Regulation of stomatal aperture in response to drought stress mediating with polyamines, nitric oxide synthase and hydrogen peroxide in Rosa canina L

Barley root tip peroxidases convert DAF-FM and DAR-4M to an NO-independent fluorescent product using H2O2 derived from polyamine catabolism by polyamine oxidases

The aim of our study was to investigate the possible involvement of barley root tip peroxidases and polyamine oxidases in the conversion of DAF-FM or DAR-4M into an NO-independent fluorescent product after the exogenous application of polyamines. Application of spermidine or spermine into the incubation medium increased H2O2 production by root tip segments in a dose-dependent manner. This spermidine- or spermine-induced increase in H2O2 production was accompanied by intensified fluorescence of both DAF-FM and DAR-4M in a polyamine dose-dependent manner, similarly to exogenously added H2O2. On the contrary, exogenous putrescine neither evoked H2O2 production nor increased DAF-FM or DAR-4M fluorescence. Application of guazatine, a polyamine oxidase inhibitor, into the incubation medium inhibited both H2O2 production and DAF-FM or DAR-4M fluorescence. Spermidine- or spermine-induced DAF-FM or DAR-4M fluorescence decreased with an increasing amount of catalase or guaiacol, a competitive substrate for peroxidase, in the incubation medium. Exogenous application of indole-3-acetic acid, a well-known activator of NO generation in roots, but not of H2O2, spermidine or spermine, induces NO accumulation in the root tips. Exogenous application of spermidine or spermine to plant tissues with high polyamine oxidase and peroxidase activity, as are the barley root tips, generates an NO-independent fluorescence signal from either DAF-FM or DAR-4M, giving a false positive signal for NO emission.

Regulation of lignan biosynthesis through signaling pathways mediated by H2O2 in Linum album cell culture in response to exogenous putrescine

Polyamines are small aliphatic amines whose metabolic reprogramming is involved in the regulation of various plant cellular reactions. Our previous study showed that polyamines increased lignan production in Linum album; however, little is known about the underlying mechanisms. This study aimed to provide more details on how putrescine (Put) regulates lignan biosynthesis in L. album cell culture. Our results showed that Put leads to podophyllotoxin (PTOX) and 6-methoxy podophyllotoxin (6MPTOX) accumulation by increasing the expression levels of phenylalanine ammonia-lyase (PAL) and pinoresinol-lariciresinol reductase (PLR) genes, encoding lignan biosynthesis regulatory enzymes. Put also increased hydrogen peroxide (H2O2) content, while its level decreased in the presence of aminoguanidine (AG) and imidazole, inhibitors of diamine oxidase (DAO) and NADPH oxidase (NOX), respectively. Elevated levels of nitric oxide (NO) and cytosolic free Ca2+ caused by Put treatment were reduced after using inhibitors of nitrate reductase (NR) and nitric oxide synthesis-like (NOS-like) enzymes, as well as Ca2+ influx. Besides, pre-treatment of cells with AG, imidazole, ethylene glycol-bis (β-aminoethyl ether)-N, N,N',N'-tetraacetic acid (EGTA) (Ca2+ chelator), Nɷ-nitro-L-arginine methyl ester (L-NAME), and Sodium tungstate (TUN) (NO generation inhibitors) diminished PAL and PLR transcript levels and PTOX and 6MPTOX accumulation, indicating the involvement of H2O2, NO, and Ca2+ in regulating lignan biosynthesis in L. album cells. Put also stimulated salicylic acid (SA) accumulation, being sensitive to all inhibitors used. Overall, this study suggests that Put-induced H2O2 generation in combination with NO and Ca2+ signals can regulate PAL and PLR genes expression and lignan production, likely in a SA-dependent manner.

Polyamines: The valuable bio-stimulants and endogenous signaling molecules for plant development and stress response

Polyamines (PAs) are nitrogenous and polycationic compounds containing more than two amine residues. Numerous investigations have demonstrated that cellular PA homeostasis plays a key role in various developmental and physiological processes. The PA balance, which may be affected by many environmental factors, is finely maintained by the pathways of PA biosynthesis and degradation (catabolism). In this review, the advances in PA transport and distribution and their roles in plants were summarized and discussed. In addition, the interplay between PAs and phytohormones, NO, and H2O2 were detailed during plant growth, senescence, fruit repining, as well as response to biotic and abiotic stresses. Moreover, it was elucidated how environmental signals such as light, temperature, and humidity modulate PA accumulation during plant development. Notably, PA has been shown to exert a potential role in shaping the domestication of rice. The present review comprehensively summarizes these latest advances, highlighting the importance of PAs as endogenous signaling molecules in plants, and as well proposes future perspectives on PA research.

Interaction of elevated CO2 and form of nitrogen nutrition alters leaf abaxial and adaxial epidermal and stomatal anatomy of wheat seedlings

Plant's stomatal physiology and anatomical features are highly plastic and are influenced by diverse environmental signals including the concentration of atmospheric CO₂ and nutrient availability. Recent reports suggest that the form of nitrogen (N) is a determinant of plant growth and nutrient nitrogen use efficiency (NUE) under elevated CO₂ (EC). Previously, we found that high nitrate availability resulted in early senescence, enhanced reactive oxygen species (ROS), and reactive nitrogen species (RNS) production and also that mixed nutrition of nitrate and ammonium ions were beneficial than sole nitrate nutrition in wheat. In this study, the interactive effects of different N forms (nitrate, ammonium, mixed nutrition of nitrate, and ammonium) and EC on epidermal and stomatal morphology were analyzed. Wheat seedlings were grown at two different CO₂ levels and supplied with media devoid of N (N₀) or with nitrate-N (NN), mixed nutrition of ammonium and nitrate (MN), or only ammonium-N (AN). The stoma length increased significantly in nitrate nutrition with a consistent reduction in stoma width. Guard cell length was higher in EC treatment as compared to AC. The guard cell width was maximum in AN-grown plants at EC. Epidermal cell density and stomatal density were lower at EC. Nitrate nutrition increased the stomatal area at EC while the reverse was true for MN and AN. Wheat plants fertilized with AN showed a higher accumulation of superoxide radical (SOR) at EC, while in NN treatment, the accumulation of hydrogen peroxide (H₂O₂) was higher at EC. Reactive oxygen species, particularly H₂O₂, can trigger mitogen-activated protein kinase (MAPK) mediated signaling and its crosstalk with abscisic acid (ABA) signaling to regulate stomatal anatomy in nitrate-fed plants. The SOR accumulation in ammonium- and ammonium nitrate-fed plants and H₂O₂ in NN-fed plants might finely regulate the sensitivity of stomata to alter water/nutrient use efficiency and productivity under EC. The data reveals that the variation in anatomical attributes viz. cell length, number of cells, etc. affected the leaf growth responses to EC and forms of N nutrition. These attributes are fine targets for effective manipulation of growth responses to EC.

Putrescine regulates stomatal opening of cucumber leaves under salt stress via the H2O2-mediated signaling pathway

The stomatal aperture is imperative for photosynthesis in higher plants. The function of polyamines (PAs) in stomatal regulation under a stressful environment has not been fully determined. In this study, we demonstrated the mechanism by which putrescine (Put) regulates stomatal changes in cucumber leaves under salt stress. The results showed that foliar application of Put alleviated the decrease of stomatal aperture and photosynthesis caused by salt stress and promoted plant growth. Exogenous Put caused a significant increase in endogenous PAs and hydrogen peroxide (H₂O₂) levels by 105.43% and 27.97%, respectively, while decreased abscisic acid (ABA) content by 67.68% under salt stress. However, application of inhibitors of aminoguanidine hydrochloride (AG), 1, 8-diaminooctane (1, 8-DO), diphenyleneiodonium chloride (DPI) and salicylhydroxamic acid (SHAM) upregulated the 9-cis-cyclocarotenoid dioxygenase (NCED) gene and downregulated the reduced glutathione synthetase (GSHS) gene. These inhibitors also decreased the stomatal aperture, levels of H₂O₂ and reduced glutathione (GSH), but increased the ABA content under salt stress and Put treatment conditions. The order of influence is AG > 1, 8-DO > DPI > SHAM. However, Put-induced downregulation of ABA content and upregulation of GSH content under salt stress were effectively blocked by N, N'-dimethylthiourea (DMTU, H₂O₂ scavenger) and 1-chloro-2,4-dinitrobenzene (CDNB, GSH scavenger) treatments. Taken together, these results suggest that Put induced the formation of H₂O₂ signaling mediates the degradation of PAs by diamine oxidase (DAO), increasing GSH content and inhibiting the accumulation of ABA in leaves, thereby promoting stomatal opening in salt-stressed cucumber leaves.