The ER-resident molecular chaperone BiP (binding protein) was overexpressed in soybean. When plants growing in soil were exposed to drought (by reducing or completely withholding watering) the wild-type lines showed a large decrease in leaf water potential and leaf wilting, but the leaves in the transgenic lines did not wilt and exhibited only a small decrease in water potential. During exposure to drought the stomata of the transgenic lines did not close as much as in the wild type, and the rates of photosynthesis and transpiration became less inhibited than in the wild type. These parameters of drought resistance in the BiP overexpressing lines were not associated with a higher level of the osmolytes proline, sucrose, and glucose. It was also not associated with the typical drought-induced increase in root dry weight. Rather, at the end of the drought period, the BiP overexpressing lines had a lower level of the osmolytes and root weight than the wild type. The mRNA abundance of several typical drought-induced genes [NAC2, a seed maturation protein (SMP), a glutathione-S-transferase (GST), antiquitin, and protein disulphide isomerase 3 (PDI-3)] increased in the drought-stressed wild-type plants. Compared with the wild type, the increase in mRNA abundance of these genes was less (in some genes much less) in the BiP overexpressing lines that were exposed to drought. The effect of drought on leaf senescence was investigated in soybean and tobacco. It had previously been reported that tobacco BiP overexpression or repression reduced or accentuated the effects of drought. BiP overexpressing tobacco and soybean showed delayed leaf senescence during drought. BiP antisense tobacco plants, conversely, showed advanced leaf senescence. It is concluded that BiP overexpression confers resistance to drought, through an as yet unknown mechanism that is related to ER functioning. The delay in leaf senescence by BiP overexpression might relate to the absence of the response to drought.

A absorção e acúmulo de Cd e seus efeitos sobre o crescimento relativo foram estudados em aguapé (Eichhornia crassipes (Mart.) Solms) e salvínia (Salvinia auriculata Aubl.), em solução nutritiva. O aguapé absorveu quantidade significativamente maior de Cd do que a salvínia, tendo a diferença aumentado com o tempo de exposição ao Cd. O Km da absorção de Cd, estatisticamente igual nas duas espécies aquáticas quando as folhas contatavam a solução nutritiva, tornou-se maior em salvínia quando se impediu fisicamente que as folhas contatassem a solução de absorção. O Vmax de absorção de Cd, por outro lado, foi sempre maior em salvínia, independentemente do contato ou não das folhas com a solução nutritiva. A quantidade de Cd adsorvido e absorvido aumentou com a elevação da concentração de Cd na solução de cultivo, nas duas espécies estudadas, tendo sido maior em salvínia, possivelmente em razão da participação da parte aérea no processo de absorção. O acúmulo de Cd nas plantas, elevado nas primeiras 12 h de exposição, decresceu rapidamente com o tempo de exposição, estabilizando após três dias de exposição. Salvínia apresentou maior acúmulo diário de Cd por unidade de peso mas aguapé maior acúmulo total por unidade experimental. Os teores de Cd aumentaram com o aumento do tempo de exposição e da concentração de Cd na solução nutritiva, nas duas partes da planta das duas espécies, especialmente nas raízes. Cerca de 80% de todo o Cd absorvido acumulou-se nas raízes de aguapé, e a distribuição não foi afetada pelo contato das folhas com a solução nutritiva. Em salvínia, quando se impediu o contato das folhas com a solução nutritiva observou-se uma distribuição do Cd aproximadamente igual à de aguapé. Quando, porém, se permitiu o contato das folhas com a solução nutritiva a parte aérea passou a contribuir com quase 50% do Cd absorvido. As taxas de crescimento relativo decresceram intensamente com o aumento da concentração de Cd na solução nutritiva nas duas espécies aquáticas, especialmente em salvínia. As concentrações de Cd para promover redução de 25% no crescimento relativo foram, em média, doze vezes menores em salvínia do que em aguapé, em razão de sua maior sensibilidade a este metal pesado.

-Seedlings of two sorghum (Sorghum bicolor (L.) Moench) genotypes with differential tolerance to salinity were exposed to 0 and 100 mM NaCl, gradually added in increments of 25 mM every 12 hours, in nutrient solution. Seven days after starting the salt treatment the growth of the shoot and root system and the inorganic and organic solutes contents were determined. Salinity reduced the dry matter yield and length of the shoot and root system in both sorghum genotypes, specially in the sensitive one. In general, it was observed an increase in Na + and Cl -transfer to the shoot, in Na + and Cl -accumulation and in the Na + /Cl -ratio but a decrease in the K + and Ca 2+ transfer to shoot and in the K + and Ca 2+ contents in the shoot, always with higher intensity in sensitive genotype. Apparently, the tolerance to high saline concentrations in sorghum seems to be related to the genotype ability to avoid accumulation of harmful levels of Na + and Cl -and, or to maintain adequate levels of K + and Ca 2+ , specially in the shoot. The soluble carbohydrates and amino acids constituted together over 98% of the total organic solutes and showed the greatest absolute increase in concentration during saline stress. Probably, the soluble carbohydrates were the most important organic solutes to contribute to the osmotic adjustment in the leaves and the amino acids in the roots. Under saline stress there was an expressive increase in proline contents, specially in the oldest leaves of sensitive genotype. The proline contents, however, even under salt stress, did not reach the levels of other organic solutes. Contrary to the general acceptance, proline does not seem to have an important role in the mechanism of salt tolerance, at least for these genotypes and under the experimental conditions applied here. ADDITIONAL INDEX TERMS:

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