The effects of ABA and putrescine, a polyamine, on cold-induced membrane leakage were investigated using primary leaves of wild-type and an ABA-deficient mutant, flacca, of tomato (Lycopersicon esculentum Mill.). The amount of chilling-induced electrolyte leakage from flacca leaves was much higher than that from the wild-type leaves. When applied exogenously ABA reduced cold-induced electrolyte leakage from leaves of both wild-type and the flacca mutant. However, the cold-induced electrolyte leakage from flacca leaves was not as pronounced as in the wild-type indicating that ABA is an important mediator in response to cold stress in the leaves. Putrescine reduced cold-induced electrolyte leakage from both wild-type and flacca leaves. Synthesis of putrescine in the leaves was increased by cold treatment. DFMO, a biosynthetic inhibitor of the polyamine, increased electrolyte leakage from cold-treated leaves, and exogenously applied putrescine decreased the enhanced leakage to the control level. Therefore, this polyamine is thought also to be involved in the response to cold stress of tomato leaves. Both ABA and putrescine were protective against cold stress, but exogenously applied ABA decreased the endogenous level of putrescine in the leaves. Furthermore, the DMFO-increased electrolyte leakage in cold-stressed leaves was completely abolished by the application of ABA. These results suggest that ABA is a major regulator in the response to cold stress in tomato leaves and that it does not exert its role via putrescine in the response to cold stress.

Advertisement calls of some cicadas are so loud that they are a nuisance to city-dwellers in Korea. We hypothesized that the densities of cicada species were directly correlated with the availability of host plant species. We conducted complete enumeration surveys of exuviae in Hyalessa fuscata, Cryptotympana atrata, Meimuna spp., and Graptopsaltria nigrofuscata in three representative habitats in Republic of Korea: metropolitan, suburban, and country. We measured resource-weighted density of each species based on the area and the number of trees, and used those values to calculate organism-weighted density, which measures the intensity of competition that an individual experiences sharing its host with others of its own species. H. fuscata was the dominant species in all three habitats. H. fuscata and C. atrata comprised a minimum of 75.2% of all cicadas across all habitats and sampling periods. Resource-weighted densities of H. fuscata and C. atrata were much higher in the metropolitan habitat than in the country habitat. Habitat was a significant factor for variations in organism-weighted densities in C. atrata and G. nigrofuscata, but it was not in Meimuna spp. and H. fuscata. Some of the results concerning the percentages of trees without exuviae and preferred plants seemed to support the host availability hypothesis in C. atrata, Meimuna spp. and G. nigrofuscata, but they may not in H. fuscata. The similarity between resource-weighted and organism-weighted densities suggests that factors other than host availability, speculatively abiotic factors and predators, may also account for the patterns of population densities in C. atrata and G. nigrofuscata.