RESUMEN
CHLOROPLASTS OF LEAVES UNDER HIGH LIGHT STRESS INITIATE SIGNALS TO THE NUCLEI OF BOTH EXPOSED AND DISTAL LEAVES IN ORDER TO ACCLIMATE AGAINST THE POTENTIAL THREAT OF OXIDATIVE DAMAGE: a process known as high light systemic acquired acclimation (HL SAA). This study explores the nature of HL SAA, synergistic interactions with other environmental stresses, and the impact of repeated HL stress on the acclimation response of exposed and distal leaves. This necessitated the development of novel experimental systems to investigate the initiation, perception, and response to HL SAA. These systems were used to investigate the HL SAA response by monitoring the induction of mRNA in distal leaves not exposed to the HL stress. Acclimation to HL is induced within minutes and the response is proportionally dependent on the quality and quantity of light. HL SAA treatments in conjunction with variations in temperature and humidity reveal HL SAA is influenced by fluctuations in humidity. These treatments also result in changes in auxin accumulation and auxin-responsive genes. A key question in retrograde signaling is the extent to which transient changes in light intensity result in a "memory" of the event leading to acclimation responses. Repeated exposure to short term HL resulted in acclimation of the exposed tissue and that of emerging and young leaves (but not older leaves) to HL and oxidative stress.
RESUMEN
In this report, we investigate the altered APX2 expression 13 (alx13) mutation of Arabidopsis thaliana, a mutation in glutamine phosphoribosyl pyrophosphate amidotransferase 2 (ATASE2), the primary isoform of the enzyme mediating the first committed step of purine biosynthesis. Light-dependent leaf variegation was exhibited by alx13 plants, with partial shading of alx13 rosettes revealing that the development of chlorosis in emerging leaves is influenced by the growth irradiance of established leaves. Chlorotic sectors arose from emerging green alx13 leaves during a phase of rapid cell division and expansion, which shows that each new cell's fate is independent of its progenitor. In conjunction with the variegated phenotype, alx13 plants showed altered high light stress responses, including changed expression of genes encoding proteins with antioxidative functions, impaired anthocyanin production and over-accumulation of reactive oxygen species. These characteristics were observed in both photosynthetically-normal green tissues and chlorotic tissues. Chlorotic tissues of alx13 leaves accumulated mRNAs of nuclear-encoded photosynthesis genes that are repressed in other variegated mutants of Arabidopsis. Thus, defective purine biosynthesis impairs chloroplast biogenesis in a light-dependent manner and alters the induction of high light stress pathways and nuclear-encoded photosynthesis genes.
RESUMEN
As the sun tracks daily through the sky from east to west, different parts of the canopy are exposed to high light (HL). The extent of and mechanisms by which a systemic acquired acclimation (SAA) response might preacclimate shaded leaves that will be subsequently exposed to full sunlight is largely undefined. We investigated the role of an Arabidopsis thaliana zinc finger transcription factor, ZAT10, in SAA. ZAT10 overexpression resulted in enhanced tolerance to photoinhibitory light and exogenous H2O2, increased expression of antioxidative genes whose products are targeted to multiple subcellular compartments. Partial HL exposure of a leaf or leaves rapidly induced ZAT10 mRNA in distal, shaded photosynthetic tissues, including the floral stem, cauline leaves, and rosette, but not in roots. Fully 86% of fivefold HL-upregulated and 71% of HL-downregulated genes were induced and repressed, respectively, in distal, shaded leaves. Between 15 and 23% of genes whose expression changed in the HL and/or distal tissues were coexpressed in the ZAT10 overexpression plants, implicating ZAT10 in modulating the expression of SAA-regulated genes. The SAA response was detectable in plants with mutations in abscisic acid, methyl jasmonate, or salicylic acid synthesis or perception, and systemic H2O2 diffusion was not detected. Hence, SAA is distinct from pathogen-stimulated systemic acquired resistance and apparently involves a novel signal or combination of signals that preacclimate photosynthetic tissues to HL.
Asunto(s)
Proteínas de Arabidopsis/genética , Arabidopsis/genética , Regulación de la Expresión Génica de las Plantas/efectos de la radiación , Luz , Ácido Abscísico/metabolismo , Ácido Abscísico/farmacología , Acetatos/metabolismo , Acetatos/farmacología , Arabidopsis/crecimiento & desarrollo , Arabidopsis/metabolismo , Proteínas de Arabidopsis/metabolismo , Ciclopentanos/metabolismo , Ciclopentanos/farmacología , Regulación de la Expresión Génica de las Plantas/efectos de los fármacos , Peróxido de Hidrógeno/metabolismo , Peróxido de Hidrógeno/farmacología , Análisis de Secuencia por Matrices de Oligonucleótidos , Estrés Oxidativo/efectos de los fármacos , Estrés Oxidativo/efectos de la radiación , Oxilipinas/metabolismo , Oxilipinas/farmacología , Fotosíntesis/efectos de los fármacos , Fotosíntesis/efectos de la radiación , Hojas de la Planta/genética , Hojas de la Planta/crecimiento & desarrollo , Hojas de la Planta/metabolismo , Plantas Modificadas Genéticamente , Especies Reactivas de Oxígeno/metabolismo , Ácido Salicílico/metabolismo , Ácido Salicílico/farmacologíaRESUMEN
There is considerable interest in the biological properties of flavonoids in terms of their antioxidant and cytoprotective actions. The interaction of the flavanone hesperetin with human skin fibroblasts (FEK4) has revealed the potential for metabolism to hesperetin glucuronide and its subsequent extrusion. As a consequence of this observation, the effectiveness of hesperetin glucuronides, in comparison with that of the aglycone form, in protecting against UV-A radiation has been investigated. The results indicate that hesperetin glucuronides, but not hesperetin, protect against UV-A-induced necrotic cell death.
Asunto(s)
Flavonoides/metabolismo , Glucurónidos/química , Hesperidina/biosíntesis , Piel/metabolismo , Línea Celular , Cromatografía Líquida de Alta Presión , Fibroblastos/metabolismo , Hesperidina/química , Humanos , Espectrometría de Masas , Piel/citologíaRESUMEN
The ultraviolet A component of sunlight causes both acute and chronic damage to human skin. In this study the potential of epicatechin, an abundant dietary flavanol, and 3'-O-methyl epicatechin, one of its major in vivo metabolites, to protect against UVA-induced damage was examined using cultured human skin fibroblasts as an in vitro model. The results obtained clearly show that both epicatechin and its metabolite protect these fibroblasts against UVA damage and cell death. The hydrogen-donating antioxidant properties of these compounds are probably not the mediators of this protective response. The protection is a consequence of induction of resistance to UVA mediated by the compounds and involves newly synthesized proteins. The study provides clear evidence that this dietary flavanol has the potential to protect human skin against the deleterious effects of sunlight.
Asunto(s)
Catequina/análogos & derivados , Catequina/farmacología , Fibroblastos/efectos de los fármacos , Estrés Oxidativo/efectos de la radiación , Piel/efectos de los fármacos , Rayos Ultravioleta , División Celular/efectos de los fármacos , División Celular/efectos de la radiación , Supervivencia Celular , Células Cultivadas , Fibroblastos/metabolismo , Fibroblastos/efectos de la radiación , Hemo Oxigenasa (Desciclizante)/genética , Hemo Oxigenasa (Desciclizante)/metabolismo , Hemo-Oxigenasa 1 , Humanos , Proteínas de la Membrana , ARN Mensajero/genética , ARN Mensajero/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Piel/metabolismo , Piel/efectos de la radiaciónRESUMEN
Bisphosphonate drugs for treating osteoporosis are excreted by the kidney. However, many of the major trials on efficacy and safety of the bisphophonates for treating osteoporosis excluded patients with significant renal compromise. Since both osteoporosis and renal insufficiency become more prevalent with age, it seems prudent for physicians to be aware of the prevalence of renal dysfunction in patients with osteoporosis who are candidates for treatment with bisphosphonates. Data on 13,831 men and women aged 20+ from the Third National Health and Nutrition Examination Survey, 1988-1994 (NHANES III) were used to study the occurrence of compromise in renal clearance function in men and women with osteopenia and osteoporosis. To estimate creatinine clearance (CCr), a measure of renal function, serum creatinine (sCr), weight and age were inserted into the Cockcoft-Gault (C-G) formula. The World Health Organization gender specific bone mineral density (BMD) cut-offs were used to define the populations with osteopenia and osteoporosis. For women ages 20-80+ with osteoporosis, the percent prevalence (95% CI) for mild to moderate compromise of CCr