Peripheral defence strategy: variation of barbaloin content in the succulent leaf parts of Aloe arborescens Miller (Liliaceae)

Abstract

A h a r b m c m is a large, multi-stemmed shrub and is one of the very common Aloe species along the Indian Ocean coast of southern Africa, from the Cape, in the south, to Zimbabwe and Malawi in the north. It is used as a hedge plant to protect agricultural fields or stock and as a horticultural plant in gardens. Barbaloin, a secondary phenolic metabolite, is distributed in the plants as part of a peripheral defence strategy. Barbaloin content was found to be highest in the youngest leaves. Within these, concentration varied at its highest in the terminal third of the leaf, at its lowest in the basal third; higher in the terminal, adaxial, leaf margin and lower in the basal, abaxial, leaf centre. The more times a leaf is cut, the higher the barbaloin content of the new growth from the leaf base that remains on the plant. This may deter animals such as elephants and kudu from eating the new growths. They may prefer to eat other plants that have not been damaged by consumption for longer periods. This phenomenon may give damaged plants the chance to renew themselves before their leaves are consumed again.

Effects of heat treatments on the stabilities of polysaccharides substances and barbaloin in gel juice from Aloe vera Miller

“…Barbaloin and aloe emodin (Sigma Chemical Co., St. Louis, MO, USA) assays were as described (Gutterman & Chauser-Volfson, 2000) with certain modifications. The supernatant of 200 ll was dripped onto pre-coated thin layer chromatographic (TLC) sheets, silica-gel GF 254 on glass (20 · 20 cm) that had been activated at 105°C for 45 min.…”

“…Aloins are generally toxic contaminants in aloe gel used in cosmetics (Gutterman & Chauser-Volfson, 2000). There are also cautionary investigations warning of possible allergic effects on some patients (Reynolds & Dweck, 1999).…”

“…Barbaloin (also named aloin), the C-glucoside of aloe emodin anthrone, localizes in the outer rind of the aloe plant, has been reported to constitute up to 30% of the aloe plantÕs dried leaf exudates (Groom & Reynolds, 1986) and proposed as a part of the defense mechanisms against herbivores (Gutterman & Chauser-Volfson, 2000). Orally administered barbaloin is poorly absorbed but is metabolized by intestinal microflora to aloe emodin, which is readily absorbed (Ishii, Tanizawa, & Takino, 1994).…”

Biochemical studies of Aloe vera (Aloe barbadensis Miller) gel of the field grown and micropropagated plants at different developmental stages

“…Similarly the total sterols were more in micropropagated plants and increases with maturity (0.56 to 2.19 mg g −1 DW). The Gutterman et al (2000) has reported the distribution of secondary phenolic metabolites as a peripheral defense strategy in the succulent leaf parts of Aloe arborescens. Due to stress micropropagative plants had steady state transcript levels for various biosynthetic enzymes resulting in higher secondary metabolite accumulation.…”

Enhanced in vitro caulogenesis and quantitative estimation of aloin through HPLC in Aloe vera

“…The main anthraquinones present in Aloe vera are aloin, aloe amodin, aloe bitter and aloe lectin (Wang 2009). It has been reported that aloin constitutes up to 30% of the dried leaf exudates (Groom & Reynolds 1986) and that aloin plays an important role in defense mechanisms against herbivores (Gutterman & Volfson 2000). In small quantities, anthraquinones act as antimicrobial (Lorenzetts et al 1964) and antiviral agents (Sims et al 1971).…”