Starch Accumulation Research Articles

Insights into multiscale structure and digestive characteristic of starch from two cultivars of chestnut during kernel development

Multiscale structure and digestive characteristic of starch during kernel development of Castanea henryi (‘Jinzhui’ (YS) and ‘Baiyan No.1’ (WS)) were investigated in this study. Structural analysis revealed that the surface of starch granules became smooth, the amylopectin content decreased (from 71.32 % to 70.47 %, from 71.44 % to 68.37 %, respectively), the chain length distribution of amylopectin reduced (the proportion of B1 chain decreased from 52.35 % to 50.60 %, from 52.22 % to 50.59 %, respectively) while the amorphous and semi-crystalline lamellae of starch increased during development, which was consistent with the decreasing relative crystallinity (from 28.79 % to 24.11 %, from 29.57 % to 23.66 %, respectively) and short-range ordering degree. The degradation of ordered structure further resulted in the increase of digestibility, especially in the late developmental stage, supported by a significant decrease of resistant starch content (from 70.21 % to 61.70 % and from 73.58 % to 58.86 %, respectively). Transcriptome analysis and RT-qPCR were performed to explore the possible molecular mechanisms affecting starch structure. The high expression of several key genes including AGPase, GBSS, SBE, SSS, ISA and PUL in late development stage might be the reason of structural changes during development. The results provided valuable information for starch accumulation during kernel development of Castanea henryi.

Red light induces starch accumulation in Chlorella vulgaris without affecting photosynthesis efficiency, unlike abiotic stress

Microalgae show great promise as sources of starch, one of the most widely consumed macromolecules. In this study, we evaluated the impact of three starch-inducing factors, namely nitrogen deprivation, supra-optimal temperature, and red light, on the physiology and starch accumulation capacity of Chlorella vulgaris. This starch accumulation was monitored by measuring the total carbohydrate content and transmission electron microscopy (TEM) imaging. Nitrogen deprivation and a supra-optimal temperature of 39 °C resulted in carbohydrate contents of 69.7 and 64.3 % of dry weight (DW) respectively. This constituted a 5.3- and 3.3-fold increase in carbohydrate productivity compared to the control, after 4 days of cultivation. During this period, carbohydrates represented over 80 % of the produced material (DW basis). However, nitrogen deprivation and supra-optimal temperature were accompanied by extensive stress, leading to lower cell division rates and damage to the photosynthetic apparatus. Red light illumination resulted in a more moderate production of carbohydrates. After 4 days of cultivation, the carbohydrate content reached 46.8 %, representing a 3.0-fold increase in productivity compared to control. The composition of the starch formed under red light was surprisingly poor in amylose, similar to transitory-type starch rather than storage starch. Most notably, the starch accumulation under red light was sustained over 7 days without affecting the rate of cell division and quantum yield efficiency. To the best of our knowledge, red light is the only factor reported so far to induce a significant starch accumulation without hindering cell division and photosynthesis efficiency, even after long-term exposure (7 days). Furthermore, all three conditions induced a cell wall thickening, albeit without affecting the recovery of accumulated starch by high-pressure homogenization. These results highlight the potential of red light as a starch inducer in Chlorella vulgaris and open up perspectives for the production of starch-based bioplastics from microalgae.

Effects of N, P, and K application rates on distribution of 13C assimilates, starch accumulation in grains and fertilizer utilization of wheat

Clarifying the appropriate application rates of N, P, and K fertilizers and the physiological mechanisms of wheat under water-saving recharge irrigation in the North China Plain would provide a theoretical basis for formulating reasonable fertilization plans for high-yield and high-efficiency wheat production. We established four treatments with different amounts of nitrogen (N), phosphorus (P2O5), and potassium (K2O) application: 0, 0, and 0 kg·hm-2 (F0), 180, 75, and 60 kg·hm-2 (F1), 225, 120, and 105 kg·hm-2 (F2), and 270, 165, and 150 kg·hm-2 (F3). During the jointing and anthesis stages of wheat, the relative water content of each treatment in the 0-40 cm soil layer was replenished to 70%, to investigate the differences in wheat flag leaf photosynthetic characteristics, distribution of 13C assimilates, grain starch accumulation, and fertilizer utilization. The results showed that the relative chlorophyll content of flag leaves, photosynthetic and chlorophyll fluorescence parameters, 13C assimilate allocation in each organ, enzyme activities involved in starch synthesis, and starch accumulation in the F1 treatment were significantly higher than that in F0 treatment, which was an important physiological basis for the 20.9% increase in grain yield. The above parameters and yield in the F2 and F3 treatments showed no significant increase compared to F1 treatment, while fertilizer productivity and agronomic efficiency of N, P, and K decreased by 17.5%-58.4% and 12.7%-50.7%, respectively. Therefore, F1 could promote flag leaf photosynthetic assimilate production and grain starch accumulation under water-saving supplementary irrigation conditions, resulting in higher grain yield and fertilizer utilization efficiency.

Understanding the Saffron Corm Development-Insights into Histological and Metabolic Aspects.

The reproduction of Crocus sativus L., a sterile triploid plant, is carried out exclusively through corms, whose size determines the saffron yield. The development of daughter corms (DC) is supported by photoassimilates supplied by the leaves as well as by the mother corms (MC). While biomass partitioning during DC development is well studied, growth dynamics in terms of cell number and size, the involved meristems, as well as carbohydrate partition and allocation, are not yet fully understood. We conducted a comprehensive study into saffron corm growth dynamics at the macroscopic and microscopic levels. Variations in carbohydrate content and enzymatic activities related to sucrose metabolism in sources and sinks were measured. Two key meristems were identified. One is involved in vascular connections between DC and MC. The other is a thickening meristem responsible for DC enlargement. This research explains how the previously described phases of corm growth correlate with variations in cell division, enlargement dynamics, and carbohydrate partitioning among organs. Results also elucidated that the end of DC growth relates to a significant drop in MC root biomass, limiting the water supply for the DC growth, and establishing the onset of leaf wilting. The lack of starch accumulation in aged leaf cells is noteworthy, as is the accumulation of lipids. We hypothesize a signaling role of sugars in DC growth initiation, stop, and leaf aging. Finally, we established a predominant role of sucrose synthase as a sucrolytic enzyme in the maintenance of the high flux of carbon for starch synthesis in DC. Together, the obtained results pave the way for the definition of strategies leading to better control of saffron corm development.

Genetic evidence for functions of Chloroplast CA in Pyropia yezoensis: decreased CCM but increased starch accumulation

In response to the changing intertidal environment, intertidal macroalgae have evolved complicated Ci utilization mechanisms. However, our knowledge regarding the CO2 concentrating mechanism (CCM) of macroalgae is limited. Carbonic anhydrase (CA), a key component of CCM, plays essential roles in many physiological reactions in various organisms. While many genes encode CA in the Pyropia yezoensis genome, the exact function of specific CA in P. yezoensis remains elusive. To explore the particular function of chloroplast CA in intertidal macroalgae, we produced chloroplast-localized βCA1 knockdown mutants of P. yezoensis through RNA interference, and Pyβca1i mutants (hereinafter referred to as ca1i) showed a notable decrease in leaf area and overall biomass, as well as decreased soluble protein and unsaturated fatty acid content under different DIC conditions. However, ca1i mutants showed relatively higher starch content compared to the wild-type. The activity of enzymes involved in the Calvin cycle, photorespiration, Pentose-phosphate pathway, and floridean starch synthesis of P. yezoensis indicated an effective starch accumulation pathway after the interference of βCA1. All results suggest that the decreased activity of PyβCA1 impaired the CCM and development of thalli of P. yezoensis, but stimulated starch accumulation in the cytoplasm through feedback to the photorespiration pathway and pentose phosphate pathway to replenish intermediates for the Calvin cycle. This study is the first to explore the specific function of chloroplast CA in intertidal macroalgae using genomic technology. The results provide valuable insights into the adaption mechanisms of intertidal macroalgae to their environment.

Soil Water Stress Effects on Potato Tuber Starch Quality Formation

Soil water stress has a significant impact on crop physiology, however, the specific response of starch quality formation in potato tubers remains unreported. Here, two potato (Solanum tuberosum L.) varieties, one with high, and the other with low tuber starch content, were grown in pots under three different soil water stress treatments, maintaining 75, 50 and 25% of soil field capacity, respectively. Soil water stress restricted potato plant growth and development, and severe stress reduced tuber yield by 47.8% relative to the control. It also inhibited tuber starch biosynthesis, which declined by 62.4% (AGPase activity) relative to the control. Furthermore, water stress reduced tuber starch accumulation by 23.6% (total starch content) relative to the control, and finally, it shortened the tuber starch gelatinization process by 1.44% (pasting temperature) compared to the control. These results reflect the soil water stress regulation mechanism on starch formation and potato tuber quality. Moreover, the study provides a scientific basis for breeding of varieties with high starch content, for improving starch quality and high-efficiency cultivation in dryland potato production.

Jasmonates Promote β-Amylase-Mediated Starch Degradation to Confer Cold Tolerance in Tomato Plants.

Cold stress severely restricts growth and development, reduces yields, and impairs quality in tomatoes (Solanum lycopersicum). Amylase-associated starch degradation and soluble sugar accumulation have been implicated in adaptation and resistance to abiotic stress. Here, we report a β-amylase (BAM) gene, SlBAM3, which plays a central role in tomato cold tolerance. The expression of SlBAM3 was triggered by cold stress. SlBAM3 knockout using the CRISPR/Cas9 system retarded starch degradation and reduced soluble sugar accumulation in tomato plants, eventually attenuating cold tolerance. Expression analysis revealed that the SlBAM3 transcript level was boosted by MeJA. Furthermore, MYC2, an essential component of the JA signaling pathway, could bind to the SlBAM3 promoter and directly activate SlBAM3 transcription, as revealed by yeast one-hybrid and dual LUC assays. In addition, the suppression of MYC2 resulted in increased starch accumulation, decreased soluble sugar content, and reduced tolerance to cold stress in tomato plants. Taken together, these findings demonstrate that JA positively regulates β-amylase-associated starch degradation through the MYC2-SlBAM3 module in tomato during cold stress. The results of the present work expand our understanding of the mechanisms underlying BAM gene activation and starch catabolism under cold stress. The regulatory module of SlBAM3 can be further utilized to breed tomato cultivars with enhanced cold tolerance.

Hydrogen-rich water irrigation promotes fruit ripening and nutritional composition in tomato

Hydrogen gas (H2), as a gaseous molecule, plays vital roles in plant growth and development. However, whether H2 plays a role in fruit ripening of tomato is still unknown. Here, we explore the effect of hydrogen-rich water (HRW) irrigation on fruit ripening and nutritional composition in tomato. HRW irrigation enhanced lightness (L* value) and redness (a* value), and declined yellowness (b* value), accelerated fruit color transition. HRW reduced chlorophyll a, chlorophyll b, and total chlorophyll content and enhanced carotenoid, lycopene, and lutein accumulation. Moreover, HRW promoted chlorophyll degradation-related and carotenoid-synthesis related gene expression. In addition, HRW modulated the cell wall component content, enhanced fruit softening-related enzyme activity, and upregulated fruit softening-related and ripening-related gene expression, but decreased fruit firmness. Also, HRW irrigation promoted the accumulation of sucrose, starch, soluble protein, and soluble sugar, as well as increasing the sugar-acid ratio and partial aroma composition. Therefore, H2 may be a promising eco-friendly way to improve tomato cultivation and other agricultural practices.

Enhanced starch accumulation in Chlorella sorokiniana as sugar platform and the expression profiling of key regulatory proteins

Microalgae can accumulate considerable starch as a renewable sugar platform for biofuel production. In this study, Chlorella sorokiniana exhibited a significant increase in starch content from 3.0% to 49.5% DM under sulfur limitation (SL) conditions, and the lower the concentration of sulfur was, the more effective it was. Direct enzymatic hydrolysis of wet biomass resulted in a glucose yield of 97.1%, indicating its potential for fermentable sugar production. However, C. sorokiniana grew slowly, and cell division and biomass accumulation decreased under SL conditions, which could be explained by the decreased photosynthetic efficiency and protein content. The sulfur replenishment (SR) confirmed the rapid response of C. sorokiniana in starch accumulation to sulfur availability. Thus, we further investigated the expression profiling of key regulatory proteins under Control-SL-SR stages. The expression of AGPase A was strongly induced in the SL stage and subsequently downregulated during SR stage, suggesting its role as a key regulatory protein for enhanced starch accumulation. Additionally, downregulation of SBE and GBE expression likely contributed to structural modifications of the starch molecules. These proteins could serve as potential targets for metabolic engineering in further improving the starch production capacity in C. sorokiniana.

Improved yield by optimizing carbon, nitrogen metabolism and hormone balance in apical kernels under low nitrogen conditions using the low nitrogen–tolerant maize variety

ContextUsing low nitrogen (N)–tolerant maize varieties serves as a viable means to curtail N fertilizer application while improving crop yield. ObjectiveTo investigate the differences in carbon and nitrogen metabolic processes, and the hormones within kernels located at varying positions along the ear, between low N–tolerant and low N–sensitive maize varieties. Furthermore, this research aims to elucidate the ramifications of these observed disparities on kernel weight and yield, particularly when cultivated under low N conditions. MethodsThe low N–tolerant maize variety (ZH311) and low N–sensitive maize variety (XY508) were applied. The in–situ filed experiment with three N fertilizer treatments of 0 N (0 kg·N ha−1), 150 N (150 kg·N ha−1) and 300 N (300 kg·N ha−1) was conducted in 2017–2019. ResultsThe apical kernel weight of ZH311 was less affected by low N (0 N and 150 N) and the yield was 25.3–22.9% higher than XY508. The kernel weight was significantly and positively correlated with kernel starch and protein content. The starch and protein contents of ZH311 apical kernels were 6.3–7.3% and 12.4–14.4%, higher than XY508 under low N. It was indicated that the main factor affecting starch accumulation in the apical kernels was Susy activity and protein accumulation was IAA/GA3, Z+ZR/GA3 and GOGAT activity by the redundancy analysis. Under low N, the Susy and GOGAT activity, IAA/GA3 and Z+ZR/GA3 in the apical kernel of ZH311 were higher than XY508 by 51.4–39.3% and 65.4–46.9%, 62.1–33.1% and 41.8–48.2%. ConclusionsWe have demonstrated to improve the maize yield by increasing the apical kernel weight, which resulted in enhancing the uniformity of the kernel weight along the ear. Under low N conditions, the low N–tolerant maize variety was shown to facilitate the starch and protein biosynthesis by increasing the activity of key enzymes in the carbon and the nitrogen metabolism processes such as Susy and GOGAT in the apical kernels, and optimizing the hormone balance between IAA/GA3 and Z+ZR/GA3, to increase the kernel weight and yield. ImplicationsThe findings of this investigation will help understand the underlying factors contributing to the yield variations exhibited among distinct low N–tolerant maize varieties when cultivated under conditions of limited N availability. These insights could serve as the theoretical basis for breeding of low N–tolerant maize varieties and practical guidance for the formulation of N fertilizer management strategies.

Foliar application of selenium promotes starch content accumulation and quality enhancement in foxtail millet grains

ContextThe northern regions of China are the core production areas for foxtail millet. However, the lack of selenium in the soil constrains local agricultural development. Foliar application of selenium is a significant method to improve selenium levels, yet few studies have systematically analyzed the effects of selenium on the quality of millet, especially its starch content. ObjectiveThis study aims to assess the effects of selenium foliar spray on the starch composition and overall content within millet grains, specifically by elucidating the mechanisms through examining changes in chlorophyll content in the flag leaves during the grain-filling stage and the activity of enzymes related to starch synthesis in the grains. Additionally, this research seeks to determine the optimal rate of selenium application that would maximize the quantity and quality of starch in millet grains. MethodsA two-year field experiment on foxtail millet was conducted with five selenium treatments (Se rates of 0, 20, 40, 60, and 100 g Se/ha, defined as T0, T1, T2, T3, T4 in this study, respectively). Grain starch content, activities of starch synthesis-related enzymes, flag leaves chlorophyll content, and antioxidant status of the flag leaves were measured at seven time points during grain filling. ResultsThe starch content in foxtail millet grains increased quadratically with the application of selenium, reaching a maximum under the T3 treatment, which enhanced the content by 15.27 % and 11.97 % over two years, respectively. The addition of selenium at low concentrations (T1-T3 treatments) not only enhanced the activities of the three starch synthesis-related enzymes, AGPase, SuSy, and SSS, but also delayed the senescence of the flag leaves, thereby promoting grain starch synthesis. In contrast, excessive selenium application (T4 treatment) expedited the aging of the flag leaves, grain starch synthesis was inhibited compared to the T3 treatment. Moreover, foliar application of selenium led to an increase in the SSS activity in the grains, which in turn reduced the content of straight-chain starch. Under the T3 treatment, the grain straight-chain starch content decreased by 22.30 % and 28.35 % over two years, respectively. ConclusionsFoliar application of selenium enhanced the activities of enzymes related to grain starch synthesis and had a dual effect on the senescence process of flag leaves, regulating the content and composition of starch in foxtail millet grains. The spraying concentration of 60 g Se/ha was most favorable for the accumulation and quality improvement of grain starch. ImplicationsThe results of this study will aid in enhancing the value-added potential of foxtail millet starch products through precise fertilization, improving the yield and quality of foxtail millet in northern China.

Regulation of carbohydrate metabolism during anther development in a thermo-sensitive genic male-sterile wheat line.

Bainong sterility (BNS) is a thermo-sensitive genic male sterile wheat line, characterised by anther fertility transformation in response to low temperature (LT) stress during meiosis, the failure of vacuole decomposition and the absence of starch accumulation in sterile bicellular pollen. Our study demonstrates that the late microspore (LM) stage marks the transition from the anther growth to anther maturation phase, characterised by the changes in anther structure, carbohydrate metabolism and the main transport pathway of sucrose (Suc). Fructan is a main storage polysaccharide in wheat anther, and its synthesis and remobilisation are crucial for anther development. Moreover, the process of pollen amylogenesis and the fate of the large vacuole in pollen are closely intertwined with fructan synthesis and remobilisation. LT disrupts the normal physiological metabolism of BNS anthers during meiosis, particularly affecting carbohydrate metabolism, thus determining the fate of male gametophytes and pollen abortion. Disruption of fructan synthesis and remobilisation regulation serves as a decisive event that results in anther abortion. Sterile pollen exhibits common traits of pollen starvation and impaired starch accumulation due to the inhibition of apoplastic transport starting from the LM stage, which is regulated by cell wall invertase TaIVR1 and Suc transporter TaSUT1.

MdbZIP44–MdCPRF2-like–Mdα-GP2 regulate starch and sugar metabolism in apple under nitrogen supply

Abstract Nitrogen (N) is regarded as an essential macronutrient and is tightly associated with carbon (C) metabolism in plants. The transcriptome data obtained from this study showed that the expression level of the apple basic leucine zipper (bZIP) transcription factor (TF) MdbZIP44 was up-regulated in ‘Oregon Spur Delicious’ (Malus domestica Borkh.) apple fruits under nitrogen supply. MdbZIP44 bound to the promoter of Mdα-GP2 gene and inhibited its expression, thereby promoting starch accumulation and decreasing glucose content in apple and tomato fruits. Besides, overexpression of MdbZIP44 promoted sucrose accumulation by regulating the activities of sucrose metabolism-related enzymes and the expression of sugar metabolism-related genes in apple callus and tomato fruits. Furthermore, biochemical assays indicated that MdbZIP44 directly interacted with MdCPRF2-like, another bZIP gene in apple. Meanwhile, this study found that MdCPRF2-like, along with the MdbZIP44 and MdCPRF2-like complex, could activate the expression of Mdα-GP2, respectively. In conclusion, this study provides a new reference for potential mechanisms underlying that MdbZIP44–MdCPRF2-like–Mdα-GP2 regulates starch and sugar metabolism under nitrogen supply.

Regulatory loops between rice transcription factors OsNAC25 and OsNAC20/26 balance starch synthesis.

Several starch synthesis regulators have been identified, but these regulators are situated in the terminus of the regulatory network. Their upstream regulators and the complex regulatory network formed between these regulators remain largely unknown. A previous study demonstrated that NAM, ATAF, and CUC (NAC) transcription factors, OsNAC20 and OsNAC26 (OsNAC20/26), redundantly and positively regulate the accumulation of storage material in rice (Oryza sativa) endosperm. In this study, we detected OsNAC25 as an upstream regulator and interacting protein of OsNAC20/26. Both OsNAC25 mutation and OE resulted in a chalky seed phenotype, decreased starch content, and reduced expression of starch synthesis-related genes, but the mechanisms were different. In the osnac25 mutant, decreased expression of OsNAC20/26 resulted in reduced starch synthesis; however, in OsNAC25-overexpressing plants, the OsNAC25-OsNAC20/26 complex inhibited OsNAC20/26 binding to the promoter of starch synthesis-related genes. In addition, OsNAC20/26 positively regulated OsNAC25. Therefore, the mutual regulation between OsNAC25 and OsNAC20/26 forms a positive regulatory loop to stimulate the expression of starch synthesis-related genes and meet the great demand for starch accumulation in the grain filling stage. Simultaneously, a negative regulatory loop forms among the 3 proteins to avoid the excessive expression of starch synthesis-related genes. Collectively, our findings demonstrate that both promotion and inhibition mechanisms between OsNAC25 and OsNAC20/26 are essential for maintaining stable expression of starch synthesis-related genes and normal starch accumulation.

Grain Chalkiness Is Decreased by Balancing the Synthesis of Protein and Starch in Hybrid Indica Rice Grains under Nitrogen Fertilization.

The important reason for the commercial value of hybrid rice suffering is due to excessive chalkiness, and the biosynthesis of starch and proteins is critical for regulating chalkiness; however, it is currently unclear how the application of N fertilizer affects grains to reduce their chalkiness and improve their quality. The 2019, 2020, and 2021 trials were conducted in a split-plot design, with high and low chalky varieties as the main plot and N fertilizer rate as the split-plot. The effects of fertilization with 75, 150, and 225 kg N ha-1 on the dynamic synthesis of starch, protein, and endogenous hormones and on the amino acid of hybrid indica rice kernels with different degrees of chalkiness were investigated. Grain physiological activity was higher in low-chalky varieties than in high-chalky varieties, and these physiological parameters were strongly associated with chalkiness formation. Higher N fertilization (150 and 225 kg N ha-1) significantly reduced the proportion of chalky grains (8.93-28.02%) and chalkiness (8.61-33.99%) compared with 75 kg N ha-1. Increased N fertilization decreased the activities of granule-bound starch synthase and starch-debranching enzyme, but significantly increased adenosine diphosphate glucose pyrophosphorylase, soluble starch synthase, and starch-branching enzyme activities, synergistically improving glutamate synthetase and glutamine synthetase enzyme activities, which tended to support the synthesis of amylopectin, α-ketoglutarate, and 3-phosphoglyceric acid-derived amino acids in the endosperm cells of the grains; this favored starch and protein accumulation in the grains at 6-30 days after anthesis. Additionally, N application promoted the synthesis of endogenous hormones 1-aminocyclopropane-1-carboxylic acid, gibberellins, and abscisic acid in grains. Hence, N fertilization reduced the rice chalkiness in hybrid indica rice varieties by balancing grain protein and starch composition and enhancing some endogenous hormone synthesis.

Effect of phenolics on soil microbe distribution, plant growth, and gall formation

Phenolic compounds, abundant secondary metabolites in plants, profoundly influence soil ecosystems, plant growth, and interactions with herbivores. In this study, we explore the intricate relationships between phenolics, soil microbes, and gall formation in Ageratina adenophora (A. adenophora), an invasive plant species in China known for its allelopathic traits. Using metabolomic and microbial profiling, significant differences in soil microbial composition and metabolite profiles were observed between bulk and rhizosphere soil samples. Phenolics influenced bacterial communities, with distinct microbial populations enriched in each soil type. Additionally, phenolics impacted soil metabolic processes, with variations observed in Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis between different soil treatments. Analysis of phenolic content in plant and soil samples revealed considerable variations, with higher concentrations observed in certain plant tissues and soil types. Bioactive phenols extracted from plant and soil samples were identified using gas chromatography/mass spectrometry (GC–MS), providing insights into the diverse chemical composition of these compounds. Furthermore, the effects of phenolics on plant growth and gall formation were investigated. Phenols exhibited both stimulatory and inhibitory effects on plant growth, with optimal concentrations promoting emergence but higher concentrations hindering growth. Gall formation was influenced by phenolic concentrations, leading to structural alterations in stem tissue and gall morphology. Histochemical analysis revealed starch and lipid accumulation in gall tissues, indicating metabolic changes induced by phenolics. The presence of phenolics disrupted tissue structures and influenced vascular bundle orientation in gall tissues. Overall, our study highlights the multifaceted roles of phenolic compounds in soil ecosystems, plant development, and gall formation, facilitating the utilization of secondary metabolites in agriculture.

The role of LED supplementary lighting in promoting graft necrotic layer formation in pumpkin-cucumber grafts

The rapid formation of the graft necrotic layer is crucial for preventing organic substance leakage and warding off external infections, significantly enhancing both the speed and quality of graft healing. This study investigates the impact of LED supplementary lighting on pumpkin-cucumber grafts, unveiling the molecular processes underlying necrotic layer formation. Specifically, three replications were conducted, where post-grafting cucumber seedlings were placed separately in healing chambers with LED light intensities of 0 μmol/(m2·s) and 50 ± 1 μmol/(m2·s) for three days. Anatomical observations, enzyme activity assays, energy product content detection, and a more comprehensive transcriptome sequencing analysis on the graft union of the rootstock and scion were conducted. Anatomical observations revealed that LED supplementary lighting accelerates the formation of the pumpkin-cucumber graft necrotic layer, establishing a complete layer by the second day post-grafting, one day earlier than the control. Additionally, at day 3 post-grafting, the activities of POD and PPO enzymes at the rootstock-scion junction significantly surpassed the control, exhibiting a remarkable increase of 74.12 % and 48.96 %, respectively (p < 0.01). Moreover, soluble sugar and ATP levels were notably higher at day 3 post-grafting in comparison to the control, showing significant differences (p < 0.05). Transcriptomic analysis unveiled that LED supplementary lighting not only enhances scion sugar metabolism but also stimulates the upregulation of sugar synthesis genes (SPP1, RPV1) and starch synthesis genes (AGPS1, WAXY, SBEⅡ), while downregulating the starch degradation gene LECRK71 when compared to the control. This orchestrated modulation leads to the accumulation of sugars and starch, providing substantial energy and material foundation for necrotic layer formation. Furthermore, LED supplementation also influences the hormone signaling transduction pathway in the scion, notably upregulating the gene Os01g0656200 involved in abscisic acid signaling when compared to the control, thereby furthering the formation of the necrotic layer. Overall, our research showed that LED supplementary lighting accelerates the formation of the necrotic layer in pumpkin-cucumber grafts by enhancing enzyme activities, sugar metabolism, genetic pathways related to starch accumulation, and influencing hormone signal transduction pathways, notably upregulating genes involved in abscisic acid signaling, providing a robust molecular foundation for early necrotic layer development compared to control conditions. These research findings not only provide a valuable reference for understanding graft healing mechanisms but also demonstrate the promising prospects of LED modern seedling technology. Additionally, the research, which is limited to specific pumpkin and cucumber varieties in graft experiments, necessitates further exploration to validate its broader applicability across diverse plant varieties and grafting methods.

Improving potato AGB estimation to mitigate phenological stage impacts through depth features from hyperspectral data

The accurate estimation of above ground biomass (AGB) is valuable in grasping the status of potato growth and assessing yield. Spectral analysis techniques play an important role in AGB estimation by virtue of its non-destructive and rapid advantages. However, the models constructed based on spectral features at the entire growth stages due to differences in phenological stages, such as vegetation indices (VIs) and locations at fixed wavelengths, can be not applicable to single growth stages. Therefore, the main objective of this study is to improve the applicability of the AGB estimation model to mitigate the impacts of phenological stages by mining depth features from hyperspectral data. The canopy hyperspectral and AGB data of potato tuber formation, tuber growth and starch accumulation stages were measured in 2017–2019. The acquired canopy hyperspectral reflectance was smoothed by Savitzky-Golay (SG) filter, and the green edge (GE), the red edge (RE), red edge chlorophyll index (CIred-edge), optimized soil adjusted vegetation index (OSAVI), green normalized difference vegetation index (GNDVI), and normalized difference vegetation index (NDVI) were extracted. The spectral changes were analyzed at different growth stages of each year. To obtain features in response to AGB changes, a new approach is proposed to analyze the hidden depth features between sensitive wavelengths by combining a successive projections algorithm (SPA) and a long-short-term memory network (LSTM). The AGB estimation models were constructed by partial least squares regression (PLSR) based on traditional VIs + GE + RE, full spectrum, sensitive wavelengths obtained by SPA, and depth features obtained by SPA-LSTM. The results showed that GE, RE and VIs alone explained only 24 %-36 % of the variation in AGB. The accuracy of estimating AGB at sensitive wavelengths obtained after SPA was higher (R2 = 0.70, RMSE = 406 kg/hm2, and NRMSE = 27.14 %) than that of conventional VIs + GE + RE (R2 = 0.51, RMSE = 536 kg/hm2, and NRMSE = 35.81 %) and full spectrum (R2 = 0.63, RMSE = 452 kg/hm2, and NRMSE = 30.19 %) in the three-year dataset. The depth features extracted by the SPA-LSTM method proposed in this study achieved the best AGB estimation (R2 = 0.82, RMSE = 318 kg/hm2, and NRMSE = 21.25 %). The applicability of the model was validated in different years and growth stages. The R2 of each year was in the range of 0.48–0.77, the RMSE was in the range of 290–367 kg/hm2, and the NRMSE was in the range of 16.69 %-25.81 %. The R2 of each growth stage within three year was in the range of 0.48–0.78, the RMSE was in the range of 184–386 kg/hm2, and the NRMSE was in the range of 14.91 %-29.45 %. The method proposed in this study mitigates the impacts of phenological stage and improves the robustness and accuracy of the AGB estimation model, which provides remote sensing technical support for realizing potato growth monitoring and yield assessment in the field.

Tetrad stage transient cold stress skews auxin-mediated energy metabolism balance in Chinese cabbage pollen.

Changing ambient temperature often impairs plant development and sexual reproduction, particularly pollen ontogenesis. However, mechanisms underlying cold stress-induced male sterility are not well understood. Here, we exposed Chinese cabbage (Brassica campestris) to different cold conditions during flowering and demonstrated that the tetrad stage was the most sensitive. After completion of pollen development at optimal conditions, transient cold stress at the tetrad stage still impacted auxin levels, starch and lipid accumulation, and pollen germination, ultimately resulting in partial male sterility. Transcriptome and metabolome analyses and histochemical staining indicated that the reduced pollen germination rate was due to the imbalance of energy metabolism during pollen maturation. The investigation of β-glucuronidase (GUS)-overexpressing transgenic plants driven by the promoter of DR5 (DR5::GUS report system) combined with cell tissue staining and metabolome analysis further validated that cold stress during the tetrad stage reduced auxin levels in mature pollen grains. Low-concentration auxin treatment on floral buds at the tetrad stage before cold exposure improved the cold tolerance of mature pollen grains. Artificially changing the content of endogenous auxin during pollen maturation by spraying chemical reagents and loss-of-function investigation of the auxin biosynthesis gene YUCCA6 by artificial microRNA technology showed that starch overaccumulation severely reduced the pollen germination rate. In summary, we revealed that transient cold stress at the tetrad stage of pollen development in Chinese cabbage causes auxin-mediated starch-related energy metabolism imbalance that contributes to the decline in pollen germination rate and ultimately seed set.

Transcriptional dynamics in source-sink tissues identifies molecular factors regulating the corm development process in saffron (Crocus sativus L.).

Geophytic plants have evolved to develop underground storage organs (USO) in the active growing season to withstand harsh environments as well as to coordinate growth and reproduction when conditions are favourable. Saffron is an autumn flowering geophyte and an expensive spice crop restricted to certain geographical locations in the world. Saffron, being sterile, does not produce seeds and thus propagates only through corms, the quality of which determines its yield. Corm development in saffron is unexplored and the underlying molecular mechanism is still elusive. In this study, we performed an extensive characterisation of the transcriptional dynamics in the source (leaf) and sink (corm) tissues during corm development in saffron. Via morphological and transcriptome studies, we identified molecular factors regulating corm development process in saffron, which defined corm development into three stages: the initiation stage demonstrates enhanced vegetative growth aboveground and swelling of shoot base belowground due to active cell division & carbohydrate storage; the bulking stage comprises of increased source and sink strength, active photosynthesis, circadian gating and starch accumulation; the maturation stage represents reduced source and sink strength, lowered photosynthesis, sugar transport, starch synthesis and cell cycle arrest. The global view of transcriptional changes in source and sink identifies similar and new molecular factors involved in the saffron corm development process compared to USO formation in other geophytes and provides a valuable resource for dissecting the molecular network underlying the corm development. We propose a hypothetical model based on data analysis, of how molecular factors via environmental cues can regulate the corm development process in saffron.