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In cut flowers, the post-harvest turgor is a critical aspect in a system in which, in the absence of the root system, transpiration water losses must be compensated. Two experiments were conducted in order to elucidate the effect of osmoprotectants (L-Proline) as well as of molecules with antitranspirant behavior (ß-aminobutyric acid - BABA or Pinolene) on the water relations and vase life of rose cut stems. Applications of L-Proline enhanced water fluxes, water conductivity, relative water content and stomatal conductance of rose cut stems in comparison to untreated plants, thus increasing the vase-life of rose cut flowers. BABA treatment reduced the stomatal conductance in rose as well as the daily water consumption, on the other hand senescence phenomena occurred earlier. The water used by pinolene treated stems was lower compared to the control and this was associated with a medium increase of the vase life. Overall, enhanced osmoregulation prolonged the vase life of cut flowers since the improved water status allowed the cut stem to partially continue its metabolic functions. On the other hand, the control of transpirational flux was functional in maintaining cellular turgor in pinolene treated cut stems, whereas with BABA, senescence phenomena occurred probably due to the activation of biochemical pathway of senescence involving abscisic acid. Taking all together, osmoregulation or direct control of transpirational fluxes may provide a promising avenue for improving the post-harvest longevity of cut roses., Advances in Horticultural Science, Vol 32 No 3 (2018): Special issue on Postharvest

This PhD Thesis address, on cut flowers vase life, physiological mechanisms aimed at maintaining and regulating tissues hydration, cellular turgor, water use and senescence phenomena. Specifically we considered the effect of compatible solutes (osmoregulation) on water status, hydration state and vase life of cut stems of rose and carnation (chapter 1). In the second chapter we evaluated the application of anti-transpirant compounds that may act indirectly or directly on rose cut stems transpiration, in order to control the water use and longevity during the vase life. Finally (Chapter 3) we assessed how anti ethylene compounds may delay senescence phenomena of carnation cut stems, with the purpose to evaluate this effect in terms of on water balance, hydration and longevity during the vase life.

Biostimulants have rapidly and widely been adopted as growth enhancers and stress protectants in agriculture, however, due to the complex nature of these products, their mechanism of action is not clearly understood. By using two algal based commercial biostimulants in combination with the Solanum lycopersicum cv. MicroTom model system, we assessed how the modulation of nitrogen metabolites and potassium levels could contribute to mediate physiological mechanisms that are known to occur in response to salt/and or osmotic stress. Here we provide evidence that the reshaping of amino acid metabolism can work as a functional effector, coordinating ion homeostasis, osmotic adjustment and scavenging of reactive oxygen species under increased osmotic stress in MicroTom plant cells. The Superfifty biostimulant is responsible for a minor amino acid rich-phenotype and could represent an interesting instrument to untangle nitrogen metabolism dynamics in response to salinity and/or osmotic stress.

A mild salinity stress (eustress) may modulate the induction of the plant defense system in horticultural crops and the synthesis of phytochemical components able to enhance plant resilience, post-harvest performance, and the nutraceutical quality of produce. However, the choice of the correct eustress type and dose to induce the synthesis of these protective phytochemicals is pivotal to avoid potential interference with plant growth and productivity. In order to study how green and red lettuce (Lactuca sativa L.) plants equilibrate the nutritional and nutraceutical components of quality with yield components, we applied iso-osmotic concentrations of three different salts (20 mM NaCl, 20 mM KCl, and 13.3 mM CaCl2, with a final total ionic concentration of 40 mM) in combination with two successive harvests in a floating raft system. The biometric parameters, mineral composition, bioactive compounds, and antioxidant activity of both cultivars were analyzed. The green cultivar had a superior response concerning biometric traits and productivity compared to the red one during the first cut but lower phytochemical content (e.g., ascorbic acid). The effect of cut order, independently of cultivar and salinity treatments, demonstrated that at the first harvest plants could redirect metabolism by increasing the lipophilic antioxidant content (LAA) at the expense of plant yield, therefore increasing plant resilience and post-harvest nutraceutical quality, whereas, at the second harvest, plants reverted principally to tissue expansion. The treatments with iso-osmotic salt concentrations did not affect K and Mg ion contents but further increased LAA and resulted only in a moderate decrease of fresh yield. The lettuce nitrate content was reduced during the second cut only when lettuce plants were treated with NaCl and especially CaCl2.

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.

Pre-treatment of tomato plants with micromolar concentrations of omeprazole (OP), a benzimidazole proton pump inhibitor in mammalian systems, improves plant growth in terms of fresh weight of shoot and roots by 49 and 55% and dry weight by 54 and 105% under salt stress conditions (200 mM NaCl), respectively. Assessment of gas exchange, ion distribution, and gene expression profile in different organs strongly indicates that OP interferes with key components of the stress adaptation machinery, including hormonal control of root development (improving length and branching), protection of the photosynthetic system (improving quantum yield of photosystem II) and regulation of ion homeostasis (improving the K+: Na+ ratio in leaves and roots). To our knowledge OP is one of the few known molecules that at micromolar concentrations manifests a dual function as growth enhancer and salt stress protectant. Therefore, OP can be used as new inducer of stress tolerance to better understand molecular and physiological stress adaptation paths in plants and to design new products to improve crop performance under suboptimal growth conditions. Highlight: Omeprazole enhances growth of tomato and increases tolerance to salinity stress through alterations of gene expression and ion uptake and transport.

Fresh sprouts constitute an appealing, nutritional and functional food product. The present study profiles the nutritional and bioactive components of quality of fresh sprouts of five select species (barley, lentil, mung bean, radish and wheat) against their postharvest performance during 4 °C cold storage. Moreover, the impact of lyophilisation followed by 30-day ambient storage was assessed on sprouts composition and quality. The highest proteins, P and K contents were observed in radish sprouts. Moreover, radish sprouts demonstrated higher hydrophilic and lipophilic antioxidant activities (HAA and LAA) by 185% and 95%, respectively, than the other species examined. Compositional and quality attributes were however influenced by storage: total soluble solids increased on average by 1.0 °Brix after day 0, while LAA activity decreased by 33% after day 1. Dry matter, proteins and nitrate contents, juice pH and HAA remained stable. Lyophilisation preserved the compositional and quality attributes of fresh sprouts as no significant differences in proteins, nitrate, K and P contents, HAA and LAA were observed compared to fresh sprouts. The current findings highlight genotypic variation and postharvest performance of fresh sprouts with respect to their functional quality and the impact of lyophilisation as an alternative processing application for their preservation.

The scarcity of good quality water frequently led to the use of saline water for the irrigation of ornamental shrubs. Therefore, their salt tolerance needs to be investigated, along with the possibility to counteract the effect of salinity exposure on plant growth and ornamental quality, possibly due to reduced growth, and nutritional imbalances. Under salt stress conditions, plants can activate mechanisms helping to withstand it, such as the production of several organic solutes that play a role in the osmotic adjustment. Aiming to this extent the exogenous application of osmolytes, such as glycine betaine (GB) and L-proline (L-P), has been tested on potted plants of Viburnum lucidum L. grown under saline irrigation. The experiment was designed as a factorial combination of two nutrient solutions (non-salt control, or 200 mM NaCl) and three osmoprotectant treatments (untreated, GB 2.5 mM, or L-P 5 mM application). Shoot and root biomass were negatively affected by salinity (-37 and -29%, respectively), but not the shoot/root ratio. A significant and positive effect of osmolytes application was found on the shoot biomass of plants treated with GB (+46%). Lateral sprouting total length per plant was also reduced by saline irrigation (-60%), but the GB application resulted in a significant increase (+102%). A positive effect of GB application was also found on the total leaf area (LA) per plant that was increased by 182% under saline conditions. Root/shoot ratio did not change with salinity. L-P application resulted in a significant increase of both shoot and root biomass per unit of LA (+40 and +85%, respectively) in comparison with the untreated control and GB.

Stress conditions experienced during growth may affect plant responses during post-harvest storage and eventually determine the overall quality of commercial products. In this context, we hypothesized that foliar applications of proline during the growth cycle and light exposure during post-harvest storage could be two important modulators of yield and quality parameters of rocket plants exposed to NaCl stress. Dry matter percentage increased upon NaCl treatment. However, fresh weight loss during storage did not change over time as a consequence of salt stress. High salinity (100 mM NaCl) moderately reduced both leaf nitrate (14%) and nitrite (3%) contents. Lipophilic (LAC) and hydrophilic (HAC) antioxidant activities also decreased by 10% at the highest salinization (average of two growth cycles). In contrast, during storage, LAC decreased whereas HAC increased. Proline applications reduced the leaf nitrate content during storage by 16%, increased carotenoids and chlorophyll contents in salinized plants and also increased the ascorbate leaf concentration in both salinized and non-salinzed plants. Light storage enhanced fresh weight loss in contrast to dark storage. However the exposure to light reduced leaf nitrate levels by 7% (average of two growth cycles) and contributed to maintain high leaf ascorbate concentrations over time. The combined control of plant physiological responses to environmental stressors and post-harvest storage parameters may affect the nutritional profile of fresh rocket and consequently should be considered to define standard production protocols to improve the nutritional qualities of commercial produce.

Closed or virtually­closed (no­drain) growing systems, where water is recovered and reused, can maximize resources use efficiency and minimize the runoff­related environmental pollution in protected floriculture. Nevertheless these systems have high investment and running costs and must rely on high quality water, which is not always available in Mediterranean coastal regions. With the aim of contributing to the improvement of hydroponic cut flower cultivation in Southern Italy, experiments were carried out on two cultivars of Curcuma alismatifolia Gagnep (‘Pink’and 'White') to verify the response of this species to a closed growing systems. In addition, the effects of increasing the salinity of the recirculating nutrient solution (0%; 0.125% and 0.25% NaCl) were investigated on the cultivar ‘Pink’. During the experiment plant growth, number of cut flower per plant, gas exchange, water relations and leaf mineral concentration were measured. The results demonstrated that nutrients and water use efficiencies can be considerably improved upon introduction of closed soilless systems. These systems are suitable for cultivation of crops with short growing cycle such as Curcuma and other bulbous crops also in presence of moderately saline water. Indeed, since to an increasing water salinity corresponded decreasing leaf area end total plant biomass, the water uptakes were reduced. There was also a clear effect of salinity on cut flower yield and mineral composition of leaves and rhizomes that suggested to adjust the fertilizer concentration to the growth phases of the plant.