorganisms are found around the mangrove habitats. For example, diverse cyanobacterial communities reside on leaf, root litter, live roots, and often form extensive mats on the surrounding sediments; many of these communities are capable of fixing atmospheric nitrogen.

Many genera widespread in these habitats including Oscillatoria , Lyngbya , Phormidium and Microcoleus are, and as heterocystous genera, Scytonema is common in some areas [ 76 ]. The filamentous cyanobacterium Microcoleus sp. Such cyanobacterial filaments colonize the roots of mangrove by gradual production of biofilm [ 77 ]. Also, bacteria may influence the mangrove ecosystem directly; they contribute inevitably in the recycling of nutrients [ 78 ]. Many potential bacteria were isolated from mangrove ecosystem such as nitrogen-fixers, phosphate solubilizers, photosynthetic anoxygenic sulfur bacteria, methanogenic and methane oxidizing bacteria, which are involved in efficient nutrient recycling [ 79 ].

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Also bacteria and fungi that either produce antibiotics [ 80 , 81 ] or resistant to antibiotics were isolated from mangrove ecosystem [ 82 , 83 ]. Salt-tolerant microorganisms can grow in habitats containing high concentrations of salts. The natural environments for salt-tolerant microbes may be similar to those of the halophytic angiosperms.

The chemical analysis of the materials excreted by the epidermal glands of halophytes revealed the presence of mineral elements and some organic compounds, such substances might be a source of nutrition to the microorganisms living on the plant body [ 84 ]. A study on the desert plants of Egypt [ 85 ] indicated that the fungal species inhabiting the surface of senescent leaves of the succulent halophyte Zygophyllum album L.

In the study of [ 84 ] on some halophyte species growing at the Qatar North East coast showed that the total bacterial count in the rhizosphere was higher than in the non-rhizosphere soil. Moreover, the bacterial counts in the soil supporting the plant species of the coastal zone were higher than those in the soil of the inland zones. Also, Gram- positive cocci predominated in the isolates from rhizosphere and non-rhizosphere soil, and the isolates with white colonies color predominated in the rhizosphere than from phyllosphere since low colonization of bacterial cells were found on the aerial parts that have high contents of mineral ions due to the activity of salt glands in most Halophytes.

Also, the bacterial counts were higher on the green parts of the plant than on the senescent parts, since the latter might have accumulated high concentrations of mineral ions as a mechanism to exclude salt to the aged parts of the plants compared to the growing ones. Moreover, the phyllosphere of the green and senescing parts were characterized by the predominance of Gram-positive bacilli and by the low percentage of isolates producing colored colonies. The general conclusion that can drawn from various published studies that soil environment and phyllosphere of halophytes support the growth of bacteria which seemed to have various mechanisms to deal with the harsh environments like salt marshes and sabkhas.

In fact, bacteria are the most abundant inhabitants of the phyllosphere and the most colonists of leaves.


On the other hand, the bacterial flora of the above ground differs substantially from that at the subterranean plant surfaces. For example, the pigmented bacteria which are rarely found in the rhizosphere, and laminate leaf surfaces and solar radiation affect the ecology of the phyllosphere and promote bacteria to produce pigments as sun screen and will not damage the cell components. There are two general strategies for osmo-adaptation of prokaryotes like bacteria under osmotic stress conditions: 1 accumulation of inorganic ions, and 2 accumulation of low molecular weight organic molecules.

The second strategy of osmo-adaptation, on the other hand, involves the accumulation of a limited range of low-molecular-weight organic solutes. These include many compounds which are called compatible solutes including amino acids like proline, glycinebetaine, simple sugars, polyols, and their derivatives.

Ecophysiology of High Salinity Tolerant Plants (Tasks for Vegetation Science) [Hardcover]

Great deals of attention have been paid to proline and glycinebetaine as compatible solutes accumulated as a result of salt or water stress. Relatively few prokaryotes are capable of de novo synthesis of these compounds. The intracellular concentrations of these solutes can be regulated in accordance with the external salt concentration, provide microorganisms with a large degree of flexibility and the possibility to adapt to a wide range of salt concentrations. However, energetically the production of massive amounts of such solutes can be costly.

Prosopis cineraria is the only species that grow rarely in desert of Qatar. The genus Prosopis contains around 45 species of spiny trees and shrubs found in the subtropical regions of Americas, Africa, Western Asia, and South Asia.

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They often thrive in arid soil and are resistant to drought, on occasion developing extremely deep root systems. The microbiology analyses of P. Gram- positive cocci and spore forming bacilli bacteria are characterized by thick cell wall that is comprised of peptidoglycan amino acid polypeptide and a sugar , and the isolated bacilli genus were spore forming that can be survive in hot, dry conditions, and high irradiation with limited damage to the cell.

These are the most dominant epiphytic form on both leaves and bark. The pigmented bacteria, red yellow, and orange, were isolated from leaves and bark which exposed to long duration of light, that pigments well keep the bacterial cells undamaged and resistant to irradiation. The observed high content of organic matter, soil nutrients, clay and moisture in the sub-canopy locations of P. The bacterial soil populations in the rhizosphere are higher than the non-rhizosphere sits and the lowest bacterial count occurred in the outer canopy soil.

Moreover, the presence of plant litter, animal droppings together with the already existed soil chemical nutrients in the sub canopy positions of P. One of the best documented spatial patterns of nutrient distributions in arid and semiarid ecosystems are the "islands of fertility" associated with shrubs and trees [ 88 ]. The components of rhizosphere system which include microorganisms, plant and soil interact with each other in a way so that the rhizosphere is distinguished from the bulk of the remaining soil.

The activity of root microorganisms is affected by soil environmental factors or by environmental factors operating indirectly through the plant. Moreover, root microorganisms can affect the plant and plant nutrient uptake, directly by colonizing the root and modifying the soil environment around the root.

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  • Bacterial growth is stimulated by a vast range of organic materials released from plant roots, which include carbohydrates, vitamins, amino acids and enzymes. Organic acids and lipids reduce the pH of the rhizosphere and also have a role in the chelation of metals [ 89 ].