Foliar spray of selected plant growth regulators affected the biochemical and antioxidant attributes of spinach in a field experiment

This study explored the effects of foliar spray of selected plant growth regulators (PGRs) on the biochemical and phenolic antioxidant attributes of spinach (Spinacia oleracea) leaves. Following foliar spray at three growth stages (40, 50, and 60 days) with selected PGRs, namely humic acid (HA), Moringa oleifera leaf extract (MOLE), and 6-benzylamino purine (6-BAP), and their mixed form, the samples of spinach leaves were harvested. The analysis of foliar-treated leaves revealed the content of proline, malondialdehyde (MDA), total soluble proteins (TSPs), total chlorophyll, and total carotenoids to be 22.45–72.32 μg/g FW, 2.41–29.13 ng/g FW, 3.21–22.45 μg/g FW, 4.173–19.700 mg/g FW, and 0.500–1.260 mg/g FW, respectively. The total phenolic content (TPC), reducing power, and DPPH° scavenging activity (IC₅₀ values) varied from 6.59 to 14.49 mg GAE/g DM, from 0.426 to 1.944 (10.0 mg/ mL extract concentration), and from 0.506 to 1.073 μg/mL, respectively. HPLC analysis showed that foliar application of PGRs also improved the content of individual phenolic acids in the leaves as compared with the controls. Overall, it was concluded that, although the use of the PGRs acted as an elicitor with respect to each growth phase and exhibited significant differences (P < 0.05) among treatments, the leading effect was exhibited by the MOLE treatment, proving it to be a better enhancer of phenolic antioxidants and other biochemicals.