Toshikazu Matsumoto

Cryopreservation of in vitro-grown apical meristems of hybrid statice by three different procedures

Abstract In vitro-grown apical meristems of hybrid statice (Limonium cv. Blue Symphonet) were cryopreserved by three cryogenic procedures; (1) vitrification with encapsulation, (2) vitrification without encapsulation, and (3) a revised encapsulation/dehydration technique. When dehydration tolerance was well developed by preconditioning and cryogenic procedures were well optimized, these three procedures produced nearly the same levels of growth recovery (70–75%). These results support our theory that the acquisition of dehydration tolerance is sufficient for specimens to survive to cryopreservation.

Effects of gibberellins on fruit set and flower-bud formation in unpollinated persimmons (Diospyros kaki)

Abstract The fruit production of Japanese persimmons cultivars ‘Fuyu’ and ‘Saijo’ is unstable unless they are pollinated. To ascertain whether gibberellins (GAs) could substitute for hand pollination, fruitlets from flowers which were excluded from pollinators during a flowering period were sprayed with 200 mg l−1 GA3 and a mixture of GA4 and GA7 (GA4+7) about 10 days after full bloom. In both cultivars GA3 was more effective than GA4+7 and GA3 significantly increased seedless fruit set. Further, to determine the lowest concentration of GA3 for practical use without severe inhibition of flowering, effects of GA3 at rates of 0, 25, 50 and 100 mg l−1 on fruit set and development of seedless fruit were examined. All treatments of GA3 at 25, 50 and 100 mg l−1 significantly reduced fruit drop in ‘Saijo’. However, even at 25 mg l−1 the spray of GA3 tended to reduce the flowering potential in the following year. In ‘Fuyu’, GA3 was incapable of inducing sufficient fruit set without reducing flowering. Fruit growth was inhibited in seedless fruits of both cultivars, even if they were treated with GA3.

Extraction of Soil Organic Nitrogen by Organic Acids and Role in Mineralization of Nitrogen in Soil

The solubilization of organic nitrogen (Norg) in soil was examined by using organic acids often present in root exudates. The organic acids tested were classified into two groups depending on their solubilizing ability for Norg in a soil sample. Oxalate, malonate, tartarate, citrate and malate could dissolve Norg by increasing their concentrations, while succinate and glutarate could not dissolve Norg even when their concentrations were increased. The amount of organic N extracted with oxalate, malonate, tartarate, citrate and malate showed a strong correlation with the sum of the amounts of Al and Fe in the extracts. Therefore, it was assumed that the solubilizing ability may be attributed to the structure of these organic acids that can form stable chelate compounds with Al and Fe (oxalate, malonate, tartarate, citrate and malate). Furthermore, the amount of 20 mM cit-rate-extractable Norg (CEON), which was the highest among the organic acids tested, showed a strong correlation with both that of 67 mM phosphate buffer, which is now being widely used as an index for estimating soil N availability in Japan, and N mineralized using an incubation method in 46 soil samples belonging to different soil types. These results suggested that CEON might be an important constituent of mineralizable Norg in soil. Therefore, organic acids secreted by crops play a role in the solubilization of available Norg surrounding the crop rhizosphere.

Survival of Tropical Apices Cooled to-196°C by Vitrification

Tropical apical meristems excised from in vitro-grown plants which were sufficiently dehydrated with a highly concentrated vitrification solution (designated PVS2, 7.8 M) survived subsequent plunging into liquid nitrogen (LN) and regenerated plants (recovery growth 80%). Excised meristems of cassava (Manihot esculenta Grantz) were precultured with 0.3 M sucrose for 16 hr and then enhanced for tolerance to PVS2 with a mixture of 2 M glycerol and 0.4 M sucrose (LS) for 20 min at 25 °C. These osmoprotected apices were then sufficiently dehydrated with PVS2, so that the cytosolic concentration required for vitrification was attained upon rapid cooling into LN. Vitrification refers to a phase transition from a liquid into amorphous glass, while avoiding crystallization. In the vitrification protocol, enhancing tolerance to PVS2 and the mitigation of injurious effects during dehydration were crucial for ensuring the survivals.