Search Results (5)

Microgreens, having short growth cycles and efficient nutrient uptake, are ideal candidates for biofortification. This study investigated the effects of selenium (Se) and zinc (Zn) on photosynthetic performance in four hydroponically grown Brassica microgreens (broccoli, pak choi, kohlrabi, and kale), using direct and modulated chlorophyll a fluorescence and chlorophyll-to-carotenoid ratios (Chl/Car). The plants were treated with Na₂SeO₄ at 0 (control), 2, 5, and 10 mg/L or ZnSO₄ × 7H₂O at 0 (control), 5, 10, and 20 mg/L. The results showed species-specific responses with Se or Zn uptake. Selenium enhanced photosynthetic efficiency in a dose-dependent manner for most species (8–26% on average compared to controls). It increased the plant performance index (PI_tot), particularly in pak choi (+62%), by improving both primary photochemistry and inter-photosystem energy transfer. Kale and kohlrabi exhibited high PSII-PSI connectivity for efficient energy distribution, with increased cyclic electron flow around PSI and reduced Chl/Car up to 8.5%, while broccoli was the least responsive. Zinc induced variable responses, reducing PI_tot at lower doses (19–23% average decline), with partial recovery at 20 mg/L (9% average reduction). Broccoli exhibited higher susceptibility, with inhibited Q_A re-oxidation, low electron turnover due to donor-side restrictions, and increased pigment ratio (+3.6%). Kohlrabi and pak choi tolerated moderate Zn levels by redirecting electron flow, but higher Zn levels impaired PSII and PSI function. Kale showed the highest tolerance, maintaining stable photochemical parameters and total electron flow, with increased pigment ratio (+4.5%) indicating better acclimation. These results highlight the beneficial stimulant role of Se and the dual essential/toxic nature of Zn, thus emphasizing genotype and dose-specific optimizations for effective biofortification. Full article

In this study, the functions of the photosynthetic machinery were evaluated using chlorophyll a fluorescence technique (PAM and JIP test) in pea plants (Pisum sativum L. cv Borec) and its LHC II oligomerization variants (mutants Costata 2/133 and Coeruleovireus 2/16). The oligomeric forms of LHCII increased in the following order: Costata 2/133 < Borec wt < Coeruleovireus 2/16. Data revealed that the mutant with higher LHCII oligomerization (Coeruleovireus 2/16) at low light intensity (LL, 150 µmol photons/m²·s) exhibited the following: (i) decreased energy dissipation and increased electron transport efficiency; (ii) higher reaction center density; (iii) increased amounts of the open reaction centers (qp) and their excitation efficiency (Φexc); and (iv) influenced the reoxidation of Q_A⁻, alleviating its interaction with plastoquinone. These effects enhanced photosynthetic performance related to PSII photochemistry (PI_ABS) and overall photosynthetic efficiency (PItotal). High light intensity (HL, 500 µmol photons/m²·s) caused a reduction in open reaction centers (qp), excitation efficiency (Φexc), photochemical energy conversion of PSII (Φ_PSII), maximum efficiency of PSII photochemistry in light (Fv′/Fm′), and linear electron transport via PSII, with more pronounced effects observed in membranes with a lower degree of LHCII oligomerization (Costata 2/133). This study provides novel experimental evidence for the pivotal role of the LHCII structural organization in determining the efficiency of light-dependent reactions of photosynthesis. Full article

The growing issue of salinity is a significant threat to global agriculture, affecting diverse regions worldwide. Nitric oxide (NO) serves as an essential signal molecule in regulating photosynthetic performance under physiological and stress conditions. The present study reveals the protective effects of different concentrations (0–300 µM) of sodium nitroprusside (SNP, a donor of NO) on the functions of the main complexes within the photosynthetic apparatus of maize (Zea mays L. Kerala) under salt stress (150 mM NaCl). The data showed that SNP alleviates salt-induced oxidative stress and prevents changes in the fluidity of thylakoid membranes (Laurdan GP) and energy redistribution between the two photosystems (77K chlorophyll fluorescence ratio F₇₃₅/F₆₈₅). Chlorophyll fluorescence measurements demonstrated that the foliar spray with SNP under salt stress prevents the decline of photosystem II (PSII) open reaction centers (qP) and improves their efficiency (Φexc), thereby influencing Q_A⁻ reoxidation. The data also revealed that SNP protects the rate constants for two pathways of Q_A⁻ reoxidation (k₁ and k₂) from the changes caused by NaCl treatment alone. Additionally, there is a predominance of Q_A⁻ interaction with plastoquinone in comparison to the recombination of electrons in Q_A Q_B⁻ with the oxygen-evolving complex (OEC). The analysis of flash oxygen evolution showed that SNP treatment prevents a salt-induced 10% increase in PSII centers in the S₀ state, i.e., protects the initial S₀–S₁ state distribution, and the modification of the Mn cluster in the OEC. Moreover, this study demonstrates that SNP-induced defense occurs on both the donor and acceptor sides of the PSII, leading to the protection of overall photosystems performance (PI_ABS) and efficient electron transfer from the PSII donor side to the reduction of PSI end electron acceptors (PItotal). This study clearly shows that the optimal protection under salt stress occurs at approximately 50–63 nmoles NO/g FW in leaves, corresponding to foliar spray with 50–150 µM SNP. Full article

Salt stress significantly impacts the functions of the photosynthetic apparatus, with varying degrees of damage to its components. Photosystem II (PSII) is more sensitive to environmental stresses, including salinity, than photosystem I (PSI). This study investigated the effects of different salinity levels (0 to 200 mM NaCl) on the PSII complex in isolated thylakoid membranes from hydroponically grown pea (Pisum sativum L.) and maize (Zea mays L.) plants treated with NaCl for 5 days. The data revealed that salt stress inhibits the photochemical activity of PSII (H₂O → BQ), affecting the energy transfer between the pigment–protein complexes of PSII (as indicated by the fluorescence emission ratio F₆₉₅/F₆₈₅), Q_A reoxidation, and the function of the oxygen-evolving complex (OEC). These processes were more significantly affected in pea than in maize under salinity. Analysis of the oxygen evolution curves after flashes and continuous illumination showed a stronger influence on the PSIIα than PSIIβ centers. The inhibition of oxygen evolution was associated with an increase in misses (α), double hits (β), and blocked centers (S_B) and a decrease in the rate constant of turnover of PSII reaction centers (K_D). Salinity had different effects on the two pathways of Q_A reoxidation in maize and pea. In maize, the electron flow from Q_A- to plastoquinone was dominant after treatment with higher NaCl concentrations (150 mM and 200 mM), while in pea, the electron recombination on Q_AQ_B- with oxidized S₂ (or S₃) of the OEC was more pronounced. Analysis of the 77 K fluorescence emission spectra revealed changes in the ratio of the light-harvesting complex of PSII (LHCII) monomers and trimers to LHCII aggregates after salt treatment. There was also a decrease in pigment composition and an increase in oxidative stress markers, membrane injury index, antioxidant activity (FRAP assay), and antiradical activity (DPPH assay). These effects were more pronounced in pea than in maize after treatment with higher NaCl concentrations (150 mM–200 mM). This study provides insights into how salinity influences the processes in the donor and acceptor sides of PSII in plants with different salt sensitivity. Full article

Excess of cadmium (Cd) in soil leads to a number of adverse effects which challenge agricultural production. Aims of this study were to investigate variations in Cd content in leaves (Zea mays L.) of different maize genotypes and to detect effects of Cd on photosynthesis through chlorophyll a fluorescence. Pot vegetation experiments with four maize genotypes and four different soil Cd levels were repeated for two years. Chlorophyll fluorescence, photosynthetic pigments and inductively coupled plasma (ICP) analysis for ear-leaf Cd and zinc (Zn) and soil Cd were carried out. Significant differences between genotypes were found for leaf Cd, where higher Cd soil concentrations resulted in higher Cd leaf concentrations. Cd uptake into maize leaves increased with increasing Cd levels in soil, which was genotype-dependent and higher and lower Cd accumulating groups were formed. Changes in chlorophyll fluorescence caused by elevated Cd levels in soil were mostly visible as changes in dissipation energy, yields of primary photosystem II photochemistry and electron transport. Decrease of reaction centers per antenna chlorophyll and increased variable fluorescence at J step (V_J) resulted in decrease of performance indexes in the highest Cd concentration. Decreases in chlorophyll fluorescence parameters suggest reduced functionality of reaction centers and problems in re-oxidation of primary quinone acceptor (Q_A). Full article