glutamate dehydrogenase (GDH; EC 1.4.1.2) while deaminat-Salt-stress effects on osmotic adjustment, ion and proline ing activity was reduced in the leaves of the salt-sensitive concentrations as well as proline metabolizing enzyme activicultivar. The total extracted glutamine synthetase activity ties were studied in two rice (Oryza sati7a L.) cultivars (GS; EC 6.3.1.2) was reduced in response to salinity but NaCl differing in salinity resistance: I Kong Pao (IKP; salt-sensihad contrasting effects on GS1 and GS2 isoforms in salt-sen-tive) and Nona Bokra (salt-resistant). The salt-sensitive cultisitive IKP. Salinity increased the activity of ferredoxin-depen-var exposed to 50 and 100 mM NaCl in nutritive solution for dent glutamate synthase (Fd-GOGAT; EC 1.4.7.1) extracted 3 and 10 days accumulated higher levels of sodium and proline than the salt-resistant cultivar and displayed lower levels of from leaves of both genotypes and increased the activity of osmotic adjustment. Proline accumulation was not related to NADH-dependent glutamate synthase (NADH-GOGAT; EC proteolysis and could not be explained by stress-induced mod-1.4.1.14) in the salt-sensitive cultivar. It is suggested that proline accumulation is a symptom of salt-stress injury in rice ifications in D 1 -pyrroline-5-carboxylate reductase (P5CR; EC and that its accumulation in salt-sensitive plants results from 1.5.1.2) or proline dehydrogenase (PDH; EC 1.5.1.2) activities recorded in vitro. The extracted ornithine -aminotransan increase in OAT activity and an increase in the endogenous ferase (OAT; EC 2.6.1.13) activity was increased by salt pool of its precursor glutamate. The physiological significance of the recorded changes are analyzed in relation to the stress in the salt-sensitive cultivar only. In both genotypes, salt stress induced an increase in the aminating activity of root functions of these enzymes in plant metabolism.

No abstract

Hydroponically grown African rice (Oryza glaberrima) was exposed for 72 h to a high Fe 2+ concentration (500 mg dm -3 ) to identify the first steps of iron toxicity response in various organs. Iron accumulated in all plant parts analysed and had only a limited impact on absorption and translocation of other nutrients. The content of the iron-storage protein ferritin increased as a consequence of transcription stimulation or increase in mRNA stability and culminated after 48 h of treatment in laminae and to a lesser extent in sheaths but was not detected in roots. Although endogenous iron concentrations were similar in sheaths and laminae, superoxide dismutase activity was stimulated only in sheaths while ascorbate peroxidase activity increased mainly in laminae. It is concluded that both ferritin synthesis and antioxidative response may play a key role in the resistance of Oryza glaberrima to iron toxicity but that their relative importance are not the same in all organs.

No abstract

Iron toxicity occurs under flooded conditions such as those prevailing in lowland rice fields and is due to an excess of ferrous ions. Ferritin is a multimeric protein responsible for Fe sequestration and storage, playing a key role in Fe homeostasis. Our aim was to study the modalities of overall ferritin synthesis in different organs of young seedlings from the African rice species (Oryza glaberrima) in relation to the putative involvement of abscisic acid (ABA) and oxidative stress in signalling processes.