Abstract
Phenolic compounds, hydroquinone and cinnamic acid derivatives have been identified as major allelochemicals with known phytotoxicity from allelopathic plant Acacia melanoxylon R. Br. Several phenolic compounds such as ferulic acid (FA), p-hydroxybenzoic acid (pHBA) and flavonoid (rutin, quercetin) constituents occur in the phyllodes and flowers of A. melanoxylon and have demonstrated inhibitory effects on germination and physiological characteristics of lettuce and perennial grasses. However, to date, little is known about the mechanisms of action of these secondary metabolites in broad-leaved weeds at ecophysiological level. The objective of this study was to determine the response of Rumex acetosa carbon isotope composition and other physiological parameters to the interaction of plant secondary metabolites (PSM) (FA and pHBA) stress and the usefulness of carbon isotope discrimination (Δ13C) as indicative of the functional performance of intrinsic water use efficiency (iWUE) at level of plant leaf. R. acetosa plant were grown under greenhouse condition and subjected to PSM stress (0, 0.1, 0.5, 1.0, and 1.5 mM) for six days. Here, we show that FA and pHBA are potent inhibitors of Δ13C that varied from 21.0‰ to 22.9‰. Higher pHBA and FA supply enhanced/retard the Nleaf and increased the Cleaf while ratio of intercellular CO2 concentration from leaf to air (Ci/Ca) was significantly decreased as compared to control. Leaf water content and leaf osmotic potential were decreased following treatment with both PSM. The Ci/Ca decreased rapidly with higher concentration of FA and pHBA. However, iWUE increased at all allelochemical concentrations. At the whole plant level, both PSM showed pronounced growth-inhibitory effects on PBM and C and N concentration, root fresh/dry weight, leaf fresh/dry weight, and root, shoot length of C3 broad leaf weed R. acetosa. Carbon isotope discrimination (Δ) was correlated with the dry matter to transpiration ratio (transpiration efficiency) in this C3 species, but its heritability and relationship to R. acetosa growth are less clear. Our FA and pHBA compounds are the potent and selective carbon isotope composition (δ13C) inhibitors known to date. These results confirm the phytotoxicity of FA and pHBA on R. acetosa seedlings, the reduction of relative water content and the induction of carbon isotope discrimination (Δ) with lower plant biomass.
Highlights
Herbicide resistance in weeds is a lethal cascade that is decreasing the crop yield and profit of the farmer worldwide [1,2]
These results confirm the phytotoxicity of ferulic acid (FA) and p-hydroxybenzoic acid (pHBA) on R. acetosa seedlings, the reduction of relative water content and the induction of carbon isotope discrimination (∆) with lower plant biomass
Natural products such as secondary metabolites from plants, fungi and bacteria can be used for the safe development of lead compounds for new bioherbicides discovery program [24]
Summary
Herbicide resistance in weeds is a lethal cascade that is decreasing the crop yield and profit of the farmer worldwide [1,2]. In the USA alone, the annual cost of crop losses due to weeds is greater than $26 billion [3]. Natural products from living organisms, plants, fungi and bacteria are a huge source of environmentally friendly “bioherbicides” that can overcome the herbicide resistance problem [6,7]. The bioherbicides or secondary metabolites might interfere with the growth, physiological and biochemical process of target plants, but their mode of action has rarely been studied [8]. Some secondary metabolites such as grandiflorone and flavesone have shown significant phytotoxicity and their mechanism of action was inhibition through hydroxyphenyl pyruvate dioxygenase enzyme [9]. Some researchers reported the inhibition of germination, plant growth and physiological processes of crop plants, weeds and vegetables by phenolic compounds
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