Black pepper (Piper nigrum L.), member of the family Piperaceae is indigenous to India and is one of the most widely used spices in the world. In this paper we report the results of our attempts to identify a set of genes differentially expressed in the leaves of Piper nigrum, which could facilitate targeted engineering of this valuable crop. A PCR-based Suppression Subtractive Hybridization (SSH) technique was used to generate a leaf-specific subtracted cDNA library of Piper nigrum. A tester population of leaf cDNA was subtracted with a root derived driver cDNA. The efficiency of subtraction was confirmed by PCR analysis using the housekeeping gene actin. On sequence analysis, almost 30% of the clones showed homology to metallothionein type-2 gene. The predominance of metallothionein transcripts in the leaf was further confirmed using Real-Time PCR analyses and Northern blot. The possible role of metallothionein type-2 homologues in the leaf is discussed along with the feasibility of using SSH technique for identification of more number of tissue-specific genes from Piper nigrum.

Foram feitos estudos de sedimentação para otimizar as condições de dispersão de suspensões aquosas de pós de alumina nanométrica com e sem dispersantes (sais de amônia de ácido poliacrílico ou rhamnolipídeos a 15%). Foram examinados diferentes dosagens de dispersante, cargas de sólidos, densidades de pasta e valores de pH. O ponto isoelétrico do pó de alumina nanométrica obtido foi pHiep = 9,2. Os experimentos mostraram que numa ampla faixa de pH e para todas as condições de carga de sólidos testadas, o ácido polimetacrílico foi mais efetivo como dispersante que o rhamnolipídeo. Os teores otimizados de dispersante para que as dispersões de alumina nanométrica atinjam estabilidade máxima, obtidos para o ácido polimetacrílico e para o rhamnolipídeo foram, respectivamente, 9,25 mg/g e 57,75 mg/g de sólidos.

Sedimentation studies have been carried out to optimize the dispersion conditions of aqueous alumina nanopowder suspensions with or without dispersants (ammonium salt of polymethacrylic acid or rhamnolipids at 15%). Different dispersant dosages, solid loadings, pulp densities and pH values were examined. The iso-electric point (IEP) of the alumina nanopowder was found to be pHiep= 9.2. The experiments revealed that the polymethacrylic acid was more effective as dispersant than rhamnolipids in a wide range of pH at all solid-loading conditions tested. Optimum dispersant dosages for polymethacrylic acid and rhamnolipids to achieve maximum stability of alumina nanodispersion at iso-electric point were found to be 9.25 mg/g and 57.75 mg/g solids, respectively.