Evaluation of direct and indirect effects of flavonoids, mineral elements and dry weight on antiradical scavenging activity in leaf material of field-grown Trifolium pratense cultivars using Path Analysis

In recent years, considerable interest has been focused on the antioxidant potential (including antiradical activity) of crops. Antiradical power (ARP) is influenced by antioxidant compounds, which in turn are controlled by mineral element status. There are relatively few studies considering the variation of assimilated mineral element content (with respective synergies and antagonisms) on secondary metabolites and resultant ARP in plants grown under open-field conditions. The present study was aimed at identifying variables affecting ARP in leaf material of Trifolium pratense L. using Path Analysis as an analytical processing tool. Variation in leaf ARP (2,2-diphenyl-1-picrylhydrazyl scavenging activity), total phenol, flavonoid, mineral element (macro- and micro-elements), and dry weight (DW) content was obtained by growing three T. pratense cultivars (Altaswede, Lucrum and Kvarta) in two nonirrigated, open-field sites (Florence and Consuma) over two consecutive years. Path Analysis then permitted the dissection of genotypic variation (for each locality) in total phenol and flavonoid, mineral element and DW effects on ARP, as well as the underlying mechanisms contributing to the associations between the respective variables and their relative importance in determining ARP. ARP, attributable to effects of DW, and flavonoid and non-flavonoid phenols, was genotype-dependent. Changing tissue DW from hydrated to intermediate levels (Florence), was the greatest positive determinant of ARP in Lucrum and Kvarta in Florence. In the intermediate to more water-stressed tissues, characteristic of Consuma, the flavonoids were direct, positive predictors of ARP in all varieties with N exercising both a negative and the greatest overall effect on ARP through the flavonoids. Altaswede was characterised by higher ARP, flavonoid and Al content than Kvarta, with Lucrum displaying intermediate levels. After more established growth (2007), the indirect impact of N, Ca and DW on both biomass and ARP via chlorophyll and flavonoid content is presented for each locality.