Plant-derived protein hydrolysates (PHs) are gaining global interest for their sustainability and positive effects on crops under abiotic stresses. However, the long-term effects of PHs on the yield and quality of greenhouse crops have not been described. Romaine lettuce (Lactuca sativa L.) and Micro-Tom tomato (Solanum lycopersicum L.) were grown with commercial growing media in 1 L pots and fertigated with four N levels (2, 5, 10, and 15 mM). PH (0 or 3 g/L) was applied as a foliar spray (PH-F) or root drench (PH-R) once every week. Compared to PH-F, PH-R effectively stimulated the yield, photosynthesis, water-use efficiency, chlorophyll contents, and antioxidant activities, and compounds regardless of N levels and species. Increasing the N level led to a total dry weight gain, and PH-R enhanced the lettuce shoot dry weight (+31%) and tomato fruit dry weight (+22%). PH-R also increased the fresh marketable yield of lettuce (+21%) and tomato (+32%). The increasing N level decreased antioxidant parameters in lettuce leaves, not in tomato fruits, whereas PH-R improved them in both species. PH-R significantly enhanced the N use and uptake efficiency. Taken together, our results suggested that the addition of PH-R effectively increased the N uptake and subsequently increased the lettuce and tomato yield and quality regardless of N levels.

Plant-derived protein biostimulants exhibit hormone-like activities promoting plant growth and yield, yet detailed investigations on hormonal function have remained limited. This study was conducted to investigate the effects of vegetal-derived-biostimulant on morphological and metabolic changes in cuttings of three herbaceous species demonstrating different rooting ability, basil (Ocimum basilicum L.), tomato (Solanum lycopersicum L.), and chrysanthemum (Chrysanthemum indicum L.), in comparison to auxin. Unrooted cuttings were applied with or without biostimulant (100, 1000, 5000, and 10,000 mg L⁻¹) or auxin [1% indole-3-butyric acid (IBA) plus 0.5% 1-naphthaleneacetic acid (NAA); 100, 200, 300, and 500 mg L⁻¹] as a basal quick-dip, stuck into inert media, and evaluated at 20 days after placement under intermittent mist. Both compounds increased adventitious rooting in all cuttings. Biostimulant required a significantly higher threshold for a series of adventitious rooting responses than auxin, and the maximum effectiveness was achieved at 5000 mg L⁻¹ for biostimulant and 100, 200, and 300 mg L⁻¹ for auxin in basil, tomato, and chrysanthemum, respectively. Adventitious rooting responses (dry mass and length) to biostimulant showed a gradual logarithmic rise as a function of increasing dosages, which was not in agreement with biphasic dose-response of auxin. Biostimulant significantly increased or tended to increase fine roots in all tested cuttings, which was not consistent with auxin. Relatively high levels of endogenous brassinosteroids (BRs) were present in non-treated cuttings of basil, tomato, and chrysanthemum in decreasing order. Both compounds had no effects or concomitantly increased or decreased BR levels in plant tissues, with fewer effects on basil and tomato, containing high BR levels, but more prominent effects on chrysanthemum, containing relatively low BR levels. Contrasting effects of biostimulant and auxin were found in antioxidant activities, which were promoted by biostimulant but inhibited by auxin either in roots or shoots. These results indicate that the hormonal effects of vegetal-derived biostimulant are primarily exerted by BR-mediated processes while involving interaction with auxin. Both the biostimulant-derived BRs and auxin were suggested to modulate endogenous BR pool via overlapping and interdependent regulatory functions, inducing morphological and metabolic changes during adventitious rooting of cuttings in a plant species-specific manner.

BACKGROUND: Protein hydrolysates (PHs) can enhance plant nitrogen nutrition and improve the quality of vegetables, depending on their bioactive compounds. A tomato greenhouse experiment was conducted under both optimal (14 mM) and suboptimal (2 mM) nitrogen (N‐NO₃) conditions. Tomatoes were treated with a new Malvaceae‐derived PH (MDPH) and its molecular fractions (MDPH1, >10 kDa; MDPH2, 1–10 kDa and MDPH3, <1 kDa).RESULTS: Under optimal N conditions, the plants increased biomass and fruit yield, and showed a higher photosynthetic pigment content in leaves in comparison with suboptimal N, whereas under N‐limiting conditions, an increase in dry matter, soluble solid content (SSC) and lycopene, a reduction in firmness, and changes in organic acid and phenolic compounds were observed. With 14 mM N‐NO₃, MDPH3 stimulated an increase in dry weight and increased yield components and lycopene in the fruit. The MDPH2 fraction also resulted in increased lycopene accumulation in fruit under 14 mM N‐NO₃. At a low N level, the PH fractions showed distinct effects compared with the whole MDPH and the control, with an increase in biomass for MDPH1 and MDPH2 and a higher pigment content for MDPH3. Regardless of N availability, all the fractions affected fruit quality by increasing SSC, whereas MDPH2 and MDPH3 modified organic acid content and showed a higher concentration of flavonols, lignans, and stilbenes.CONCLUSION: The molecular weight of the peptides modifies the effect of PHs on plant performance, with different behavior depending on the level of N fertilization, confirming the effectiveness of fractioning processes. © 2024 The Author(s). Journal of the Science of Food and Agriculture published by JohnWiley & Sons Ltd on behalf of Society of Chemical Industry.