Interaction of Gibberellin With Photoinduction in the Initiation of the Dormant Phase in Vernalized Hordeum bulbosum L

Vernalized plants of H. bulbosum growing in short (8-h) photoperiods may be induced to form bulbs after exposure to a number of long (16-h) photoperiods. This response was enhanced significantly by application of gibberellic acid (GA3) just before, concurrently with, or at the end of the photoinductive treatment. Exogenous GA3 induced bulb formation even with subthreshold photoinductive treatment but failed to do so without it (i.e. in short days throughout). Thus, induction of bulb initiation under long days may involve both a gibberellin-like factor and one that is unlike gibberellin. Plants treated with GA3 before, or concurrently with, photoinductive treatments produced the bulb at a lower internode than those treated later or not at all. Gibberellin may affect bulb initiation by sensitizing a receptive internode. The non-gibberellin-like factor also produced under long days is required for expression of bulb formation.