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Aluminium toxicity and problems concerning tolerance and ecological performance are discussed briefly. Differential tolerance of plant genotypes to aluminium stress is a more promising approach to increase our understanding of aluminium tolerance in plants. Induction of Al tolerance and its characterization are also reviewed. The cytogenetic effects of aluminium on plants are discussed in depth. Efforts have been made to compare the relative sensitivity of various plant species including micro-and macro-flora to aluminium, and uptake and transport of aluminium are taken into account with phytotoxicity and their interactions with nutrients. Present knowledge concerning the physiology and biochemistry of aluminium with regard to phytotoxicity is discussed and offers some ways for increasing the Al tolerance. This review shows the complexity of the toxicity mechanisms of trace elements. aluminium / phytotoxicity / tolerance / Al stress Résumé-Toxicité de l'aluminium pour les plantes : mise au point. L'article fait le point sur la toxicité de l'aluminium, la tolérance des plantes à cet élément et leur performances écologiques. La tolérance au stress provoqué par l'aluminium varie d'un génotype de plante à l'autre et cette approche est prometteuse pour améliorer notre compréhension de la tolérance à l'aluminium. L'induction de la tolérance à l'aluminium et sa caractérisation sont également passées en revue. Les effets cytogénétiques de l'aluminium sur les plantes font l'objet d'une discussion approfondie. On compare la sensibilité relative à l'aluminium des diverses espèces de plantes, de la macroflore à la microflore. On traite de l'absorption et du transport de l'aluminium, ainsi que de sa phytotoxicité et de ses interactions avec les nutriments. La connaissance actuelle concernant la physiologie et la biochimie de l'aluminium en relation avec la phytotoxicité est discutée et offre certaines possibilités pour accroître la tolérance à l'aluminium. Cette mise au point montre la complexité des mécanismes liés à la toxicité des éléments traces.

We studied salt stress-induced biochemical changes in young, hydroponically grown plants of mangrove, Bruguiera parviflora (Rhizophoraceae). Our focus was on the effect of NaCI (applied at 100, 200, 400, or 500 mM) on leaf pigments, total soluble proteins, total free amino acids, carbohydrates, polyphenols, and proline. The total Chl content increased for 14 d after treatment with 100 m/Vl NaCI, then gradually stabilized. At 400 mM, the total Chl content slowly decreased over the 45-d test period. However, the Chl a:b ratio remained unchanged in isolated chloroplasts and in leaf tissue. Percent changes in the carotenolds content followed the same trend as for Chl, except for a 1.5-fold decrease during the 400-mM NaCI treatment, compared with the control. The total sugar content increased by 2.5-fold by Day 45 after treatment with 400 mM NaCI, whereas the starch content measured in the same treatment decreased by 40 to 45%. Leaf protein content decreased as salinity increased, which suggests either a possible disruption in the protein synthesis mechanism or, more likely, an increase in proteolytic activity. The total amino-acid pool increased steadily, by four-fold, in the 45-d, 400-mM treatment. Both proline and polyphenols accumulated with increasing levels of salinity, which confirms the role of proline as a stress-induced protective metabolite in the adaptive process of this species. Our results showed that a true mangrove such as B. parviflora can easily be sustained and propagated under low-salinity conditions. At high levels of salinity (-400 mM, beyond which they could not survive), the plants became adapted to salt stress after two to three weeks. During this adaptive period, changes in pigment and protein levels also occurred. The accumulation of proline and polyphenols played a key role in the plant's stressinduced adjustment to NaCI under hydroponic culture conditions. Keywords: Bruguiera parviflora, hydroponic culture, mangrove, proline accumulation, salt-stressThe rich biological diversity in the mangrove ecosystems of tropical and subtropical inter-tidal zones constitutes an economic resource for coastal people. The mangrove is an ecologically important component that protects the adjacent land from erosion by tidal waves, cyclones, and storms (Banijbatana, 1957). These trees also prevent the accumulation of terrigenous nutrients that affect nearby reefs (Dubinsky and Stambier, 1996). The survival of most of these mangroves is now threatened, largely due to human interference that has resulted in changes in tidal patterns and salinity gradients. Investigations of salinization and desalinization are likely to yield valuable information on salt adaptability by mangroves.Bruguiera parviflora (Rhizophoraceae) is a major member in the tropical mangrove ecosystem. This family of mangrove has a viviparous mode of germination and is tolerant to changes in salinity gradients. *Corresponding author; fax +91-674-550274 e-mail a b das@hotmaiI.comThe effects of salt on mangroves have been studied in relation to ...

Zinc toxicity and problems with regard to tolerance and ecological significance are briefly discussed. Differential tolerance of plant genotypes exposed to zinc toxicity is a more promising approach to enrich our understanding of zinc tolerance in plants. Knowledge concerning the physiology and biochemistry with regard to phytotoxicity, uptake and transport of zinc and tolerance and its characterization are also discussed. The cytotoxic effects of zinc on plants are elucidated. The major change was seen in the nucleus of the root tip cells due to zinc toxicity. The chromatin material was highly condensed and some of the cortical cells showed disruption and dilation of nuclear membrane in presence of 7.5 mM zinc. The cytoplasm became structureless, disintegration of cell organelles and the development of vacuoles were also observed. The number of nucleoli also increased in response to zinc resulting in the synthesis of new protein involved in heavy metal tolerance. This review may help in interdisciplinary studies to assess the ecological significance of metal stress. phytotoxicity / tolerance / transport / uptake / accumulation / zinc Résumé-Effet de la toxicité des métaux sur la croissance et le métabolisme des plantes : I. Zinc. La toxicité du zinc et les problèmes de tolérance ou de conséquence écologique liés sont brièvement discutés. L'approche en terme de tolérance différentielle des génotypes de plantes exposées à la toxicité du zinc est prometteuse pour l'enrichissement de notre compréhension de la tolérance des plantes au zinc. Les connaissances de la physiologie et la biochimie face à la phytotoxicité, à l'absorption et au transport du zinc, ainsi que la tolérance et sa caractérisation sont aussi discutées dans ce papier. Les effets cytotoxiques du zinc sur les plantes sont maintenant élucidés. La modification majeure concerne le noyau des cellules de l'extrémité des racines. La chromatine est fortement condensée et certaines des cellules corticales montrent la rupture et la dilatation de leur membrane nucléaire en présence de 7.5 mM de zinc. De plus, le cytoplasme perd sa structure, la désintégration d'organites et le développement de vacuoles sont aussi observés. Enfin, le nombre de nucléoles augmente en réponse au zinc. Ils résultent de la synthèse d'une nouvelle protéine impliquée dans la tolérance aux métaux lourds. Cette synthèse bibliographique pourra aider les études interdisciplinaires à évaluer les conséquences écologiques des stress dus aux métaux. phytotoxicité / tolérance / transport / absorption / accumulation / zinc

Zinc toxicity and problems with regard to tolerance and ecological significance are briefly discussed. Differential tolerance of plant genotypes exposed to zinc toxicity is a more promising approach to enrich our understanding of zinc tolerance in plants. Knowledge concerning the physiology and biochemistry with regard to phytotoxicity, uptake and transport of zinc and tolerance and its characterization are also discussed. The cytotoxic effects of zinc on plants are elucidated. The major change was seen in the nucleus of the root tip cells due to zinc toxicity. The chromatin material was highly condensed and some of the cortical cells showed disruption and dilation of nuclear membrane in presence of 7.5 mM zinc. The cytoplasm became structureless, disintegration of cell organelles and the development of vacuoles were also observed. The number of nucleoli also increased in response to zinc resulting in the synthesis of new protein involved in heavy metal tolerance. This review may help in interdisciplinary studies to assess the ecological significance of metal stress. phytotoxicity / tolerance / transport / uptake / accumulation / zinc Résumé-Effet de la toxicité des métaux sur la croissance et le métabolisme des plantes : I. Zinc. La toxicité du zinc et les problèmes de tolérance ou de conséquence écologique liés sont brièvement discutés. L'approche en terme de tolérance différentielle des génotypes de plantes exposées à la toxicité du zinc est prometteuse pour l'enrichissement de notre compréhension de la tolérance des plantes au zinc. Les connaissances de la physiologie et la biochimie face à la phytotoxicité, à l'absorption et au transport du zinc, ainsi que la tolérance et sa caractérisation sont aussi discutées dans ce papier. Les effets cytotoxiques du zinc sur les plantes sont maintenant élucidés. La modification majeure concerne le noyau des cellules de l'extrémité des racines. La chromatine est fortement condensée et certaines des cellules corticales montrent la rupture et la dilatation de leur membrane nucléaire en présence de 7.5 mM de zinc. De plus, le cytoplasme perd sa structure, la désintégration d'organites et le développement de vacuoles sont aussi observés. Enfin, le nombre de nucléoles augmente en réponse au zinc. Ils résultent de la synthèse d'une nouvelle protéine impliquée dans la tolérance aux métaux lourds. Cette synthèse bibliographique pourra aider les études interdisciplinaires à évaluer les conséquences écologiques des stress dus aux métaux. phytotoxicité / tolérance / transport / absorption / accumulation / zinc