Abstract
Bearberry (Arctostaphylos uva-ursi) is a medicinal plant traditionally employed for the treatment of urinary tract infections due to high contents of arbutin (hydroquinone β-D-glucoside), which is now mainly used as a natural skin-whitening agent in cosmetics. Bearberry has also been proposed as a natural antioxidant additive due to the high contents of phenolic compounds in leaves. We studied the variation on phenolic compounds in 42 wild populations of bearberry, aiming to elucidate if intrinsic biological, climatic, and/or geographic factors affect phenolic contents across its natural distribution in the Iberian Peninsula. Bearberry leaves were collected during autumn over a three-year period (2014–2016) in populations across a latitude and altitude gradient. Methanolic extracts showed a wide range of variation in total phenols content, and different phenolic profiles regarding arbutin (levels of this major constituent varied from 87 to 232 mg/g dr wt), but also catechin and myricetin contents, which were affected by geographic and climatic factors. Moderate levels of variation on genome size—assessed by flow cytometry—and on two plastid DNA regions were also detected among populations. Genetic and cytogenetic differentiation of populations was weakly but significantly associated to phytochemical diversity. Elite bearberry genotypes with higher antioxidant capacity were subsequently identified.
Highlights
The synthesis of plant specialized metabolites varies in time, and space, as it plays a crucial role in plant adaptation to environmental conditions, Plants 2020, 9, 1250; doi:10.3390/plants9091250 www.mdpi.com/journal/plantsPlants 2020, 9, 1250 while genetic variation accounts for chemodiversity [1]
Analysis of extracts prepared from leaves collected in 2015 from 94 plants (Figure 2b) showed a wide phytochemical variation, from 110.5 ± 3.6 mg GAE/g dr wt (PI-4) to 200.9 ± 9.8 mg GAE/g dr wt (LO-4) in total phenolic contents, while arbutin contents ranged between 87.1 ± 0.4 mg/g dr wt (ET-2) and 211.5 ± 5.9 mg/g dr wt (LI-2)
For the major phenolic constituents, we found that arbutin contents differed from the low mean contents of this flavonoid detected in populations AF and LC (32.8 ± 9.8 ranged from 91.1 ± 5.0 (LB-2) to 232.4 ± 2.8 mg/g dr wt (PT-5), while catechin contents ranged from front to 5.7 ± 1.9 and 5.3 ± 0.5 mg/g dr wt, respectively)
Summary
The synthesis of plant specialized metabolites varies in time (i.e., ontogeny, phenology, and induced defenses), and space, as it plays a crucial role in plant adaptation to environmental conditions, Plants 2020, 9, 1250; doi:10.3390/plants9091250 www.mdpi.com/journal/plants. Plants 2020, 9, 1250 while genetic variation accounts for chemodiversity [1]. Among these compounds, phenols have a diverse array of mono- and polymeric structures that fulfil a broad range of physiological roles [2]. The biosynthesis of specialized metabolites is greatly affected by environmental factors such as temperature, precipitation, or solar radiation, which are in turn often subjected to latitudinal, longitudinal, or altitudinal gradients. Phenolic compounds accumulation is a general response to enhanced levels of UV-B (280–315 nm) radiation. Specific compound variation has been reported in plants growing in the Mediterranean region during the summer and at high altitudes, where a higher incidence of UV-B occurs and cinnamic acids and flavonoids showed the highest UV absorption rates [3].
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