No abstract

Effects of solarization on microbial communities in soil were investigated with an incubation experiment and in a greenhouse experiment with isolated bed culture of tomato (Solanum lycopersicum L.) by molecular techniques. Microbial biomass carbon in soil was decreased by about half in the incubation experiment treated with 45°C for 14 days and the greenhouse experiment with solarization for 45 days. Bacterial and fungal communities in soil were affected by the heat and solarization treatments in both the experiments and greatly different from the communities in the unheated soil or the soil before solarization. Copy number of amoA gene of ammonia-oxidizing bacteria in soil was decreased to one-tenth or less by the treatments in both the experiments. This study revealed that the solarization made a great impact on the abundance and composition of microbial communities in soil.

Flower opening is important for floricultural crops. The mechanisms flower opening associated with the expansion of petal cells were investigated in Eustoma grandiflorum (Raf.) Shinn. Eustoma petals showed marked changes in their fresh weight, shape, and color during flower opening. Concurrently, petal cell-wall extensibility increased. This suggests that petal growth through flower opening is mainly caused by cell expansion. Expansin and xyloglucan endotransglycosylase/hydrolase (XTH) are known as representative proteins that loosen cell walls in plants. Three expansins and one XTH gene were isolated from opening Eustoma petals. We monitored for the first changes in their protein abundance in growing petals by Western blot analysis using antibodies to specifically detect expansin or XTH. The accumulation of these proteins marked the highest amount in petals when the flower was blooming and the petals were bending outwards. Thus, we showed that expansins participate in continuous petal growth from bud to opening flower and XTH plays a role in rapid petal growth accompanied by dynamic changes in petal fresh weight and petal shape.

Solarization makes a great impact on the abundance of ammonia oxidizers and nitrifying activity in soil. To elucidate fluctuations in the abundance of ammonia oxidizers and nitrification in solarized soil, copy numbers of amoA gene of ammonia-oxidizing bacteria (AOB) and archaea (AOA), viable number of ammonia oxidizers and inorganic nitrogen contents were investigated in greenhouse experiments. The copy number of amoA gene and the viable number of ammonia oxidizers were determined by the quantitative polymerase chain reaction and most probable number methods, respectively. Abundance of AOB based on the estimation of amoA gene copy numbers and viable counts of ammonia oxidizers was decreased by the solarization treatment and increased during the tomato (Solanum lycopersicum L.) cultivation period following the solarization. Effect of solarization on the copy number of amoA gene of AOA was less evident than that on AOB. The proportion of nitrate in inorganic nitrogen contents was declined by the solarization and increased during the tomato cultivation period following the solarization. Positive correlations were found between the proportion of nitrate in inorganic nitrogen content and the copy number of bacterial or archaeal amoA gene or the viable number of ammonia oxidizers; the copy number of bacterial amoA gene showed a strong correlation with the viable number of ammonia oxidizers. The present study revealed influences of solarization on the fluctuation in the abundance of ammonia oxidizers and dynamics of inorganic nitrogen contents in soil and the results indicate that the determination of amoA gene of AOB is possibly a quick and useful diagnostic technique for evaluating suppression and restoration of nitrification following solarization.