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- Author or Editor: Masahumi Johkan x
- HortScience x
In this study, we determined the effects of raising seedlings with different light spectra such as with blue, red, and blue + red light-emitting diode (LED) lights on seedling quality and yield of red leaf lettuce plants. The light treatments we used were applied for a period of 1 week and consisted of 100 μmol·m−2·s−1 of blue light, simultaneous irradiation with 50 μmol·m−2·s−1 of blue light and 50 μmol·m−2·s−1 of red light, and 100 μmol·m−2·s−1 of red light. At the end of the light treatment, that is 17 days after sowing (DAS), the leaf area and shoot fresh weight (FW) of the lettuce seedlings treated with red light increased by 33% and 25%, respectively, and the dry weight of the shoots and roots of the lettuce seedlings treated with blue-containing LED lights increased by greater than 29% and greater than 83% compared with seedlings grown under a white fluorescent lamp (FL). The shoot/root ratio and specific leaf area of plants irradiated with blue-containing LED lights decreased. At 45 DAS, higher leaf areas and FWs were obtained in lettuce plants treated with blue-containing LED lights. The total chlorophyll (Chl) contents in lettuce plants treated with blue-containing and red lights were less than that of lettuce plants treated with FL, but the Chl a/b ratio and carotenoid content increased under blue-containing LED lights. Polyphenol contents and the total antioxidant status (TAS) were greater in lettuce seedlings treated with blue-containing LED lights than in those treated with FL at 17 DAS. The higher polyphenol contents and TAS in lettuce seedlings at 17 DAS decreased in lettuce plants at 45 DAS. In conclusion, our results indicate that raising seedlings treated with blue light promoted the growth of lettuce plants after transplanting. This is likely because of high shoot and root biomasses, a high content of photosynthetic pigments, and high antioxidant activities in the lettuce seedlings before transplanting. The compact morphology of lettuce seedlings treated with blue LED light would be also useful for transplanting.
Habenaria radiata is a terrestrial orchid with beautiful bird-shaped petals. The wild H. radiata population has been severely affected by environmental disruption and overexploitation. In micropropagation of H. radiata, although aseptic germination has been studied, tissue culture methods have not yet been established. Shoot apexes and leaf explants from vegetative plants and flower stalks, stolons, and floret explants from reproductive plants were chosen for this study. Explants were cultured on half-strength inorganic salts and full-strength vitamins of Murashige and Skoog (1/2 MS) medium containing 30 g·L−1 sucrose, 8 g·L−1 agar (pH 5.6) supplemented with 4.44 μM N6-benzyladenine, and 0.54 μM α-naphthaleneacetic acid. After 8 weeks of culture, the highest survival rate was obtained with floret explants excised from plants at the reproductive phase. In floret culture, the number of adventitious bud formation per explant was 5.4 per upper floret and 4.0 per lower floret. Dark preconditioning, which inhibited browning and contamination, of explants before shoot apex culture increased survival rates of explants (53%) and bud formation (83%). Consequently, a tissue culture method using florets and shoot apexes as explant material was established for H. radiata.
Adventitious shoots can be regenerated from the cut surface of the primary shoot and lateral branches in decapitated plants in vivo. This inherent regenerative ability of plants is useful for mass propagation. In the present study, we conducted histological observations of shoot regeneration and applied auxin and cytokinin to decapitated seedlings in four tomato cultivars. The cultivars produced different numbers of adventitious shoots after decapitation; ‘Petit’ produced the largest number of adventitious shoots (78.5 ± 10.2) and ‘Momotaro’ produced the fewest (12.1 ± 3.3). Histological observation of ‘Petit’ revealed that adventitious shoots regenerated from calli formed at the cut surface of stems. Adventitious shoot formation was inhibited by the presence of lateral branches. Shoot regeneration was prevented by application of 1-naphthaleneacetic acid to ‘Petit’. Application of 6-benzyladenine promoted shoot regeneration in ‘Momotaro’. These results suggest auxin synthesized de novo from the lateral branches inhibited shoot regeneration after decapitation and endogenous cytokinin might stimulate shoot regeneration. Chemical names: 1-naphthaleneacetic acid (NAA); 6-benzyladenine (BA)