We don't exactly know how plants sense that they have been touched but amyloplasts do not appear to be part of the picture. Their hypothesis has something to say about phototropic effects, but not photoperiodism. Their hypothesis could conceivably apply to thigmotropic growth but they were mainly thinking about light and gravity effects. Alternation of light and dark over a 24 hour period is necessary to set and maintain the rhythms. Clock effects die away in continuous darkness, or continuous light for that matter.
Auxin promotes lateral root initiation but inhibits root elongation.
Since abscission involves separation of cells prior to shedding of plant parts it is natural that a pectinase should be produced to break down the pectin in the middle lamella. Long days may have some influence on breaking dormancy, but are not usually sufficient in themselves.