Participation of ABA Metabolism and ROS Generation in Sugar Starvation-Induced Senescence of Rice Flag Leaves

Background: Both sucrose and abscisic acid (ABA) play pivotal role in the regulation of plant leaf senescence. However, the exact mechanism by which sugar starvation , ABA, and reactive oxygen species (ROS) interact with each other during leaf senescence remains largely unknown. In this study, the genotype-dependent alteration in temporal patterns of sugar concentration during leaf senescence and its relation to ABA metabolism and ROS generation were investigated by using the premature senescence of flag leaf ( psf ) mutant and its wild type. Results: Results showed that sugar starvation-induced leaf senescence was closely associated with the endogenous ABA concentration and ROS level in senescent leaves. Sugar starvation accelerated leaf senescence, concomitantly with the marked increase in ABA concentration and malonaldehyde (MDA) accumulation in detached leaves. Conversely, exogenous sugar treatment significantly suppressed the ABA concentration ad ROS level in detached leaves, thus leaf senescence was delayed by exogenous sugar supply. Pharmacological tests revealed that ABA biosynthesis inhibitor (NDGA) delayed the sugar starvation-induced leaf senescence, while ABA catabolism inhibitor (DNCZ) accelerated leaf senescence and significantly increased the endogenous ABA content in senescent leaves. For the expression patterns of ABA synthesis and catabolism related genes induced by sugar starvation, exogenous sucrose supply, NDGA and DNCZ. sugar starvation up-regulated the OsABA8ox1 transcript, while exogenous sucrose and NDGA down-regulated the transciptional expressions of OsNCED1 , OsNCED4 and OsNCED5 and OsABA8ox2 and OsABA8ox3 e by sugar starvation and DNCZ, while the transcript of was increased. Conclusion: Together, our results demonstrated that the rise in endogenous ABA content during sugar starvation-induced leaf senescence is mostly caused by the suppression of ABA catabolism, rather than the enhancement of ABA biosynthesis, and the expression of ABA metabolic genes determines the equilibrium between ABA biosynthesis and catabolism that eventually influence cross-talk between endogenous factors. The breaking for the equilibrium between ABA biosynthesis and catabolism was strongly responsible for sugar starvation-induced leaf senescence, which was resulted from the suppression of ABA catabolism, rather than the enhancement of ABA biosynthesis .

Methyl viologen can affect mitochondrial function in Arabidopsis

Reactive oxygen species (ROS) are key signalling intermediates in plant metabolism, defence, and stress adaptation. The chloroplast and mitochondria are centres of metabolic control and ROS production, which coordinate stress responses in other cell compartments. The herbicide and experimental tool, methyl viologen (MV) induces ROS generation in the chloroplast under illumination, but is also toxic in non-photosynthetic organisms. We used MV to probe plant ROS signalling in compartments other than the chloroplast. Taking a genetic approach in Arabidopsis thaliana, we used natural variation, QTL mapping, and mutant studies with MV in the light, but also under dark conditions, when the chloroplast electron transport is inactive. These studies revealed a light-independent MV-induced ROS-signalling pathway, suggesting mitochondrial involvement. Mitochondrial Mn SUPEROXIDE DISMUTASE was required for ROS-tolerance and the effect of MV was enhanced by exogenous sugar, providing further evidence for the role of mitochondria. Mutant and hormone feeding assays revealed roles for stress hormones in organellar ROS-responses. The radical-induced cell death1 mutant, which is tolerant to MV-induced ROS and exhibits altered mitochondrial signalling, was used to probe interactions between organelles. Our studies implicate mitochondria in the response to ROS induced by MV.

Influence of type and concentration of sugars, supplemented with 8-hydroxyquinoline sulphate, on the vase life of waxflower

A study was conducted to test the effect of 58.5 mM maltose, glucose, fructose, galactose and sucrose, and sucrose concentrations of 14.6, 29.2, 58.5 and 117.0 mM supplemented with 200 mg L-18-hydroxyquinoline sulphate (HQS) on the vase life and stem fresh weight changes in waxflower (Chamelaucium Desf.). The effect of the interaction between sucrose and HQS concentrations on the vase life of the cultivar ‘Alba’ was also investigated. All the types of exogenous sugar significantly increased the vase life of flowers, but decreased the vase life of leaves of waxflower cultivars compared with the deionized water controls, except the leaves of ‘Lady Stephanie’, ‘Purple Pride’ and ‘Mullering Brook’. The flower vase life of almost all the cultivars treated with sucrose was not significantly different from the life of the cultivars kept in fructose and glucose, except ‘Laura Mae Pearl’, whose flower vase life in sucrose was significantly lower (9.7%) than in fructose. By contrast, the vase life of flowers of the cultivars treated with sucrose was longer than of those in maltose and galactose. At sucrose concentrations of up to 117.0 mM coupled with 200 mg L-1HQS, the flower vase life of six out of eight cultivars significantly increased, except in ‘Laura Mae Pearl’ and ‘Mullering Brook’, whose flower vase life was maximized at the concentrations of 29.2 and 58.5 mM respectively, while the vase life of their leaves decreased. Sucrose concentrations from 14.6 to 29.2 mM coupled with 50 mg L-1HQS maximized vase life for both the flowers and leaves of ‘Alba’. Cultivars with a longer vase life of flowers maintained stem fresh weight above the initial stem fresh weight longer.

Sugar promotes vegetative phase change in Arabidopsis thaliana by repressing the expression of MIR156A and MIR156C

Nutrients shape the growth, maturation, and aging of plants and animals. In plants, the juvenile to adult transition (vegetative phase change) is initiated by a decrease in miR156. In Arabidopsis, we found that exogenous sugar decreased the abundance of miR156, whereas reduced photosynthesis increased the level of this miRNA. This effect was correlated with a change in the timing of vegetative phase change, and was primarily attributable to a change in the expression of two genes, MIR156A and MIR156C, which were found to play dominant roles in this transition. The glucose-induced repression of miR156 was dependent on the signaling activity of HEXOKINASE1. We also show that the defoliation-induced increase in miR156 levels can be suppressed by exogenous glucose. These results provide a molecular link between nutrient availability and developmental timing in plants, and suggest that sugar is a component of the leaf signal that mediates vegetative phase change.

Effect of sucrose in a holding solution on some processes associated with ageing of cut carnations

Vase-life of cut carnations and their response to a preservative (8-HQS+S) depended on the sucrose and reducing sugar content in the petals at the time of harvest. The reducing sugar level decreased in the wilted flowers kept in water and increased above the initial level in the carnations given sucrose in a holding solution. This increase in reducing sugars was small or 2-3 fold in the flowers with high and low initial sugar levels, respectively. Changes in the endogenous sucrose levels in the petals were less pronounced but a trend (i.e. increase-decrease) was also dependent on the initial sucrose level. Considerable sucrose accumulation was found in the leaves of plants placed in the solution of 5% sucrose plus 200 ppm 8-HQS. Use of an exogenous sugar in a holding solution prevented an increase in free amino acids in carnation petals, a symptom for flower ageing. Carnations placed in a preservative solution had a had anthocyanin content then the control flowers. Lower activities of acid phosphatases and RNases were found in the flowers placed in the solutions tested as compared to those kept in water.

Chemoenzymatic Synthesis of Two New Halogenated Coumarin Glycosides as Potential Antifungal Agents

Two new potential antifungal coumarin glycosides, 6-chlorocoumarin 7- O- β-D-glucopyranoside (1) and 7-hydroxy-4-trifluoromethyl-coumarin 5- O- β-D-glucopyranoside (2), were synthesized via enzyme-mediated glycosylation of the respective aglycone, 6-chloro-7-hydroxycoumarin and 5,7-dihydroxy-4-trifluoromethylcoumarin, using transgenic hairy roots of Polygonum multiflorum. Instead of application of the isolated enzyme and exogenous sugar donors, hairy roots of P. multiflorum were successfully adapted as a whole-cell biocatalyst.

Contributions of Francisella tularensis subsp. novicida Chitinases and Sec Secretion System to Biofilm Formation on Chitin

ABSTRACT Francisella tularensis, the zoonotic cause of tularemia, can infect numerous mammals and other eukaryotes. Although studying F. tularensis pathogenesis is essential to comprehending disease, mammalian infection is just one step in the ecology of Francisella species. F. tularensis has been isolated from aquatic environments and arthropod vectors, environments in which chitin could serve as a potential carbon source and as a surface for attachment and growth. We show that F. tularensis subsp. novicida forms biofilms during the colonization of chitin surfaces. The ability of F. tularensis to persist using chitin as a sole carbon source is dependent on chitinases, since mutants lacking chiA or chiB are attenuated for chitin colonization and biofilm formation in the absence of exogenous sugar. A genetic screen for biofilm mutants identified the Sec translocon export pathway and 14 secreted proteins. We show that these genes are important for initial attachment during biofilm formation. We generated defined deletion mutants by targeting two chaperone genes (secB1 and secB2) involved in Sec-dependent secretion and four genes that encode putative secreted proteins. All of the mutants were deficient in attachment to polystyrene and chitin surfaces and for biofilm formation compared to wild-type F. novicida. In contrast, mutations in the Sec translocon and secreted factors did not affect virulence. Our data suggest that biofilm formation by F. tularensis promotes persistence on chitin surfaces. Further study of the interaction of F. tularensis with the chitin microenvironment may provide insight into the environmental survival and transmission mechanisms of this pathogen.

Opportunistic heterotrophy in gametophytes of the homosporous fern Ceratopteris richardii

Fern gametophytes are extremely shade-tolerant, potentially existing for long periods under conditions of extreme light limitation. Many previous studies have demonstrated an increase in gametophyte growth and incidence of spontaneous transition to sporophyte morphology (apogamy) under culture on media containing exogenous sugar. However, these studies did not verify sugar uptake or quantify relative growth on media containing different sugar types. Here, we examine the extent of heterotrophy and underlying mechanisms of sugar transport in photosynthetic gametophytes of the fern Ceratopteris richardii Brongn. Exogenous sugar uptake, growth, and sugar transport were evaluated with assays of exogenous glucose depletion, experimental culture of gametophytes under different sugar and light conditions, and bioinformatic approaches. The glucose from the growth media was significantly depleted by gametophytes growing under all conditions, especially those in the dark compared with those exposed to higher light. Gametophyte area increased similarly when cultured on equimolar concentrations of either glucose or the disaccharide sucrose, likely due to preferential uptake of one of the monomers of sucrose. Although at least one gene with similarity to sucrose transporters is expressed in germinating spores, our results suggest a reliance on monosaccharide transport for exogenous sugar uptake. Glucose assimilation in both light and dark conditions constitutes nutritional opportunism and may enhance gametophyte survival in very low light.