Do allelochemicals operate independent of substratum factors?

Abstract

“The plant world is not colored green; it is colored morphine, caffeine, tannin, phenol, terpene, canavanine, latex, phytohaem-agglutinin, oxalic acid, saponin, L-dopa, etc.”Janzen [1].Plants synthesize a variety of secondary metabolites playing various roles in plant defense, plant interference (allelopathy), nutrient dynamics, waste elimination, mycorrhizae formation, and substratum ecology [2]. The term “plant allelochemical” was coined by Whittaker and Feeny [3]. Although both primary and secondary metabolites are being considered as allelochemicals, we will discuss only secondary metabolites as allelochemicals for the present discussion. Conn [4] suggested that secondary metabolites are compounds that do not have a direct role in the growth and reproduction of an organism. Although we should not use the terms “allelochemical” and “secondary metabolites” as synonyms, secondary substances largely act as allelochemicals [3]. Secondary metabolites can be very close to primary metabolites structurally. While kaurenoic acid and proline are primary metabolites, the closely related compounds abioetic acid and pipecolic acid are considered secondary metabolites [5]. Berenbaum [6] opined that the two terms (allelochemical and secondary metabolites) are not interchangeable. Secondary metabolites, however, may have some role in primary metabolism. For example, some allelochemicals may act as biosynthetic intermediates, growth regulators, or storage molecules for elements in short supply [7]. Secondary metabolites may exist in the dynamic equilibrium and may be recycled to primary metabolism [8]. Antioxidants such as vitamins A, C, and E can reduce phytotoxicity of photosensitizing allelochemicals [9]. Vitamins and the medicines we refer to as “antibiotics” could be considered allelochemicals, labeling the vitamins “pro-metabolites.” In their role of protection in the producing organisms, the antioxidants function as would be anticipated with and without the intrusion of allelochemical interpretation. Various forms of B I n are needed by different organisms, depending on what “repair” or “completion”