https://zenodo.org/record/1003263/files/Cushnie%20et%20al%20%282011%29%20post-peer%20reviewed%20version.pdf

Recent advances in understanding the antibacterial properties of flavonoids

This review presents a comprehensive and systematic study of the field of plant biostimulants and considers the fundamental and innovative principles underlying this technology. The elucidation of the biological basis of biostimulant function is a prerequisite for the development of science-based biostimulant industry and sound regulations governing these compounds. The task of defining the biological basis of biostimulants as a class of compounds, however, is made more complex by the diverse sources of biostimulants present in the market, which include bacteria, fungi, seaweeds, higher plants, animals and humate-containing raw materials, and the wide diversity of industrial processes utilized in their preparation. To distinguish biostimulants from the existing legislative product categories we propose the following definition of a biostimulant as ‘a formulated product of biological origin that improves plant productivity as a consequence of the novel or emergent properties of the complex of constituents, and not as a sole consequence of the presence of known essential plant nutrients, plant growth regulators, or plant protective compounds’. The definition provided here is important as it emphasizes the principle that biological function can be positively modulated through application of molecules, or mixtures of molecules, for which an explicit mode of action has not been defined. Given the difficulty in determining a ‘mode of action’ for a biostimulant, and recognizing the need for the market in biostimulants to attain legitimacy, we suggest that the focus of biostimulant research and validation should be upon proof of efficacy and safety and the determination of a broad mechanism of action, without a requirement for the determination of a specific mode of action. While there is a clear commercial imperative to rationalize biostimulants as a discrete class of products, there is also a compelling biological case for the science-based development of, and experimentation with biostimulants in the expectation that this may lead to the identification of novel biological molecules and phenomenon, pathways and processes, that would not have been discovered if the category of biostimulants did not exist, or was not considered legitimate.

/pdf/biostimulants-in-plant-science-a-global-perspective-1r6nv19z4e.pdf

Biostimulants in Plant Science: A Global Perspective.

Somatic embryogenesis - Stress-induced remodeling of plant cell fate.

Traditional medicine has remained as the most affordable and easily accessible source of treatment in the primary healthcare system of resource poor communities in Zimbabwe. The local people have a long history of traditional plant usage for medicinal purposes. Despite the increasing acceptance of traditional medicine in Zimbabwe, this rich indigenous knowledge is not adequately documented. Documentation of plants used as traditional medicines is needed so that the knowledge can be preserved and the utilized plants conserved and used sustainably. The primary objective of this paper is to summarize information on traditional uses of medicinal plants in south-central Zimbabwe, identifying research gaps and suggesting perspectives for future research. This study is based on a review of the literature published in scientific journals, books, reports from national, regional and international organizations, theses, conference papers and other grey materials. A total of 93 medicinal plant species representing 41 families and 77 genera are used in south-central Zimbabwe. These plant species are used to treat 18 diseases and disorder categories, with the highest number of species used for gastro-intestinal disorders, followed by sexually transmitted infections, cold, cough and sore throat and gynaecological problems. Shrubs and trees (38% each) were the primary sources of medicinal plants, followed by herbs (21%) and climbers (3%). The therapeutic claims made on medicinal plants documented in south-central Zimbabwe are well supported by literature, with 82.8% of the plant species having similar applications in other regions of Zimbabwe as well as other parts of the world and 89.2% having documented biological and pharmacological properties. This study illustrates the importance of traditional medicines in the treatment and management of human diseases and ailments in south-central Zimbabwe. Traditional medicines still play an important role in meeting basic health care of local communities in Zimbabwe.

/pdf/traditional-use-of-medicinal-plants-in-south-central-59iy4yc1j3.pdf

Traditional use of medicinal plants in south-central Zimbabwe: review and perspectives

The advancements made in tissue culture techniques has made it possible to regenerate various horticultural species in vitro as micropropagation protocols for commercial scale multiplication are available for a wide range of crops. Clonal propagation and preservation of elite genotypes, selected for their superior characteristics, require high degree of genetic uniformity amongst the regenerated plants. However, plant tissue culture may generate genetic variability, i.e., somaclonal variations as a result of gene mutation or changes in epigenetic marks. The occurrence of subtle somaclonal variation is a drawback for both in vitro cloning as well as germplasm preservation. Therefore, it is of immense significance to assure the genetic uniformity of in vitro raised plants at an early stage. Several strategies have been followed to ascertain the genetic fidelity of the in vitro raised progenies comprising morpho-physiological, biochemical, cytological and DNA-based molecular markers approaches. Somaclonal variation can pose a serious problem in any micropropagation program, where it is highly desirable to produce true-to-type plant material. On the other hand, somaclonal variation has provided a new and alternative tool to the breeders for obtaining genetic variability relatively rapidly and without sophisticated technology in horticultural crops, which are either difficult to breed or have narrow genetic base. In the present paper, sources of variations induced during tissue culture cycle and strategies to ascertain and confirm genetic fidelity in a variety of in vitro raised plantlets and potential application of variants in horticultural crop improvement are reviewed.

/pdf/somaclonal-variations-and-their-applications-in-34x0z8l3la.pdf

Somaclonal variations and their applications in horticultural crops improvement

Plant tissue culture has become one of the fundamental tools of plant science research. It is extensively employed in the production, conservation and improvement of plant resources. The presence of somaclonal variation in populations derived from tissue culture is affecting the use of tissue culture negatively and has remained a major problem. Conversely, it is a source of new desirable clones/variants with better agronomic traits. In this review, we summarize the possible causes, detection methods and desirability of variants. Somaclonal variation is one of the most researched and reviewed topics. Hence, we restricted ourselves to outlining various examples which may be used as important references for researchers who intend to identify and/or characterize somaclonal variants while using tissue culture for research and production. Emphasis is placed on the negative effects of somaclonal variation. However, this review also includes examples of some useful variants generated as a result of somaclonal variation.

Somaclonal variation in plants: causes and detection methods

Since the discovery of topolins as naturally occurring aromatic cytokinins (CKs), they have emerged as genuine alternatives to the long serving CKs such as benzyladenine, zeatin and kinetin in plant tissue culture (PTC). Globally, the past 15 years has witnessed a surge in the use of topolins and their derivatives in research laboratories. Topolins, especially the meta-topolin and its derivatives have been employed for culture initiation, protocol optimization and for counteracting various in vitro induced physiological disorders in many species. Evidence from various studies indicate the rising popularity and advantages (although not universal for all species) of topolins compared to other CKs. In this review, we assess the use of topolins in PTC with emphasis on their metabolism, structure–activity relations and effect on morphogenesis in vitro. In addition, the review provides a detailed list of species that have been used to study the effect of topolins in comparison with other CKs, the growth parameters affected and recommended concentrations are also provided.

Topolins: A panacea to plant tissue culture challenges?

Aloe species are highly-prized for their ornamental value and have been utilized for centuries in traditional medicine. Due to their habitat loss and exploitation for medicinal and ornamental plant trade, many species in this genus have become threatened. One of the most important globally rated medicinal species in Aloe genus is A. arborescens. The current study evaluated the roles of different aromatic cytokinin types and concentrations on direct organogenesis, in vitro bioactive secondary metabolite production and antioxidant activity of regenerated shoots of A. arborescens. There was an increase in the number of adventitious shoots produced per explant with an increase in concentration in cultures treated with meta-topolin (mT), meta-topolin riboside (mTR), meta-methoxytopolin (MemT) and benzyladenine riboside (BAR), reaching an optimum at either 5.0 or 7.5 μM. Overall, the treatment with 5.0 μM mT gave the largest number of transplantable shoots (regenerated shoots with length greater than 10 mm). Rooted shoots were successfully acclimatized after 8 weeks with a survival frequency above 90 % and no observable morphological abnormalities. Variable amounts of total iridoids, phenolics, flavonoids and condensed tannins were detected in regenerated shoots from all the cytokinin treatments. An increased free-radical scavenging activity with an increase in concentration was recorded in regenerated shoots from mT and mTR treatments, reaching an optimum at 7.5 μM concentration. The present study shows that the choice of cytokinin type and concentration exogenously supplied during tissue culture markedly influences not only shoot proliferation but also the in vitro production of bioactive secondary metabolites.

In vitro plant regeneration, secondary metabolite production and antioxidant activity of micropropagated Aloe arborescens Mill

Medicinal plants: An invaluable, dwindling resource in sub-Saharan Africa.

The effects of five topolins (meta-Topolin, mT; meta-Topolin riboside, mTR; meta-Methoxy topolin, MemT; meta-Methoxy topolin riboside, MemTR and meta-Methoxy topolin 9-tetrahydropyran-2-yl, MemTTHP) on the phenolic content and subsequent acclimatization potential of micropropagated ‘Williams’ bananas were compared to benzyladenine (BA). Sterile shoot-tip explants were cultured on modified Murashige and Skoog (MS) media containing 10, 20 or 30 μM of the above aromatic cytokinins (CKs) for 42 days. Phenolic contents were quantified spectrophotometrically. Growth parameters and photosynthetic pigments of the greenhouse-acclimatized plants were determined after 5 months. Total phenolic levels were highest in 10 μM mT-treated plantlets within the aerial parts and 30 μM MemTTHP for the underground parts. In the underground parts, 10 μM mT resulted in the production of the highest amount of proanthocyanidins which was approximately five-fold higher than in the control plants. Furthermore, 10 μM MemTTHP-treated plantlets had significantly higher total flavonoids (30.1 ± 0.24 mg CE/g DW) within the aerial parts. Plantlets regenerated using MemT, MemTR and MemTTHP had significantly longer roots and better shoot/root ratios compared to the control and BA-treated plants. In terms of root fresh weight, it was significantly higher in MemT-treated plantlets than in the control and BA treatments. Chlorophyll a/b ratio was significantly improved with the use of MemT, mTR and mT compared to control. Current findings indicate the potential of topolins in stimulating the accumulation of phenolic compounds in micropropagated plantlets. In view of the importance of plant secondary metabolites, their substantial accumulation probably enhanced the acclimatization and subsequent ex vitro survival of the micropropagated plantlets. Topolins, particularly, the new derivative MemTTHP could be an alternative CK for the micropropagation of plant species based on their stimulatory effect on ex vitro rooting that inevitably enhances acclimatization competence. Furthermore, topolins are demonstrated as potential elicitors in micropropagation.

Adeyemi O. Aremu

Papers

Somaclonal variation in plants: causes and detection methods

Topolins: A panacea to plant tissue culture challenges?

In vitro plant regeneration, secondary metabolite production and antioxidant activity of micropropagated Aloe arborescens Mill

Medicinal plants: An invaluable, dwindling resource in sub-Saharan Africa.

Assessment of the role of meta-topolins on in vitro produced phenolics and acclimatization competence of micropropagated ‘Williams’ banana