Results and discussion
Influence of co-cultivation periods for transformation of garlic calluses
We had previously developed a highly efficient regen- eration of the apical from calluses(Hasegawa et al. 1996). With this regeneration system, we obtained an average regeneration frequency of 70%. In studying various garlic we observed that the culture periods and temperature of co-cultivation were important factors. The periods of co-cultivation dif- fered according to plant species in the literature. Longer periods of co-cultivation seem effective for efficient transfer of the Ti plasmid to plant cells. In citrange explants, the numbers of spots stained with GUS increased sharply from days 1 to 5 Cervera al. Cao that low effi ciency of transformation in earlier work on et(James and Dandekar 1991) was due to an insufficient length of co-cultivation, since a prolonged period of co-cultivation from 2 to 4 days increased GUS expres sion by almost 100-fold(De Bondt et al. 1994)However, it was more difficult to eliminate Agro- bacterium after longer periods of co-cultivation. Cer vera et al. (1998) reported that the 5-day culture period resulted in overgrowth of Agrobacterium and a subsequent decrease in the frequency of transformed shoots, although 5-day co-cultivation was the most effective for increasing the frequency of tran- sient GUS expression in citrange explants. Therefore, the period of co-cultivation should be optimized. We investigated the effect of varying the periods of co-cul- tivation with transient expression of the uid A gene. Co-cultivation for 3 days showed much higher GUS expression compared with 1- or 2-day co-cultivations(Fig. 1). However, transient GUS exprssion did not vary significantly over 3- to 6-day co-cultivation. Agro bacterium could be substantially eliminated from the co-culture medium of the 3-day co-cultivation in garlic calluses. Thus, we used a 3-day co-cultivation rou tinely
Influence of temperature on the transformation of garlic calluses Dillen et al. (1997) indicated that temperature plays an important role in transformation with A. tumefa- ciens. In their results, the best transformation effi- ciency was obtained at 22 oC in both Phaseolus acuti- folius callus and tobacco leaves, irrespective of the type of helper plasmids. Although 25 oC is commonly