**5. Conclusions**

Inducing regenerate tissues from pluripotent cells is a fascinating event. So far, botanists have already shown that they were able to get regeneration plants from callus in many plant species [49, 65–67]. However, why and how plants achieve this process is still unknown, especially in molecular levels. Here, we propose a hypothesis among phytohormone, osmotic stress, and carbohydrate metabolisms on HRC induction based on current knowledge and our findings (**Figure 2**). According to our model, levels of endogenous IAA upregulated by osmotic stress treatment can promote sugar uptake via CIN and SUT, which result in carbohydrate accumulation during callus induction stages. Similar to auxin, endogenous ABA level is also enhanced under osmotic stress, thus modulating starch accumulation during formation of HRC by downregulating α-amylase activity. Our studies indicated that exogenous auxin or ABA treatment alone is not sufficient for embryonic or organogenic callus formation, which only increased the plant regeneration rate for 35 and 5%, separately [5]. However, when we combine both ABA and anthranilic acid treatment together, the regeneration frequency can be promoted to 80% similar to osmotic stress treatment, suggesting that there must be some interaction between these two phytohormones. The roles of accumulated carbohydrates in HRC could be used as osmotic agents for further metabolism changes or be consumed as an energy

**41**

provided the original work is properly cited.

and Wen-Lii Huang2

1 Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan

\*Address all correspondence to: wlhuang@mail.ncyu.edu.tw

2 Department of Agronomy, National Chiayi University, Chiayi, Taiwan

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

\*

*Cross Talk among Phytohormone Signal and Carbohydrate Metabolism Involving Regenerable…*

The authors would like to thank Professor Li-Fei Liu, Department of Agronomy, National Taiwan University, to establish the high efficiency of the shoot regeneration system by osmotic stress treatment in rice callus culture. We would like to thank the Council of Agriculture, Taiwan, ROC, for providing the funding to finish

source in later regeneration stages. In conclusion, the culture system of shoot regeneration in rice callus is a two-step process. Our studies suggested that induction of highly regenerable callus is more important than different kinds of treatment during the shoot regeneration stage. Besides, osmotic stress triggers a serial of change of endogenous hormone metabolism, sensing, and signal transduction, which leads to increase of sucrose uptake and starch accumulation and provides

*DOI: http://dx.doi.org/10.5772/intechopen.83556*

**Acknowledgements**

**Conflict of interest**

**Author details**

Hsiang-Ting Lee1

this study.

sufficient carbon source for further shoot regeneration.

The authors have no conflict of interest.

**Figure 2.**

*Working hypothesis of highly regenerable callus induction under osmotic stress treatment in rice.*

*Cross Talk among Phytohormone Signal and Carbohydrate Metabolism Involving Regenerable… DOI: http://dx.doi.org/10.5772/intechopen.83556*

source in later regeneration stages. In conclusion, the culture system of shoot regeneration in rice callus is a two-step process. Our studies suggested that induction of highly regenerable callus is more important than different kinds of treatment during the shoot regeneration stage. Besides, osmotic stress triggers a serial of change of endogenous hormone metabolism, sensing, and signal transduction, which leads to increase of sucrose uptake and starch accumulation and provides sufficient carbon source for further shoot regeneration.
