Inflorescence development in female cannabis plants is mediated by photoperiod and gibberellin

Abstract

In cannabis seedlings, the initiation of solitary flowers is photoperiod-independent. However, when cannabis reaches the adult stage, short-day photoperiod (SD) triggers branching of the shoot apex and a reduction in internode length, leading to development of a condensed inflorescence. We demonstrate that SD affects cannabis plants in two distinct phases: the first includes rapid elongation of the internodes and main stem,and occurring from Day 5 to Day 10 of plant cultivation under SD; in the second phase,elongation of newly developed internodes ceases, and a condensed inflorescence is formed. Exposure of plants to alternating photoperiods revealed that inflorescence onset requires at least three consecutive days of SD, and SD is consistently required throughout inflorescence maturation to support its typical condensed architecture. This photoperiod-dependent morphogenesis was associated with a decrease in gibberellin (GA₄) and auxin levels in the shoot apex. Reverting the plants to a long-day photoperiod (LD) increased GA₄ and auxin levels, leading to inflorescence disassembly, internode elongation, and subsequent resumption of LD growth patterns. Similar developmental patterns were observed under SD following the application of exogenous GA (and not auxin), which also impeded inflorescence development. Nevertheless, additional studies will help to further evaluate auxin’s role in these developmental changes. We propose a crucial role for GA in sexual reproduction and inflorescence development in female cannabis by mediating photoperiod signaling in the inflorescence tissues.

Acknowledgements

The plant material (rooted cuttings) was supplied by Canndoc Ltd, a certified commercial cultivation producer in Israel. We are grateful for the cooperation and advice of Neri Barak, the founder and president of Canndoc Ltd. This work was supported by the Chief Scientist of the Israeli Ministry of Agriculture and Rural Development grant 20-01-0177.

Author contributions

H.A., R.K.G., and B.S.R. wrote the original draft. H.A., N.B., R.K.G., and B.S.R. planned the experiments. H.A. and Y.S. carried out the experiments. A.S., M.C.W., and F.S. conducted and analyzed the endogenous hormone analyses. Y.S. conducted the cannabinoid analysis. A.S., R.K.G., N.B., and B.S.R. finalized the manuscript.

Data availability

All created data are presented in this article and in the supplementary materials.

Conflict of interest statement

The authors declare no conflicts of interest.

Supplementary Data

Supplementary data is available at Horticulture Research online.

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