Growth media effects on shoot physiology, nodule numbers and symbiotic nitrogen fixation in soybean

AbstractSeveral research groups (both in South Africa and other countries) are currently involved in research aimed at improving symbiotic nitrogen fixation (SNF) and root nodule sustainability in soybean [Glycine max (L.) Merr.]. In many of these experiments potted plants are used, and in this paper the importance of careful selection of growth media is demonstrated. Bradyrhizobium japonicum-inoculated soybean seedlings were cultivated in pots containing N-free growth media (sand, fine vermiculite or coarse vermiculite) or a growth medium containing low concentrations of water-soluble nitrogen predominantly in the form of ammonium (mixture of potting soil, sand and vermiculite). The effects of growth media on shoot physiology were assessed by measurement of plastochron index, chlorophyll content and CO2 assimilation rates. Nodule numbers, nitrogenase activity and nodule ureide content were also determined. Although similar source–sink relationships were maintained in plants cultured in the various growth media, large effects on nodule numbers and SNF were observed. Shoot phenotype and physiology did not provide any insight into these belowground effects. The presence of mineral N, or sand as culture medium, led to the formation of more abundant nodules but with low SNF activity. Vermiculite, irrespective of particle size, resulted in plants with root systems housing nodules with high SNF activity. It is concluded that choice of growth media for cultivating soybean plants under controlled growth conditions is an important consideration, especially in multi-institution collaborations where comparability between experiments is a pre-requisite

Thermostabilisation of human serum butyrylcholinesterase for detection of its inhibitors in water and biological fluids

The ability of gelatine-trehalose to convert the normally fragile, dry human serum BChE into a thermostable enzyme and its use in the detection of cholinesterase inhibitors in water and biological fluids is described. Gelatine or trehalose alone is unable to protect the dry enzyme against exposure to high temperature, while a combination of gelatine and trehalose were able to protect the enzyme activity against prolonged exposure to temperature as high as +50°C. A method for rapid, simple and inexpensive means of screening for cholinesterase inhibitors such as carbamates and organophosphates in water, vegetables and human blood has been developed.<br>A capacidade da gelatina-trehalose em converter a frágil BChE do soro humano em uma enzima termoestável e seu uso na descoberta de inibidores de colinesterase em água e fluidos biológicos é apresentado. A Gelatina ou trehalose são incapazes de proteger a enzima seca BchE do soro humano contra exposição a elevadas temperaturas, enquanto que uma combinação de gelatina e trehalose são capazes de proteger a atividade de enzima contra exposição prolongada a temperaturas elevadas e da ordem de 50° C. Um método barato, simples e rápido de screening para inibidores de colinesterase tal como carbamatos e organofosfatos em água, verduras e sangue humano foi desenvolvido