Aluminium localization and toxicity symptoms related to root growth inhibition in rice (Oryza sativa L.) seedlings.

We correlated root growth inhibition with aluminium (Al3+) localization and toxicity symptoms in rice roots using seedlings of two genotypes (tolerant and sensitive) that were exposed to different AlCl3 concentrations. Al3+ localization was evaluated by hematoxylin in primary roots and by morin in cross-sections of the root tips. Neutral invertase enzyme activity and callose (1→3, β-D-glucan) accumulation were observed and compared with Al3+ accumulation sites. Root growth was inhibited by Al3+ in a concentration-specific manner and proportional to the increase of hematoxylin staining, being more pronounced in the sensitive genotype. Morin staining showed the presence of Al3+ deep within the roots of the sensitive genotype, indicating that the metal was able to penetrate beyond the first few cell layers. In the tolerant genotype, Al3+ penetration was restricted to the first two cell layers. Ruptures in exodermis and epidermis layers by lateral root protrusions in both genotypes allowed Al3+ to enter into the roots. More intense activity of invertase in roots of the tolerant genotype was also observed, which could be related to greater root growth of this cultivar when submitted to Al3+ stress. Moreover, Al3+-induced callose accumulation was a late response occurring in the same areas where Al3+ was present.

Mechanisms for Solvent Tolerance and Application of Extremophile with Organic Solvent Tolerance / 微生物学通报

Organic solvent tolerant microorganism(OSTM) is a novel extremophile and it hasn't been systematically studied until 1980s.Relying on certain mechanisms,the OSTM is able to effectively de-fend and decrease the toxicity from organic solvents,which enable the OSTM to be potentially applied in the industrial fields such as whole-cell catalysis and environmental treatment,etc.The comprehen-sively understanding of the mechanisms involved in organic solvent tolerance of OSTM could be com-bined with genetic engineering in order to modify and optimize the various specifications of OSTM,and further broaden its application in other industrial areas.Latest studies on the tolerant mechanisms of OSTM,in this paper,will be reviewed from four aspects such as vesicle exocytosis and changes of phos-pholipid composition in membrane,etc.Besides,the application of OSTM in whole-cell catalysis and other fields will be introduced.

Identifying water stress-response mechanisms in citrus by in silico transcriptome analysis

Water deficit is one of the most critical environmental stresses to which plants are submitted during their life cycle. The evolutionary and economic performance of the plant is affected directly by reducing its survival in the natural environment and its productivity in agriculture. Plants respond to water stress with biochemical and physiological modifications that may be involved in tolerance or adaptation mechanisms. A great number of genes have been identified as transcriptionally regulated for water deficit. EST sequencing projects provide a significant contribution to the discovery of expressed genes. The identification and determination of gene expression patterns is important not only to understand the molecular bases of plant responses but also to improve water stress tolerance. In our citrus transcriptome survey we have attempted to identify homologs to genes known to be induced and regulated under water stress conditions. We have identified 89 transcripts whose deduced amino acid sequences share similarities with proteins involved in uptake and transport of water and ion, 34 similar to components of the osmolyte metabolism, 67 involved in processes of membranes and proteins protection and 115 homologs of reactive oxygen species scavenger. Many drought-inducible genes identified are known to be regulated by development, salt, osmotic and low temperature. Their possible roles in specific or general mechanisms of water stress citrus responses are discussed.