Copper boosts the biostimulant activity of a vegetal-derived protein hydrolysate in basil: morpho-physiological and metabolomics insights

Abstract

In addition to be used as a plant protection agent, copper (Cu) is also an essential micronutrient for plant growth and development. The bioavailability of Cu in agricultural systems can be limited due to its specific physical–chemical characteristics, leading to imbalances in plant production. To address this issue, an experimental trial was conducted on Genovese basil (Ocimum basilicum L.) in protected conditions to comparatively evaluate the effects of a vegetable protein hydrolysate (VPH), free Cu and Cu complexed with peptides and amino acids of vegetal origin (Cu and Cu-VPH, respectively), and a combination of VPH and Cu-VPH (VPH+Cu-VPH). The study showed that the combined application of VPH+Cu-VPH led to a significant average increase of 16.3% in fresh yield compared to the untreated Control and Cu treatment. This finding was supported by an improved photosynthetic performance in ACO2 (+29%) and Fv/Fm (+7%). Furthermore, mineral analysis using ICP OES demonstrated that Cu and Cu-VPH treatments determined, on average, a 15.1-, 16.9-, and 1.9-fold increase in Cu in plant tissues compared to control, VPH, and VPH+Cu-VPH treatments, respectively. However, the VPH+Cu-VPH treatment induced the highest contents of the other analyzed ions, except for P. In particular, Mg, Mn, Ca, and Fe, which take part in the constitution of chlorophylls, water splitting system, and photosynthetic electron transport chain, increased by 23%, 21%, 25%, and 32% compared to respective controls. Indeed, this improved the photosynthetic efficiency and the carboxylation capacity of the plants, and consequently, the physiological and productive performance of Genovese basil, compared to all other treatments and control. Consistently, the untargeted metabolomics also pointed out a distinctive modulation of phytochemical signatures as a function of the treatment. An accumulation of alkaloids, terpenoids, and phenylpropanoids was observed following Cu treatment, suggesting an oxidative imbalance upon metal exposure. In contrast, a mitigation of oxidative stress was highlighted in Cu-VPH and VPH+Cu-VPH, where the treatments reduced stress-related metabolites. Overall, these results highlight an interaction between Cu and VPH, hence paving the way towards the combined use of Cu and biostimulants to optimize agronomic interventions.

Higher Plant-Derived Biostimulants: Mechanisms of Action and Their Role in Mitigating Plant Abiotic Stress

“…Thus, by improving fertilizer efficiency, biostimulants could reduce its application dosage. Additionally, hPDBs exhibit protective effects against the excessive accumulation of PHEs in plants grown in contaminated soils, modulating the levels of Cu [ 55 ], Cd [ 46 ], Pb, and Ni [ 111 ]. The application of biostimulants has also proven beneficial in mitigating the toxic effects of salt stress.…”

“…The accumulation of phytoalexin precursors and terpenoid phytoalexins in lettuce was especially remarkable under abiotic stress conditions [ 69 ]. On the other hand, in Genovese basil, treatment with Trainer ® alleviated terpenoid and phytoalexin accumulation after exposure to high Cu levels, which indicates the formulation exerted a protective effect against the oxidative stress induced by this metal [ 55 ].…”

“…Furthermore, the induction of phenolic accumulation by hPDBs is also described in crops subjected to salinity [ 84 , 124 ], an effect which could alleviate the oxidative stress associated with this condition, given the antioxidant capacity of phenolic compounds. Conversely, hPDBs are also reported to reduce phenolic concentrations in spinach plants [ 105 ], tomato roots [ 112 ], cabbage seedlings [ 39 ], and Genovese basil subjected to Cu toxicity [ 55 ].…”

“…It has been shown that under adverse conditions, the alkaloid content in plants tends to increase, as alkaloids help to alleviate stress by scavenging ROS [ 136 ]. Interestingly, although pretreatment with hPDBs is capable of inducing a higher alkaloid content in stressed plants [ 68 , 89 , 95 ], it may also result in a reduction, indicating that the biostimulant mitigates oxidative stress by an alternative pathway, obviating the need for enhanced alkaloid synthesis [ 55 , 68 ].…”

“…Electron transfer and photosynthetic efficiency can be quantified by measuring different parameters, many of which are improved by hPDB application. Thus, improvements were observed in photochemical efficiency (Fv/Fm ratio) in lettuce [ 74 ] and Genovese basil [ 55 ], photosystem II and photochemical efficiency in spinach [ 105 ], and net photosynthesis in olive trees [ 93 ]. In conditions of high salinity, hPDB application in Arabidopsis [ 37 ], maize [ 132 ], pea [ 97 ], okra [ 92 ], and lettuce [ 68 ] alleviated the stress impact, preserving their photosynthetic parameters, being comparable with those of control plants.…”