Plant secondary metabolites are unique sources for pharmaceuticals, food additives, flavors, and industrially important biochemicals. Accumulation of such metabolites often occurs in plants subjected to stresses including various elicitors or signal molecules. Secondary metabolites play a major role in the adaptation of plants to the environment and in overcoming stress conditions. Environmental factors viz. temperature, humidity, light intensity, the supply of water, minerals, and CO2 influence the growth of a plant and secondary metabolite production. Drought, high salinity, and freezing temperatures are environmental conditions that cause adverse effects on the growth of plants and the productivity of crops. Plant cell culture technologies have been effective tools for both studying and producing plant secondary metabolites under in vitro conditions and for plant improvement. This brief review summarizes the influence of different abiotic factors include salt, drought, light, heavy metals, frost etc. o...

https://www.tandfonline.com/doi/pdf/10.4161/psb.6.11.17613

Influence of abiotic stress signals on secondary metabolites in plants

Compared with the other major nutrients, phosphorus is by far the least mobile and available to plants in most soil conditions. Although phosphorus is abundant in soils in both organic and inorganic forms, it is frequently a major or even the prime limiting factor for plant growth. The bioavailability of soil inorganic phosphorus in the rhizosphere varies considerably with plant species, nutritional status of soil and ambient soil conditions. To circumvent phosphorus deficiency, phosphate-solubilizing microorganisms (PSM) could play an important role in supplying phosphate to plants in a more environmentally-friendly and sustainable manner. The solubilization of phosphatic compounds by naturally abundant PSM is very common under in vitro conditions; the performance of PSM in situ has been contradictory. The variability in the performance has thus greatly hampered the large-scale application of PSM in sustainable agriculture. Numerous reasons have been suggested for this, but none of them have been conclusively investigated. Despite the variations in their performance, PSM are widely applied in agronomic practices in order to increase the productivity of crops while maintaining the health of soils. This review presents the results of studies on the utilization of PSM for direct application in agriculture under a wide range of agro-ecological conditions with a view to fostering sustainable agricultural intensification in developing countries of the tropics and subtropics.

/pdf/role-of-phosphate-solubilizing-microorganisms-in-sustainable-2n609bzoeh.pdf

Role of phosphate-solubilizing microorganisms in sustainable agriculture — A review

Plants acquire phosphorus from soil solution as phosphate anion. It is the least mobile element in plant and soil contrary to other macronutrients. It precipitates in soil as orthophosphate or is adsorbed by Fe and Al oxides through legend exchange. Phosphorus solubilizing bacteria play role in phosphorus nutrition by enhancing its availability to plants through release from inorganic and organic soil P pools by solubilization and mineralization. Principal mechanism in soil for mineral phosphate solubilization is lowering of soil pH by microbial production of organic acids and mineralization of organic P by acid phosphatases. Use of phosphorus solubilizing bacteria as inoculants increases P uptake. These bacteria also increase prospects of using phosphatic rocks in crop production. Greater efficiency of P solubilizing bacteria has been shown through co-inoculation with other beneficial bacteria and mycorrhiza. This article incorporates the recent developments on microbial P solubilization into classical knowledge on the subject.

/pdf/phosphorus-solubilizing-bacteria-occurrence-mechanisms-and-3q13ez9xcn.pdf

Phosphorus solubilizing bacteria: Occurrence, mechanisms and their role in crop production

Pollution of the biosphere by the toxic metals is a global threat that has accelerated dramatically since the beginning of industrial revolution. The primary source of this pollution includes the industrial operations such as mining, smelting, metal forging, combustion of fossil fuels and sewage sludge application in agronomic practices. The metals released from these sources accumulate in soil and in turn, adversely affect the microbial population density and physico-chemical properties of soils, leading to the loss of soil fertility and yield of crops. The heavy metals in general cannot be biologically degraded to more or less toxic products and hence, persist in the environment. Conventional methods used for metal detoxification produce large quantities of toxic products and are cost-effective. The advent of bioremediation technology has provided an alternative to conventional methods for remediating the metal-poisoned soils. In metal-contaminated soils, the natural role of metal-tolerant plant growth promoting rhizobacteria in maintaining soil fertility is more important than in conventional agriculture, where greater use of agrochemicals minimize their significance. Besides their role in metal detoxification/removal, rhizobacteria also promote the growth of plants by other mechanisms such as production of growth promoting substances and siderophores. Phytoremediation is another emerging low-cost in situ technology employed to remove pollutants from the contaminated soils. The efficiency of phytoremediation can be enhanced by the judicious and careful application of appropriate heavy-metal tolerant, plant growth promoting rhizobacteria including symbiotic nitrogen-fixing organisms. This review presents the results of studies on the recent developments in the utilization of plant growth promoting rhizobacteria for direct application in soils contaminated with heavy metals under a wide range of agro-ecological conditions with a view to restore contaminated soils and consequently, promote crop productivity in metal-polluted soils across the globe and their significance in phytoremediation.

Role of plant growth promoting rhizobacteria in the remediation of metal contaminated soils

Most agronomic soils contain large reserves of total phosphorus [P], but the fixation and precipitation of P cause P deficiency, and in turn, restrict the growth of crops severely. Phosphorus replenishment, especially in sustainable production systems, remains a major challenge as it is mainly fertilizer-dependent. Though the use of chemical P fertilizers is obviously the best means to circumvent P deficiency in different agro-ecosystems, their use is always limited due to its spiralling cost. A greater interest has, therefore, been generated to find an alternative yet inexpensive technology that could provide sufficient P to plants while reducing the dependence on expensive chemical P fertilizers. Among the heterogeneous and naturally abundant microbes inhabiting the rhizosphere, the phosphate solubilizing microorganisms (PSM) including bacteria have provided an alternative biotechnological solution in sustainable agriculture to meet the P demands of plants. These organisms in addition to providing P to plants also facilitate plant growth by other mechanisms. Despite their different ecological niches and multiple functional properties, P-solubilizing bacteria have yet to fulfil their promise as commercial bio-inoculants. Current developments in our understanding of the functional diversity, rhizosphere colonizing ability, mode of actions and judicious application are likely to facilitate their use as reliable components in the management of sustainable agricultural systems.

Plant growth promotion by phosphate solubilizing bacteria

Crops absorb phosphorous in the form of soluble orthophosphate ion The solubility of phosphate is inhibited by the presence of iron and aluminium in acidic soils and calcium in neutral and alkaline soils This leads to fixation of phosphorous, making it not available to crop plants The phosphate solubilizing bacteria (phosphobacteria) secretes some kinds of organic acids which act on insoluble phosphates and convert the same into soluble form, thus providing phosphorous to plant An experiment was conducted to enumerate the population density of phosphobacteria in the rhizosphere soils of brinjal, chilly, cotton, green grain, groundnut, maize, paddy, ragi, sorghum and turmeric using Ketznelson and Bose medium following dilution plate technique Efforts have been made to isolate phosphobacteria from these soils and isolated strains were inoculated in specific media containing specific substrates to produce growth regulating substances such as IAA and GA3 and phosphatase enzyme The result showed that the population levels of phosphobacteria were higher in the rhizosphere soil of groundnut plant Further, all the strains of phosphobacteria were able to produce phytohormones and phosphatase enzyme under in vitro conditions

https://www.ajol.info/index.php/ajb/article/download/137805/127368

In vitro production of growth regulators and phosphatase activity by phosphate solubilizing bacteria

Distribution Pattern and Screening of Phosphate Solubilizing Bacteria Isolated from Different Food and Forage Crops

Callus cultures were initiated from nodal segments and leaf explants of Gymnema sylvestre on Murashige and Skoog (1962) medium containing basic salts and 30 g/l sucrose supplemented with different concentrations (0.10, 0.25, 0.5, 1.0, 2.0 and 5.0 mg/l) of 2,4-dichlorophenoxy acetic acid (2,4-D), �-naphthalene acetic acid (NAA), indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), kinetin (KN) and 6-benzyladenine (BA). Callus induction was observed in 0.5 mg/l of 2, 4-D supplemented medium for both explants. At the initial stage, some parts of explants enlarged and gave raise to pale yellowish calli after 2-3 weeks of incubation. The harvested cell biomass was subjected to extraction of active principles. In this study, cell biomass extracts were compared with extracts from leaves of naturally growing gymnema plants. HPLC analysis of these extracts showed that the main components of the active principles namely gymnemic acids and gymnemagenin were present in sufficiently large amounts in the cultured undifferentiated cells.

/pdf/in-vitro-studies-on-effects-of-plant-growth-regulators-on-2399kv6eyu.pdf

In vitro studies on effects of plant growth regulators on callus and suspension culture biomass yield from Gymnema sylvestre R.Br

The objective of this study was to develop a rapid system for regeneration of the important medicinal plant, Ocimum gratissimum L, from nodal explant. Single node explants were inoculated on basal MS (Murashige and Skoog, 1962) medium containing 3% (w/v) sucrose, supplemented with different concentrations and combinations of 6-benzylaminopurine (BAP), kinetin (KN), indole-3-acetic acid (IAA) or indole-3-butyric acid (IBA) for direct plant regeneration. Maximum numbers of shoot (14.3± ± ± ±1.5) were observed on the medium containing 0.5 mg/l BAP and 0.25 mg/l IAA after four weeks of culture. Regenerated shoots were separated and rooted on same half strength MS medium supplemented with 0.5 mg/l of IAA alone for three weeks. Well-developed complete plantlets were transferred on to specially made plastic cup containing soilrite. Acclimatized plantlets were successfully grown in garden soil.

/pdf/in-vitro-multiplication-of-ocimum-gratissimum-l-through-2dh0copc4p.pdf

C. Gopi

Papers

In vitro production of growth regulators and phosphatase activity by phosphate solubilizing bacteria

Distribution Pattern and Screening of Phosphate Solubilizing Bacteria Isolated from Different Food and Forage Crops

In vitro studies on effects of plant growth regulators on callus and suspension culture biomass yield from Gymnema sylvestre R.Br

In vitro multiplication of Ocimum gratissimum L. through direct regeneration

Somatic embryogenesis and plant regeneration from leaf callus of Ocimum basilicum L.