Plant Alkaloids: Main Features, Toxicity, and Mechanisms of Action

Abstract

Alkaloids are one of the largest groups of plant secondary metabolites, being present in several economically relevant plant families. Alkaloids encompass neuroactive molecules, such as caffeine and nicotine, as well as life-saving medicines including emetine used to fight oral intoxication and the antitumorals vincristine and vinblastine. Alkaloids can act as defense compounds in plants, being efficient against pathogens and predators due to their toxicity. Fast perception of aggressors and unfavorable environmental conditions, followed by efficient and specific signal transduction for triggering alkaloid accumulation, are key steps in successful plant protection. Toxic effects, in general, depend on specific dosage, exposure time, and individual characteristics, such as sensitivity, site of action, and developmental stage. At times, toxicity effects can be both harmful and beneficial depending on the ecological or pharmacological context. Different strategies are used to study alkaloid metabolism and accumulation. An efficient approach is to monitor gene expression, enzyme activities, and concentration of precursors and of the alkaloid itself during controlled attacks of pathogens and herbivores or upon the simulation of their presence through physical or chemical stimulation. Detailed understanding of alkaloid biosynthesis and mechanisms of action is essential to improve production of alkaloids of interest, to discover new bioactive molecules, and to sustainably exploit them against targets of interest, such as herbivores, pathogens, cancer cells, or unwanted physiological conditions.

Antibacterial and Phytochemical Properties of Crude Leaf Extracts of Moringa oleifera Lam., Pterocarpus santalinoides L’Herit DC and Ceiba pentandra L. on Some Clinical Bacterial Isolates in Nigeria

“…The mode of action of tannins involves the precipitation of proteins, bringing about inactivation of microbial adhesin and cell transport proteins, binds to metals and other macromolecules making them unavailable to the microorganisms [57,58]. Other plants isolate such as steroids, alkaloids and flavonoids have been reported to show significant antimicrobial effects against infectious organisms in addition to their other roles as anti-oxidants, anti-diarhoetic, anti-inflammation and enzyme inhibitors among others [11,12,19,20,22,59].…”

“…These phytochemical constituents may function individually and or synergistically in their mode of action to inhibit the growth of pathogenic organisms and positively affect other physiological processes [17]. Isolated chemical compounds from plant extracts such as Tannins, terpenoids, alkaloids, polyphenols, terpinoids and flavonoids have been reported to exhibit antimicrobial activities against microbials [18,19,20,21].…”

Skrining Fitokimia Lima Jenis Tumbuhan Paku Polypodiaceae Dari Provinsi Riau

“…Skrining fitokimia kualitatif dilakukan untuk mengetahui ada atau tidaknya kandungan metabolit sekunder dari golongan alkaloid, flavonoid, saponin, steroid, tanin, dan terpenoid pada paku yang diteliti berdasarkan Sangi et a.l (2008), Deepa et al (2014) dan Raman et al (2018) (flavonoid, steroid dan terpenoid) memberikan hasil yang berbeda pada rimpang dan daun. Alkaloid merupakan golongan metabolit sekunder dijumpai pada sebagian besar golongan tumbuhan (Matsuura & Fett-Neto 2015). Alkaloid merupakan golongan senyawa organik, yang mempunyai komponen dasar nitrogen basa (Sangi et al 2008).…”

“…Alkaloid merupakan golongan senyawa organik, yang mempunyai komponen dasar nitrogen basa (Sangi et al 2008). Pada tumbuhan, senyawa ini berperan dalam pertahanan tanaman terhadap herbivora dan serangan pathogen karena toksisitasnya (Deepa et al 2014;Matsuura & Fett-Neto 2015). Pada penelitian ini, hasil uji golongan alkaloid menunjukkan bahwa pada rimpang dan daun semua jenis paku Polypodiaceae mengandung alkaloid.…”

Potential of Mangrove Apples (Sonneratia alba) as a Botanical Insecticide

“…In the results of phytochemical screening test extract on mangrove apples there were alkaloid compounds (Reagent Dragendorf and Wagner) on all solvents, which arose brownish green color and there was sediment on alkaloids. The toxicity of plant alkaloids can vary greatly, generally affecting nerve or cell replacement (Mithöfer and Boland in Matsuura and Fett-Neto, 2015).…”