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.

中文翻译：

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雌性大麻植物的花序发育是由光周期和赤霉素介导的


在大麻幼苗中，单花的萌生与光周期无关。然而，当大麻达到成虫阶段时，短日照周期（SD）会引发芽尖的分枝和节间长度的缩短，从而导致浓缩花序的发育。我们证明 SD 在两个不同的阶段影响大麻植物：第一个阶段包括节间和主茎的快速伸长，发生在 SD 下植物栽培的第 5 天到第 10 天；在第二阶段，新发育的节间停止伸长，并形成压缩花序。将植物暴露于交替的光周期表明花序开始需要至少连续三天的 SD，并且在整个花序成熟过程中始终需要 SD 以支持其典型的浓缩结构。这种光周期依赖性形态发生与茎尖赤霉素（GA4）和生长素水平的降低有关。将植物恢复到长日光周期 (LD) 会增加 GA4 和生长素水平，导致花序分解、节间伸长以及随后恢复 LD 生长模式。在应用外源 GA（而不是生长素）后，在 SD 下观察到类似的发育模式，这也阻碍了花序发育。尽管如此，更多的研究将有助于进一步评估生长素在这些发育变化中的作用。我们提出 GA 通过介导花序组织中的光周期信号在雌性大麻的有性繁殖和花序发育中发挥关键作用。