The emerging role of plant biostimulants in enhancing nutrient efficiency is important for maintaining soil fertility under sub-optimal nutrient regimens. We aimed to elucidate the morpho-physiological and biochemical effects as well as mineral composition changes of greenhouse jute (Corchorus olitorius L.) treated with a commercial vegetal-derived biostimulant from a tropical plant extract (PE; Auxym^®, Italpollina, Rivoli Veronese, Italy). Plants were sprayed in weekly intervals with a solution containing 2 mL·L⁻¹ PE. Jute plants were supplied with three nutrient solution concentrations: full-, half-, and quarter-strength. Decreasing macronutrient concentrations in the nutrient solution (NS), especially at quarter-strength, triggered a decrease in several morphological (plant height, leaf number, and dry biomass) and physiological (net CO₂ assimilation rate (A_CO2) and SPAD (Soil Plant Analysis Development) index) parameters. PE application triggered specific ameliorative effects in terms of fresh yield at both half- and quarter-strength nutrient solution (15.5% and 29.5%, respectively). This was associated with an enhancement in A_CO2, SPAD index, and especially the nutritional status (high nitrate, K, and Mg contents, and low Na content). The foliar application of PE, strongly increased chlorophyll b content, enhancing jute plant adaptation to fluctuating light and therefore the efficiency of photosynthesis, positively affecting starch, soluble proteins, and total amino acids content but only when jute plants were irrigated with full-strength NS, compared to the respective control treatment. At lower nutrient strength, PE reprogrammed the nitrogen distribution, allowing its remobilization from glutamate, which was quantitatively the major amino acid under lower nutrient strength, but not from chlorophylls, thus maintaining efficient photosynthesis. We confirmed that PE Auxym^® acts in a balanced manner on the main metabolic pathways of the plant, regulating the uptake and transport of mineral nutrients and protein synthesis, increasing the accumulation of essential amino acids under full nutritive solutions, and re-distributing nitrogen from amino acids to allow leaf growth and expansion even under sub-optimal nutrient conditions. Overall, the use of natural plant biostimulants may be a potential solution in low-input conditions, where environmental constraints and restricted use of fertilizers may affect potential crop productivity.

Consumer demand for fresh and functional horticultural products is on the rise. Perilla frutescens, L. Britt (Lamiaceae) is a potential specialty/niche crop for consumption and therapeutic uses with high contents of phenolic and volatile compounds. Plant growth, mineral composition, polyphenol profile and aroma volatile components of two perilla genotypes in response to salinity (non-salt control, 10, 20 or 30 mM NaCl) applied as chemical eustressor were assessed. Salinity suppressed growth and yield of both genotypes, although the red-pigmented genotype was less sensitive than the green-pigmented one. Mild (10 mM NaCl) and moderate (20 and 30 mM NaCl) salinity suppressed foliar potassium, magnesium, nitrate and chlorophyll a concentrations of both genotypes and increased the levels of rosmarinic acid, total polyphenols and target aroma volatile components. Green perilla showed higher yield and biomass production and higher content of protein, dry matter, calcium, magnesium, perilla ketone and cis-jasmone, whereas red perilla exhibited higher content of potassium, chlorophyll a, rosmarinic acid, total polyphenols, perilla aldehyde and benzaldehyde. Our findings support that chemical eustressors such as mild to moderate salinity offer valuable means to manipulate phytochemical and aroma profiles.

Nutritional eustress such as salinity or nutrient stress applied in soilless systems, is a convenient pre-harvest factor efficient in modulating the phytochemical components of horticultural crops, by triggering defensive mechanisms and accumulating plant secondary metabolites in plants tissues. Nevertheless, genetic material (cultivars with different pigmentation) dictates lettuce metabolites and physiological response to extrinsic eustress, with red leaf cultivars being highly nutrient packed notwithstanding the stress. Product quality can be meliorated equally by applying several cuts, a practice proven to increase bioactive compounds accumulation. In this study, we analyzed the effects of four salinity levels (1, 10, 20 and 30 mM NaCl) on green and red pigmented Salad Bowl lettuce (Lactuca sativa L. var. acephala) in two successive harvests cultivated in a floating raft system. The morphological parameters, mineral composition, leaf gas exchanges, bioactive compounds, and antioxidant activity of both cultivars were assessed. The green cultivar exhibited superior crop productivity but was more prone to salinity effect than the red cultivar. Irrespective of cultivar and cut order, the net photosynthesis decreased with increasing salinity in the nutrient solution. The second cut incurred higher dry biomass, greater accumulation of most minerals and higher photosynthetic activity. In red lettuce, 20 mM NaCl proved adequate eustress to increase phytonutrients and beneficial minerals (K, Ca, and Mg) with minimal loss of yield. Mild salinity and sequential harvest have proven effective pre-harvest tools in positively modulating the quality of lettuce. Eustress interaction with genotype was demonstrated as a promising field for future breeding programs targeting select genotypes for agronomic application of eustress to improve the nutraceutical value of vegetable crops.

Considering that functional components of plant foods are mainly secondary-metabolism products, we investigated the shaping of health-promoting compounds in hydroponically grown butterhead lettuce (Lactuca sativa L. var. capitata) as a function of the strength of the nutrient solution utilized. To this aim, untargeted metabolomics profiling, in vitro antioxidant capacity (total phenolics, 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), cupric reducing antioxidant capacity (CUPRAC), and ferric reducing antioxidant power (FRAP) assays), and the inhibition of selected enzyme activities were investigated in two butterhead lettuce cultivars with different pigmentation, i.e., green and red Salanova. Full-strength nutrition, together with half- and quarter-strength solutions of macronutrients, was tested. Our results indicate that by reducing the nutrients strength, we could elicit a distinctive shaping of the phenolic profile of lettuce. It is noteworthy that only specific classes of phenolics (namely, lignans and phenolic acids, followed by flavones and anthocyanins) were modulated by the induction of nutritional eustress (fold-change values in the range between −5 and +11). This indicates that specific responses, rather than a generalized induction of phenolic compounds, could be observed. Nonetheless, a genotype-dependent response could be observed, with the red cultivar being much more responsive to nutritional deprivation than the green Salanova lettuce. Indeed, analysis of variance (ANOVA) confirmed a genotype x nutrition interaction in red Salanova (p < 0.001). As a consequence of the changes in phenolic composition, also the antioxidant capacity (p < 0.001) and amylase inhibition (p < 0.001) properties were affected by the growing conditions. However, the effect on cholinesterase and tyrosinase inhibition was poorly affected by the nutritional strength. Provided that yields are not compromised, the application of a controlled nutritional eustress in hydroponically cultivated lettuce may represent a valuable strategy to produce food with tailored functional features in a sustainable manner.

Tobacco cultivation is characterized by high amounts of waste biomasses whose disposal frequently represents a complex and expensive problem. A study was conducted to evaluate thepotential of pre-harvest light air-cured (Burley) and dark fire-cured (Kentucky) tobacco waste biomasses as a source of bioactive compounds (nutraceutical ingredients) such as polyphenols. Pre-harvest waste materials (topping fresh materials and residual stalks at final harvest) were collected to determine dry matter, total polyphenols content (TPC; Folin assay), and DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,20-azino-bis(3-ethylbenzothiazoline-60-sulfonic acid) diammonium salt) antioxidant capacity. Polyphenols quali-quantitative profiles obtained by Orbitrap Q Exactive of both tobacco types were also determined. Total pre-harvest waste biomass amounted to 3956.9 and 1304.4 kg d.w. ha⁻¹ in light air-cured (Burley) and dark fire-cured (Kentucky) tobacco types, respectively. Polyphenols content, expressed as g kg⁻¹ dry weight (d.w.), ranged between 4.6 and 15.7 g kg⁻¹ d.w. and was generally greater in leaves than in stalks. Considering both leaves and stalks, the light air-cured (Burley) tobacco crop yielded 22.1 kg ha⁻¹ of polyphenols, while the dark fire-cured (Kentucky) tobacco yielded 12.0 kg ha⁻¹. DPPH and ABTS were significantly greater in leaves than in stalks waste biomass in both types of tobacco. The most abundant components were quinic and chlorogenic acids, rutin, and luteolin rutinoside.