Effects of water stress on phenolic content and antioxidant activity of African nightshades

Abstract

Okello OP, Gweyi JPO, Nawiri Mp, Musila W. 2017. Effects of water stress on phenolic contents and antioxidant activity of African nightshades. Biofarmasi J Nat Prod Biochem 15: 79-95. This study aimed at mapping out the distribution of different African Nightshade species in Siaya and Kisii Counties of Kenya and to determine water stress effect on total antioxidant capacity and total phenolic content of two selected African nightshade namely, giant nightshade (Solanum scabrum) and black nightshade (Solanum villosum). Before selection of the two varieties, the study involved farmer field visits, mapping of nightshades present and administration of semi-structured questionnaires to farmers to determine the indigenous vegetables being grown, the nightshade species grown and factors affecting their production. The experiments were conducted both in the field and greenhouse conditions. Watering intervals were at 15 cbars, 50 cbars, and 85 cbars. Data on the number of secondary buds, leaf area, shoot height, shoot and root dry weights were gathered. The total antioxidant capacity and the total phenolic content were recorded using DPPH radical scavenging method and Folin-Ciolcalteu method, respectively. The data collected were subjected to ANOVA. In both counties where production was 100% under small scale, Solanum scabrum was the main variety grown is Siaya County (36%) while in Kisii the main variety was Solanum villosum (32%). There were significant differences (P≤0.05) among treatments in leaf area, plant height, shoot biomass, number of secondary buds, leaf and root total phenolic content and leaf and root antioxidant activity. At all stress levels, Solanum scabrum exhibited the tallest plants with a maximum height of 45.17cm at 15cbars, while Solanum villosum had the shortest plants at all stress levels, with the shortest one being recorded at 16.65 cm at 85 cbars. S. scabrum also had the highest root dry weight (7.78g), shoot dry weight (50.78g) and highest leaf area of (304.45cm2). However, Solanum villosum had the highest number of secondary buds at all stress levels with the highest being 24 at 15 cbars. Concerning phytochemicals, Solanum villosum had a higher concentration of both the total phenolics and antioxidant activity in the shoots (46.41g GAE/Kg DM total phenolic content and 52.68% total antioxidant activity). Meanwhile, Solanum scabrum had a higher concentration in the roots (25.06gGAE/Kg DM total phenolic content and 27.18% total antioxidant activity). Water stress cause a decline in all growth parameters but increased phytochemical accumulation in nightshade accessions grown. It is therefore suggested that for better yields, irrigation should be performed at every 15 cbars, however for adequate phytochemical accumulation, the irrigation should be carried out at 50 cbars. Further research to explore and quantify other phytochemical components as affected by different watering regimes need to be undertaken.

The effect of different ammonium to nitrate ratios on antioxidant activity, morpho-physiological and phytochemical traits of Moldavian balm (Dracocephalum moldavica)

“…In addition, results suggested that coumaric acid and quercetin are potent antioxidants with proven therapeutic efficacy 81 , 82 . Our experiment is also in consistent with other researches (Jakovljević et al 84 , Okello et al 83 , Prinsi et al 31 ). On a large scale, high phenolics content are directly related to higher resistance of plants to pests and diseases, and thus a precise regulation of N supplementation could present agroecosystem related advantages by reducing pesticide usage in agriculture.…”

Response of Black Nightshade to Different Cropping Systems and the Effect on Physiological Parameters and Mineral Composition

“…Notably, the leaf area yielded by Ogembo Oyaro et al [65] ranged from 120 to 130 cm 2 on two different African nightshades grown in a greenhouse is in accordance with the results of the present study. On the contrary, the results of leaf area (304.45 cm 2 ) obtained by Okello et al [64] are higher than leaf area of 121.7 cm 2 obtained from the current study under the greenhouse condition. Leaf area development is directly related to the yield of African nightshades since the edible part is the leaf [64].…”

“…However, in our study, low-chlorophyll content observed in greenhouse-grown plants may be linked to fertiliser deficiency and high humidity and temperatures [63]. A study by Okello et al [64] reported that Solanum scabrum had a higher leaf area of 304.45 cm 2 under greenhouse cultivation subjected to the different levels of irrigation water stress. Notably, the leaf area yielded by Ogembo Oyaro et al [65] ranged from 120 to 130 cm 2 on two different African nightshades grown in a greenhouse is in accordance with the results of the present study.…”

Dynamics of accumulation of phenolic compounds, anthocyanins, and photosynthetic pigments in the vegetative organs of the wheat plants under continuous drought stress

“…Phenolic compounds, which are secondary metabolites, perform various defense functions in plant organs during stress. Studies conducted by Okello et al (2017) showed that Solanum scabrum and Solanum villosum plants respond differently to water deficiency. As a result of stress, phenolic compounds accumulate more in the roots of S. scabrum and the leaves of S. villosum.…”

“…The phenols accumulated in the roots act as osmolytes, participate in the maintenance of turgor in the root cells and increase the osmotic potential. In the leaves, phenolic compounds participate in the defense of enzymes under stress, protection of the structure and integrity of the membrane, and utilization of reactive oxygen species (Okello et al, 2017).…”