Plants possess powerful resources of secondary metabolites and can be used for pharmaceutical applications and development of new drugs.
Cucumis sativus belongs to Cucurbitaceae family and is known to be rich in cucurbitacins. Cucurbitacins have become interesting subjects in science due to their medicinal and toxic properties [
1]. They are usually concentrated in fruits and roots at maturity and are responsible for bitter taste of cucumber. Seeds exhibit very low concentration of cucurbitacins [
2]. The diversity of cucurbitacins lies in side chain derivatives that contribute to pharmacological actions [
3]. They are known according to their structural composition and designated by the letters: A, B, C, D, E, F, G, H, I, J, K, L, O, P, Q, R and S. Cucurbitacins have also been identified outside the cucurbitaceae family including members of Scrophulariaceae, Begoniaceae, Primulaceae, Liliaceae, Tropaeolaceae and Rosaceae families [
2]. Various cucurbitacins are made from chemical modification of cucurbitane (19(10–9ß)-abeo-5α-lanostane) with numerous activities such as anti-inflammatory, antitumor promotion, chemopreventive, hepatoprotective, anti-microbial, anthelmintic, antifeedant and antioxidant [
4]. CuE is one of the cucurbitacins and is an active secondary methabolite with inhibition of cell adhesion actions [
5] and modulatory activity effect on the peripheral human lymphocytes [
6]. The compound has also been found to be a strong antifeedant for the flea beetle, bilirubin–albumin binding in human plasma and with inhibitory activity on cancer cell proliferation, actin polymerization and permeability [
5]. The compound also acts as agent to protect against certain diseases in plants due to its toxicity property [
7,
8]. Cu E displays superior cytotoxicity due to more hydrophobicity than the other cucurbitacins [
9].
Elicitors refer to chemicals that can trigger physiological and morphological responses in plants. They include abiotic such as metal ions and inorganic compounds, and biotic such as fungi, bacteria, viruses or herbivores. Elicitors application on plants causes accumulation of a range of plant defensive secondary metabolites. The elicitor signal perception leads to initiation of a signal transduction network which activates biosynthesis of transcription factors regulating plant secondary metabolism [
10]. There are various elicitors as inducers of secondary metabolites such as methionine, tryptophan, methyl jasmonate (MeJA), salicylic acid, benzothiadiazole ß-glucan, chitosan and chitin oligomers [
11].
The present study was conducted to determine the effect of two plant inducers including potassium phosphite (KPhi) and chitosan on CuE production in different organs of cucumber plant using HPLC approach. Administration of plant ethanolic extracts was also investigated on prevention of E. coli PTCC 1399 and Pseudomonas aeruginosa PTCC 1430 bacterial growth under inducers application. To the best of our knowledge, this is the first time that the elicitor effect of KPhi and chitosan is reported on the accumulation of CuE bioactive compound and on enhancement of antimicrobial properties of plant extract.