Photosynthetic Efficiency in Flag Leaves and Ears of Winter Wheat during Fusarium Head Blight Infection

Fusarium head blight (FHB) is one of the most serious fungal diseases of wheat (Triticum aestivum L.). It causes major reduction of grain yield and quality, while the safety of wheat products is at risk due to mycotoxin contaminations. To contribute to a better understanding of mechanisms governing more efficient defense strategies against FHB, an evaluation of photosynthetic efficiency was performed during different phases of infection, i.e., before visual symptoms occur, at the onset and after the development of disease symptoms. Six different winter wheat varieties were artificially inoculated with the most significant causal agents of FHB (Fusarium graminearum and F. culmorum) at two different locations. Photosynthetic efficiency was assessed in flag leaves and ears of inoculated and untreated (control) plants based on measurements of chlorophyll a fluorescence rise kinetics and the calculation of JIP-test parameters. Obtained results indicate that the response of wheat to Fusarium infection includes changes in photosynthetic efficiency which can encompass alternating reductions and increases in photosynthetic performance during the course of the infection in both flag leaves and ears. FHB-induced photosynthetic adjustments were shown to be somewhat variety-specific, but location was shown to be a more significant factor in modulating the response of wheat to Fusarium infection. Changes in chlorophyll a fluorescence rise kinetics could be detected prior to visible symptoms of the disease. Therefore, this method could be applied for the early detection of Fusarium infection, particularly the analysis of L-band appearance, which showed a similar response in all inoculated plants, regardless of variety or location.

Hydrogen peroxide reduces sensitivity to aluminum in canola?

The objective of this study was to evaluate the effect of aluminum and the mitigating potential of H2O2 on the stress and antioxidant responses in canola (Brassica napus var. oleifera (Moench) Delile) affecting the emergence and initial growth of plants. Canola seeds, cultivar Hyola 61, were treated with different concentrations of H2O2 solution (0.0, 0.075, and 0.15 M), and later sown under different concentrations of aluminum (0.0, 10, 20, and 30 mmolc dm-3). After 20 days of plant emergence, survival and growth characteristics were evaluated. 20, 30, 40, 50, and 60 days after emergence, height, chlorophyll index, chlorophyll a fluorescence, and the activity of superoxide dismutase in the roots were determined. The canola is sensitive to aluminum, and the treatment of seeds with H2O2 0.15 M mitigated the stress caused by the highest dose of aluminum. H2O2 treatment enabled high emergence but did not favor seedling survival or growth. The H2O2 did not increase SOD activity. The chlorophyll a fluorescence characteristics proved the sensitivity of canola to aluminum, but the presence of H2O2 maintained the stability and functionality of photosystem II.

Photosynthetic Efficiency and Anatomical Structure of Pepper Leaf (Capsicum annuum L.) Transplants Grown under High-Pressure Sodium (HPS) and Light-Emitting Diode (LED) Supplementary Lighting Systems

The aim of this study was to evaluate the effects of various supplemental greenhouse lighting systems, i.e., high-pressure sodium lamps and mixtures of red and blue light-emitting diodes, on the photochemical efficiency, anatomical leaf structure, and growth of the two pepper cultivars. The intensity levels of the photosynthetically active radiation were the same for both light treatments. In this study, the relative chlorophyll content was measured. Additionally, certain parameters of chlorophyll a fluorescence were measured under ambient light or after dark adaptation. The obtained results showed that the application of light-emitting diodes (LEDs) as supplemental lighting positively affected the anatomical leaf characteristics and plant growth. The leaves of both pepper cultivars were thicker and had larger palisade parenchyma cells under LED supplemental lighting compared to leaves grown under high-pressure sodium (HPS) lamps. Moreover, the mesophyll cells of seedlings grown under LEDs contained more chloroplasts than those growing under HPS lighting. The chlorophyll a fluorescence measurements of pepper seedlings grown under LEDs showed significant increases in photosynthetic apparatus performance index (PI) values compared to plants grown under HPS lamps; however, the values for this index were higher in cv. ‘Aifos’ as compared to cv. ‘Palermo’. We recommend that supplemental lighting systems are applied with caution, as their performance appears to depend not only on the light spectrum but also on the cultivar.

Impact of Selected PSII Parameters on Barley DH Lines Biomass and Yield Elements

In our study, we focused on the link among various parameters of chlorophyll a fluorescence and yield elements in the barley doubled haploid (DH) lines. There were significant differences in all studied DH lines, both in yield components and parameters of chlorophyll a fluorescence. The most variable parameter was overall performance index of PSII (PI) while the least was the amount of energy trapped in PSII reaction centers (TRo/CS). Considering yield components, high variation was also observed in the subsequent order from highest to lowest variation: biomass, thousand-grain weight (TGW) and grain number per plant (GNP). Significant negative correlation was found among the following fluorescence parameters: PI and light energy absorption (ABS/CS), as well as between maximum photochemical efficiency (Fv/Fm) and TGW, and between biomass and electron acceptors pool size from PSII (Area). Conversely, significant positive correlation was found between: Area and PI, Area and energy used for electron transport (ETo/CS), Area and GNP, PI and ETo/CS, PI and GNP, ABS/CS and TRo/CS, as well as between ETo/CS and GNP. Yield components combined with fluorescence parameters of chlorophyll a expressed with canonical variate analysis did not clearly distinguish the barley DH lines into hulled and hull-less groups. The mean value for these groups significantly differs only for ETo/CS and TGW values. The other parameters are distributed almost uniformly in hulled and hull-less lines. However, certain hull-less DH lines possess higher yield parameters compared to parental forms, which suggests a possibility of occurrence of transgression effects. The results suggest the chance to find valuable hull-less forms that are desired by breeders and plant producers, since these forms possess favorable functional features.

Calcium amendment for improved germination, plant growth, and leaf photosynthetic electron transport in oat (Avena sativa) under NaCl stress

Calcium (Ca2+) is an essential nutrient element for plants as it stabilizes the membrane system structure and controls enzyme activity. To investigate the effects of Ca2+ on plant growth and leaf photosynthetic electron transport in oat (Avena sativa) under NaCl stress, oat seeds and plants were cultivated in nutrient solutions with single NaCl treatment and NaCl treatment with CaCl2 amendment. By measuring the seed germination rate, plant growth, Na+ and Cl- accumulation in leaves, ion leakage in seedlings and leaves, prompt chlorophyll a fluorescence (PF) transient (OJIP), delayed chlorophyll a fluorescence (DF), and modulated 820 nm reflection (MR) values of the leaves at different growth phases, we observed that Ca2+ alleviated the inhibition of germination and plant growth and decreased Na+ and Cl- accumulation and ion leakage in the leaves under NaCl stress. NaCl stress changed the curves of the OJIP transient, induced PF intensity at P-step (FP) decrease and PF intensity at J-step (FJ) increase, resulted in obvious K and L bands, and altered the performance index of absorption (PIABS), the absorption of antenna chlorophyll (ABS/RC), electron movement efficiency (ETo/TRo), and potential maximum photosynthetic capacity (FV/FM) values. With the time extension of NaCl stress, I1 and I2 in the DF curve showed a decreasing trend, the lowest values of MR/MRO curve increased, and the highest points of the MR/MRO curve decreased. Compared with NaCl treatment, the extent of change induced by NaCl in the values of OJIP, DF and MR was reduced in the NaCl treatment with CaCl2 amendment. These results revealed that Ca2+ might improve the photosynthetic efficiency and the growth of salt-stressed plants by maintaining the integrity of oxygen-evolving complexes and electron transporters on the side of the PSI receptor and enhancing the relationship between the functional units of the photosynthetic electron transport chain. The findings from this study could be used for improving crop productivity in saline alkali lands.