RESUMO
Leaf senescence is often associated with increased oxidative damage to cellular macromolecules by reactive oxygen species. However, very little is known about other radicals: gaseous free radical nitric oxide and related molecules--reactive nitrogen species. This review brings a short survey of the questions.
Assuntos
Óxido Nítrico/química , Plantas/química , Plantas/enzimologia , Espécies Reativas de Nitrogênio/química , Dioxigenases/metabolismo , Óxido Nítrico/toxicidade , Desenvolvimento Vegetal , Plantas/toxicidadeRESUMO
We studied changes in antioxidant protection during ageing and senescence in chloroplasts of tobacco (Nicotiana tabacum L., cv. Wisconsin) with introduced SAG(12) promoter fused with ipt gene for cytokinin synthesis (transgenic plants with increased levels of cytokinins, SAG) or without it (control). Old leaves of SAG plants as well as their chloroplasts maintained higher physiological parameters compared to controls; accordingly, we concluded that their ageing was diverted due to increased cytokinin content. The chloroplast antioxidant protection did not decrease as well. Although antioxidant protection usually decreased in whole leaves of senescing control plants, ascorbate peroxidase (APX) and dehydroascorbate reductase (DHAR) activity, which maintained the high redox state of ascorbate, increased in chloroplasts of old control leaves.
Assuntos
Antioxidantes/fisiologia , Senescência Celular/fisiologia , Cloroplastos/metabolismo , Nicotiana/citologia , Nicotiana/fisiologia , Plantas Geneticamente Modificadas/citologia , Citocininas/biossíntese , Folhas de Planta/metabolismo , Plantas Geneticamente Modificadas/genética , Plantas Geneticamente Modificadas/fisiologia , Fatores de Tempo , Nicotiana/genética , Nicotiana/metabolismoRESUMO
The differences between two maize (Zea mays L.) inbred lines and their F1 hybrids in their response to chilling periods of various duration (1, 2, 3 or 4 weeks) and subsequent return to optimum temperatures were analysed by the measurement of the photosystem (PS) 1 and 2 activity, the photosynthetic pigments' content and the activity of antioxidant enzymes. The PS2 activity and the chlorophyll content decreased in plants subjected to 3 or 4 weeks of chilling, but not in those subjected to 1 or 2 weeks of chilling. This decrease was more pronounced in inbreds compared to their hybrids. The activity of superoxide dismutase did not much change with the increasing length of chilling period in the inbreds but decreased in the hybrids, the glutathione reductase activity increased in both types of genotypes but more in the inbred lines, while for ascorbate peroxidase and catalase the changes in parents-hybrids relationship did not show any specific trend. The PS1 activity and the carotenoids' content was not much affected.
