Among several naturally occurring environmental factors, temperature is considered to play a predominant role in controlling proper growth and flowering in geophytes. Most of them require a "warm-cold-warm" sequence to complete their annual cycle. The temperature optima for flower meristem induction and the early stages of floral organogenesis vary between nine and 25 °C, followed, in the autumn, by a several-week period of lower temperature (4-9 °C), which enables stem elongation and anthesis. The absence of low temperature treatment leads to slow shoot growth in spring and severe flowering disorders. Numerous studies have shown that the effects of the temperature surrounding the underground organs during the autumn-winter period can lead to important physiological changes in plants, but the mechanism that underlies the relationship between cold treatment and growth is still unclear. In this mini-review, we describe experimental data concerning the temperature requirements for flower initiation and development, shoot elongation, aboveground growth and anthesis in bulbous plants. The physiological processes that occur during autumn-winter periods in bulbs (water status, hormonal balance, respiration, carbohydrate mobilization) and how these changes might provoke disorders in stem elongation and flowering are examined. A model describing the relationship between the cold requirement, auxin and gibberellin interactions and the growth response is proposed.
Keywords: bulb; flowering; geophytes; temperature.