Fig. 4.

Grafting with lbo-1. (A) lbo rootstock did not promote branching in Ws-4 shoots. Ws-4 rootstock repressed lbo shoot branching nearly to Ws-4 self-graft levels, whereas max4-9 rootstock did not repress lbo shoots. These grafting results mean that the normal enzymatic action of LBO in Ws-4 roots can produce an upwardly mobile product that can repress branching (although not completely) and that this product requires MAX4 enzyme action (i.e., MAX4 is upstream of LBO). Mean ± SEM (n = 19–36). ****P < 0.0001 (t test). (B) lbo rootstock represses branching in max1-1 (background Col-0) mutant shoots to the same extent as Ws-4 rootstock compared with max4-9. This inhibition by lbo rootstocks means that the enzyme action of MAX1 in lbo mutant rootstock produces a mobile product that can fully restore max1 branching and that this product requires MAX4 action. Mean ± SEM (n = 15–20). (C) The max2-1 rootstock reduced branching in the lbo-1 mutant shoot compared with max1-1 max2-1 double-mutant rootstock. This finding suggests that LBO (in max2) can produce a mobile branching inhibitor and that this product requires MAX1 action upstream of LBO. The rationale for using max2-1 (in Col-0) rootstock here was that impaired signaling is expected to increase production of strigolactones and mobile intermediates (17) and that max1 and max2 were not available in the Ws-4 ecotype. Mean ± SEM (n = 20–23). **P < 0.01 (t test).