Seed filling in maize and hormones crosstalk regulated by exogenous application of uniconazole in semiarid regions

Integrated metabolomic and transcriptomic analyses of regulatory mechanisms associated with uniconazole-induced dwarfism in banana

BACKGROUND

Uniconazole is an effective plant growth regulator that can be used in banana cultivation to promote dwarfing and enhance lodging resistance. However, the mechanisms underlying banana dwarfing induced by uniconazole are unknown. In uniconazole-treated bananas, gibberellin (GA) was downregulated compared to the control groups. An integrative analysis of transcriptomes and metabolomes was performed on dwarf bananas induced by uniconazole and control groups. The key pathways involved in uniconazole-induced dwarfism in banana were determined according to the overlap of KEGG annotation of differentially expressed genes and (DEGs) differential abundant metabolites (DAMs).

RESULTS

Compared with the control groups, the levels of some flavonoids, tannins, and alkaloids increased, and those of most lipids, amino acids and derivatives, organic acids, nucleotides and derivatives, and terpenoids decreased in uniconazole-treated bananas. Metabolome analysis revealed the significant changes of flavonoids in uniconazole-treated bananas compared to control samples at both 15 days and 25 days post treatment. Transcriptome analysis shows that the DEGs between the treatment and control groups were related to a series of metabolic pathways, including lignin biosynthesis, phenylpropanoid metabolism, and peroxidase activity. Comprehensive analysis of the key pathways of co-enrichment of DEGs and DAMs from 15 d to 25 d after uniconazole treatment shows that flavonoid biosynthesis was upregulated.

CONCLUSIONS

In addition to the decrease in GA, the increase in tannin procyanidin B1 may contribute to dwarfing of banana plants by inhibiting the activity of GA. The increased of flavonoid biosynthesis and the change of lignin biosynthesis may lead to dwarfing phenotype of banana plants. This study expands our understanding of the mechanisms underlying uniconazole-induced banana dwarfing.

Effect of Plant Growth Regulators on Cotton Seedling Root Growth Parameters and Enzyme Activity

It is well known that the survival rate of cotton seedlings is low, and the growth and development status at this stage is crucial to improve productivity. Plant hormones are important factors that promote the growth and development of cotton seedlings. Growth regulators have the same function as plant hormones. The purpose of this research is to explore the effects of different concentrations of growth regulators on cotton root morphological parameters and enzyme activities, and to find suitable plant growth regulators and their optimal concentrations to improve the growth of the cotton seedling root system. Three cotton varieties, "Zhongmian 619" (Z619), "Xinluzao 27" (Z27), and "Xinluzao 39" (Z39), and three growth regulators, gibberellin (GA₃), salicylic acid (SA), and paclobutrazol (PP₃₃₃), at three concentrations were used in our experiment. In Z619 and Z27, 0.050 mg/L GA₃ significantly increased the total root length. Similarly, 0.010 mmol/L SA significantly increased the root growth parameters of Z619 and Z39. In Z619, 0.1 mg/L PP₃₃₃ significantly increased the total root length and total surface area and reduced the average root diameter. For all three cotton varieties, 0.050 mg/L GA₃ increased peroxidase (POD) activity in the roots. In Z27 and Z39, 0.80 mg/L GA₃ increased superoxide dismutase (SOD) activity in the roots. All SA concentrations increased SOD activity in roots of Z619 and Z27; 0.10 mg/L PP₃₃₃ significantly increased SOD and POD activities in the roots of Z619 and significantly increased SOD activity in Z27. Principal component analysis indicated that 0.10 mmol/L SA was the optimal treatment for promoting the development of the roots of Z619 and 0.050 mmol/L SA was the optimal treatment for promoting the development of the roots of Z27 and Z39.

Uniconazole Augments Abscisic Acid in Promoting Somatic Embryogenesis in Cotton (Gossypium hirsutum L.)

During somatic embryogenesis (SE), somatic cells initiate embryogenic development under appropriate conditions. Uniconazole, a plant growth regulator, was found to inhibit the proliferation of callus but promoted the conversion of callus into an embryogenic callus (EC) in cotton. The supplementation of uniconazole in the culture medium significantly suppressed the endogenous auxin [indole acetic acid (IAA)] level in callus tissues in both the callus initiation and proliferation stage but enhanced the abscisic acid (ABA) level only in the callus proliferation stage. Exogenous ABA and uniconazole showed cooperative effects on promoting the differentiation rate of callus into EC. These findings were verified by RNA-seq analysis, which elucidated that the genes involved in the IAA biosynthesis, metabolism, and signaling, and ABA metabolism pathways were regulated by uniconazole during the callus development and SE. Overall, the results suggest that uniconazole could modulate callus proliferation and callus differentiation rate by regulating the endogenous levels of IAA and ABA.

Melatonin improves the seed filling rate and endogenous hormonal mechanism in grains of summer maize

The unpredictable precipitation and water deficit conditions in semiarid regions significantly reduce the yield of summer maize. The exogenous application of plant growth regulators can be used as a strategy to enhance plant stress tolerance and improve the growth and yield of maize under semiarid conditions. Here, we studied the protective role of melatonin application on maize yield using grain filling rate and hormonal crosstalk in maize grains. In the first field experiment, seeds were soaked with melatonin at a concentration of 0 (SM₀ ), 25 (SM₁ ), 50 (SM₂ ), and 75 μM (SM₃ ) μM. In contrast, in the second experiment, melatonin was applied on the foliage at the ninth leaf stage at a concentration of 0 (FM₀ ), 25 (FM₁ ), 50 (FM₂ ), and 75 (FM₃ ) μM. Our findings showed that melatonin treatments as seed soaking significantly increased single seed weight, seed filling rate in superior, medium and inferior seeds by regulating the hormone levels compared to foliar application. Application of melatonin significantly increased the zeatin+zeatin riboside (Z+ZR), indole-3-acetic acid (IAA), and gibberellic acid (GA) contents. However, it significantly inhibited the contents of abscisic acid (ABA) during the seed filling period. The content of Z+ZR, IAA, and GA was positively correlated with the maximum seed filling rate, seed weight, and mean filling rate in middle, superior and lower seeds, while the ABA was negatively correlated. The ABA content in inferior seeds was positively correlated with the maximum and mean seed filling rate. In semiarid regions, melatonin treatment of SM₂ and FM₂ significantly increased the dry matter per plant, 100-grain weight, seed filling rate, IAA, Z+ZR, GA contents, ear characteristics, and maize yield.

Effect of uniconazole and nitrogen level on lodging resistance and yield potential of maize under medium and high plant density

Lodging in maize results in grain yield reduction. This experiment investigated the effects of different application rates of the growth retardant, uniconazole (UCZ), and nitrogen (N) on medium and high maize population densities on lodging resistance and yield. UCZ was applied to maize seeds at concentrations of 0 (U₀ ) and 25 (U₂₅ ) mg kg^-1 , and three different N application rates, 0 (N₀ ), 150 (N₁₅₀ ) and 225 (N₂₂₅ ) kg ha^-1 , at plant densities of 75,000 (D₁ ) and 105,000 plants ha^-1 (D₂ ). UCZ application, different N rates and plant population density affected the lodging resistance and yield attributes of maize. The diameter, plumpness, cortex penetration and bending strengths of the internodes were enhanced with UCZ and N application at medium and high plant density, where maximum values were obtained with U₂₅ N₁₅₀ D₁ . Internode length increased in the high-density population and higher N rate, whereas UCZ reduced internode length, where maximum internode length was obtained with U₀ N₂₂₅ D₂ . Plant height, centre of gravity height, ear and height above ear-bearing node were higher with the high N rate, while UCZ reduced it significantly. UCZ, N rate and plant density enhanced lignin accumulation in the third internode and ear-bearing internode, where maximum values were obtained with U₂₅ N₁₅₀ D₁ . Yield and yield attributes were also improved by UCZ, N rate and population density. Treatment with U₂₅ N₁₅₀ D₂ significantly improved grain yield of maize compared with the other treatments.

Drought Stress Impacts on Plants and Different Approaches to Alleviate Its Adverse Effects

Drought stress, being the inevitable factor that exists in various environments without recognizing borders and no clear warning thereby hampering plant biomass production, quality, and energy. It is the key important environmental stress that occurs due to temperature dynamics, light intensity, and low rainfall. Despite this, its cumulative, not obvious impact and multidimensional nature severely affects the plant morphological, physiological, biochemical and molecular attributes with adverse impact on photosynthetic capacity. Coping with water scarcity, plants evolve various complex resistance and adaptation mechanisms including physiological and biochemical responses, which differ with species level. The sophisticated adaptation mechanisms and regularity network that improves the water stress tolerance and adaptation in plants are briefly discussed. Growth pattern and structural dynamics, reduction in transpiration loss through altering stomatal conductance and distribution, leaf rolling, root to shoot ratio dynamics, root length increment, accumulation of compatible solutes, enhancement in transpiration efficiency, osmotic and hormonal regulation, and delayed senescence are the strategies that are adopted by plants under water deficit. Approaches for drought stress alleviations are breeding strategies, molecular and genomics perspectives with special emphasis on the omics technology alteration i.e., metabolomics, proteomics, genomics, transcriptomics, glyomics and phenomics that improve the stress tolerance in plants. For drought stress induction, seed priming, growth hormones, osmoprotectants, silicon (Si), selenium (Se) and potassium application are worth using under drought stress conditions in plants. In addition, drought adaptation through microbes, hydrogel, nanoparticles applications and metabolic engineering techniques that regulate the antioxidant enzymes activity for adaptation to drought stress in plants, enhancing plant tolerance through maintenance in cell homeostasis and ameliorates the adverse effects of water stress are of great potential in agriculture.

Combating Dual Challenges in Maize Under High Planting Density: Stem Lodging and Kernel Abortion

High plant density is considered a proficient approach to increase maize production in countries with limited agricultural land; however, this creates a high risk of stem lodging and kernel abortion by reducing the ratio of biomass to the development of the stem and ear. Stem lodging and kernel abortion are major constraints in maize yield production for high plant density cropping; therefore, it is very important to overcome stem lodging and kernel abortion in maize. In this review, we discuss various morphophysiological and genetic characteristics of maize that may reduce the risk of stem lodging and kernel abortion, with a focus on carbohydrate metabolism and partitioning in maize. These characteristics illustrate a strong relationship between stem lodging resistance and kernel abortion. Previous studies have focused on targeting lignin and cellulose accumulation to improve lodging resistance. Nonetheless, a critical analysis of the literature showed that considering sugar metabolism and examining its effects on lodging resistance and kernel abortion in maize may provide considerable results to improve maize productivity. A constructive summary of management approaches that could be used to efficiently control the effects of stem lodging and kernel abortion is also included. The preferred management choice is based on the genotype of maize; nevertheless, various genetic and physiological approaches can control stem lodging and kernel abortion. However, plant growth regulators and nutrient application can also help reduce the risk for stem lodging and kernel abortion in maize.

Hormonal changes with uniconazole trigger canopy apparent photosynthesis and grain filling in wheat crop in a semi-arid climate

Phytohormones are important for the growth and development of plants. The objective of the experiment was to investigate the effect of foliar application of uniconazole (UCZ) at the four-leaf stage on hormone crosstalk and production of winter wheat. An experiment was carried out during 2015-2016 and 2016-2017 growth season in a semi-arid region, where UCZ at a concentration of 0 (CK, distilled water), 15 (FU₁₅), 30 (FU₃₀), and 45 (FU₄₅) mg L^-1 were sprayed on wheat crop at the four-leaf stage at a rate of 138.8 mL m^-2. UCZ alters the endogenous hormone contents in flag leaves and in grains. UCZ inhibited gibberellic acid (GA) in flag leaves and in grains where the lower GA with UCZ improved the zeatin + zeatin riboside (Z + ZR) and abscisic acid (ABA) contents. The lower GA and higher Z + ZR and ABA contents with UCZ-treated plants improved the chlorophyll content and canopy apparent photosynthesis (CAP) as well as the grain-filling characteristics. The Z + ZR and ABA in flag leaves were positively correlated with chlorophyll content and CAP value while negatively with GA. Moreover, the Z + ZR and ABA were positively correlated with maximum grain weight, mean grain-filling rate, and maximum grain-filling rate, while negatively with GA level. Treatment FU₃₀ significantly improved the chlorophyll content, CAP value, spike weight, grain-filling characteristics, and hormone contents of Z + ZR and ABA while it decreased the GA level. The hormone crosstalk with UCZ significantly increased the yield of wheat crop, where FU₃₀ treatment performs better.

Effects of Gibberellin (GA4+7) in Grain Filling, Hormonal Behavior, and Antioxidants in High-Density Maize (Zea mays L.)

Dense plant cultivation is an efficient approach to improve maize production by maximizing the utilization of energy and nutrients. However, dense plant populations may aggravate the abortion rate of young grains, resulting in fewer kernels per ear. The rate and duration of grain-filling play decisive roles in maize grain yield. Therefore, to increase plant density, enhancing the grain-filling rate, extending the growth period of individual maize plants and regulating crop senescence would be the first priority. In this study, we examined the regulatory effects of GA₄₊₇ under two application methods: shanks and silks were moistened by cotton full with GA₄₊₇ solution at concentrations of 0, 10, 60, and 120 mg L^-1. The results showed that GA₄₊₇ improved the grain-filling rate by increasing the content of auxin, gibberellin, zeatin, and abscisic acid in grains compared to control plants. In addition, the auxin, gibberellin, and zeatin contents in the grains were positively and significantly correlated with the maximum grain weight and the maximum and mean grain-filling rates. Moreover, GA₄₊₇ increased the activities of superoxide dismutases, catalases, and peroxidases and reduced the malondialdehyde content in leaves compared with untreated plants. At the concentration of 60 mg L^-1, GA₄₊₇ showed the greatest effect on shank and silk applications (Sh-60 and Si-60) followed by 10 mg L^-1 (Sh-10) for shank treatment and 120 mg L^-1 (Si-120) for silk treatment. Our results suggest that a concentration of 60 mg L^-1 GA₄₊₇ for shank and silk application may be efficiently used for changing the level of hormones in grains and antioxidant enzymes in ear leaves, which may be useful for enhancing grain-filling rate and delaying leaf senescence, resulting in an increase in maize grain yield.

Abscisic acid-enhanced starch accumulation of bioenergy crop duckweed (Spirodela polyrrhiza)

To meet the increasing energy consumption around the world and fight global climate change, there is an urgent need to explore renewable energy crops to replace the traditional energy sources. Duckweed (Spirodela polyrrhiza) is widely distributed in the world and has high starch and low lignin contents, which is perhaps an ideal feedstock for bioenergy production. To investigate the effects of abscisic acid (ABA) on duckweed biomass and starch accumulation, Spirodela polyrrhiza was cultivated at different ABA concentrations. The results showed that the highest starch content in duckweed (21.8% dry weight) was achieved in 1.0 × 10-2 mg L-1 ABA medium, 70.3% higher than that of the control medium without ABA. The number of starch granules in 1.0 × 10-2 mg L-1 ABA medium was far more than that in the control medium. The highest adenosine diphosphate (ADP)-glucose pyrophosphorylase (AGPase) activity was observed in the 1.0 × 10-2 mg L-1 ABA medium, which was caused by the up-regulation expression of ADP-glucose pyrophosphorylase 2 (APL2). Further investigations on cell ultra-structures and stomatal property of the duckweed indicated that ABA increased the number and size of starch granules and stomatal size in duckweed cells. These enhancements lead to a greatly improved energy flow in the aquatic plant from photosynthesis to carbon storage, making duckweed a potential renewable bioenergy crop.

The Effects of Endogenous Hormones on the Flowering and Fruiting of Glycyrrhiza uralensis

Although endogenous hormones play an important role in flower bud differentiation and seed-filling, their effects on the flowering and fruiting of Glycyrrhiza uralensis Fisch. remain unknown. In the present study, we investigate the differences in the levels of endogenous hormones gibberellic acid (GA), abscisic acid (ABA), zeatin riboside (ZR), and indoleacetic acid (IAA) between the fruiting and seedless plants of G. uralensis Fisch. at different growth stages. We also determine the correlations of the endogenous hormone with the rates of flower and fruit falling, rate of empty seeds, rate of shrunken grains, and thousand kernel weight (TKW). The results demonstrate that the IAA and ZR levels of the flowering plants are significantly higher than those of the nonflowering plants at the flower bud differentiation stage. The GA and ABA levels of exfoliated inflorescence plants are considerably higher than those of the flowering and fruiting plants; the rates of falling flowers and fruit are negatively correlated with the IAA level and positively correlated with the ABA level. The ABA content of nonflowering plants is significantly higher than that of fruiting plants. The ZR:GA and IAA:ABA ratios are significantly positively correlated with TKW. The IAA:GA and IAA:ABA ratios are significantly negatively correlated with the rates of empty and shrunken seeds. Thus, we speculate that high IAA and ZR contents are good for flower bud differentiation and seed-filling, and low ABA and ZR contents are beneficial to flower bud development and seed-filling.

Plant growth regulators interact with elevated temperature to alter heat stress signaling via the Unfolded Protein Response in maize

Plants are increasingly exposed to high temperatures, which can cause accumulation of unfolded protein in the endoplasmic reticulum (ER). This condition, known as ER stress, evokes the unfolded protein response (UPR), a cytoprotective signaling pathway. One important branch of the UPR is regulated by splicing of bZIP60 mRNA by the IRE1 stress sensor. There is increasing evidence that commercial plant growth regulators may protect against abiotic stressors including heat stress and drought, but there is very little mechanistic information about these effects or about the regulatory pathways involved. We evaluated evidence in the B73 Zea mays inbred for differences in the activity of the UPR between permissive and elevated temperature in conjunction with plant growth regulator application. Treatment with elevated temperature and plant growth regulators increased UPR activation, as assessed by an increase in splicing of the mRNA of the IRE1 target bZIP60 following paclobutrazol treatment. We propose that plant growth regulator treatment induces bZIP60 mRNA splicing which 'primes' plants for rapid adaptive response to subsequent endoplasmic reticulum-stress inducing conditions.

Plant growth regulators interact with elevated temperature to alter heat stress signaling via the Unfolded Protein Response in maize

Plants are increasingly exposed to high temperatures, which can cause accumulation of unfolded protein in the endoplasmic reticulum (ER). This condition, known as ER stress, evokes the unfolded protein response (UPR), a cytoprotective signaling pathway. One important branch of the UPR is regulated by splicing of bZIP60 mRNA by the IRE1 stress sensor. There is increasing evidence that commercial plant growth regulators may protect against abiotic stressors including heat stress and drought, but there is very little mechanistic information about these effects or about the regulatory pathways involved. We evaluated evidence in the B73 Zea mays inbred for differences in the activity of the UPR between permissive and elevated temperature in conjunction with plant growth regulator application. Treatment with elevated temperature and plant growth regulators increased UPR activation, as assessed by an increase in splicing of the mRNA of the IRE1 target bZIP60 following paclobutrazol treatment. We propose that plant growth regulator treatment induces bZIP60 mRNA splicing which 'primes' plants for rapid adaptive response to subsequent endoplasmic reticulum-stress inducing conditions.

Plant Density and Nitrogen Supply Affect the Grain-Filling Parameters of Maize Kernels Located in Different Ear Positions

Although yield output of maize (Zea mays L.) has improved markedly over the last century, procedures for improving the grain-filling process remain elusive. Our aim in this study was to relate grain-filling variation in maize (including kernels in apical and middle positions in the ears) to plant density and nitrogen (N) application rate using a crossed experimental design. We also investigated changes in zeatin riboside (ZR), indole-3-acetic acid (IAA), abscisic acid (ABA), and gibberellic acid (GA) in the kernels during the grain-filling period. Two high-yield maize varieties cultivated extensively in China were field grown under normal (67,500 pl ha-1) and high (97,500 pl ha-1) densities, and supplied with low, normal and high (0, 180, and 360 kg N ha-1) concentrations of N. Kernel weight (KW), the maximum grain-filling rate (Gmax), the average grain-filling rate (Gave), and the kernel weight increment achieving Gmax (Wmax) were all significantly depressed under high density (HD) conditions, but increased N supply partially offset the losses. The apical kernels were more sensitive to density and N application rate than middle kernels. Correlation analysis indicated that plant density and N rate affected KW mainly by influencing the grain-filling rate. Variation in ZR, IAA, and ABA content tracked the variation in KW, but variation in GA content did not. Furthermore, the grain-filling parameters (closely related to TKW) had strong canonical correlation with the content of all hormones across the filling period and ZR content had the strongest relationship. Based on our study, high N supply is beneficial to optimize grain-filling parameters and improve KW of maize kernels under crowded condition.