Drought at the grain filling stage of wheat will cause premature leaf senescence, thus leading to considerable loss of wheat yield. Therefore, this paper aims to establish a cultivation technology for strong drought resistance, delayed senescence, and yield improvement based on the analysis of hormones homeostasis obtained by applying chemical control substances. Experiments were conducted with two genotypes of wheat. Four water irrigation treatments were applied to impose the water deficit, including well-watered control treatment (WW), mild water deficit (MiWD), moderate water deficit (MoWD), and severe water deficit (SWD). Exogenous abscisic acid (ABA) was sprayed on the plants at the anthesis stage of the wheat. As a result, exogenous ABA reduced initial senescence rate (r₀), total duration of chlorophyll (Chl_total), rapid senescence phase (Chl_loss), and the accumulated temperature at an inflection point (M) but improved the persistence phase (Chl_per) of flag leaves under all of the four treatments. However, exogenous ABA produced inconsistent effects on photoassimilate relocation and grain weight under different treatments. It produced positive regulatory effects on grain weight under WW, MiWD, and MoWD treatments. On the one hand, spraying ABA during the persistence phase of flag leaves reduced the ratios of zeatin to gibberellin (Z/GA₃), spermine to spermidine (Spm/Spd), and salicylic acid to ABA (SA/ABA), which prolonged active photosynthesis by stimulating high level of proline (Pro) and increased the activities of antioxidant enzymes, such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX). Therefore, drought tolerance was enhanced, and more photosynthetic assimilates were accumulated. On the other hand, the rapid senescence phase and the transport rate of assimilates into grains were accelerated, resulting in higher grain weight, yield, and water use efficiency (WUE). However, under SWD treatment, exogenous ABA improved the ratio of SA/ABA, leading to low Pro content and low antioxidant enzyme activity of flag leaves in the rapid loss phase. Meanwhile, drought resistance declined and the transport duration of assimilates into grains was shortened, thus making photosynthetic assimilates redundant. Therefore, exogenous ABA can lead to the reduction in grain weight, yield, and WUE of wheat under SWD treatment.

Premature senescence after anthesis reduces crop yields. Delaying leaf senescence could maintain photosynthetic activity for a longer period and lead to a higher photosynthetic rate. Recent studies have provided some insights into the interaction between cytokinin and nitrogen (N) in the regulation of plant development. In the present study, foliar application of exogenous 6-benzylaminopurine (6-BA) and lovastatin, an inhibitor of cytokinin synthesis, was combined with three N rates [0 kg ha⁻¹ (low nitrogen, LN), 240 kg ha⁻¹ (normal nitrogen, NN), and 360 kg ha⁻¹ (high nitrogen, HN)] in two wheat cultivars, Wennong 6 (with a staygreen phenotype) and Jimai 20 (with a non-staygreen phenotype). Flag leaf senescence was assessed using a Gompertz growth curve. Grain mass, dry matter accumulation and distribution, total N of flag leaf, and concentrations of zeatin riboside (ZR) and abscisic acid (ABA) were also used to evaluate the functional characteristics of flag leaves. Grain mass was negatively correlated with initial senescence rate (r₀) and duration of rapid chlorophyll loss (Chl_loss), whereas it was positively correlated with maximum senescence rate (r_max), average senescence rate (r_aver), persistence phase (Chl_per), total duration of flag leaf (Chl_total) and inflection point cumulative temperature (M). Compared to Jimai 20, Wennong 6 had larger r_aver, Chl_per, and Chl_total. The concentration of ZR was highest under the 6-BA × NN treatment, followed by the 6-BA × HN and 6-BA × LN treatments. However, the concentration of ABA showed the opposite trend. It was concluded that the staygreen phenotype Wennong 6 was associated with greater grain mass and altered cytokinin metabolism and could be classified as a functional staygreen type. Foliar application of 6-BA interacting with N at the NN level (240 kg ha⁻¹) may be a beneficial strategy for improving grain yield of wheat by regulating endogenous hormones and the flag leaf senescence process. Increasing endogenous cytokinin promoted the transport of dry matter to grain.

The objective of this study was to investigate whether and how exogenous abscisic acid (ABA) is involved in mediating starch accumulation in the grain and redistribution of carbohydrates during grain filling of two wheat cultivars with different staygreen characteristics. At blooming stage, plants of Wennong 6 (a staygreen cultivar) and Jimai 20 (control) were sprayed with 10 mg L⁻¹ abscisic acid (ABA) for 3 days. The application of ABA significantly (P < 0.05) increased grain filling rate, starch accumulation rate and content, remobilization of dry matters to kernels, and 1000-grain weight of the two cultivars. Exogenous ABA markedly (P < 0.05) increased grain yield at maturity, and Wennong 6 and Jiami 20 showed 14.14% and 4.86% higher compared yield than the control. Dry matter accumulation after anthesis of Wennong 6 was also significantly (P < 0.05) influenced by exogenous ABA, whereas that of Jimai 20 was unchanged. Application of ABA increased endogenous zeatin riboside (ZR) content 7 days after anthesis (DAA), and spraying ABA significantly increased endogenous indole-3-acetic acid (IAA) and ABA contents from 7 to 21 DAA and decreased gibberellin (GA₃) content at 14 DAA, but increased GA₃ content from 21 to 35 DAA. The results suggested that increased yield of staygreen was due to greater starch assimilation owing to a higher filling rate and longer grain-filling duration.

The components and contents of high-molecular-weight glutenin subunits (HMW-GS) in wheat grains affect glutenin macropolymer (GMP) size, which is considered an important flour quality trait in wheat. Four wheat cultivars (Shiluan 02-1, Yannong 24, Jinan 17 and Lumai 21) with different end-use qualities were used to investigate the HMW-GS and GMP contents, and the GMP particle distributions in grain produced under irrigated and rainfed conditions. The percent volume of GMP particles and the contents of HMW-GS and GMP were affected by genotype and soil water. Genotype × soil water interaction was significant only for GMP particles <12 μm and >100 μm in the growing season of 2010–2011. Irrigated and rainfed conditions had different influences on the GMP particle distribution in the four cultivars. Compared to irrigated treatment, the rainfed treatment had higher accumulations of HMW-GS and GMP, especially in cultivars Yannong 24, Jinan 17 and Lumai 21. Rainfed conditions also increased the proportion of large size particles of GMP, indicating that different water regimes had an effect on grain quality. According to correlation coefficients (r), the contents of HMW-GS and GMP in grains were negatively correlated with the volume of <12 μm GMP particles, but positively correlated with GMP particles >100 μm.