The membrane reactions of Pseudomonas putida S12 to environmental stress were investigated. Cells reacted to the addition of six different heavy metals with an increase in the ratio of trans to cis unsaturated fatty acids. A correlation among the increase in the trans/cis ratio, the toxic effects of the heavy metals, and nonspecific permeabilization of the cytoplasmic membrane, as indicated by an efflux of potassium ions, was measured. Cells previously adapted to toxic concentrations of toluene exhibited increased tolerance to all applied concentrations of zinc compared with nonadapted cells. Cells exposed to different temperatures grew optimally at 30؇C. The degree of saturation of the membrane fatty acids of these cells decreased with decreasing temperature. An increase in the trans/cis ratio of unsaturated fatty acids took place only at higher temperatures. Osmotic stress, expressed as reduced water activity, was obtained by using different types of solutes. Only in the presence of toxic concentrations of sodium chloride or sucrose did the trans/cis ratio increase. At no applied water activity a significant effect of glycerol on the trans/cis ratio was measured. When cells were exposed to different pHs, a distinct optimum cis/trans isomerase activity was measured at pHs between 4.0 and 5.0, whereas at higher or lower pHs no reaction occurred. This optimum coincided with a loss of viability between pH 4 and 5.

Methods for sweet potato storage, previously developed at a research station, were tested on‐farm by subsistence farmers in Lake Zone, Tanzania. On‐farm testing confirmed that the methods were suitable but indicated that practical and simple improvements were necessary, without which losses in the proportion of market‐quality roots from the store could be as high as 79%. These practical improvements were mainly concerned with the position of stores on the farms. The addition of a new step, dehaulming, improved the recovery of market‐quality roots by 48%. However, although the storage methods were developed in order to improve farmer income, most farmers said they would use the stored roots as a subsistence staple for household food security. Variations among the farmers in their attitudes to storing sweet potato suggest that, when transferring methods from the research station to the farm, it is necessary to target those most able to adopt the approach. Additionally, the farmers considered that local market traders may not be keen to sell stored roots. Therefore, other actors in the value chain, such as market traders and consumers, ought to be included in the process of transferring methods from the research station to the farm. Copyright © 2008 John Wiley & Sons, Ltd

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