•PH and SWE application effects on lettuce at 0 or 40 mM NaCl was explored.•PH treatment reduced Na and Cl contents while increased those of S, K and Mg.•Glucosinolates, phytoalexins and jasmonates ...were modulated by the biostimulants.•The protein hydrolysate and the seaweed elicited distinct metabolic processes.
The use of plant biostimulants such as seaweed extracts (SWE) and protein hydrolysates (PH) has grown in the recent years due to their beneficial effects on yield under both optimal and sub-optimal conditions such as salt stress. The comprehension of the mode of action of these two important categories of biostimulants on plant performance will allow to use them more efficiently under different growth conditions. This study aimed to examine the efficacy of a seaweed and plant-based biostimulants on greenhouse lettuce (Lactuca sativa L.) grown under non-saline (0 mM NaCl) and saline conditions (40 mM NaCl) in terms of growth, yield, SPAD index, leaf mineral composition and metabolomic profiling. Shoot fresh weight of lettuce was reduced by 15.3% under 40 mM of NaCl. Nonetheless, it was boosted by both used biostimulants by 9 and 18%, on average, under 0 and 40 mM NaCl salinity, respectively. Na content under saline conditions was reduced in the presence of the biostimulants treatment, where PH reduced it significantly by 15.6% and SWE by 9.4%. On the other hand, Cl content was significantly reduced only under PH treatment. Both biostimulants elicited a broad metabolic reprogramming, involving the accumulation of stress-related compounds such as glucosinolates, terpenoid phytoalexins, and jasmonates. Interestingly, distinctive metabolomic signatures could be observed following the application of the different biostimulants under salinity conditions. In more detail, PH promoted the accumulation of glucosinolates and phytoalexins precursors, while SWE induced a down accumulation of secondary metabolites. Our findings indicate different processes being modulated by PH and SWE, with possible synergistic effects, thus paving the way towards integrated strategies to alleviate the detrimental effects of salinity in lettuce.
Lettuce is a common vegetable in hydroponic production. In this paper, a selenium (Se)-biofortification method was provided. The Se content, speciation, and the effects of different concentrations of ...selenate and selenite on lettuce growth and amino acids were investigated. The results showed that lettuce had strong ability to accumulate exogenous selenium, and inorganic Se could be effectively converted into organic Se. The proportion of organic Se in the shoots under treatment with 4 μmol L−1 selenite was 100%. Selenomethionine was the main organic Se, accounting for 51% (selenate) and 90% (selenite) of the total Se. Adding Se improves photosynthesis of lettuce and promotes growth. The growth with 2 μmol L−1 selenate and 4 μmol L−1 selenite was better than CK, and the shoot fresh weight was increased by 143.22% and 166.98%, respectively. Furthermore, the optimum Se application is 2 μmol L−1, and some areas can apply 4 μmol L−1 selenite. But Se-excessive areas are not recommended to grow selenium-rich foods. Therefore, lettuce has strong biofortification potential.
•Selenomethionine is the predominant selenium speciation in Se-biofortified.•No potential risk was found with apply low concentrations of exogenous selenium.•Selenite is safer and more effective for selenium supplementation.•Se-biofortified lettuce may be a suitable selenium supplement for increasing Se intake human.
At higher temperatures, lettuce seeds may not germinate, resulting in problems for crop establishment in the field and production. This study aimed to evaluate the maternal effect for thermotolerance ...on lettuce seeds and find enzymatic markers. We used the thermoinhibition tolerant cultivar ‘Everglades’, the sensitive ‘Verônica’, their reciprocal hybrids, F1 and F2 generation. Seeds were submitted to germination and enzymatic tests (catalase, superoxide dismutase, ascorbate peroxidase, and endo- β-mannanase). Germination (first and final counting) and speed index were compared through Tukey’s test. ‘Everglades’ and its reciprocal hybrids, have not been influenced by temperature regarding germination compared to the other treatments. Also, the maternal effect was observed for the F1 generation. Higher temperatures interfere with the activity of all enzymes evaluated, consequently in the physiological parameters. However, superoxide dismutase and endo- β-mannanase have shown direct and more expressive correlation with changes on the physiological parameters compared to the other enzymes. Thus, it is possible to conclude that those enzymes can be used as markers for thermotolerant genotype selection.
Resumo: Sob altas temperaturas, sementes de alface não germinam, resultando em problemas para o estabelecimento da cultura em condição de campo. Esse trabalho analisou a possibilidade de presença de efeito maternal na termotolerância em sementes de alface e buscou marcadores enzimáticos para tal. Usaram-se as cultivares Everglades (tolerante) e ‘Verônica’ (sensível), bem como seus híbridos recíprocos e a geração F2. As sementes foram analisadas quanto à germinação, bem como atividade enzimática (catalase, superóxido dismutase, ascorbato peroxidase e endo-β-mananase). O percentual de germinação; (primeira contagem e final), bem como a velocidade (IVG) foram analisados por meio de ANOVA e teste de Tukey. A cultivar Everglades e seus híbridos recíprocos não foram influenciados pela germinação em alta temperatura quando comparados com os outros tratamentos. Além disso, o efeito maternal foi observado na geração F1. Altas temperaturas interferem na atividade de todas as enzimas analisadas nesta pesquisa, consequentemente também nos parâmetros fisiológicos. Contudo, a superóxido dismutase e a endo-β-mananase tiveram suas variações altamente correlacionadas com as mudanças nos parâmetros fisiológicos. O presente trabalho evidenciou o efeito materno para a termotolerância em sementes de alface, bem como o uso da superóxido dismutase e endo-β-mananase como marcadores enzimáticos para tal característica.
Modified atmosphere packaging (MAP) has the potential to extend the shelf-life of fresh-cut lettuce mainly by limiting the oxidation processes. However, exposure to light conditions has been ...described as causing browning and quality loss. The influence of O
2 partial pressures (
pO
2) and light exposure during storage on the shelf-life of fresh-cut Romaine lettuce was studied. Fresh-cut lettuce was exposed daily during storage to different light conditions: light (24
h), darkness (24
h) and photoperiod (12
h light
+
12
h darkness). Changes in respiration rate, headspace gas composition, sensory quality, colour, electrolyte leakage, stomatal opening, water loss, texture and compositional constituents related to browning such as vitamin C and individual and total phenolic compounds were evaluated. Different weight samples (75–275
g), packaged with an initial
pO
2 of 0.5–2.0
kPa balanced with N
2, reached
pO
2 from 0.1 to 1.5 at the steady-state. Atmospheres with low
pO
2 (0.2–0.5) at the steady-state preserved lettuce quality by the control of browning and the prevention of off-odours and off-flavours. Light exposure during storage positively influenced the number of open stomata (74% in light vs 24% in darkness) which contributed slightly to weight loss. Consumption of O
2 in samples exposed to light differed significantly from those stored in photoperiod or darkness (10.6
±
7.0, 18.3
±
3.5 and 25.8
±
8.6
nmol
O
2
kg
−1
s
−1, respectively). Packages exposed to light showed higher
pO
2 compared with packages stored in darkness while those exposed to photoperiod had intermediate values. Moreover, location of the packages in the shelves affected package headspace gas composition and thus, packages near the front of the shelves showed higher
pO
2 than those at the back. The different light conditions did not influence the content of vitamin C or the individual and total phenolic compounds. This study shows that under light conditions respiration activity was compensated by photosynthesis resulting in a higher
pO
2. Thus, browning of fresh-cut Romaine lettuce can be promoted by light exposure during storage as it increases headspace
pO
2.
Salicylic acid (SA) is a phytohormone that plays a key role in the regulation of the defense response against environmental variables in plants, and it provides increased yield and stress tolerance ...when exogenously applied to plants as a growth regulator. The role of SA-mediated signals in abiotic stress tolerance varies according to the species, stressor, application method, and dose. This study investigated the effects of salicylic acid (SA, 0.1 mg ml−1) or β-cyclodextrin encapsulated salicylic acid (e-SA, 0.1 mg ml−1) treatments on growth parameters, gas exchange, photosynthesis efficiency, and antioxidant capacity in lettuce seedlings exposed to polycyclic aromatic hydrocarbon pollution. Fluorene (FLN, 100 mg L−1) contamination resulted in a 27% growth rate and a 14% water content reduction in lettuce leaves. Significant suppressions of stomatal conductance, carbon assimilation, and PSII photochemistry were detected in plants under stress. FLN + SA and FLN + e-SA treatments regulated plant-water relations by stimulating proline accumulation and relieving stomatal limitations. As indicated by the high Fv/Fm ratio, photosynthesis efficiency was recovered in FLN + SA and FLN + e-SA group plants. FLN stress caused high oxidative stress in lettuce leaves and increased lipid peroxidation level by 40%. However, especially e-SA application to plants under stress, increased SOD activity by 3-fold and CAT activity by 80% and was successful in preventing H2O2 accumulation and lipid peroxidation. Both SA and e-SA treatments partially activated the AsA-GSH cycle. As a result, direct SA application was effective in mitigating stress-induced physiological limitations with high SA accumulation in the tissues, while encapsulated SA treatment was more effective in regulating photosynthetic and biochemical reactions, alleviating oxidative damage by activating the antioxidant defense, and promoting growth under stress with moderate SA accumulation.
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•PAH contamination caused oxidative stress and growth reduction in lettuce.•SA treatments relieved stomatal limitation and photosynthesis inhibition.•Foliar e-SA application resulted in moderate hormone accumulation in tissues.•Both, SA and e-SA induced antioxidant enzyme activities in stressed plants.•Encapsulated SA was more effective in providing resilience to FLN stress.
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