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Polyamines, small aliphatic polycations, have been suggested to play key roles in a number of biological processes. In this paper, attempts were made to investigate the possibility of improving dehydration tolerance of citrus in vitro plants by exogenous application of spermine (Spm). 'Red Tangerine' (Citrus reticulata Blanco) in vitro plants pretreated with 1 mM Spm exhibited less wilted phenotype and lower water loss and electrolyte leakage than the control under dehydration. Spm-pretreated plants contained higher endogenous polyamine content during the course of the experiment relative to the control, particularly at the end of dehydration, coupled with higher expression levels of ADC and SPMS. Histochemical staining showed that the Spm-pretreated leaves were stained to a lower extent than those without Spm pretreatment, implying generation of less reactive oxygen species (ROS). On the contrary, activities of peroxidase (POD) and superoxide dismutase (SOD) in the Spm-pretreated samples were higher than the control at a given time point or during the whole experiment, suggesting that Spm exerted a positive effect on antioxidant systems. In addition, significantly smaller stomatal aperture size was observed in Spm-pretreated epidermal peels, which showed that stomatal closure was promoted by polyamines. All of these data suggest that Spm pretreatment causes accumulation of higher endogenous polyamines and accordingly leads to more effective ROS scavenging (less tissue damage) and stimulated stomatal closure (lower water loss) upon dehydration, which may function collectively to enhance dehydration tolerance.

staining. However, these visualization methods require either expensive or hazardous radioactive chemicals and Microsatellite DNA markers are widely used in genetic research.are time-consuming. Electrophoresis with MetaPhor Their use, however, can be costly and throughput is sometimes limited. The objective of this paper is to introduce a simple, low-cost, high-agarose gels (Cambrex Corporation, East Rutherford, throughput system that detects amplification products from microsa-NJ) has been used to separate alleles of microsatellite tellite markers by nondenaturing polyacrylamide gel electrophoresis. markers, but the resolution is lower than nondenaturingThis system is capable of separating DNA fragments that differ by polyacrylamide gels and the cost is currently five times as little as two base pairs. The electrophoresis unit holds two vertical more than that of nondenaturing polyacrylamide gels. 100-sample gels allowing standards and samples from a 96-well plateCapillary electrophoresis also has been used to deterto be analyzed on a single gel. DNA samples are stained during mine length polymorphisms of microsatellite markers electrophoresis by ethidium bromide in the running buffer. In addi- (Marino et al., 1995), but this method requires sophistition, one of the gel plates is UV-transparent so that gels can be cated instruments and fluorescently tagged primers, photographed immediately after electrophoresis without disassemwhich are expensive. Here we describe an inexpensive bling the gel-plate sandwich. Electrophoresis runs are generally less than two hours. The cost per gel, excluding PCR cost, is currently and relatively high-throughput system developed for the estimated at about $2.60, or less than $0.03 per data point. This system purpose of genotyping with microsatellite markers. has been used successfully with soybean [Glycine max (L.) Merr.] and wheat (Triticum aestivum L.) microsatellite markers and could 1828

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