Diversity of responses to nitrogen deficiency in distinct wheat genotypes reveals the role of alternative electron flows in photoprotection.

Nitrogen (N) deficiency represents an important limiting factor affecting photosynthetic productivity and the yields of crop plants. Significant reported differences in N use efficiency between the crop species and genotypes provide a good background for the studies of diversity of photosynthetic and photoprotective responses associated with nitrogen deficiency. Using distinct wheat (Triticum aestivum L.) genotypes with previously observed contrasting responses to nitrogen nutrition (cv. Enola and cv. Slomer), we performed advanced analyses of CO2 assimilation, PSII, and PSI photochemistry, also focusing on the heterogeneity of the stress responses in the different leaf levels. Our results confirmed the loss of photosynthetic capacity and enhanced more in lower positions. Non-stomatal limitation of photosynthesis was well reflected by the changes in PSII and PSI photochemistry, including the parameters derived from the fast-fluorescence kinetics. Low photosynthesis in N-deprived leaves, especially in lower positions, was associated with a significant decrease in the activity of alternative electron flows. The exception was the cyclic electron flow around PSI that was enhanced in most of the samples with a low photosynthetic rate. We observed significant genotype-specific responses. An old genotype Slomer with a lower CO2 assimilation rate demonstrated enhanced alternative electron flow and photorespiration capacity. In contrast, a modern, highly productive genotype Enola responded to decreased photosynthesis by a significant increase in nonphotochemical dissipation and cyclic electron flow. Our results illustrate the importance of alternative electron flows for eliminating the excitation pressure at the PSII acceptor side. The decrease in capacity of electron acceptors was balanced by the structural and functional changes of the components of the electron transport chain, leading to a decline of linear electron transport to prevent the overreduction of the PSI acceptor side and related photooxidative damage of photosynthetic structures in leaves exposed to nitrogen deficiency.

Effect of copper oxide and zinc oxide nanoparticles on photosynthesis and physiology of Raphanus sativus L. under salinity stress.

The study evaluates the impact of two metal oxide nanoparticles: copper oxide (CuO) and zinc oxide (ZnO) on the growth and physiology of Raphanus sativus L. (radish) under salinity stress. Fifteen days old seedlings of R. sativus were subjected to different concentrations of salt stress (0 mM, 150 mM, and 300 mM NaCl) alone and in interaction with 100 mgL-1 metal oxide nanoparticle treatments (CuO and ZnO NPs via foliar spray) for 15 days. The results confirmed the severe effects of salinity stress on the growth and physiology of radish plants by decreasing nutrient uptake, leaf area, and photosystems photochemistry and by increasing proline accumulation, anthocyanin, flavonoids content, and antioxidant enzyme activities which is directly linked to increased oxidative stress. The foliar application of CuO and ZnO NPs alleviated the adverse effects of salt stress on radish plants, as indicated by improving these attributes. Foliar spray of ZnO NPs was found efficient in improving the leaf area, photosynthetic electron transport rate, the PSII quantum yield, proton conductance and mineral content in radish plants under NaCl stress. Besides, ZnO NPs decreased the NaCl-induced oxidative stress by declining proline, anthocyanin, and flavonoids contents and enzymatic activities such as superoxide dismutase (SOD), ascorbate peroxidase (APX) and guaiacol peroxidase (GOPX). Thus, our study revealed that ZnO NPs are more effective and have beneficial effects over CuO NPs in promoting growth and reducing the adverse effects of NaCl stress in radish plants.

Pre-Acclimation to Elevated Temperature Stabilizes the Activity of Photosystem I in Wheat Plants Exposed to an Episode of Severe Heat Stress.

The importance of high temperature as an environmental factor is growing in proportion to deepening global climate change. The study aims to evaluate the effects of long-term acclimation of plants to elevated temperature on the tolerance of their photosynthetic apparatus to heat stress. Three wheat (Triticum sp. L.) genotypes differing in leaf and photosynthetic traits were analyzed: Thesee, Roter Samtiger Kolbenweizen, and ANK 32A. The pot experiment was established in natural conditions outdoors (non-acclimated variant), from which a part of the plants was placed in foil tunnel with elevated temperature for 14 days (high temperature-acclimated variant). A severe heat stress screening experiment was induced by an exposition of the plans in a growth chamber with artificial light and air temperature up to 45 °C for ~12 h before the measurements. The measurements of leaf photosynthetic CO2 assimilation, stomatal conductance, and rapid kinetics of chlorophyll a fluorescence was performed. The results confirmed that a high temperature drastically reduced the photosynthetic assimilation rate caused by the non-stomatal (biochemical) limitation of photosynthetic processes. On the other hand, the chlorophyll fluorescence indicated only a moderate level of decrease of quantum efficiency of photosystem (PS) II (Fv/Fm parameter), indicating mostly reversible heat stress effects. The heat stress led to a decrease in the number of active PS II reaction centers (RC/ABS) and overall activity o PSII (PIabs) in all genotypes, whereas the PS I (parameter ψREo) was negatively influenced by heat stress in the non-acclimated variant only. Our results showed that the genotypes differ in acclimation capacity to heat stress, and rapid noninvasive techniques may help screen the stress effects and identify more tolerant crop genotypes. The acclimation was demonstrated more at the PS I level, which may be associated with the upregulation of alternative photosynthetic electron transport pathways with clearly protective functions.

Quantitative response of wheat to sowing dates and irrigation regimes using CERES-Wheat model.

An experiment was conducted at Punjab Agricultural University, Ludhiana during 2014-15 and 2015-16, keeping four sowing dates {25th Oct (D1), 10th Nov (D2), 25th Nov (D3) and 10th Dec (D4)} in main plots and five irrigation schedules {irrigation at 15 (FC15), 25 (FC25), 35 (FC35) and 45 (FC45) % depletion of soil moisture from field capacity (FC) and a conventional practice} in sub plots. The objective of the study was to evaluate the performance of CERES-Wheat model for simulating yield and water use under varying planting and soil moisture regimes. The simulated and observed grain yield was higher in D1, with irrigation applied at FC15 as compared to all other sowing date and irrigation regime combinations. Simulated grain yield decreased by 19% with delay in sowing from 25th October to 10th December because of 8% reduction in simulated crop evapotranspiration. Simulated evapotranspiration decreased by 16%, wheat grain yield by 23% and water productivity by 15% in drip irrigation at 45% depletion from field capacity as compared to drip irrigation at 15% of field capacity. It was further revealed that the model performed well in simulating the phenology, water use and yield of wheat.

Agronomical traits associated with yield and yield components of winter wheat as affected by nitrogen managements.

Nitrogen fertilizer is one of the key elements to increase the yield and significance of winter wheat. The experiment was established in the split zone design and was repeated three times. The nitrogen application level is set to 4 treatments, 75, 150, 225 and 300 kg ha-1 are arranged in the main plot, and different nitrogen application ratios are arranged in the sub-plots, respectively 5:5 (50%+50%) and 6: 4 (60%) + 40%). Nitrogen fertilizer was applied before sowing, jointing stage, flowering stage and filling stage. The experimental plot is 12 m2 (3 m × 4 m). The results showed that under the conditions of 225 kg/hm2 nitrogen application and 60%+40% nitrogen application rate, the yield of Jintai 182 was the highest compared with other treatment groups. With the increase of nitrogen application rate, the number of ears, grains per ear, thousand-grain weight and grain yield all increase first and then decrease. Each factor reached the highest 225 N kg / hm2, 417.17, 30.74, 40.96 g and 6182.11 kg / hm2. Compared with 75 kg/hm2 topdressing fertilizer, 225 kg/hm2 is a more suitable nitrogen fertilizer application rate for winter wheat. Within a reasonable range of nitrogen fertilizer application, there is a significant positive correlation between nitrogen content and winter wheat yield. By studying the amount of nitrogen fertilizer and a reasonable ratio of base fertilizer to topdressing, the utilization rate of nitrogen fertilizer can be maximized and excessive application of nitrogen fertilizer can be avoided.