Can combining copper with protein hydrolysate intensify the biostimulant effects?

By: Petronia Carillo1, Giovanna Marta Fusco1, Youssef Rouphael2, Giuseppe Colla3

1Department of Environmental, Biological and Pharmaceutical Sciences and Technologies, University of Campania “Luigi Vanvitelli”, Via Vivaldi 43, 81100 Caserta, Italy 2Department of Agricultural Sciences, University of Naples Federico II, 80055 Portici, Italy 3Department of Agriculture and Forest Sciences, University of Tuscia, 01100 Viterbo, Italy

basilic plant

Ensuring a balanced supply of nutrients to promote optimal plant health and sustainable production is a fundamental aspect of modern agriculture. Although micronutrients are needed in smaller quantities than macronutrients, they play a crucial role in various metabolic and physiological processes in plants. Copper (Cu), an essential micronutrient for plant growth and development, is contained in several enzymes like superoxide dismutase (Cu/Zn-SOD) which help plants cope with oxidative stress by neutralizing harmful reactive oxygen species. Copper also contributes to stress tolerance by enhancing the plant’s ability to manage oxidative damage caused by environmental stressors. Vegetal-protein hydrolysates have been recognized to have strong biostimulant effects by stimulating primary and secondary metabolism of plants. Moreover, protein hydrolysates can increase plant uptake of nutrients and their transport in plant tissues. Starting from the above considerations, a greenhouse trial was carried out to evaluate the interactive effects between a vegetal-derived protein hydrolysate and copper on promoting growth and biochemical traits of Genovese basil (Ocimum basilicum L.).

Treatments included a vegetal-derived protein hydrolysate (VPH), free Cu (from copper sulphate), Cu complexed with vegetal-derived peptides (Cu-VPH), and a combination of VPH and Cu-VPH (VPH+Cu-VPH). Foliar treatments began seven days after transplanting and involved five distinct treatments: 1) copper (58.5 mg/L); 2) VPH Trainer® (Hello Nature, Rivoli Veronese, Italy) (4 ml/L); 3) Cu-VPH Scudo® (Hello Nature, Rivoli Veronese, Italy (0.5 ml/L); 4) VPH (3.7 ml/L)+Cu-VPH (0.5 ml/L). Except in VPH treatment, copper concentration in foliarly applied solutions of all treatments was 45 mg/L. Untreated control served as comparison group. Foliar applications were repeated every week. The results are summarised in Figure 1. The results of the study revealed a significant accumulation of secondary metabolites, particularly alkaloids, terpenoids, and phenylpropanoids, in response to Cu treatment. Indeed, the higher content of these metabolites served as a protective mechanism against oxidative stress-induced damage, indicative of the plant’s response to unfavourable environmental conditions. In contrast, Cu-VPH treatments exhibited lower levels of these stress-related compounds, indicative of a healthier plant phenotype with reduced ROS levels and oxidative damage. However, both Cu and Cu-VPH treatments led to higher Cu levels in plant tissues compared to control. The Cu-VPH treatment regimen while still inducing significant alterations in transpiration rates and reduced water use efficiency (WUEi), maintained high leaf nutrient levels (Ca, Mn, Fe), photosynthesis and fresh yield showing a trade-off between nutrient uptake and water conservation strategies. The VPH treatment enhanced the Electron Transport Chain (ETC) activity, thereby promoting more efficient photosynthesis and ultimately leading to increased yield. Additionally, it boosts the uptake of essential minerals such as calcium (Ca), manganese (Mn), and iron (Fe), further supporting plant growth and health. The VPH+Cu-VPH treatment regimen determined a significant increase of morpho-physiological and biochemical characteristics compared to other approaches. In fact, this treatment significantly improved the plants’ carboxylation activity (ACO2) and maximum potential quantum efficiency of Photosystem II (Fv/Fm), suggesting an optimized Cu utilization. Interestingly, the combined treatment also led to higher levels of other essential ions, such as Mg, Mn, Ca and Fe, crucial for chlorophyll formation and photosynthesis. The improvement in nutrients use efficiency enhanced fresh basil yield, highlighting the effectiveness of the VPH+Cu-VPH treatment approach. The VPH+Cu-VPH combination also resulted in a notable increase in tryptophan content, accompanied by inhibition of stem elongation and promotion of plant compactness. These morphological alterations contributed to an overall improvement in yield, suggesting a synergistic effect between VPH and Cu-VPH treatments on basil growth and development. The study highlights the potential of combining Cu with biostimulants like VPH to increase crop yield and nutrient use efficiency. By enhancing Cu bioavailability and alleviating oxidative stress, these combined treatments offer a sustainable approach to improving crop productivity while minimizing environmental impact. This research underscores the importance of innovative techniques in promoting agricultural sustainability and addressing the challenges of modern farming practices.

Figure 1. Beneficial effects of foliar treatments with copper sulphate (Cu), vegetal-derived protein hydrolysate (VPH), copper complexed with peptides (Cu-VPH), and Cu-VPH enriched with protein hydrolysate (VPH+Cu-VPH) vs. untreated control (Control). Abbreviations: carboxylation activity (ACO2), electron transport chain (ETC), maximum potential quantum efficiency of Photosystem II (Fv/Fm).

More information on the basil trail is available on the following scientific article:

Rouphael Y, Carillo P, Ciriello M, Formisano L, El-Nakhel C, Ganugi P, Fiorini A, Miras Moreno B, Zhang L, Cardarelli M, Lucini L, Colla G (2023). Copper boosts the biostimulant activity of a vegetal-derived protein hydrolysate in basil: morpho-physiological and metabolomics insights. Front. Plant Sci. 14:1235686. doi: 10.3389/fpls.2023.1235686