Abstract
It has been shown in protonemata of Physcomitrella patens that branch appears at the region irradiated with microbeam blue light (Uenaka et al., 2005). In this study, the effect of fluence rate of microbeam blue light on the branch position was investigated. When microbeam blue light of 10 or 30 W m-2 was irradiated, branch was induced within the microbeam area (Weak light response, WR). However, branch appeared outside the microbeam area when blue light of 200 or 400 W m-2 was used (Strong light response, SR). Interestingly, in case of SR, branch formed at the apical side of microbeam, suggesting that cell polarity is also involved in the determination of branch position. When blue light determination of branch position was investigated in PHOTOTROPIN disruptants, reduction in the blue light sensitivity was found. These evidences indicate that branch position in P. patens is regulated through phototropins and cell polarity.
