Ozawa S, Yasutani I, Fukuda H, Komamine A, Sugiyama M
Biological Institute, Faculty of Science, Tohoku University, Sendai, Japan.
Development. 1998 Jan;125(1):135-42. doi: 10.1242/dev.125.1.135.
In Arabidopsis thaliana, shoot redifferentiation and root redifferentiation can be induced at high frequency from hypocotyl and root explants by a two-step culture method. Tissues are precultured on callus-inducing medium and then transferred onto shoot-inducing medium for shoot redifferentiation or onto root-inducing medium for root redifferentiation. In an attempt to dissect these organogenic processes genetically, we characterized the responses in tissue culture of srd1, srd2 and srd3 mutants that were originally isolated as temperature-sensitive strains with defects in shoot redifferentiation (Yasutani, I., Ozawa, S., Nishida, T., Sugiyama, M. and Komamine, A. (1994) Plant Physiol. 105, 815-822). These mutants exhibited temperature sensitivity at different steps of organogenesis, which allowed the identification of three states associated with organogenic competence: IC (incompetent); CR (competent with respect to root redifferentiation); and CSR (competent with respect to shoot and root redifferentiation). Hypocotyl explants were shown to be in the IC state at the initiation of culture and to enter the CSR state, via the CR state, during preculture on callus-inducing medium, whereas root explants seemed to be in the CR state at the initiation of culture. The transition from IC to CR and that from CR to CSR appeared to require the functions of SRD2 and SRD3, respectively. It appears that explants in the CSR state redifferentiate shoots with the aid of the products of SRD1 and SRD2 when transplanted onto shoot-inducing medium. Histological examination of the srd mutants revealed that the function of SRD2 is required not only for organogenesis but also for the reinitiation of cell proliferation in hypocotyl explants during culture on callus-inducing medium. Linkage analysis using RFLP markers indicated that SRD1, SRD2, and SRD3 are located at the lower region, the central region, and the upper region of chromosome 1, respectively.
在拟南芥中，通过两步培养法可以从下胚轴和根外植体高频诱导芽再分化和根再分化。组织先在愈伤组织诱导培养基上预培养，然后转移到芽诱导培养基上进行芽再分化，或转移到根诱导培养基上进行根再分化。为了从遗传学角度剖析这些器官发生过程，我们对srd1、srd2和srd3突变体在组织培养中的反应进行了表征，这些突变体最初是作为芽再分化有缺陷的温度敏感菌株分离得到的（Yasutani, I., Ozawa, S., Nishida, T., Sugiyama, M.和Komamine, A. (1994) Plant Physiol. 105, 815 - 822）。这些突变体在器官发生的不同步骤表现出温度敏感性，这使得能够鉴定出与器官发生能力相关的三种状态：IC（无能力）；CR（对根再分化有能力）；以及CSR（对芽和根再分化有能力）。下胚轴外植体在培养开始时处于IC状态，在愈伤组织诱导培养基上预培养期间通过CR状态进入CSR状态，而根外植体在培养开始时似乎处于CR状态。从IC到CR的转变以及从CR到CSR的转变似乎分别需要SRD2和SRD3的功能。当移植到芽诱导培养基上时，处于CSR状态的外植体似乎借助SRD1和SRD2的产物再分化出芽。对srd突变体的组织学检查表明，SRD2的功能不仅对于器官发生是必需的，而且对于在愈伤组织诱导培养基上培养期间下胚轴外植体细胞增殖的重新启动也是必需的。使用RFLP标记的连锁分析表明，SRD1、SRD2和SRD3分别位于第1号染色体的下部区域、中部区域和上部区域。
