Our results show that phytochrome is involved in both
negative and positive phototropism in Arabidopsisroots.
Firstly, phyA and phyB mediate the positive red-light-based photoresponse in roots since single mutants (and
the double phyAB mutant) were severely impaired in this
response (Figure 4). Secondly, in blue-light-based
negative phototropism, phyAand phyAB(but not phyB)
were inhibited in the response compared to the WT
(Figure 6). In addition, in a recent study, we found that in
root gravitropism, phyBand phyAB(but not phyA) were
inhibited in the response compared to the WT