Changes in Properties of Barley Leaf Mitochondria Isolated from NaCl-Treated Plants

Abstract

Treatment of barley (Hordeum vulgare) seedlings with 400 millimolar NaCI for 3 days resulted in a reduction in plant growth and an increase in the leaf content in ions (K+ + Na ) and proline. Purified mitochondria were successfully isolated from barley leaves. Good oxidative and phosphorylative properties were observed with malate as substrate. Malate-dependent electron transport was found to be only partly inhibited by cyanide, the remaining oxygen uptake being SHAM sensitive. The properties of mitochondria from NaCI-treated barley were modified. The efficiency of phosphorylation was diminished with only a slight decrease in the oxidation rates. In both isolated mitochondria and whole leaf tissue of treated plants, the lower respiration rate was due to a lower cytochrome pathway activity. In mitochondria, the activity of the alternative pathway was not modified by salt treatment, whereas this activity was increased in whole leaf tissue. The possible participation of the altemative pathway in response to salt stress will be discussed.Among crop plants, barley seems to be rather resistant to deleterious effects of NaCI salinity. However, under conditions of high saline environment barley plants do show growth reduction. In this context, changes in ion uptake (2), proline levels (33), gene expression (24), or more recently, changes in metabolic rates in roots (8) have been investigated. However, no work has been done on the role of mitochondria in leaves of barley plants submitted to high NaCl stress.The isolation and purification of green leaf mitochondria from barley was performed, and the oxidative and phosphorylative properties of these mitochondria were compared between control plant and the treated with 400 mM NaCl. The effects of salt on cyanide resistance were also investigated in both isolated mitochondria and whole leaf tissue to look for a role of the alternative pathway in salt-treated barley leaves. Uptake and compartmentation of ions in whole plant organs require energy mainly in the form of ATP generated from respiration (32). The production of compatible solutes is linked not only to the supply of reducing power and carbon skeletons, but also to energy production which depends on the efficiency of the phosphorylation process. Knowledge about respiratory metabolism during saline stress conditions is still lacking. In this context, the role of the nonphosphorylating cyanide-resistant pathway, which is a common feature of higher plant respiration (18, 28), is not fully elucidated. Some reports show that the activity ofthis alternative pathway could be modified in stress situations (17,25 MATERIALS AND METHODS Plant

Molecular Genetic Alteration of Plant Respiration (Silencing and Overexpression of Alternative Oxidase in Transgenic Tobacco)

“…This is consistent with the finding that there was minimal AP activity in wt cells under these conditions. Nonetheless, the AP is known to be active in vivo under a wide range of conditions (Azcon-Bieto et al, 1983;Jolivet et al, 1990;Palet et al, 1991;Robinson et al, 1992;Rychter et al, 1992;Hoefnagel et al, 1994). In wt tobacco suspension cells, a mechanism exists whereby the capacity and activity of the AP is adjusted in response to changes in the activity of the CP McIntosh, 1992b, 1994).…”

“…This indicates that AOX can support the respiration of wt cells and that this may be a critical function if the CP is impaired. Conditions that may impair CP activity in plants include chilling temperatures (Prasad et al, 1994), nutrient deprivation (Bingham and Farrar, 1989;Hoefnagel et al, 1994), salt stress (Jolivet et al, 1990), high COz (Palet et al, 1991), and Pi limitation (Rychter et al, 1992 …”

O estresse salino retarda o desenvolvimento morfofisiológico e a ativação de galactosidases de parede celular em caules de Vigna unguiculata

“…Estes resultados também reforçam a necessidade de que estudos sobre estresse salino sejam também analisados levando-se em conta o desenvolvimento morfofi siológico das plântulas (Sousa et al 2004). De modo geral, os resultados aqui apresentados foram similares aos observados por outros autores (Jolivet et al 1990, em Triticum aestivum; Lutts et al 1995, em Oryza sativa; Kurban et al 1998, em Vigna radiata; Lovato et al 1999, em Stylosanthes humilis; Ruiz et al 1999…”

Ultrastructural and antioxidative changes in lupine embryo axes in response to salt stress

“…The effect of salinity on mitochondrial respiration is often reported but the data are contradictory. There are published data showing that respiration rate increase in response to salt stress [37], while others show that it can decrease [38]. It is likely that these responses probably differ according to species, plant organ, developmental stage, and the severity of salinity treatment [39].…”