High Nitric Oxide Concentration Inhibits Photosynthetic Pigment Biosynthesis by Promoting the Degradation of Transcription Factor HY5 in Tomato

The Crucial Role of SlGSNOR in Regulating Postharvest Tomato Fruit Ripening

S-nitrosoglutathione reductase (GSNOR) is a well-known regulator in controlling protein S-nitrosylation modification and nitric oxide (NO) homeostasis. Here, a GSNOR inhibitor N6022 and SlGSNOR silencing were applied to investigate the roles of SlGSNOR in tomato fruit postharvest ripening. We found that the application of N6022 and S-nitrosoglutathione (GSNO, a NO donor), and SlGSNOR silencing delayed the transition of fruit skin color by improving total chlorophyll level by 88.57%, 44.78%, and 91.03%, respectively. Meanwhile, total carotenoid and lycopene contents were reduced by these treatments. Concurrently, the activity of chlorophyll biosynthesis enzymes and the expression of related genes were upregulated, and the transcript abundances of total carotenoid bioproduction genes were downregulated, by N6022 and GSNO treatments and SlGSNOR silencing. In addition, fruit softening was postponed by N6022, GSNO, and SlGSNOR silencing, through delaying the decrease of firmness and declining cell wall composition; structure-related enzyme activity; and gene expression levels. Furthermore, N6022, GSNO, and SlGSNOR silencing enhanced the accumulation of titratable acid; ascorbic acid; total phenol; and total flavonoid, but repressed the content of soluble sugar and soluble protein accompanied with the expression pattern changes of nutrition-related genes. In addition, the endogenous NO contents were elevated by 197.55%; 404.59%; and 713.46%, and the endogenous SNOs contents were enhanced by 74.65%; 93.49%; and 94.85%; by N6022 and GSNO treatments and SlGSNOR silencing, respectively. Altogether, these results indicate that SlGSNOR positively promotes tomato postharvest fruit ripening, which may be largely on account of its negative roles in the endogenous NO level.

Impact of Sodium Nitroprusside on the Photosynthetic Performance of Maize and Sorghum

Nitric oxide (NO) is an important molecule in regulating plant growth, development and photosynthetic performance. This study investigates the impact of varying concentrations (0-300 µM) of sodium nitroprusside (SNP, a donor of NO) on the functions of the photosynthetic apparatus in sorghum (Sorghum bicolor L. Albanus) and maize (Zea mays L. Kerala) under physiological conditions. Analysis of the chlorophyll fluorescence signals (using PAM and the JIP-test) revealed an increased amount of open PSII reaction centers (qP increased), but it did not affect the number of active reaction centers per PSII antenna chlorophyll (RC/ABS). In addition, the smaller SNP concentrations (up to 150 μM) alleviated the interaction of QA with plastoquine in maize, while at 300 μM it predominates the electron recombination on QAQB-, with the oxidized S2 (or S3) states of oxygen evolving in complex ways in both studied plant species. At the same time, SNP application stimulated the electron flux-reducing end electron acceptors at the PSI acceptor side per reaction center (REo/RC increased up to 26%) and the probability of their reduction (φRo increased up to 20%). An increase in MDA (by about 30%) and H2O2 contents was registered only at the highest SNP concentration (300 µM). At this concentration, SNP differentially affected the amount of P700+ in studied plant species, i.e., it increased (by 10%) in maize but decreased (by 16%) in sorghum. The effects of SNP on the functions of the photosynthetic apparatus were accompanied by an increase in carotenoid content in both studied plants. Additionally, data revealed that SNP-induced changes in the photosynthetic apparatus differed between maize and sorghum, suggesting species specificity for SNP's impact on plants.

Advances in Nitric Oxide Signalling and Metabolism in Plants

More than 15,000 scientific articles published since the late 1950s related to RNS action or detection in various plant materials are listed in the Web of Science database [...]

Physiological, transcriptome and co-expression network analysis of chlorophyll-deficient mutants in flue-cured tobacco

BACKGROUND

Photosynthetic pigments in higher plants, including chlorophyll (Chl) and carotenoids, are crucial for photosynthesis and photoprotection. Chl-deficient tobacco seedlings generally have a lower photosynthesis rate and higher nitrate-nitrogen (NO₃-N) content, which causes a profound influence on tobacco yield and quality. In this study, a stable albino leaf mutant (Al) and slight-green leaf mutant (SG) obtained from the common flue-cured tobacco (Nicotiana tabacum L.) cultivar 'Zhongyan 100' (ZY100) by mutagenesis with ethyl methanesulfonate (EMS) were used as materials. The differences between the Chl-deficient mutants and the wild-type (WT) were analyzed in terms of biomass, photosynthetic fluorescence parameters, and carbon- and nitrogen-related physiological parameters. RNA sequencing (RNA-seq) and weighted gene co-expression network analysis (WGCNA) were used to explore the key pathways and candidate genes regulating differentiated chlorophyll and nitrate content.

RESULTS

The results showed that, when compared to the WT, the Chl content and biomass of mutant plants were considerably lower while the NO₃-N content was substantially elevated. The net photosynthetic rate, photosynthetic fluorescence parameters, carbohydrate, soluble protein, and carbon- and nitrogen-related enzyme activities all decreased in leaves of mutants and the development of chloroplasts was abnormal. Applying more nitrogen improved the growth and development of mutants, whereas NO₃-N content distinctively increased compared with that of the WT. Through transcriptome sequencing, the downregulated genes in mutants were enriched in plant hormone signal transduction and nitrogen metabolism, which are involved in pigment biosynthesis and the carbon fixation pathway. In addition, two hub genes and seven transcription factors identified from the blue module through WGCNA were likely to be key candidate factors involved in chlorophyll synthesis and nitrate accumulation.

CONCLUSION

Our results demonstrated that differences in chlorophyll and nitrate content were caused by the combined effects of chloroplast development, photosynthesis, as well as related biological activity. In addition, transcriptome results provide a bioinformatics resource for further functional identification of key pathways and genes responsible for differences in chlorophyll and nitrate content in tobacco plants.