Bioprospecting for Rhizobacteria with the Ability to Enhance Drought Tolerance in Lessertia frutescens.

Lessertia frutescens is a multipurpose medicinal plant indigenous to South Africa that is used for the management of cancer, stomach ulcers, wounds, etc. The use and demand for the raw materials from this plant have been increasing steadily over the years, putting strain on the dwindling wild populations. Although cultivation may provide relief to the strained supply, the persistent drought climate poses a threat to the plant's growth and productivity. This study explored three plant-growth-promoting rhizobacteria isolates, TUTLFNC33, TUTLFNC37 and TUTLFWC74, obtained from the root nodules of Lessertia frutescens as potential bioinoculants that can improve yield, biological activities and the production of secondary metabolites in the host plant. Isolate TUTLFNC37 was identified as the most promising isolate for inoculation of Lessertia frutescens under drought conditions as it induced drought tolerance through enhanced root proliferation, osmolyte proline accumulation and stomatal closure. Superior biomass yield, phenolics, triterpenes and antioxidant activity were evident in the extracts of Lessertia frutescens inoculated with TUTLFNC37 and under different levels of drought. Furthermore, the metabolomics of the plant extracts demonstrated the ability of the isolate to withstand drastic changes in the composition of unique metabolites, sutherlandiosides A-D and sutherlandins A-D. Molecular families which were never reported in the plant (peptides and glycerolipids) were detected and annotated in the molecular networks. Although drought had deleterious effects on Lessertia frutescens, isolate TUTLFNC37 alleviated the impact of the stress. Isolate TUTLFNC37 is therefore the most promising, environmentally friendly alternative to harmful chemicals such as nitrate-based fertilizers. The isolate should be studied to establish its field performance, cross infectivity with other medicinal plants and competition with inherent soil microbes.

The Potential of Rhizobacteria to Mitigate Abiotic Stress in Lessertia frutescens.

Lessertia frutescens is a multipurpose medicinal plant indigenous to South Africa. The curative ability of the medicinal plant is attributed to its rich phytochemical composition, including amino acids, triterpenoids, and flavonoids. A literature review of some of the phytochemical compounds, particularly amino acids, in L. frutescens shows a steady decrease in concentration over the years. The reduction of the phytochemical compounds and diminishing biological activities may be attributed to drought and salt stress, which South Africa has been grappling with over the years. Canavanine, a phytochemical which is associated with the anticancer activity of L. frutescens, reduced slightly when the plant was subjected to salt stress. Like other legumes, L. frutescens forms a symbiotic relationship with plant-growth-promoting rhizobacteria, which facilitate plant growth and development. Studies employing commercial plant-growth-promoting rhizobacteria to enhance growth and biological activities in L. frutescens have been successfully carried out. Furthermore, alleviation of drought and salt stress in medicinal plants through inoculation with plant growth-promoting-rhizobacteria is well documented and effective. Therefore, this review seeks to highlight the potential of plant-growth-promoting rhizobacteria to alleviate the effect of salt and drought in Lessertia frutescens.

Effects of UV-B radiation on seed yield of Glycine max and an assessment of F1 generation progeny for carryover effects.

Glycine max (L.) Merr plants were grown outdoors in potted sand exposed to elevated ultraviolet-B (UV-B) radiation provided by filtered fluorescent lamps to determine the effects of UV-B on seed yield and UV-B-induced carryover effects in the F1 generation. Increased UV-B radiation had no detectable effects on reproductive parameters except for a reduction on seed number per plant and an increase in the number of unseeded pods per plant and dry weight of unseeded pods per plant in the field supplemental UV-B experiment. Studies on carryover effects in the greenhouse progeny growth trial also showed no effect of parental treatment with UV-B on biomass production, and most symbiotic-N traits and plant metabolite measured. However, the concentrations of N in nodules and starch in roots were significantly increased in the F1 generation progeny from elevated UV-B radiation relative to their F1 counterparts from ambient radiation. Assessing the effects of seed size on plant growth and symbiotic function in the F1 progeny showed that total biomass, dry matter yield of individual organs (leaves, stems, roots and nodules), total plant N and fixed-N rose with increasing seed size. Seed concentration of flavonoids was also enhanced with increasing seed size. These findings suggest that subtle changes did occur in the F1 generation progeny of parental plants exposed to elevated UV-B with potential to accumulate with further exposure to elevated UV-B radiation.

Responses to ultraviolet-B radiation by purely symbiotic and NO3-fed nodulated tree and shrub legumes indigenous to southern Africa.

Purely symbiotic and NO3-fed nodulated seedlings of Virgilia oroboides (Bergius) T.M. Salter, Cyclopia maculata (L.) Vent and Podalyria calyptrata Willd. were exposed to biologically effective ultraviolet-B radiation (UV-B) to assess the effects of above- and below-ambient UV-B on growth, symbiotic function and metabolite concentrations. Seedlings were grown outdoors either on tables under ambient or 34 or 66% above-ambient UV-B conditions (UV-B100 control, UV-B134 and UV-B166, respectively), or in chambers providing below-ambient (22% of ambient) UV-B (UV-B22) along with a UV-A control and a photosynthetically active radiation (PAR) control. Exposure of seedlings to UV-B166 radiation reduced (P < or = 0.05) leaf and stem dry mass by 34 and 39%, respectively, in C. maculata, and reduced leaf nitrogen concentration (%N) by 12% in V. oroboides. Nodule %N in C. maculata and stem %N in P. calyptrata also decreased (P < or = 0.05) in response to UV-B22 radiation compared with the UV-A control, but not compared with the PAR control. Concentrations of flavonoids, soluble sugars and starch were unaltered by the UV-B treatments. Application of 1 mM NO3 to UV-B166-treated seedlings increased whole-plant dry mass of V. oroboides and P. calyptrata by 47 and 52%, respectively. Dry mass of organs, nodule %N and total N concentration of these species also increased with NO3 application. However, NO3 supply decreased (P < or = 0.05) nodule dry mass, stem %N and leaf %N as well as root and leaf anthocyanin concentrations in C. maculata. In terms of UV-B x N interactions, dry mass of stems, roots, nodules and total biomass of NO3-fed C. maculata seedlings were reduced, and nodule %N, total N and leaf anthocyanins were depressed by the UV-B134 and UV-B166 treatments relative to UV-B100-treated seedlings. Although we found that above-ambient UV-B had no effects on growth and symbiotic function of V. oroboides and P. calyptrata seedlings, feeding NO3 to these species increased (P < or = 0.05) seedling growth. In contrast, purely symbiotic C. maculata seedlings were sensitive to the UV-B166 radiation treatment, and adding NO3 further increased their sensitivity to both the UV-B134 and UV-B166 treatments.

Response of purely symbiotic and NO3-fed nodulated plants of Lupinus luteus and Vicia atropurpurea to ultraviolet-B radiation.

The effects of elevated UV-B radiation on growth, symbiotic function and concentration of metabolites were assessed in purely symbiotic and NO3-fed nodulated plants of Lupinus luteus and Vicia atropurpurea grown outdoors either on tables under supplemental UV-B radiation or in chambers covered with different types of plexi-glass to attenuate solar ultraviolet radiation. Moderately and highly elevated UV-B exposures simulating 15% and 25% ozone depletion as well as sub- ambient UV-B did not alter organ growth, plant total dry matter and N content per plant in both L. luteus and V. atropurpurea. In contrast, elevated UV-B increased (P <0.05) flavonoid and anthocyanin concentrations in roots and leaves of L. luteus, but not of V. atropurpurea. Feeding nodulated plants of L. luteus under elevated UV-B radiation with 2 mM NO3 increased (P <0.05) nodule, leaf and total dry matter, and whole plant N content. With V. atropurpurea, NO3 reduced (P <0.05) nodule activity, root %N and concentrations of flavonoids, anthocyanins in roots and leaves and soluble sugars in roots, in contrast to an observed increase (P <0.05) in nodule dry matter per plant. Similarly, supplying 2 mM NO3 to L. luteus plants exposed to sub-ambient UV-B radiation significantly reduced individual organ growth, plant total biomass, nodule dry matter, nodule %N, and whole plant N content, as well as root concentrations of flavonoids, anthocyanins, soluble sugars, and starch of L. luteus, but not V. atropurpurea plants. These results show no adverse effect of elevated UV-B radiation on growth and symbiotic function of L. luteus and V. atropurpurea plants. However, NO3 supply promoted growth in L. luteus plants exposed to the highly elevated UV-B radiation.

Effects of UV-B radiation on plant growth, symbiotic function and concentration of metabolites in three tropical grain legumes.

Vigna unguiculata (L.) Walp. (cowpea), Glycine max (L.) Merr (soybean) and Phaseolus vulgaris (L.) (common bean) plants were exposed to UV-B radiation at above- and below-ambient levels, and their effects on growth, symbiotic performance and root concentration of metabolites were assessed. Moderately and highly elevated UV-B exposures averaging 32 and 62% above ambient had no effect on plant total dry matter, nodule number, nodule mass, nodule size, N fixed or root concentration of flavonoids, anthocyanins, soluble sugars and starch in the three species studied. However, N concentrations were markedly reduced in roots of G. max and P.vulgaris, and in leaves of P. vulgaris, which contrasted with the significant increase in stems and leaves of V.unguiculata. Below-ambient UV-B exposures averaging 22% of ambient also altered growth and metabolism of these legumes. Total plant dry matter, nodule number, nodule dry mass, N fixed and root starch concentrations in V.unguiculata decreased relative to both visible and UV-A radiation controls, whereas in G. max and P. vulgaris, these parameters were not altered. Root concentrations of flavonoids and anthocyanins in all species tested were also unchanged with below-ambient UV-B exposures. Taken together, growth and symbiotic function of these species remained unaltered with exposure to above-ambient UV-B, but differed in their response to below-ambient UV-B radiation.

Effects of elevated ultraviolet-B radiation on native and cultivated plants of southern Africa.

Seventeen herb, shrub and tree species of commercial and ecological importance in southern Africa were exposed at one location to ultraviolet-B (UV-B, 280-315 nm) radiation approx. 35 % above clear-sky background (control). The aims were to assess how UV-B affects canopy area, dry mass, and some biochemical and morphological properties of leaves, and to investigate whether differences between species are related to growth form of the plants. There was no pattern of response to UV-B related to growth form. Leaves of trees had altered chlorophyll a and b, carotenoid and flavonoid concentrations, but those of shrubs or herbs did not. Non-structural carbohydrates were unaffected. Smaller canopy areas and dry masses were observed under enhanced UV-B, but these were not statistically different among growth forms. There was a general insensitivity of species to elevated UV-B. Only five species had significantly altered leaf biochemical and morphological properties, canopy area and dry mass, the changes differing in magnitude. There was no consistent pattern of change in leaf thickness or biochemical composition with increased UV-B. Correlation analyses did not support the view that growth is less negatively affected in species with thick leaves or in those where leaf thickness increases, or in species with naturally high leaf flavonoid contents or that are able to synthesize additional flavonoids in response to UV-B enhancement. The analyses did not support the hypothesis that growth was inhibited by starch accumulation in leaves under elevated UV-B. However, changes in leaf shape did correlate with canopy area and dry mass, showing the importance of photomorphogenetic changes caused by UV-B which affect species' performance. We conclude that generalizations on plant sensitivity to UV-B based on growth form and functional type could be misleading, and that the great majority of economically important species of the region are likely to be insensitive to future UV-B increases. Notable exceptions include the Colophospermum mopane tree ecotypes chota and leslie and the arable annual Vigna unguiculata, both of which are traditional sources of livelihood to rural African populations and of importance to African industry and agriculture.