Effects of Low Temperature at Booting Stage on Sucrose Metabolism and Endogenous Hormone Contents in Winter Wheat Spikelet

Low spring temperatures often occur during the winter wheat booting stage, when the young ears are very sensitive to cold. In this study, we used two wheat varieties differing in cold sensitivity (sensitive variety Yangmai 18 and tolerant variety Yannong 19) to examine the effect of low temperature on wheat grain number at booting stage. Low temperature stress was simulated in an artificial climate chamber at 4°C for 60 h in 2016 and at 2, 0, or −2°C for 24 h in morphological assays, showing that the development of wheat spikelets was inhibited and floret growth was delayed following low temperature stress. However, an increase in the sucrose content of young panicles was also observed, and the activity of enzymes involved in sucrose metabolism was dynamically altered. Sucrose phosphate synthase activity was enhanced, and sucrose synthase activity significantly increased after treatment at 4 and 2°C, respectively. However, activities of sucrose synthase and invertase decreased with a reduction in temperature. Gene expression assays further revealed downregulation of TaSuS1 expression and upregulation of TaSuS2, while expression of CWINV was inhibited. Moreover, phytohormone content assays showed an increase in the content of abscisic acid in young wheat ears, but a decrease in the content of auxin and gibberellins. The grain number per spike and 1000-grain weight also showed a downward trend following low temperature stress. Overall, these findings suggest that low temperature at booting induces abscisic acid accumulation in winter wheat, altering the activity of the enzymes involved in sucrose metabolism, which leads to an accumulation of sucrose in the young ears, thereby having a negative effect on wheat production

Salicylic Acid Reduces Wheat Yield Loss Caused by High Temperature Stress by Enhancing the Photosynthetic Performance of the Flag Leaves

High temperature stress during grain filling substantially decreases wheat productivity; thus, to ensure food security, heat tolerance in wheat must be developed. It remains unclear whether exogenous salicylic acid (SA) can induce tolerance to high temperatures in wheat at the grain-filling stage. In this study, a two-year pot culture experiment using the wheat cultivar ‘Yangmai 18’ was conducted from 2018 to 2020. The plants were pre-sprayed with SA from the heading stage (SAH), anthesis stage (SAA), 5 days after anthesis (DAA; SA5), and 10 DAA (SA10). After that, the wheat plants were subjected to high temperature stress (G) simulated using a passive warming method during the period between 15 and 19 DAA. The results showed that, compared with the normal temperature control group (NN), high temperature stress at the grain-filling stage significantly reduced the yield and photosynthetic capacity of wheat. The application of SA at different stages reduced the yield loss and the damage to the photosynthetic capacity caused by high temperature stress; the effectiveness of the treatments in descending order was SAAG > SA5G > SA10G > SAHG. Exogenous SA treatment increased the amount and proportion of dry matter distributed in the stem sheaths and leaves and grains, and decreased the amount and proportion of dry matter distributed in the rachises and glumes at the maturity stage, thereby reducing the yield loss under high temperature stress. The application of SA significantly increased the leaf area, stomatal density, chlorophyll content, soluble protein content, maximum photochemical efficiency (Fv/Fm), actual photochemical efficiency (ΦPSII), and activity of sucrose phosphate synthase (SPS) of the wheat flag leaves under high temperature stress at the grain-filling stage, thereby improving the photosynthetic performance of the flag leaves under stress. In summary, exogenous SA significantly restored the photosynthetic capacity of wheat flag leaves injured by post-anthesis high temperature stress, which effectively alleviated the inhibition of wheat growth caused by the stress and ultimately reduced the yield loss. Spraying SA at the anthesis stage had the greatest effect abating the loss of yield and reduced photosynthetic performance under high temperature stress

Salicylic Acid Reduces Wheat Yield Loss Caused by High Temperature Stress by Enhancing the Photosynthetic Performance of the Flag Leaves

High temperature stress during grain filling substantially decreases wheat productivity; thus, to ensure food security, heat tolerance in wheat must be developed. It remains unclear whether exogenous salicylic acid (SA) can induce tolerance to high temperatures in wheat at the grain-filling stage. In this study, a two-year pot culture experiment using the wheat cultivar ‘Yangmai 18’ was conducted from 2018 to 2020. The plants were pre-sprayed with SA from the heading stage (SAH), anthesis stage (SAA), 5 days after anthesis (DAA; SA5), and 10 DAA (SA10). After that, the wheat plants were subjected to high temperature stress (G) simulated using a passive warming method during the period between 15 and 19 DAA. The results showed that, compared with the normal temperature control group (NN), high temperature stress at the grain-filling stage significantly reduced the yield and photosynthetic capacity of wheat. The application of SA at different stages reduced the yield loss and the damage to the photosynthetic capacity caused by high temperature stress; the effectiveness of the treatments in descending order was SAAG > SA5G > SA10G > SAHG. Exogenous SA treatment increased the amount and proportion of dry matter distributed in the stem sheaths and leaves and grains, and decreased the amount and proportion of dry matter distributed in the rachises and glumes at the maturity stage, thereby reducing the yield loss under high temperature stress. The application of SA significantly increased the leaf area, stomatal density, chlorophyll content, soluble protein content, maximum photochemical efficiency (Fv/Fm), actual photochemical efficiency (ΦPSII), and activity of sucrose phosphate synthase (SPS) of the wheat flag leaves under high temperature stress at the grain-filling stage, thereby improving the photosynthetic performance of the flag leaves under stress. In summary, exogenous SA significantly restored the photosynthetic capacity of wheat flag leaves injured by post-anthesis high temperature stress, which effectively alleviated the inhibition of wheat growth caused by the stress and ultimately reduced the yield loss. Spraying SA at the anthesis stage had the greatest effect abating the loss of yield and reduced photosynthetic performance under high temperature stress

Spearman correlation coefficients between daily air pollutant concentrations and weather conditions in Beijing (2009∼2010).

*<p><i>P</i><0.05.</p

Summary statistics of daily death numbers, air pollution concentrations and weather conditions in Beijing, China (2009∼2010).

a<p>Twenty-four-hour average for CO, NO₂ and PM₁₀.</p>*<p>minimum.</p>**<p>the 25^th, 50^th (median) and 75^th percentile, respectively.</p>***<p>maximum.</p

Locations of twelve monitoring stations in Beijing.

<p>Locations of twelve monitoring stations in Beijing.</p

Percent increase of daily mortality associated with an IQR increase of CO, NO₂ and PM₁₀ with single model and principal component analysis in Beijing (mean and 95% CI), using 8 df/year.^a

a<p>We applied current-day (lag 0 day) temperature and relative humidity and 2-day moving average of air pollutant concentrations (lag01), and applied 8 df per year for time, 3 df to temperature, humidity and barometric pressure.</p>*<p><i>P</i><0.05.</p