Changes in the growth parameters and in enzyme activities were studied in roots and leaves of 14-days old maize grown in a nutrient solution containing various copper concentrations (i.e. 0.01 to 10 #M). A significant decrease in root and leaf biomass was only found at 10 #M Cu. In contrast, changes in several enzyme activities occured at lower copper concentrations in the solution, corresponding to different threshold values which are lower than those observed for growth parameters. Peroxidase (POD) activity significantly increased in all investigated plant organs (i.e. 3rd-leaf, 4th-leaf and roots) in relation to their copper content. Additionally, glucose-6-phosphate dehydrogenase (G-6-PDH), and isocitrate dehydrogenase (ICDH) activities decreased in the leaves, especially in the 4th-leaf. However, the activity of malic enzyme (ME), G-6-PDH, glutamate dehydrogenase (GDH) and ICDH increased with the copper content in roots. According to the relationship between POD activity and copper content, the toxic critical value was set at 26 mg Cu per kg dry matter (DM) in roots and 21 mg Cu per kg DM in the 3rd-leaf. In roots, a new isoenzyme of peroxidase appeared for copper content above 12.6 mg Cu kg DM -~ . Measurement of enzyme activity, especially that of POD and Cu-specific changes in the (iso)peroxidase pattern, might be used as biomarkers to assess the phytotoxicity for maize grown on copper-contaminated substrata.

Energy charge, adenine nucleotide levels, and protein synthesis were studied during the transfer of rice seedlngs from air to anoxia. Within minutes, the energy charge value dropped from 0.90 in air to 0.50 in the seed and 0.60 in the coleoptile after the transfer to a nitrogen atmosphere, and then increased to a value of 0.80 during the subsequent hours. The sum of nucleotides also dropped to 60% of the value in air in the seeds and to 30% in the coleoptiles. However, during the anaerobic growth of coleoptiles, a considerable increase in the nucleotide pool occurred.The incorporation of amino acids into proteins was measured at different stages in anoxic treatment. In rice embryo, we observed a considerable protein synthesis correlated with a high value of energy charge under anoxia. The analysis oflabeled proteins by two-dimensional polyacrylamide gel electrophoresis showed a modified pattern of polypeptides synthesized during anoxic treatment. Some of these proteins were intensively labeled and appeared to be induced by anaerobic treatment.Our data indicate that high metabolic activity occurs in rice embryo under anoxia, which can be correlated with a high energy charge value. These phenomena may be part of the mechanisms which permit the adaptation of rice embryos to anaerobiosis.In nonchlorophyllous plant tissues and in animals, it is generally assumed that ATP synthesis is drastically reduced when oxidative phosphorylation is inhibited by a lack of 02. The knowledge of the balance between ATP regeneration and utilization for metabolic work should permit a better understanding of the mechanisms used by these organisms to survive under anoxic conditions.In animal tissues, there is a rapid inhibition of protein synthesis after a few min of anoxia (10,12 Preliminary data obtained in our laboratory indicate that rice embryos or coleoptiles germinated in anoxia or transferred from air to nitrogen have a high energy charge (20, 21) and an active RNA (2) and DNA synthesis (16).The purpose of this paper is to study the effect of anoxia on adenine nucleotide levels, energy charge, and incorporation of labeled amino acids into proteins in rice embryos. The correlation between energy charge and protein synthesis in anoxia is discussed, and anoxic protein patterns sustain the hypothesis of an adaptation of rice embryo to anaerobic conditions. MATERIALS AND METHODSPlant Materials. Rice seeds (Oryza sativa L., var. Cigalon) cultivated by the Station d'Amelioration des Plantes (INRA, Montpellier, France) were mechanically husked and sterilized with commercial (NaOCl (150 g Cl/l), as described previously (16).Germination of Rice Seeds. Seeds were placed in glass flasks with water and shaken at 26 C in darkness. They remained under aerobic conditions for 40 to 48 h until coleoptiles reached 4 to 5 mm.For anoxia, samples were placed in a nitrogen flow (100 ml/ min), as previously described (16). Oxygen content was checked with an 02 analyzer (WOM, Mecanalyse, France) or by gas chromatography. PO2 in N2 was lower than...

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Alcohol dehydrogenase (ADH) activity was present in roots and shoots of 48-h rice embryos and rose in response to anoxia. The increase was accompanied by changes in the ADH isozyme pattern. Translatable levels of mRNA for two ADH peptides increases as early as 1 h after the beginning of anoxic treatment. Adh mRNA was detected in aerobically grown rice embryos by hybridization to maize Adh1 cDNA: its level increased significantly after 3 h of anoxia.

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