Chl Degradation Research Articles

Integrated transcriptomics, metabolomics and physiological analyses reveal differential response mechanisms of wheat to cadmium and/or salinity stress.

Many soils face dual challenges of cadmium (Cd) contamination and salinization. However, the response of crops, especially wheat, to combined Cd and salinity stress is not understood. Here, wheat was grown in a hydroponic model for 14 days under single and combined Cd and NaCl stresses. Growth parameters, tissue Cd2+ and Na+ contents, and leaf chlorophyll (Chl), O2•-, and MDA levels were determined. Comparative transcriptomic and metabolomic analyses of the leaves were performed. The results showed that combined stress had a greater inhibitory effect on Chl contents and generated more O2•- and MDA, resulting in more severe wheat growth retardation than those under Cd or NaCl stress. Stress-induced decrease in Chl levels may be attributed to the inhibition of Chl biosynthesis, activation of Chl degradation, or a decline in glutamate content. Cd addition weakened the promotional effect of NaCl on SOS1 gene expression, thereby increasing the Na+ content. Contrastingly, NaCl supplementation downregulated the Nramp and ZIP gene expressions related to Cd uptake and transport, thereby impeding Cd2+ accumulation. All stresses enhanced tryptophan content via promoting tryptophan biosynthesis. Meanwhile, Cd and NaCl stresses activated phenylpropanoid biosynthesis and purine metabolism, respectively, thereby increasing the levels of caffeic acid, fumaric acid, and uric acid. Activating the TCA cycle was important in the wheat's response to combined stress. Additionally, NaCl and combined stresses affected starch and sucrose metabolism, resulting in sucrose and trehalose accumulation. Our findings provide a comprehensive understanding of the response of wheat to the combined Cd and salinity stress.

NAC Transcription Factor PpNAP4 Promotes Chlorophyll Degradation and Anthocyanin Synthesis in the Skin of Peach Fruit.

Chlorophyll (Chl) catabolism and anthocyanin synthesis play pivotal roles in determining the final skin color of fruits during maturation. However, in peach (Prunus persica) fruit, the regulatory mechanism governing skin color, especially the Chl catabolism, remains largely elusive. In this study, we identified ten Chl catabolic genes (CCGs), with PpSGR emerging as a key regulator in Chl degradation in peaches. Furthermore, a NAC-like, activated by AP3/P1 (NAP) transcription factor (TF), PpNAP4, was identified as a positive modulator of Chl breakdown. PpNAP4 induced the expression of PpSGR and other CCGs, including PpPPH, PpPAO, and PpTIC55-2, by directly binding to their promoters. Overexpression of PpNAP4 resulted in a heightened expression of these genes and accelerated Chl degradation. Notably, PpNAP4 also positively regulated the expression of PpANS and PpMYB10.1, one key structural gene and a core transcriptional regulator of anthocyanin synthesis, thereby contributing to fruit coloration. In summary, our findings elucidate that PpNAP4 serves as a pivotal regulator in determining the final skin color of peach by orchestrating Chl degradation and anthocyanin accumulation through direct activation of multiple CCGs and anthocyanin related genes.

Chlorophyllase (PsCLH1) and light-harvesting chlorophyll a/b binding protein 1 (PsLhcb1) and PsLhcb5 maintain petal greenness in Paeonia suffruticosa ‘Lv Mu Yin Yu’

IntroductionGreen flowers are not an adaptive trait in natural plants due to the challenge for pollinators to discriminate from leaves, but they are valuable in horticulture. The molecular mechanisms of green petals remain unclear. Tree peony (Paeonia suffruticosa) is a globally cultivated ornamental plant and considered the ‘King of Flowers’ in China. The P. suffruticosa ‘Lv Mu Yin Yu (LMYY)’ cultivar with green petals could be utilized as a representative model for understanding petal-specific chlorophyll (Chl) accumulation and color formation. ObjectivesIdentify the key genes related to Chl metabolism and understand the molecular mechanism of petal color changes. MethodsThe petal color parameter was analyzed at five developmental stages using a Chroma Spectrophotometer, and Chl and anthocyanin accumulation patterns were examined. Based on comparative transcriptomes, differentially expressed genes (DEGs) were identified, among which three were functionally characterized through overexpression in tobacco plants or silencing in ‘LMYY’ petals. ResultsDuring flower development and blooming, flower color changed from green to pale pink, consistent with the Chl and anthocyanin levels. The level of Chl demonstrated a similar pattern with petal epidermal cell striation density. The DEGs responsible for Chl and anthocyanin metabolism were characterized through a comparative transcriptome analysis of flower petals over three critical developmental stages. The key chlorophyllase (PsCLH1) and light-harvesting chlorophyll a/b binding protein 1 (PsLhcb1) and PsLhcb5 influenced the Chl accumulation and the greenness of ‘LMYY’ petals. ConclusionPsCLH1, PsLhcb1, and PsLhcb5 were critical in accumulating the Chl and maintaining the petal greenness. Flower color changes from green to pale pink were regulated by the homeostasis of Chl degradation and anthocyanin biosynthesis. This study offers insights into underlying molecular mechanisms in the green petal and a strategy for germplasm innovation.

The interplay of growth-regulating factor 5 and BZR1 in coregulating chlorophyll degradation in poplar.

Chlorophyll (Chl) is essential for plants to carry out photosynthesis, growth and development processes. Growth-regulating factors (GRFs) play a vital role in regulating Chl degradation in plants. However, the molecular mechanism by which GRF5 regulates Chl degradation in poplar remains unknown. Here we found that overexpression of PpnGRF5-1 increased Chl content in leaves and promoted chloroplast development in poplar. Overexpression of PpnGRF5-1 in poplar delayed Chl degradation induced by external factors, such as hormones, darkness and salt stress. PpnGRF5-1 responded to brassinosteroid (BR) signalling during BR-induced Chl degradation and reduced the expression levels of Chl degradation and senescence-related genes. PpnGRF5-1 inhibited the expression of Chl b reductases PagNYC1 and PagNOL. PpnGRF5-1 could interact with PagBZR1 in the nucleus. PagBZR1 also inhibited the expression of PagNYC1. In addition, we found that the protein-protein interaction between PagBZR1 and PpnGRF5-1 enhanced the inhibitory effect of PpnGRF5-1 on the Chl b reductases PagNYC1 and PagNOL. BZR1 and GRF5-1 were upregulated, and NOL and NYC1 were downregulated in triploid poplars compared to diploids. This study revealed a new mechanism by which PpnGRF5-1 regulates Chl degradation in poplars and lays the foundation for comprehensively analysing the molecular mechanism of Chl metabolism in triploid poplars.

Genome-wide identification of GA2ox genes family and analysis of PbrGA2ox1-mediated enhanced chlorophyll accumulation by promoting chloroplast development in pear

BackgroundChlorophyll (Chl) is an agronomic trait associated with photosynthesis and yield. Gibberellin 2-oxidases (GA2oxs) have previously been shown to be involved in Chl accumulation. However, whether and how the PbrGA2ox proteins (PbrGA2oxs) mediate Chl accumulation in pear (Pyrus spp.) is scarce.ResultsHere, we aimed to elucidate the role of the pear GA2ox gene family in Chl accumulation and the related underlying mechanisms. We isolated 13 PbrGA2ox genes (PbrGA2oxs) from the pear database and identified PbrGA2ox1 as a potential regulator of Chl accumulation. We found that transiently overexpressing PbrGA2ox1 in chlorotic pear leaves led to Chl accumulation, and PbrGA2ox1 silencing in normal pear leaves led to Chl degradation, as evident by the regreening and chlorosis phenomenon, respectively. Meanwhile, PbrGA2ox1-overexpressing (OE) tobacco plants discernably exhibited Chl built-up, as evidenced by significantly higher Pn and Fv/Fm. In addition, RNA sequencing (RNA-seq), physiological and biochemical investigations revealed an increase in abscisic acid (ABA), methyl jasmonate (MeJA), and salicylic acid (SA) concentrations and signaling pathways; a marked elevation in reducing and soluble sugar contents; and a marginal decline in the starch and sucrose levels in OE plants. Interestingly, PbrGA2ox1 overexpression did not prominently affect Chl synthesis. However, it indeed facilitated chloroplast development by increasing chloroplast number per cell and compacting the thylakoid granum stacks. These findings might jointly contribute to Chl accumulation in OE plants.ConclusionOverall, our results suggested that GA2oxs accelerate Chl accumulation by stimulating chloroplast development and proved the potential of PbrGA2ox1 as a candidate gene for genetically breeding biofortified pear plants with a higher yield.

Potassium and jasmonic acid —Induced nitrogen and sulfur metabolisms improve resilience against arsenate toxicity in tomato seedlings

Despite the well-known individual roles of potassium (K+) and jasmonic acid (JA) in plant responses to various stresses, their combined effects on improving tolerance to metalloid arsenate (AsV) toxicity and their influence on physiological and biochemical mechanisms remain largely unexplored. Therefore, the present study was conducted to explore the concomitant role of K+ and JA in nitrogen (N) and sulfur (S) metabolisms and regulation of antioxidant system in tomato seedlings under AsV toxicity conditions. The obtained data reveal that K+ and/or JA boosted the tolerance of tomato (Solanum lycopersicum L.) seedlings to AsV toxicity. However, the effect of a combined dose of K+ and JA was found to be more efficient as compared to the alone application. Seedlings subjected to AsV exhibited suppressed morphological attributes (shoot and root length, shoot and root fresh weight, and shoot and root dry weight), and physio-biochemical characteristics. Also, AsV-treated tomato seedlings showed enhanced reactive oxygen species (ROS) and increased the activity of ROS-producing enzymes (O2•— -generating NADPH oxidase activity and H2O2-generating glycolate oxidase] and also a chlorophyll (Chl) degrading enzyme [chlorophyllase (Chlase) activity]. However, the exogenous supply of K+ and JA synergistically inhibited Chl degradation and overproduction of ROS by suppressing their responsible enzymes activity. Moreover, it induced gas exchange parameters and activity of enzymes responsible for the photosynthesis process (carbonic anhydrase and Rubisco), Chl biosynthesis (δ-aminolevulinic acid dehydratase), and suppressed Chlase activity, and overproduction of ROS and their producing enzymes activity. Most interestingly, the combined application of K+ and JA substantially increased N and S content and their assimilation by upregulating the activity of enzymes involved in these key pathways (nitrate reductase, nitrite reductase, glutamine synthetase, glutamate synthase, ATP sulfurylase, adenosine 5-phosphosulfate reductase, O-acetylserine (thiol) lyase and sulfide reductase). The obtained results strongly reveal that the combined application of K+ and JA improved tolerance of tomato seedlings to AsV toxicity by enhancing N and S assimilation pathways and antioxidant system.

Strigolactone and nitric oxide collaborate synergistically to boost tomato seedling resilience to arsenic toxicity via modulating physiology and antioxidant system

Arsenic (As) poses a significant environmental threat as a metalloid toxin, adversely affecting the health of both plants and animals. Strigolactones (SL) and nitric oxide (NO) are known to play crucial roles in plant physiology. Therefore, the present experiment was designed to investigate the potential cumulative role of SL (GR24–0.20 μM) and NO (100 μM) in mitigating the adverse effect of AsV (53 μM) by modulating physiological mechanisms in two genotypes of tomato (Riogrand and Super Strain 8). A sample randomized design with four replicates was used to arrange the experimental pots in the growth chamber. 45-d old both tomato cultivars under AsV toxicity exhibited reduced morphological attributes (root and shoot length, root and shoot fresh weight, and root and shoot dry weight) and physiological and biochemical characteristics [chlorophyll (Chl) a and b content, activity of δ-aminolevulinic acid dehydratase activity (an enzyme responsible for Chl biosynthesis), and carbonic anhydrase activity (an enzyme responsible for photosynthesis), and enhanced Chl degradation, overproduction of reactive oxygen species (ROS) and lipid peroxidation due to enhanced malondialdehyde (MDA) content. However, the combined application of SL and NO was more effective in enhancing the tolerance of both varieties to AsV toxicity compared to individual application. The combined application of SL and NO improved growth parameters, biosynthesis of Chls, NO and proline. However, the combined application significantly suppressed cellular damage by inhibiting MDA and overproduction of ROS in leaves and roots, as confirmed by the fluorescent microscopy study and markedly upregulated the antioxidant enzymes (catalase, peroxidase, superoxide dismutase, ascorbate dismutase and glutathione reductase) activity. This study provides clear evidence that the combined application of SL and NO supplementation significantly improves the resilience of tomato seedlings against AsV toxicity. The synergistic effect of SL and NO was confirmed by the application of cPTIO (an NO scavenger) with SL and NO. However, further molecular studies could be imperative to conclusively validate the simultaneous role of SL and NO in enhancing plant tolerance to abiotic stress.

Natural variation in STAYGREEN contributes to low-temperature tolerance in cucumber.

Low-temperature (LT) stress threatens cucumber production globally; however, the molecular mechanisms underlying LT tolerance in cucumber remain largely unknown. Here, using a genome-wide association study (GWAS), we found a naturally occurring single nucleotide polymorphism (SNP) in the STAYGREEN (CsSGR) coding region at the gLTT5.1 locus associated with LT tolerance. Knockout mutants of CsSGR generated by clustered regularly interspaced palindromic repeats (CRISPR)/CRISPR-associated nuclease 9 exhibit enhanced LT tolerance, in particularly, increased chlorophyll (Chl) content and reduced reactive oxygen species (ROS) accumulation in response to LT. Moreover, the C-repeat Binding Factor 1 (CsCBF1) transcription factor can directly activate the expression of CsSGR. We demonstrate that the LT-sensitive haplotype CsSGRHapA , but not the LT-tolerant haplotype CsSGRHapG could interact with NON-YELLOW COLORING 1 (CsNYC1) to mediate Chl degradation. Geographic distribution of the CsSGR haplotypes indicated that the CsSGRHapG was selected in cucumber accessions from high latitudes, potentially contributing to LT tolerance during cucumber cold-adaptation in these regions. CsSGR mutants also showed enhanced tolerance to salinity, water deficit, and Pseudoperonospora cubensis, thus CsSGR is an elite target gene for breeding cucumber varieties with broad-spectrum stress tolerance. Collectively, our findings provide new insights into LT tolerance and will ultimately facilitate cucumber molecular breeding.

Transcriptomic-metabolomic analysis of magnesium-stimulated in peel coloration of Satsuma mandarin

Magnesium (Mg) has been found to promote the color change citrus peel, but the underlying mechanism remains unclear. In this study, Mg application treatment significantly increased the Mg content in the peel of Satsuma mandarin fruit during the expansion stage (90–150 days after flowering). Mg fertilizer treatment was also found to significantly reduce chlorophyll (Chl) a content and increase β, β-xanthophyll (β-cryptoxanthin, zeaxanthin, neoxanthin), and abscisic acid (ABA) content in the flavedo during the key period of color change in Satsuma mandarin (165–195 days after flowering). Under Mg fertilizer treatment, Chl biosynthesis genes (CitGGDR, CitCHLH, CitCHLM, CitCHL27, and CitPORA) was down-regulated and that of Chl degradation genes (CitNYC, CitPPH, CitPAO, and CitRCCR) was up-regulated, which resulted in a lower Chl content in the flavedo than the control. Moreover, Mg fertilizer treatment up-regulated carotenoid biosynthesis genes (CitPSY, CitPDS, CitZDS, CitLCYb1, CitLCYb2, CitZEP, CitNCED2, and CitNCED3), leading to the accumulation of β, β-xanthophyll and ABA in the flavedo. Mg fertilizer treatment also promoted sugar (mainly fructose, glucose, and sucrose) accumulation in fruit flavedo, which showed significant negative correlations with Chl, α-carotene, lutein, and β-carotene, but positive correlations with β, β-xanthophyll compositions, and ABA in the flavedo. An analysis integrating transcriptome and metabolome data revealed that Mg may promote the color change of Satsuma mandarin fruit flavedo by regulating various metabolic pathways related to peel coloration, such as sugar accumulation, Chl degradation, carotenoid and ABA biosynthesis, and carbon fixation. The results can explain the regulatory pathways and networks of Mg-induced citrus peel coloration.

2,4-Epibrassinolide delays leaf senescence in pak choi (Brassica rapa subsp. chinensis) by regulating its chlorophyll metabolic pathway and endogenous hormones content

• EBR decreased the degradation of Chl and its derivatives. • EBR reduced the activity of Chl degradation pathway related enzymes. • EBR decreased the expression of Chl degradation related genes. • EBR reduced the JA and ABA accumulation in pak choi.

Concentration-dependent impacts of exogenous methyl jasmonate (MeJA) on chlorophyll degradation of apple fruit during ripening

Although jasmonates (JAs) have been proved to regulate degreening of apple fruit, the relevant molecular mechanisms have not yet been clarified. Previous reports revealed that the effects of JAs on degreening of harvested horticultural crops might be dependent on concentration applied. Whether a similar result can be obtained from apple fruit is still unclear. This research explored the impacts of different concentrations of methyl jasmonate (MeJA) treatment on chlorophyll (Chl) degradation of postharvest apple fruit. Apples (Malus × domestica Borkh.) of commercial maturity were treated with 10 or 1500 µM MeJA and then stored at 20 ± 0.5 °C. The results indicated that exogenous 10 µM MeJA delayed degreening and ripening of apple fruit, whereas 1500 µM MeJA treatment had the opposite effects. Treatment with 10 µM MeJA alleviated Chl-oxidation by reducing Chl-peroxidase (POX) activity and reactive oxygen species (ROS) levels in chloroplast of apple peel during ripening, whereas 1500 µM MeJA treatment had the opposite effects. Activities of Magnesium-dechelatase (MDcase) and pheophytinase (PPH) in apple peel were differentially suppressed by 10 µM MeJA treatment while promoted by 1500 µM MeJA treatment during ripening. Application of 10 µM MeJA delayed the peak of endogenous jasmonic acid (JA) content, reduced jasmonate resistant 1 (JAR1) content and allene oxide synthase (AOS) activity, and differentially down-regulated expression of MdNYC3, MdNYE1a, MdPPH1, MdPAO6, MdPAO8, MdRCCR2 and MdMYC2a in apple peel during ripening, whereas opposite results were obtained from the 1500 µM MeJA-treated apple fruit. At the late ripening stage, MdHCAR expression in apple peel was promoted by 10 µM MeJA treatment while reduced by 1500 µM MeJA treatment. Transcript levels of MdNYC1 and MdNOL2 were generally reduced by both treatments at the late ripening stage. Transient overexpression of MdMYC2a accelerated Chl degradation of apple peel by promoting PPH and MDcase activities and enhancing expression of the above Chl catabolic genes (CCGs), except MdHCAR whose expression was down-regulated by it during ripening. The AOS activity, JA and JAR1 contents in apple peel were increased after transient overexpression of MdMYC2a during ripening. These data indicated that the PAO pathway and Chl-oxidation were regulated by JA signal in apple peel during ripening, and exogenous MeJA regulated Chl degradation of apple fruit in a concentration-dependent manner.

ABI5 promotes heat stress-induced chlorophyll degradation by modulating the stability of MYB44 in cucumber.

The yellowing of leaves caused by the decomposition of chlorophyll (Chl) is a characteristic event during senescence, which can be induced by various environmental stresses. However, the molecular mechanisms of high temperature-induced Chl degradation in horticultural plants remain poorly understood. Here, we found that heat stress induced Chl degradation and the expression of ABI5 and MYB44 in cucumber. Silencing of ABI5 compromised heat stress-induced Chl degradation, and the transcription of pheophytinase (PPH) and pheophorbide a oxygenase (PAO), two key genes in Chl catabolic pathway, but silencing of MYB44 exhibited the opposite results. Furthermore, ABI5 interacted with MYB44 in vitro and in vivo. ABI5 positively regulated heat stress-induced Chl degradation through two pathways. ABI5 directly bound to PPH and PAO promoters to promote their expression, leading to accelerating Chl degradation. On the other hand, the interaction between ABI5 and MYB44 reduced the binding of MYB44 to PPH and PAO promoters and led to the ubiquitination-depended protein degradation of MYB44, thereby alleviating the transcription inhibitory effect of MYB44 on PPH and PAO. Taken together, our findings propose a new regulatory network for ABI5 in regulating heat stress-induced Chl degradation.

Application of Cytokinin under Modified Atmosphere (MA) Delays Yellowing and Prolongs the Vase Life of Davallia solida (G. Forst.) Sw. Leaves

Cut leaves of Davallia solida are widely used in bouquet greenery. However, the leaves wilt and yellow after seven days. Postharvest applications of exogenous cytokinins (CKs), a plant growth regulator (PGR), preventing senescence in many green leafy plants, were studied by pulsing cut D. solida leaves with 6-benzylamiopurine (BA) at a concentration of 100 ppm, or thidiazuron (TDZ) at a concentration of 10 μM for 24 h, compared with distilled water as a control, and then placing the ferns in a controlled room (21 + 2 °C, 70–80% relative humidity (RH), under cool-white fluorescent lights for 12 h/d). Pulsing with BA and TDZ delayed leaf yellowing while preserving chlorophyll (Chl) content. This was due to reduced Chl-degrading enzyme activities on day 8 of the vase life of the leaves, resulting in longer display life of 11.1 and 11.5 days, respectively. TDZ delayed Chl breakdown on day 8 of the vase life of leaves more than was the case for BA. Subsequently, leaves were pulsed in 10 μM TDZ, or distilled water for 24 h, and then 10 leaves from each treatment were packaged in a 25 × 30 cm, 25-μm thickness BOPP bag. All the packages were stored at 10 °C in 10 h/d light for one, two and three weeks, then unpacked and placed in distilled water. Pulsing with TDZ before one-week storage delayed leaf yellowing, maintained Chl content and extended their vase life to 9.6 days compared with one-, two-, and three-week control leaves, which had a vase life of 6.2, 5.8, and 3.6 days, respectively. After one week, the relative fresh weight of the leaves and water uptake did not alter between the control and TDZ groups. The activities of Chl degradation enzymes in the leaves of D. solida pulsed with TDZ prior to storage were significantly suppressed, related to higher Chl content and a lower percentage of leaf yellowing than the control, resulting in a longer vase life of 9.0 days, while the control lasted 7.0 days. A 10 µM TDZ pulsing treatment significantly prevented the yellowing of D. solida fronds during the vase period or storage period, and one-week storage under MA with light conditions is recommended for retaining postharvest quality after storage.

Growth and Physiological Response of Viola tricolor L. to NaCl and NaHCO3 Stress

Soil salinization is an important environmental problem worldwide and has a significant impact on the growth of plants. In recent years, the mechanisms of plant salt tolerance have received extensive attention from researchers. In this paper, an experiment was implemented to assess the potential effect of different NaCl and NaHCO3 (sodium bicarbonate-an alkaline salt) concentrations (25 mmol·L-1, 50 mmol·L-1, 100 mmol·L-1, 150 mmol·L-1 and 200 mmol·L-1) on the growth, antioxidant enzymes, osmoprotectants, photosynthetic pigments and MDA of Viola tricolor L. to reveal the physiological response and explore the maximum concentrations of NaCl and NaHCO3 stress that V. tricolor can tolerate. The results showed that NaCl and NaHCO3 treatments had significant effects on osmoprotectants, antioxidant enzymes, photosynthetic pigments, MDA content and the plant height growth of V. tricolor. On day 14 of the NaCl and NaHCO3 stress, the height growth of V. tricolor was significantly greater than CK when the concentration of NaCl and NaHCO3 was less than 100 mmol·L-1. Soluble protein (SP) was significantly greater than CK when the NaCl concentration was less than 150 mmol·L-1 and the NaHCO3 concentration was less than 200 mmol·L-1; soluble sugar (SS) was significantly greater than CK under all NaCl and NaHCO3 treatments; proline (Pro) was significantly greater than CK when the NaCl concentration was 150 mmol·L-1 and the NaHCO3 concentration were 150 and 200 mmol·L-1, respectively. Peroxidase (POD) was significantly greater than CK when the NaCl concentration was less than 200 mmol·L-1 and the NaHCO3 concentration was less than 150 mmol·L-1; superoxide dismutase (SOD) was significantly greater than CK when the NaCl concentration was 50 mmol·L-1 and the NaHCO3 concentrations were 50, 100 and 150 mmol·L-1, respectively; catalase (CAT) was significantly greater than CK when the NaCl and NaHCO3 concentrations were 25, 50 and 100 mmol·L-1, respectively. Chlorophyll (Chl) was significantly lower than CK when the NaCl and NaHCO3 concentrations were greater than 100 mmol·L-1. Malondialdehyde (MDA) gradually increased with the increase in the NaCl and NaHCO3 concentrations. Membership function analysis showed that the concentrations of NaCl and NaHCO3 that V. tricolor was able to tolerate were 150 mmol·L-1 and 200 mmol·L-1, respectively. Beyond these thresholds, osmoprotectants and antioxidant enzymes were seriously affected, Chl degradation intensified, the photosynthetic system was seriously damaged, and the growth of V. tricolor was severely affected. According to a comprehensive ranking of results, the degree of NaCl stress on V. tricolor was lower than that from NaHCO3 when the treatment concentration was lower than 50 mmol·L-1, but higher than that from NaHCO3 when it exceeded 50 mmol·L-1.

Chlorophyll breakdown during fruit ripening: Qualitative analysis of phyllobilins in the peel of apples (Malus domestica Borkh.) cv. ‘Gala’ during different shelf life stages

Chlorophyll (Chl) degradation is an important process of fruit ripening, mediated by the pheophorbide a oxygenase/phyllobilin (PaO/PB) pathway. Chl is catabolized to linear tetrapyrrolic phyllobilins that resemble the bile pigments. Determining the optimal harvest date is of pivotal importance for the fruit industry. Among the physiological changes at the onset of ripening and during shelf life, the breakdown of Chl appears as a promising indicator for fruit maturity. In addition, PBs are a frequently overlooked component of the human diet with antioxidant and antiproliferative activities. However, their relevance for a healthy diet and their potential as ripening indicator in fruit cannot be evaluated yet, as details on emergence and composition of PBs in fruit are yet elusive. Using apple (Malus × domestica Borkh.) cv. ‘Gala’ as a model fruit, the Chl content and the emergence and identity of PBs were analyzed during a controlled shelf life period using UV/Vis spectroscopy and ultra-high pressure liquid chromatography coupled to high resolution quadrupole-time of flight-mass spectrometry (UHPLC-Q-TOF-MS). An in-house database with chromatographic and MS data from 51 PBs, revealed ten chlorophyll catabolites, including five NCCs, one YCC, and four DNCCs (including a previously unknown one). PBs were identified with increasing abundance and diversity from the onset of Chl degradation, suggesting a potential role as ripening indicators.

STRONG STAYGREEN inhibits DNA binding of PvNAP transcription factors during leaf senescence in switchgrass.

Fine tuning the progression of leaf senescence is important for plant fitness in nature, while the "staygreen" phenotype with delayed leaf senescence has been considered a valuable agronomic trait in crop genetic improvement. In this study, a switchgrass (Panicum virgatum L.) CCCH-type Zinc finger gene, Strong Staygreen (PvSSG), was characterized as a suppressor of leaf senescence as overexpression or suppression of the gene led to delayed or accelerated leaf senescence, respectively. Transcriptomic analysis marked that chlorophyll (Chl) catabolic pathway genes were involved in the PvSSG-regulated leaf senescence. PvSSG was identified as a nucleus-localized protein with no transcriptional activity. By yeast two-hybrid screening, we identified its interacting proteins, including a pair of paralogous transcription factors, PvNAP1/2 (NAC-LIKE, ACTIVATED BY AP3/PI). Overexpression of PvNAPs led to precocious leaf senescence at least partially by directly targeting and transactivating Chl catabolic genes to promote Chl degradation. PvSSG, through protein-protein interaction, repressed the DNA-binding efficiency of PvNAPs and alleviated its transactivating effect on downstream genes, thereby functioning as a "brake" in the progression of leaf senescence. Moreover, overexpression of PvSSG resulted in up to 47% higher biomass yield and improved biomass feedstock quality, reiterating the importance of leaf senescence regulation in the genetic improvement of switchgrass and other feedstock crops.

The effects of nitrogen application on the growth, photosynthesis, and antioxidant activity of Amaranthus viridis

Amaranthus viridis is a functional food due to its antioxidant activity. The aim of this study was to investigate the responses of photosynthesis, growth, and antioxidant properties in A. viridis to nitrogen (N) applications. A. viridis plants were cultivated under low N (LN), medium N (MN), and high N (HN), and harvested at the reproductive phase. The dry mass and plant height of A. viridis plants increased with elevated N, and the dry mass of HN was saturated. Net photosynthetic rate, stomatal conductance, and water-use efficiency in the leaves at HN were strengthened. Meanwhile, under HN, chlorophylls (Chl), their precursors, and degradation intermediates in the leaves were highly accumulated, and the minor route of Chl degradation pathway was induced dramatically. However, 2,2-diphenyl-1-picrylhydrazyl radical-scavenging, ferrous iron-chelating, and reducing power in the extracts were reduced under HN. Conclusively, an appropriate N application balanced the yield and antioxidant properties of A. viridis.

Identification of candidate genes and clarification of the maintenance of the green pericarp of weedy rice grains.

The weedy rice (Oryza sativa f. spontanea) pericarp has diverse colors (e.g., purple, red, light-red, and white). However, research on pericarp colors has focused on red and purple, but not green. Unlike many other common weedy rice resources, LM8 has a green pericarp at maturity. In this study, the coloration of the LM8 pericarp was evaluated at the cellular and genetic levels. First, an examination of their ultrastructure indicated that LM8 chloroplasts were normal regarding plastid development and they contained many plastoglobules from the early immature stage to maturity. Analyses of transcriptome profiles and differentially expressed genes revealed that most chlorophyll (Chl) degradation-related genes in LM8 were expressed at lower levels than Chl a/b cycle-related genes in mature pericarps, suggesting that the green LM8 pericarp was associated with inhibited Chl degradation in intact chloroplasts. Second, the F2 generation derived from a cross between LM8 (green pericarp) and SLG (white pericarp) had a pericarp color segregation ratio of 9:3:4 (green:brown:white). The bulked segregant analysis of the F2 populations resulted in the identification of 12 known genes in the chromosome 3 and 4 hotspot regions as candidate genes related to Chl metabolism in the rice pericarp. The RNA-seq and sqRT-PCR assays indicated that the expression of the Chl a/b cycle-related structural gene DVR (encoding divinyl reductase) was sharply up-regulated. Moreover, genes encoding magnesium-chelatase subunit D and the light-harvesting Chl a/b-binding protein were transcriptionally active in the fully ripened dry pericarp. Regarding the ethylene signal transduction pathway, the CTR (encoding an ethylene-responsive protein kinase) and ERF (encoding an ethylene-responsive factor) genes expression profiles were determined. The findings of this study highlight the regulatory roles of Chl biosynthesis- and degradation-related genes influencing Chl accumulation during the maturation of the LM8 pericarp.

Taxifolin delays the degradation of chlorophyll in pakchoi (Brassica rapa L subsp. chinensis) by regulating the ascorbate-glutathione cycle

The effects of taxifolin (TF) treatment on chlorophyll (Chl) degradation and the ascorbate-glutathione (AsA-GSH) cycle were evaluated in pakchoi. Compared with a control and other treatment concentrations, 1000 mg L−1 TF treatment had the greatest green retention effect on pakchoi. This treatment delayed the degradation of Chl and its derivatives and inhibited the activities of chlorophyllase, Mg-dechelatase, pheophytinase, and pheophorbide a oxygenase. The expression of Chl degradation (BrNYC1, BrNOL, BrCLH, BrSGR1, BrSGR2, BrPPH, BrPAO, and BrRCCR) and senescence (BrSAG12) related-genes was also suppressed, leading to better quality pakchoi. In addition, TF treatment alleviated decreases in total ascorbic acid, reduced ascorbic acid, dehydroascorbic acid, total glutathione, reduced glutathione, and oxidized glutathione, while enhancing the activities of ascorbic acid peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase, and glutathione reductase. This contributed to maintained high free radical scavenging ability and lower membrane lipid peroxidation. These results demonstrate that TF can regulate the AsA-GSH cycle and maintain the activity to scavenge reactive oxygen species, thus reducing membrane lipid oxidation and ultimately reducing nutrient loss and Chl degradation in pakchoi.

1-Methylcyclopropene retard the yellowing of postharvest pak choi (Brassica rapa subsp. Chinensis) by regulating pigments and transcription factors during storage at 20 °C

To explore which transcription factors (TFs) modulate the pigment metabolism associated with pak choi yellowing after 1-methylcyclopropene (1-MCP) fumigation during storage at 20 °C, omics technology were carried out. 5 μL L−1 1-MCP treatment slowed the decline of total chlorophyll (Chl) contents and Chl fluorescence parameters. The total levels in carotenoid and flavonoid did not change much during storage, regardless of whether undergoing 1-MCP treatment, which might be linked to the down-regulated expression of most pigment synthesis associated genes. The bilirubin contents and its synthesis gene HO1 expression soared, which were inhibited by 1-MCP; however, the contents of bilirubin were low. The correlation analysis between Chl degradation genes and TFs revealed that BcAP2/BcERF, BcMYB, BcNACs, BcbZip, BcbHLH, BcWRKY, and BcC2H2 were the major potential TFs involved in leaf yellowing of pak choi. The numbers of TFs concerning in Chl catabolism were more than those of TFs relating to the catabolism of carotenoid and flavonoid; TFs concerning in Chl catabolism were also the most abundant TFs that respond to 1-MCP. The variation of carotenoid, flavonoid and bilirubin during storage were irrelevant to the yellowing of pak choi. BcNACs and BcWRKYs may positively regulate Chl breakdown; BcAP2/BcERFs, BcMYBs, BcbZips, BcbHLHs, and BcC2H2s may act as both transcriptional activators and repressors in Chl degradation process. Thus, 1-MCP may regulate the transcriptome expression of upstream TFs, and therefore, maintained low expression of Chl degradation associated genes, inhibited Chl degradation, helping to retard leaf yellowing of pak choi.