Plant-derived protein hydrolysates (PHs) are gaining prominence as biostimulants due to their potential to improve yield and nutritional quality even under suboptimal nutrient regimens. In this study, we investigated the effects of foliar application of a legume-derived PH (0 or 4 mL L−1) on greenhouse baby spinach (Spinacia oleracea L.) under four nitrogen (N) fertilization levels (0, 15, 30, or 45 kg ha−1) by evaluating morphological and colorimetric parameters, mineral composition, carbohydrates, proteins, and amino acids. The fresh yield in untreated and biostimulant-treated spinach plants increased in response to an increase in N fertilization from 1 up to 30 kg ha−1, reaching a plateau thereafter indicating the luxury consumption of N at 45 kg ha−1. Increasing N fertilization rate, independently of PH, lead to a significant increase of all amino acids with the exception of alanine, GABA, leucine, lysine, methionine, and ornithine but decreased the polyphenols content. Interestingly, the fresh yield at 0 and 15 kg ha−1 was clearly greater in PH-treated plants compared to untreated plants by 33.3% and 24.9%, respectively. This was associated with the presence in of amino acids and small peptides PH ‘Trainer®’, which act as signaling molecules eliciting auxin- and/or gibberellin-like activities on both leaves and roots and thus inducing a “nutrient acquisition response” that enhances nutrients acquisition and assimilation (high P, Ca, and Mg accumulation) as well as an increase in the photochemical efficiency and activity of photosystem II (higher SPAD index). Foliar applications of the commercial PH decreased the polyphenols content, but on the other hand strongly increased total amino acid content (+45%, +82%, and +59% at 0, 15, and 30 kg ha−1, respectively) but not at a 45-kg ha−1-rate. Overall, the use of PH could represent a sustainable tool for boosting yield and nitrogen use efficiency and coping with soil fertility problems under low input regimens.

Many Trichoderma are successfully used to improve agriculture productivity due to their capacity for biocontrol and to stimulate plant growth and tolerance to abiotic stress. This research elucidates the effect of applications with Trichoderma harzianum strain T22 (T22), or biopolymer (BP) alone or in combination (BP + T22 or BP + 6-pentyl-α-pyrone (6PP); a Trichoderma secondary metabolite) on the crop performance, nutritional and functional quality of greenhouse tomato (Solanum lycopersicum L. cultivar Pixel). T22 elicited significant increases in total yield (+40.1%) compared to untreated tomato. The content of lycopene, an important antioxidant compound in tomatoes, significantly increased upon treatment with T22 (+ 49%), BP + T22 (+ 40%) and BP + 6PP (+ 52%) compared to the control. T22 treatments significantly increased the content of asparagine (+37%), GABA (+87%) and MEA (+102%) over the control; whereas BP alone strongly increased GABA (+105%) and MEA (+85%). The synthesis of these compounds implies that tomato plants are able to reuse the photorespiratory amino acids and ammonium for producing useful metabolites and reduce the pressure of photorespiration on plant metabolism, thus optimizing photosynthesis and growth. Finally, these metabolites exert many beneficial effects for human health, thus enhancing the premium quality of plum tomatoes.

Hordeum maritimum With. is a wild salt tolerant cereal present in the saline depressions of the Eastern Tunisia, where it significantly contributes to the annual biomass production. In a previous study on shoot tissues it was shown that this species withstands with high salinity at the seedling stage restricting the sodium entry into shoot and modulating over time the leaf synthesis of organic osmolytes for osmotic adjustment. However, the tolerance strategy mechanisms of this plant at root level have not yet been investigated. The current research aimed at elucidating the morphological, physiological and biochemical changes occurring at root level in H. maritimum and in the salt sensitive cultivar Hordeum vulgare L. cv. Lamsi during five-weeks extended salinity (200 mM NaCl), salt removal after two weeks of salinity and non-salt control. H. maritimum since the first phases of salinity was able to compartmentalize higher amounts of sodium in the roots compared to the other cultivar, avoiding transferring it to shoot and impairing photosynthetic metabolism. This allowed the roots of wild plants to receive recent photosynthates from leaves, gaining from them energy and carbon skeletons to compartmentalize toxic ions in the vacuoles, synthesize and accumulate organic osmolytes, control ion and water homeostasis and re-establish the ability of root to grow. H. vulgare was also able to accumulate compatible osmolytes but only in the first weeks of salinity, while soon after the roots stopped up taking potassium and growing. In the last week of salinity stress, the wild species further increased the root to shoot ratio to enhance the root retention of toxic ions and consequently delaying the damages both to shoot and root. This delay of few weeks in showing the symptoms of stress may be pivotal for enabling the survival of the wild species when soil salinity is transient and not permanent.

The possibility of prolonging space missions—and consequently the permanence of humans in space—depends on the possibility of providing them with an adequate supply of fresh foods to meet their nutritional requirements. This would allow space travelers to mitigate health risks associated with exposure to space radiation, microgravity and psychological stress. In this review, we attempt to critically summarize existing studies with the aim of suggesting possible solutions to overcome the challenges to develop a bio-regenerative life support system (BLSS) that can contribute to life support, supplying food and O2, while removing CO2 on the International Space Station (ISS). We describe the physical constraints and energy requirements for ISS farming in relation to space and energy resources, the problems related to lighting systems and criteria for selecting plants suitable for farming in space and microgravity. Clearly, the dimensions of a growth hardware that can be placed on ISS do not allow to produce enough fresh food to supplement the stored, packaged diet of astronauts; however, experimentation on ISS is pivotal for implementing plant growth systems and paves the way for the next long-duration space missions, including those in cis-lunar space and to the lunar surface.

Arbuscular mycorrhizal fungi (AMF) are a promising tool to improve plant nutrient use efficiency (NUE) and tolerance against abiotic stresses. Moreover, AMF can potentially increase plant productivity and reduce the negative externalities of the agricultural sector. Our study aimed to elucidate whether AMF (containing Rhizoglomus irregulare and Funneliformis mosseae) could positively affect not only tomato growth and productivity but also the nutritional and nutraceutical quality of yellow-pigmented type (‘Giagiù’) and red-pigmented type (‘Lucariello’) tomatoes (Solanum lycopersicum L.). These cherry tomatoes are landraces of the Protected Designation of Origin (PDO) ‘Pomodorino del Piennolo del Vesuvio’ (PPV), one of the most typical agricultural products of the Campania region (Southern Italy). AMF rose fruit yield by increasing the number of fruits per plant (+49% and +29% in ‘Giagiù’ and ‘Lucariello’, respectively) but not of the fruit mean mass. AMF increased lycopene (+40%), total ascorbic acid (TAA; +41%), alanine (+162%), gamma-Aminobutyric acid (GABA; +101%) and branched-chain amino acids (BCAAs; +53%) in ‘Lucariello’. In ‘Giagiù’, AMF increased calcium (+63%), zinc (+45%), ASP (+70%), GABA (+53%) and the essential amino acids arginine (+58%) and lysine (+45%), also indicating a genotype-specific response. In both landraces, AMF improved nutrient uptake and biosynthesis of important molecules involved in the control the oxidative stress and cellular pH. In addition to the beneficial effects of human health, the molecules influenced by the AMF treatment are expected to extend the shelf life of tomato fruits, thus further promoting the useful agronomic application of AMF for premium tomatoes marketed fresh or in pendulums (‘piennoli’).