Expression level of a flavonoid 3'-hydroxylase gene determines pathogen-induced color variation in sorghum

Fungal invasion-induced accumulation of salicylic acid promotes anthocyanin biosynthesis through MdNPR1-MdTGA2.2 module in apple fruits

In the field, necrosis area induced by pathogens is usually surrounded by a red circle in apple fruits. However, the underlying molecular mechanism of this phenomenon remains unclear. In this study, we demonstrated that accumulated salicylic acid (SA) induced by fungal infection promoted anthocyanin biosynthesis through MdNPR1-MdTGA2.2 module in apple (Malus domestica). Inoculating apple fruits with Valsa mali or Botryosphaeria dothidea induced a red circle surrounding the necrosis area, which mimicked the phenotype observed in the field. The red circle accumulated a high level of anthocyanins, which was positively correlated with SA accumulation stimulated by fungal invasion. Further analysis showed that SA promoted anthocyanin biosynthesis in a dose-dependent manner in both apple calli and fruits. We next demonstrated that MdNPR1, a master regulator of SA signaling, positively regulated anthocyanin biosynthesis in both apple and Arabidopsis. Moreover, MdNPR1 functioned as a co-activator to interact with and enhance the transactivation activity of MdTGA2.2, which could directly bind to the promoters of anthocyanin biosynthetic and regulatory genes to promote their transcription. Suppressing expression of either MdNPR1 or MdTGA2.2 inhibited coloration of apple fruits, while overexpressing either of them significantly promoted fruit coloration. Finally, we revealed that silencing either MdNPR1 or MdTGA2.2 in apple fruits repressed SA-induced fruit coloration. Therefore, our data determined that fungal-induced SA promoted anthocyanin biosynthesis through MdNPR1-MdTGA2.2 module, resulting in a red circle surrounding the necrosis area in apple fruits.

Biosynthesis and differential spatial distribution of the 3-deoxyanthocyanidins apigenidin and luteolinidin at the interface of a plant-cyanobacteria symbiosis exposed to cold

Aquatic ferns of the genus Azolla (Azolla) form highly productive symbioses with filamentous cyanobacteria fixing N2 in their leaf cavities, Nostoc azollae. Stressed symbioses characteristically turn red due to 3-deoxyanthocyanidin (DA) accumulation, rare in angiosperms and of unknown function. To understand DA accumulation upon cold acclimation and recovery, we integrated laser-desorption-ionization mass-spectrometry-imaging (LDI-MSI), a new Azolla filiculoides genome-assembly and annotation, and dual RNA-sequencing into phenotypic analyses of the symbioses. Azolla sp. Anzali recovered even when cold-induced DA-accumulation was inhibited by abscisic acid. Cyanobacterial filaments generally disappeared upon cold acclimation and Nostoc azollae transcript profiles were unlike those of resting stages formed in cold-resistant sporocarps, yet filaments re-appeared in leaf cavities of newly formed green fronds upon cold-recovery. The high transcript accumulation upon cold acclimation of AfDFR1 encoding a flavanone 4-reductase active in vitro suggested that the enzyme of the first step in the DA-pathway may regulate accumulation of DAs in different tissues. However, LDI-MSI highlighted the necessity to describe metabolite accumulation beyond class assignments as individual DA and caffeoylquinic acid metabolites accumulated differentially. For example, luteolinidin accumulated in epithelial cells, including those lining the leaf cavity, supporting a role for the former in the symbiotic interaction during cold acclimation.

Phenylpropanoids Following Wounding and Infection of Sweet Sorghum Lines Differing in Responses to Stalk Pathogens

Sweet sorghum (Sorghum bicolor) lines M81-E and Colman were previously shown to differ in responses to Fusarium thapsinum and Macrophomina phaseolina, stalk rot pathogens that can reduce the yields and quality of biomass and extracted sugars. Inoculated tissues were compared for transcriptomic, phenolic metabolite, and enzymatic activity during disease development 3 and 13 days after inoculation (DAI). At 13 DAI, M81-E had shorter mean lesion lengths than Colman when inoculated with either pathogen. Transcripts encoding monolignol biosynthetic and modification enzymes were associated with transcriptional wound (control) responses of both lines at 3 DAI. Monolignol biosynthetic genes were differentially coexpressed with transcriptional activator SbMyb76 in all Colman inoculations, but only following M. phaseolina inoculation in M81-E, suggesting that SbMyb76 is associated with lignin biosynthesis during pathogen responses. In control inoculations, defense-related genes were expressed at higher levels in M81-E than Colman. Line, treatment, and timepoint differences observed in phenolic metabolite and enzyme activities did not account for observed differences in lesions. However, generalized additive models were able to relate metabolites, but not enzyme activities, to lesion length for quantitatively modeling disease progression: in M81-E, but not Colman, sinapic acid levels positively predicted lesion length at 3 DAI when cell wall-bound syringic acid was low, soluble caffeic acid was high, and lactic acid was high, suggesting that sinapic acid may contribute to responses at 3 DAI. These results provide potential gene targets for development of sweet sorghum varieties with increased stalk rot resistance to ensure biomass and sugar quality.

Wall-associated kinase-like gene RL1 contributes to red leaves in sorghum

Red leaves are common in trees but rare in cereal crops. Red leaves can be used as raw materials for anthocyanin extraction and may have some adaptive significance for plants. In this study, we discovered a red leaf phenotype in the F₁ hybrids derived from a cross between two sorghum accessions with green leaf. Histological analysis of red leaves and green leaves showed that red compounds accumulate in mesophyll cells and gradually spreads to the entire leaf blade. In addition, we found chloroplasts degraded more quickly in red leaves than in green leaves based on transmission electron microscopy. Metabolic analysis revealed that flavonoids including six anthocyanins are more abundant in red leaves. Moreover, transcriptome analysis revealed that expression of flavonoid biosynthesis genes was upregulated in red leaves. These observations indicate that flavonoids and anthocyanins in particular, are ideal candidates for the red compounds accumulating in red leaves. Segregation analysis of the red leaf phenotype suggested a genetic architecture consisting of three dominant genes, one (RL1 for RED LEAF1) of which we mapped to a 55-kb region on chromosome 7 containing seven genes. Sequencing, reverse transcription-polymerase chain reaction, and transcriptome analysis suggested Sobic.007G214300, encoding a wall-associated kinase, as the most likely candidate for RL1. Fine mapping the red leaf gene and identifying the metabolites that cause red leaf in sorghum provide us with a better understanding of the red leaf phenotype in the natural population of sorghum.

Metabolic and Transcriptomic Profiling of Lilium Leaves Infected With Botrytis elliptica Reveals Different Stages of Plant Defense Mechanisms

Botrytis elliptica, the causal agent of gray mold disease, poses a major threat to commercial Lilium production, limiting its ornamental value and yield. The molecular and metabolic regulation mechanisms of Lilium's defense response to B. elliptica infection have not been completely elucidated. Here, we performed transcriptomic and metabolomic analyses of B. elliptica resistant Lilium oriental hybrid "Sorbonne" to understand the molecular basis of gray mold disease resistance in gray mold disease. A total of 115 differentially accumulated metabolites (DAMs) were detected by comparing the different temporal stages of pathogen infection. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed the differentially expressed genes (DEGs) and DAMs were enriched in the phenylpropanoid and flavonoid pathways at all stages of infection, demonstrating the prominence of these pathways in the defense response of "Sorbonne" to B. elliptica. Network analysis revealed high interconnectivity of the induced defense response. Furthermore, time-course analysis of the transcriptome and a weighted gene coexpression network analysis (WGCNA) led to the identification of a number of hub genes at different stages, revealing that jasmonic acid (JA), salicylic acid (SA), brassinolide (BR), and calcium ions (Ca2+) play a crucial role in the response of "Sorbonne" to fungal infection. Our work provides a comprehensive perspective on the defense response of Lilium to B. elliptica infection, along with a potential transcriptional regulatory network underlying the defense response, thereby offering gene candidates for resistance breeding and metabolic engineering of Lilium.

The Sorghum Grain Mold Disease Complex: Pathogens, Host Responses, and the Bioactive Metabolites at Play

Grain mold is a major concern in sorghum [Sorghum bicolor (L.) Moench] production systems, threatening grain quality, safety, and nutritional value as both human food and livestock feed. The crop's nutritional value, environmental resilience, and economic promise poise sorghum for increased acreage, especially in light of the growing pressures of climate change on global food systems. In order to fully take advantage of this potential, sorghum improvement efforts and production systems must be proactive in managing the sorghum grain mold disease complex, which not only jeopardizes agricultural productivity and profitability, but is also the culprit of harmful mycotoxins that warrant substantial public health concern. The robust scholarly literature from the 1980s to the early 2000s yielded valuable insights and key comprehensive reviews of the grain mold disease complex. Nevertheless, there remains a substantial gap in understanding the complex multi-organismal dynamics that underpin the plant-pathogen interactions involved - a gap that must be filled in order to deliver improved germplasm that is not only capable of withstanding the pressures of climate change, but also wields robust resistance to disease and mycotoxin accumulation. The present review seeks to provide an updated perspective of the sorghum grain mold disease complex, bolstered by recent advances in the understanding of the genetic and the biochemical interactions among the fungal pathogens, their corresponding mycotoxins, and the sorghum host. Critical components of the sorghum grain mold disease complex are summarized in narrative format to consolidate a collection of important concepts: (1) the current state of sorghum grain mold in research and production systems; (2) overview of the individual pathogens that contribute to the grain mold complex; (3) the mycotoxin-producing potential of these pathogens on sorghum and other substrates; and (4) a systems biology approach to the understanding of host responses.

Genome-wide association analysis reveals seed protein loci as determinants of variations in grain mold resistance in sorghum

GWAS analysis revealed variations at loci harboring seed storage, late embryogenesis abundant protein, and a tannin biosynthesis gene associated with sorghum grain mold resistance. Grain mold is the most important disease of sorghum [Sorghum bicolor (L.) Moench]. It starts at the early stages of grain development due to concurrent infection by multiple fungal species. The genetic architecture of resistance to grain mold is poorly understood. Using a diverse set of 635 Ethiopian sorghum accessions, we conducted a multi-stage disease rating for resistance to grain mold under natural infestation in the field. Through genome-wide association analyses with 173,666 SNPs and multiple models, two novel loci were identified that were consistently associated with grain mold resistance across environments. Sequence variation at new loci containing sorghum KAFIRIN gene encoding a seed storage protein affecting seed texture and LATE EMBRYOGENESIS ABUNDANT 3 (LEA3) gene encoding a protein that accumulates in seeds, previously implicated in stress tolerance, were significantly associated with grain mold resistance. The KAFIRIN and LEA3 loci were also significant factors in grain mold resistance in accessions with non-pigmented grains. Moreover, we consistently detected the known SNP (S4_62316425) in TAN1 gene, a regulator of tannin accumulation in sorghum grain to be significantly associated with grain mold resistance. Identification of loci associated with new mechanisms of resistance provides fresh insight into genetic control of the trait, while the highly resistant accessions can serve as sources of resistance genes for breeding. Overall, our association data suggest the critical role of loci harboring seed protein genes and implicate grain chemical and physical properties in sorghum grain mold resistance.

Proton-Coupled Electron Transfers of Defense Phytochemicals in Sorghum (Sorghum bicolor (L.) Moench)

Sorghum (Sorghum bicolor (L.) Moench) produces a range of defense phytochemicals containing a quinone core structure: sorgoleone allelochemical, flavonoid phytoalexins, and a broad spectrum of polyphenols. Those phytochemicals react with the components of cellular and agroecosystems to form stable semiquinone radicals engaging in different proton-coupled electron transfer reactions. This unique redox reactivity of plant phenolics could be used to develop bioactive food ingredients and green pesticides. To achieve those application goals, chemical phenotyping methods sensitive to quinone-semiquinone-dihydroxybenzene redox cycles (e.g., electrochemical conversion with fluorescence detection) are in demand. Chemometrics-based fingerprinting tools could facilitate on-farm screening of target traits for breeding innovations.

TRANSPARENT TESTA GLABRA1, a Key Regulator in Plants with Multiple Roles and Multiple Function Mechanisms

TRANSPARENT TESTA GLABRA1 (TTG1) is a WD40 repeat protein. The phenotypes caused by loss-of-function of TTG1 were observed about half a century ago, but the TTG1 gene was identified only about twenty years ago. Since then, TTG1 has been found to be a plant-specific regulator with multiple roles and multiple functional mechanisms. TTG1 is involved in the regulation of cell fate determination, secondary metabolisms, accumulation of seed storage reserves, plant responses to biotic and abiotic stresses, and flowering time in plants. In some processes, TTG1 may directly or indirectly regulate the expression of downstream target genes via forming transcription activator complexes with R2R3 MYB and bHLH transcription factors. Whereas in other processes, TTG1 may function alone or interact with other proteins to regulate downstream target genes. On the other hand, the studies on the regulation of TTG1 are very limited. So far, only the B3-domain family transcription factor FUSCA3 (FUS3) has been found to regulate the expression of TTG1, phosphorylation of TTG1 affects its interaction with bHLH transcription factor TT2, and TTG1 proteins can be targeted for degradation by the 26S proteasome. Here, we provide an overview of TTG1, including the identification of TTG1, the functions of TTG1, the possible function mechanisms of TTG1, and the regulation of TTG1. We also proposed potential research directions that may shed new light on the regulation and functional mechanisms of TTG1 in plants.

Root lodging is a physical stress that changes gene expression from sucrose accumulation to degradation in sorghum

BACKGROUND

Sorghum (Sorghum bicolor L.) is used as a raw material for biofuels because it accumulates sugars at high levels in the stem. Lodging of sorghum occurs when the soil is wet and very high winds blow across the field. In root lodging, the roots are pulled loose from the soil, causing the plant to fall over. Lodging reduces the yield of nonstructural carbohydrates. It is not yet clear which genes show changes in expression when sorghum falls over. We compared whole-gene expression in the mature stems of intact and lodged sorghum plants, with a focus on comparisons from the perspective of differences in sugar accumulation or degradation.

RESULTS

Lodging decreased sucrose content, starch content, and ratio of sucrose to total sugars in the stems of the sorghum cultivar SIL-05. Particular paralogs of SWEET and TMT family genes, which encode sucrose or hexose transporters, or both, were significantly highly expressed in intact or lodged sorghum stems. In intact stems, genes encoding the glucose-6-phosphate translocator, aquaporins, and enzymes involved in photosynthesis and starch synthesis were highly expressed. In lodged sorghum stems, expression of genes associated with sucrose or starch degradation or energy production was increased. Notably, expression of genes encoding enzymes catalyzing irreversible reactions and associated with the first steps of these metabolic pathways (e.g. INV, SUS, and hexokinase- and fructokinase-encoding genes) was significantly increased by lodging. Expression of SUT, SPS, and SPP was almost the same in intact and lodged sorghum.

CONCLUSIONS

Specific paralogs of sucrose-associated genes involved in metabolic pathways and in membrane transport were expressed in the stems of sorghum SIL-05 at the full-ripe stage. Root lodging drastically changed the expression of these genes from sucrose accumulation to degradation. The changes in gene expression resulted in decreases in sugar content and in the proportion of sucrose to hexoses in the stems of lodged plants.

Expression of Flavone Synthase II and Flavonoid 3'-Hydroxylase Is Associated with Color Variation in Tan-Colored Injured Leaves of Sorghum

Sorghum (Sorghum bicolor L. Moench) exhibits various color changes in injured leaves in response to cutting stress. Here, we aimed to identify key genes for the light brown and dark brown color variations in tan-colored injured leaves of sorghum. For this purpose, sorghum M36001 (light brown injured leaves), Nakei-MS3B (purple), and a progeny, #7 (dark brown), from Nakei-MS3B × M36001, were used. Accumulated pigments were detected by using high-performance liquid chromatography: M36001 accumulated only apigenin in its light brown leaves; #7 accumulated both luteolin and a small amount of apigenin in its dark brown leaves, and Nakei-MS3B accumulated 3-deoxyanthocyanidins (apigeninidin and luteolinidin) in its purple leaves. Apigenin or luteolin glucoside derivatives were also accumulated, in different proportions. Differentially expressed genes before and after cutting stress were identified by using RNA sequencing (RNA-seq). Integration of our metabolic and RNA-seq analyses suggested that expression of only flavone synthase II (FNSII) led to the synthesis of apigenin in M36001, expression of both FNSII and flavonoid 3'-hydroxylase (F3'H) led to the synthesis of apigenin and luteolin in #7, and expression of both flavanone 4-reductase and F3'H led to the synthesis of 3-deoxyanthocyanidins in Nakei-MS3B. These results suggest that expression of FNSII is related to the synthesis of flavones (apigenin and luteolin) and the expression level of F3'H is related to the balance of apigenin and luteolin. Expression of FNSII and F3'H is thus associated with dark or light brown coloration in tan-colored injured leaves of sorghum.

The Sorghum Gene for Leaf Color Changes upon Wounding (P) Encodes a Flavanone 4-Reductase in the 3-Deoxyanthocyanidin Biosynthesis Pathway

Upon wounding or pathogen invasion, leaves of sorghum [Sorghum bicolor (L.) Moench] plants with the P gene turn purple, whereas leaves with the recessive allele turn brown or tan. This purple phenotype is determined by the production of two 3-deoxyanthocyanidins, apigeninidin and luteolinidin, which are not produced by the tan-phenotype plants. Using map-based cloning in progeny from a cross between purple Nakei-MS3B (PP) and tan Greenleaf (pp) cultivars, we isolated this gene, which was located in a 27-kb genomic region around the 58.1 Mb position on chromosome 6. Four candidate genes identified in this region were similar to the maize leucoanthocyanidin reductase gene. None of them was expressed before wounding, and only the Sb06g029550 gene was induced in both cultivars after wounding. The Sb06g029550 protein was detected in Nakei-MS3B, but only slightly in Greenleaf, in which it may be unstable because of a Cys252Tyr substitution. A recombinant Sb06g029550 protein had a specific flavanone 4-reductase activity, and converted flavanones (naringenin or eriodictyol) to flavan-4-ols (apiforol or luteoforol) in vitro Our data indicate that the Sb06g029550 gene is involved in the 3-deoxyanthocyanidin synthesis pathway.

The Sorghum Gene for Leaf Color Changes upon Wounding (P) Encodes a Flavanone 4-Reductase in the 3-Deoxyanthocyanidin Biosynthesis Pathway

Upon wounding or pathogen invasion, leaves of sorghum [Sorghum bicolor (L.) Moench] plants with the P gene turn purple, whereas leaves with the recessive allele turn brown or tan. This purple phenotype is determined by the production of two 3-deoxyanthocyanidins, apigeninidin and luteolinidin, which are not produced by the tan-phenotype plants. Using map-based cloning in progeny from a cross between purple Nakei-MS3B (PP) and tan Greenleaf (pp) cultivars, we isolated this gene, which was located in a 27-kb genomic region around the 58.1 Mb position on chromosome 6. Four candidate genes identified in this region were similar to the maize leucoanthocyanidin reductase gene. None of them was expressed before wounding, and only the Sb06g029550 gene was induced in both cultivars after wounding. The Sb06g029550 protein was detected in Nakei-MS3B, but only slightly in Greenleaf, in which it may be unstable because of a Cys252Tyr substitution. A recombinant Sb06g029550 protein had a specific flavanone 4-reductase activity, and converted flavanones (naringenin or eriodictyol) to flavan-4-ols (apiforol or luteoforol) in vitro. Our data indicate that the Sb06g029550 gene is involved in the 3-deoxyanthocyanidin synthesis pathway.

Ternary WD40 Repeat-Containing Protein Complexes: Evolution, Composition and Roles in Plant Immunity

Plants, like mammals, rely on their innate immune system to perceive and discriminate among the majority of their microbial pathogens. Unlike mammals, plants respond to this molecular dialog by unleashing a complex chemical arsenal of defense metabolites to resist or evade pathogen infection. In basal or non-host resistance, plants utilize signal transduction pathways to detect "non-self," "damaged-self," and "altered-self"- associated molecular patterns and translate these "danger" signals into largely inducible chemical defenses. The WD40 repeat (WDR)-containing proteins Gβ and TTG1 are constituents of two independent ternary protein complexes functioning at opposite ends of a plant immune signaling pathway. They are also encoded by single-copy genes that are ubiquitous in higher plants, implying the limited diversity and functional conservation of their respective complexes. In this review, we summarize what is currently known about the evolutionary history of these WDR-containing ternary complexes, their repertoire and combinatorial interactions, and their downstream effectors and pathways in plant defense.

Serotonin attenuates biotic stress and leads to lesion browning caused by a hypersensitive response to Magnaporthe oryzae penetration in rice

The hypersensitive response (HR) of plants is one of the earliest responses to prevent pathogen invasion. A brown dot lesion on a leaf is visual evidence of the HR against the blast fungus Magnaporthe oryzae in rice, but tracking the browning process has been difficult. In this study, we induced the HR in rice cultivars harboring the blast resistance gene Pit by inoculation of an incompatible M. oryzae strain, which generated a unique resistance lesion with a brown ring (halo) around the brown fungal penetration site. Inoculation analysis using a plant harboring Pit but lacking an enzyme that catalyzes tryptamine to serotonin showed that high accumulation of the oxidized form of serotonin was the cause of the browning at the halo and penetration site. Our analysis of the halo browning process in the rice leaf revealed that abscisic acid enhanced biosynthesis of serotonin under light conditions, and serotonin changed to the oxidized form via hydrogen peroxide produced by light. The dramatic increase in serotonin, which has a high antioxidant activity, suppressed leaf damage outside the halo, blocked expansion of the browning area and attenuated inhibition of plant growth. These results suggest that serotonin helps to reduce biotic stress in the plant by acting as a scavenger of oxygen radicals to protect uninfected tissues from oxidative damage caused by the HR. The deposition of its oxide at the HR lesion is observed as lesion browning.

The sorghum SWEET gene family: stem sucrose accumulation as revealed through transcriptome profiling

BACKGROUND

SWEET is a newly identified family of sugar transporters. Although SWEET transporters have been characterized by using Arabidopsis and rice, very little knowledge of sucrose accumulation in the stem region is available, as these model plants accumulate little sucrose in their stems. To elucidate the expression of key SWEET genes involved in sucrose accumulation of sorghum, we performed transcriptome profiling by RNA-seq, categorization using phylogenetic trees, analysis of chromosomal synteny, and comparison of amino acid sequences between SIL-05 (a sweet sorghum) and BTx623 (a grain sorghum).

RESULTS

We identified 23 SWEET genes in the sorghum genome. In the leaf, SbSWEET8-1 was highly expressed and was grouped in the same clade as AtSWEET11 and AtSWEET12 that play a role in the efflux of photosynthesized sucrose. The key genes in sucrose synthesis (SPS3) and that in another step of sugar transport (SbSUT1 and SbSUT2) were also highly expressed, suggesting that sucrose is newly synthesized and actively exported from the leaf. In the stem, SbSWEET4-3 was uniquely highly expressed. SbSWEET4-1, SbSWEET4-2, and SbSWEET4-3 were categorized into the same clade, but their tissue specificities were different, suggesting that SbSWEET4-3 is a sugar transporter with specific roles in the stem. We found a putative SWEET4-3 ortholog in the corresponding region of the maize chromosome, but not the rice chromosome, suggesting that SbSWEET4-3 was copied after the branching of sorghum and maize from rice. In the panicle from the heading through to 36 days afterward, SbSWEET2-1 and SbSWEET7-1 were expressed and grouped in the same clade as rice OsSWEET11/Xa13 that is essential for seed development. SbSWEET9-3 was highly expressed in the panicle only just after heading and was grouped into the same clade as AtSWEET8/RPG1 that is essential for pollen viability. Five of 23 SWEET genes had SNPs that caused nonsynonymous amino acid substitutions between SIL-05 and BTx623.

CONCLUSIONS

We determined the key SWEET genes for technological improvement of sorghum in the production of biofuels: SbSWEET8-1 for efflux of sucrose from the leaf; SbSWEET4-3 for unloading sucrose from the phloem in the stem; SbSWEET2-1 and SbSWEET7-1 for seed development; SbSWEET9-3 for pollen nutrition.

Metabolic patterns associated with the seasonal rhythm of seed survival after dehydration in germinated seeds of Schismus arabicus

BACKGROUND

Seed of Shismus arabicus, a desert annual, display a seasonal tolerance to dehydration. The occurrence of a metabolic seasonal rhythm and its relation with the fluctuations in seed dehydration tolerance was investigated.

RESULTS

Dry seeds metabolism was the least affected by the season, while the metabolism of germinated and dehydrated seeds exhibit distinct seasonal patterns. Negative associations exist between amino acids, sugars and TCA cycle intermediates and seed survival, while positive relations exist with seed germination. In contrast, associations between the level of secondary metabolites identified in the dehydrated seeds and survival percentage were evenly distributed in positive and negative values, suggesting a functional role of these metabolites in the establishment of seed dehydration tolerance.

CONCLUSION

Our results indicate the occurrence of metabolic biorhythms in germinating and dehydrating seeds associated with seasonal changes in germination and, more pronouncedly, in seed dehydration tolerance. Increased biosynthesis of protective compounds (polyphenols) in dehydrating seeds during the winter season at the expenses of central metabolites likely contributes to the respective enhanced dehydration tolerance monitored.