REGULATION OF TUBER INDUCTION IN POTATO BY DAYLENGTH AND PHYTOCHROME
Phytochrome is known to be involved in photoperiodic responses such as tuberization and flowering because the effects of a red light night-break can be reversed by a far-red light treatment given immediately afterwards-a well- documented characteristic of phytochrome responses. Which of the several phytochromes that are known to exist is/are responsible for the photoperiodic response, however, has not been shown.
Transgenic short-day requiring Solanum tuberosum ssp. andigena plants have been produced which have much lower levels of phytochrome B as a result of antisense technology. These plants are now able to tuberize in long days as well as short days. The reduction in phytochrome B levels has thus led to the loss of the photoperiodic control of tuberization in these plants and implicates phytochrome B in this response.
Preliminary grafting experiments have indicated that a graft-transmissible tuberinducing signal is produced in the transgenic plants in long days as well as short days, whereas in wild-type plants this signal is only produced in short days. The existence of a possible inhibitor of tuberisation is also discussed.