Effects of spraying exogenous cytokinin or spermine on the starch physicochemical properties of waxy maize exposed to post-silking high temperature

Effects of exogenous brassinosteroids on the starch structure, physicochemical properties and digestibility of wheat under high-temperature stress at the early grain-filling stage

The starch synthesis of wheat was seriously affected by high temperature stress, which affected its yield and quality. At the same time, plant hormones are often used to regulate crop production and mitigate environmental stress in times of adversity. However, whether Brassinosteroids (BRs) can alleviate the adverse effects of high-temperature stress on wheat starch and its internal mechanism are still unclear. Therefore, a two-year field experiment was carried out from 2020 to 2022 to explore the effects of exogenous BRs spraying on the wheat yield, morphological structure and physicochemical properties of starch under high-temperature stress at the early grain-filling stage. The results showed that exogenous spraying of BRs under high-temperature stress increased the activity of key enzymes involved in starch synthesis, the contents of amylose (25.34 %) and amylopectin (11.57 %) were increased on average in two years, and ultimately increased the yield. On the other hand, BRs increased the number of B-type (49.90 %) and C-type starch granules (23.19 %), decreased the number of A-type starch granules (6.38 %) under high-temperature stress, and reduced the chain length of B1 (5.04 %) and B2 (4.88 %) chains of amylopectin. Moreover, BRs decreased crystallinity (25.40 %), gelatinization enthalpy (4.76 %) and 1047/1022 cm-1 (1.25 %), thereby improving the cooking quality of the starch. Through further analysis of the rheological properties and digestibility of starch, BRs improved the processing quality of starch and increased the content of resistant starch (RS, 15.77 %), which provided insights for the processing and utilization of food. In summary, under high-temperature stress, exogenous BRs increased wheat yield and improved starch quality. We recommend BRs as an effective management measure to mitigate high-temperature stress to cope with future climate change.

Effect of high temperature on maize yield and grain components: A meta-analysis

Global warming poses a significant challenge to global food security, with maize playing a vital role as a staple crop in ensuring food availability worldwide. Therefore, investigating the impact of high temperature (HT) on maize cultivation is imperative for addressing food security concerns. Despite numerous studies exploring the effects of HT on maize growth and yield, a comprehensive understanding of these effects remains elusive due to variations in experimental environments, varieties, and growth stages. To solve these limitations, a meta-analysis was conducted to assess the effects of HT on maize yield and grain components, synthesizing data from 575 observations across 34 studies. The findings indicate that 1) HT significantly reduced grain yield by 32.7-40.9 % and grain starch content by 2.8-10.5 %; 2) the vicinity of kernel development stage (include silking, blister, milk) is the period when maize kernels are most sensitive to HT; 3) a significant negative correlation was observed between HT degree and their impact on grain yield (R2 = 0.38, P = 0.043); and 4) the effects of HT days and degrees on maize yield were equally important. In conclusion, this meta-analysis establishes a theoretical framework for enhancing the resilience of maize production and cultivation practices by comprehensively evaluating the impact of HT on yield and grain components.

Effects of exogenous salicylic acid on starch physicochemical properties and in vitro digestion under heat stress during the grain-filling stage in waxy maize

Waxy maize starch serves as a pivotal component in global food processing and industrial applications, while high temperature (HT) during the grain-filling stage seriously affects its quality. Salicylic acid (SA) has been recognized for its role in enhancing plant heat resistance. Nonetheless, its regulatory effect on the quality of waxy maize starch under HT conditions remains unclear. In this study, two waxy maize varieties, JKN2000 (heat-tolerant) and SYN5 (heat-sensitive) were treated with SA after pollination and then subjected to HT during the grain-filling stage to explore the effect of SA on grain yield and starch quality. The results indicate that exogenous SA under HT treatment led to an increase in kernel weight and starch content in both varieties. Moreover, SA reduced the HT-induced holes on the surfaces of starch granules, enlarged the starch granule size, elevated the amylopectin branching degree, and reduced amylopectin average chain length. Consequently, improvements of pasting viscosity and the decrease of retrogradation percentage of starch were observed with SA under HT. Exogenous SA reduced HT-induced rapidly digestible starch content in SYN5, but had no significant effect on that in JKN2000. In summary, SA pretreatment effectively alleviated the detrimental effects of HT on starch pasting and thermal properties of waxy maize.

Starch structural and functional properties of waxy maize under different temperature regimes at grain formation stage

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Excessive high temperature (>35 °C) enlarges and corrodes the starch granules.

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Heat stress increases the proportion of amylopectin long chains.

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Extremely high temperature induces the lowest pasting viscosity and the highest retrogradation of starch.

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This study provides scientific basis for the deterioration of waxy maize starch under severe high temperature.

Global warming affects crop productivity, but the influence is uncertain under different temperature regimes. The impact of growth temperatures (T0, 28 °C/20 °C; T1, 32 °C/24 °C; T2, 36 °C/28 °C; T3, 40 °C/32 °C) at grain formation stage on the waxy maize starch physicochemical properties of Suyunuo5 (heat-sensitive hybrid) and Yunuo7 (heat-tolerant hybrid) was studied. Compared with T0, T2 and T3 resulted in a higher number of starch granules with more pitted or uneven surface due to the enhanced enzymatic activities of α-amylase and β-amylase. Meanwhile, large starch granule size, long amylopectin chain-length, and high relative crystallinity under T2 and T3 resulted in low pasting viscosities and gelatinization enthalpy and high retrogradation percentage, especially under T3. The low coefficient variation of gelatinization temperatures indicated that the differences were meaninglessness. The influence of T1 on the pasting viscosities were more obvious in Suyunuo5. In conclusion, high temperatures at grain formation stage deteriorated the starch pasting and retrogradation properties.