Is light really a prerequisite for leaf initiation?

MSc-thesis abstract (submitted 6 February 2017): Leaf initiation is strongly influenced by environmental conditions. Light acting as a morphogenic signal, can induce auxin and cytokinin levels, thereby inducing leaf initiation.
In previous studies, light was stated as a prerequisite for true leaf initiation. However, their results can be further investigated, for instance the effects of sucrose signalling and in vitro environment on leaf initiation.

The objectives of this study are to investigate whether leaf initiation occurs during skotomophorgenesis, whether the cease of leaf initiation in darkness is permanent, and what the effects are of external sucrose and the in vitro environment (compared to soil) on leaf initiation.
We utilized in vitro medium (with 60 mM or without sucrose supplementation) and soil as culture substrates for tomato seedlings.

The results show that light is not required for the initiation of the first two true leaves; sucrose can continuously induce leaf initiation during skotomorphogenesis via sucrose signal and/or due to increased energy status.
After initial photomorphogenesis, light is required for leaf initiation, even in in vitro medium with sucrose.
In vitro environment influences leaf initiation: in seedlings grown in vitro without sucrose, leaf initiation stopped even in light, while soil-grown seedlings kept normal leaf initiation in light.