| Vol. 4 |
Li-Lin WANG, Ming-Quan WANG and Xiang-Ming WANG
Genetic Laboratory, Department of Biology, Wuhan University, Wuchang, Hubei, China
Fifty-one rice strains were tested for the reaction of excised shoot apex to in vitro culture.Six of them belonged to wild Oryza species, 17 were cultivars of O.sativa subsp. keng (Japonica), 24 were of subsp. hsien (Indica), and the remaining four were cultivar X wild F1 plants. the explant was taken from the apex of seedlings at the 6-leaf stage. The explant size was approximately 2 mm. The medium used was the basic medium recommended by Matsuo (1974, p. 477-8). All except a Keng cultivar (Lido) regenerated plantlets in the test-tubes with frequencies ranging from 8% to 67% of cultured apices, which were about 50 per strain (Table 1). The cultured apex differentiated roots first and then shoots also.
Table 1. Regeneration of plantlets from cultured shoot apices
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Material No. of strains % regeneration
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Keng (Japonica) cultivars,
excluding Lido 16 8.0-20.0
Lido 1 0
Hsien (Indica) cultivars 1 19.6
21 21.3-48.0
2 52.0-58.3
O.rufipogon,
Dongxiang wild 1 69.8
Jiangyong wild 1 62.0
Zhangpu wild 1 54.9
O. perennis 1 75.0
O. nivara 1 60.0
O. latifolia 1 66.0
F1 plants,
Ewan 3 (Keng)x O. latifolia 1 30.0
Baoxuan 2 (Hsien)xO.latifolia 1 62.5
Baoxuan 2 X O.perennis 1 66.7
O.sativa X O.rufipogon 1 54.0
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Almost all the apices regenerated plantlets directly without formation of callus. An exception was the wild rice from Jiangyong County, Hunan Province, which regenerated plantlets after callus formation.
Cultivar Baoxuan 2, a photoperiod-sensitive Indica from Guangxi, was used for a series of experiments on the effect of different culture media. An addition of zeatin to the basic medium promoted the differentiation of panicle primordia or the generative development of the cultured apex. ABA was also effective in promoting panicle differentiation. On the contrary, NH4SO3 was inhibitive to panicle differentiation. The physiological condition of the donor plant was important for the fate of cultured apices. Plants receiving 3-5 cycles of 10-hour short- days, as well as the control plants, produced leaf primordia only during the first month of culture. But the plants receiving 7 cycles of short-days were capable of differentiating primary branches of the panicle during the first month when cultured on a zeatin-supplemented medium (2-4 ppm). Furthermore, the plants regenerated from these apices showed significantly earlier heading in the greenhouse than those derived from donor plants treated with 0-5 cycles of short-days.
These results suggest that in vitro culture of the rice shoot apex can be used for the study of mechanisms of floral initiation. The genetic background of the explant would play a role in the floral initiation of regenerated plants. The rate of regeneration of plantlets seemed to be higher in wild species than in cultivars, and higher in Indica than in Japonica cultivars.
| Vol. 4 |