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Takashi Nishizawa and Kenji Saito

Tomato plants (Lycopersicon esculentum Mill `Ougata-fukuju' and `Korokoro') were grown in a soil or a hydroponic culture to study effects of rooting volume restriction on plant growth and carbohydrate concentrations. In soil culture, leaf lengths decreased linearly as container volume decreased, while plant height did not decrease linearly, irrespective of fruiting. The root to shoot ratio decreased in smaller volume containers, irrespective of fruiting, because dry mass accumulation in the stem and leaves was relatively less inhibited than that in the roots. Total plant dry mass did not differ between fruiting and deblossomed plants, irrespective of container volume. In hydroponic culture, plant height in small containers (37 cm3) was similar to that in large containers (2024 or 4818 cm3). The root to shoot ratio of the plants grown in small containers was lower than that of the plants grown in large containers, mainly due to less inhibition of the dry mass accumulation in the stem than in the leaves. When small containers were almost filled with roots (28 days after transplanting), soluble sugar and starch concentrations in leaves became ≈2-fold higher in the plants grown in small than in those grown in large containers. At the end of experiment (42 days after transplanting), sucrose and starch concentrations in the stem were higher in plants grown in small than in those grown in large containers. However, soluble sugar and starch concentrations in the leaves did not differ between treatments.

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Takashi Nishizawa and Yoshihiro Shishido

June-bearing strawberry plants (Fragaria ×ananassa Duch. `Morioka 16') were forced in a greenhouse and either allowed to fruit or deflowered continuously. Plants were harvested at the start of the experiment (day 0), at full bloom (day 35), during rapid growth of green fruit (day 53), at first fruit coloring (day 63), at full coloring of the primary and some secondary fruit in the primary and secondary inflorescences (day 68), and at overripe of many primary and secondary fruit in the primary and secondary inflorescences (day 81). Dry matter accumulation in the vegetative organs in fruiting plants was less than that in deflowered plants as the fruit matured, but the total plant dry mass did not differ significantly between treatments throughout the forcing period. Reducing sugar and sucrose concentrations in roots, crown, and old leaves decreased continuously until day 68, particularly in roots. The concentrations did not differ between treatments. Starch concentrations in roots declined rapidly in both treatments between day 0 and day 35, and then the decline slowed. Starch level was significantly lower in the roots of fruiting plants from day 35 through fruit harvest. These results suggest that carbohydrate reserves in roots of forced June-bearing strawberry plants are used primarily to support the growth of inflorescences and developing leaves. They are less available for fruit growth and maturation since the levels are already relatively low by this stage.

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Wilawan Kumpoun, Takashi Nishizawa, Yoshie Motomura, Tanidchaya Puthmee and Toshiyuki Aikawa

Green mango (Mangifera indica L.) ‘Nam Doc Mai See Thong’ fruit were dipped in 2-chloroethylphosphonic acid solution (50 ppm) for 5 minutes, kept at 25 °C for 3 days, cold stored at 5 °C for 35 days and then transferred to 25 °C for 7 days. The skin color of the cold-stored fruit partly changed to dark-brown with surface depression. In addition, desiccated white-corky pulp tissues developed mainly along to the dark-brownish skin. Histological and biochemical analyses revealed that the formation of white-corky pulp tissues was correlated with starch accumulation in the hypodermal cells. Cell wall polymers of the white-corky pulp tissues were characterized by both a lower amount of solubilized pectins and higher amount of hemicelluloses than those of normally ripened (NR) tissues. The highest fatty acid unsaturation was observed in the NR pulps under chilling conditions followed by the white-corky pulp tissues under chilling conditions and the NR tissues without chilling. These results suggested that the disordered membrane caused by chilling inhibited the subsequent cascade of secondary reactions, such as the cell wall degradation. The skin damage derived from chilling injury (CI) is a direct factor inducing abnormal desiccation in the adjacent pulp, resulting in the formation of white-corky pulp tissues.

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Thanidchaya Puthmee, Kenji Takahashi, Midori Sugawara, Rieko Kawamata, Yoshie Motomura, Takashi Nishizawa, Toshiyuki Aikawa and Wilawan Kumpoun

The transpiration rate of cuticular membrane and fissures that comprise the netting on fruits of three netted melon cultivars, Life, Andesu, and Gurandoru, were measured during fruit development. Fissures in the equatorial region first developed vertically, then became interconnected by horizontal fissures as the fruit developed. Some cracks remained along the net, even at the fruit ripening stage, regardless of cultivar. Both lignified and suberized cell wall layers in the net tissues of the cultivar Life were thinner than those of the other cultivars, probably because of the shorter developmental period of fruits in the variety. Nevertheless, net transpiration rate did not differ significantly among cultivars at the fruit ripening stage. Peroxidase (POD) activity in the skin tissues of ‘Life’ was lower than that in ‘Andesu’ and ‘Gurandoru’ throughout fruit development and was not correlated with climacteric ethylene production. Among these cultivars, significantly higher ethylene production occurred in ‘Life’ fruit at the ripening stage. This can accelerate membrane permeability of hypodermal tissues, resulting in rapid fruit softening. Our results indicate that the net tissues of netted melons can be as waterproof as cutinized membranes if suberized cell wall layers with wax depositions develop below the net fissures at the fruit ripening stage.

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Takashi Nishizawa, Satoshi Taira, Masanori Nakanishi, Masanori Ito, Masahiro Togashi and Yoshie Motomura

Acetaldehyde and ethanol production by muskmelon fruit were promoted by short-term shading of the plants for 5 days from 10 to 15 days prior to fruit maturation. Sucrose concentrations in the fruit flesh were reduced by shading, while fructose and glucose concentrations did not differ. Shading also accelerated the development of a “water-soaked” appearance in the flesh.

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Takashi Nishizawa, Sayuri Nagasawa, Yuko Mori, Yuko Kondo, Yuka Sasaki, Jorge B. Retamales and Arturo Lavin