Search

The increase in the atmospheric CO2concentration is predicted to influence wheat production and grain quality and nutritional properties. In the present study, durum wheat (Triticum durumDesf. cv. Sula) was grown under two different CO2(400 versus 700 μmol mol–1) concentrations to examine effects on the crop yield and grain quality at different phenological stages (from grain filling to maturity). Exposure to elevated CO2significantly increased aboveground biomass and grain yield components. Growth at elevated CO2diminished the elemental N content as well as protein and free amino acids, with a typical decrease in glutamine, which is the most represented amino acid in grain proteins. Such a general decrease in nitrogenous compounds was associated with altered kinetics of protein accumulation, N remobilization, and N partitioning. Our results highlight important modifications of grain metabolism that have implications for its nutritional quality.

A pot experiment with wheat plants was carried out to study how late application of nitrogen (N) fertilizer affects the use of pre‐anthesis N reserves during the grain‐filling period. Increasing doses of N fertilizer were applied (0, 40, and 52 mg N plant–1), either in two amendments (growth stages GS20 and GS30, according to Zadoks scale) or in three amendments (GS20, GS30, and GS37). The experiment was arranged in a complete randomized three‐block design with 129 plants per treatment. The plants were watered daily, harvested every 2 d between anthesis and maturity, and were separated into roots, leaf sheaths, leaf blades, and ears for further N determination. Grain N concentration improved due to a late N application in GS37 by 14% (higher N dose) and by 7% (further splitting the same N‐fertilizer dose, respectively). The higher the N‐fertilizer dose applied, the greater was the amount of pre‐anthesis reserves in vegetative organs, these reserves became later available for remobilization. Although splitting the same N dose in three amendments did not increase the N reserves, these reserves were more efficiently remobilized allowing an improvement in grain N concentration. The fertilizer management did not change the temporary pattern of N accumulation in the ear, but did induce a change in the amount of N remobilized and in the contribution of each organ (root, leaf sheath, leaf blade) to this remobilization. Late N amendment allowed a greater N availability of leaf blades and ear N reserves (from 20% up to 26% and from 19% up to 22%, respectively) for remobilization towards the grain, decreasing the root contribution from 28% down to 15%, while the contribution of leaf sheaths was maintained around 35% irrespective of the N applied.

The photorespiration cycle plays an important role in avoiding carbon drainage from the Calvin cycle and in protecting plants from photoinhibition. The role of photorespiration is frequently underestimated in C4plants, since these are characterized by low photorespiration rates. The aim of this work was to study the relationship between CO2assimilation, PS II photochemistry and the xanthophyll cycle when the photorespiratory cycle is disrupted in Zea mays L. To this end, the photorespiration inhibitor phosphinothricin (PPT) was applied individually or together with the photorespiratory C2acids, glycolate and glyoxylate to maize leaves. Application of PPT alone led to the inhibition of CO2assimilation. Moreover, feeding with glycolate or glyoxylate enhanced the effect of PPT on CO2assimilation. Our results confirm that the avoidance of the accumulation of the photorespiratory metabolites glycolate, glyoxylate or phosphoglycolate, is of vital importance for coordinated functioning between the glycolate pathway and CO2assimilation. Relatively early changes in PS II photochemistry also took place when the photorespiratory cycle was interrupted. Thus, fluorescence photochemical quenching (qP) was slightly reduced (10%) due to the application of PPT together with glycolate or glyoxylate. A decrease in the efficiency of excitation-energy capture by open PS II reaction centres (F′v/F′m) and an increase in thermal energy dissipation (non-photochemical quenching, NPQ) were also measured. These observations are consistent with a limitation of activity of the Calvin cycle and a subsequent lower demand for reduction equivalents. The increase in NPQ is discussed on the basis of changes in the xanthophyll cycle in maize, which seem to provide a limited protective role to avoid photoinhibition when the glycolate pathway is blocked. We conclude that C2photorespiratory acids can act as physiological regulators between the photorespiratory pathway and the Calvin cycle in maize

Phosphinothricin (PPT) and aminooxyacetic acid (AOA) cause a blockage in the photorespiratory pathway and consequently the photosynthesis rate is diminished. Treatments with photorespiratory inhibitors, which last more than 1 h, induce a depletion in the ratios of Fv/Fm, Fv/Fo and Fm/Fo. A good linear relation between the photochemical efficiency of PS II and the quantum yield of the CO2assimilation with both inhibitors was observed. With AOA treatment the photosynthetic quantum yield was practically nill while a depletion of 12 % was observed in the ratio Fv/Fm. With PPT treatment there was a similar decrease in net CO2assimilation and the ratio Fv/Fm. The RUBISCO activity, and not the photochemical efficiency of PS II, would probably be the cause that explains the decrease of photosynthesis rate. A relationship between the 3-PGA content in the leaves and the photochemical efficiency of PS II was observed when the interruption of photorespiration took place. We propose that the Calvin cycle metabolites, and especially those that require ATP and/or NADPH for their metabolism, as for example 3-PGA or triose-P, would control the photosynthetic electron transport capacity when the photorespiration is blocked.

Nitrate (NO3−) and ammonium (NH4+) are the main forms of nitrogen available in the soil for plants. Excessive NH4+accumulation in tissues is toxic for plants and exclusive NH4+-based nutrition enhances this effect. Ammonium toxicity syndrome commonly includes growth impairment, ion imbalance and chlorosis among others. In this work, we observed high intraspecific variability in chlorophyll content in 47 Arabidopsis thaliananatural accessions grown under 1 mM NH4+or 1 mM NO3−as N-source. Interestingly, chlorophyll content increased in every accession upon ammonium nutrition. Moreover, this increase was independent of ammonium tolerance capacity. Thus, chlorosis seems to be an exclusive effect of severe ammonium toxicity while mild ammonium stress induces chlorophyll accumulation.