ABSTRACT

The scions of the unvernalized rapeseed plants were grafted into the stocks of the vernalized and anvernalized rapeseed plants, respectively, under green house conditions. As a result, flowering was soon observed in the scions grafted was made into the vernalized stocks, but not in those grafted into the unvernalized stocks, because of the high level of gibberellin in the vernalized rapeseed plants that was latter transferred to the grafted scions.

INTRODUCTION

There were reports that presented evidences of the transfer of some genetic characters and materials after grafting (Ohta, Y.,1991; Guan, C. Y. et al., 1995). However, there has been found no reports about transferring endogenous gibberellin, and subsequently induced flowering, in the process of graft in rapeseed species. It was under this consideration that the present research was carried out.

MATERIALS AND METHODS

This experiment was conducted in a green house, inside which the temperature was kept at 20±2℃ , and lighting for 16 hrs. Gan You No.5 (B. napus), a winterness rapeseed was utilized in this experiment. All trial plants were allotted into 4 groups (treatments), i.e. (1) the unvernalized and the (2) vernalized rapeseed plants, and (3) the unvernalized rapeseed plants as stocks and (4) the vernalized rapeseed plants as stocks that were to be grafted by the unvernalized scions. On September 3, all trial rapeseeds were sowed in the pots, which was 15.5 cm in height and diameter, and was filled with no-soil mixture (Stringam, 1971). Each treatment consisted of 5 pots, and in each pot were sowed 3 seeds, out of which only 1 seedling was let grow for following experiment. An additional 10 pots were also seeded to grow mother plants as the source of unvernalized scions. When 4 or 5 leaves the plants of the groups 2 and 4 were moved to an chamber to be vernalized for a period of 6 weeks under a temperature ranging from 4-6℃. Then, on October 15, these plants were shifted to the green house again, when they were assayed for the content of gibberellin. Graft was also conducted on the same day by means of splitting and joining. On October 30, all plants were assayed for gibberellin content.

The level of Gibberellin was assayed by a radio-immunological analysis (Zhan, Y. and Guan, C.Y., 1993), with samples approximately 250 mg that had been taken from each treatment, pre-mixed with 2 ml of 95% athyl alcohol, and then stored at -20℃ in a refrigerator. The time of florescence was also recorded for all groups as the date when no less than 50% flowering per group was observed.

RESULTS

The results of the first assay indicated that the content of endogenous gibberellin was 90.2 pg/mg F.W. in the top stems of unvernalized rapeseed plants, but that of the vernalized rapeseed plants was as hight as 215.3 pg/mg F.W., which was over 1 time higher than in the unvernalized groups. The results of the second assay revealed the existence of significantly higher level of endogenous gibberellin in the top stems of the vernalized than unvernalized rapeseed stocks, into which the unvernalized scions were grafted (Table 1).

Table 1 A comparison of the levels of gibberellin in the top stems of rapeseed

plants between 4 treatments as assayed 15 days after grafting (pg/mg F.W.)

The data of flowering was recorded for all 4 treatments, as was showed in Table 2. It was clearly noticed that flowering was observed in the vernalized rapeseed plants and the unvernalized scions grafted into unvernalized rapeseed plants, but not in the other 2 groups.

Table 2 The date of flowering observed in all 4 treatments (month, day)

DISCUSSION AND CONCLUSION

Under green house condition, the vernalized rapeseed plants were able to flowering, but the unvernalized were not. Similarly, flowering was observed in the unvernalized scions that were grafted into the vernalized rapeseed stock, but not flowering in the unvernalized scions that were grafted into the unvernalized rapeseed stocks. The chief reason might be that the vernalized rapeseed plants and stocks had higher levels of gibberellin than the unvernalized, which was latter transferred to the grafted, though unvernalized, scions, and subsequently led to the induced flowering. Physiological researches in plants have already revealed that gibberellin, in most cases, are synthesized in the root, and then transported to the top stem via the xylem. It also seems likely that, with the evidence from the present experiment, gibberellin can be transported from the root of the stock to the top stem of the grafted sicons through the xylem.

References

1. Guan, C.Y. and G.R. Stringam (1995). Studies of graft transfer of heritable traits in rapeseed (Brassica napus L.). Proceedings of 9^th International Rapeseed Congress. p749-752.

2. Ohta, Y.(1991). Graft transformation the mechanism for graft induced changes in higher plants. Euphytica, 55, 91-99.

3. Zhang Yan and C.Y. Guan (1993). Studies on the relationship between the endogenous gibberilic acids content (GA) and the flower bud differentiation in rapeseed (Brassica napus L.). Acta Agronomic Sinica,19(4),365-371.