The flower inducing mechanism of Silene armeria L.

Investigations on the flower induction were carried out with Silene armeria L., a plant species flowering under all conditions after a treatment at LD, 5° C or 32° C. Two strains E ₁ and L ₁ differing in their photoperiodic and temperature requirements, were used in the present research, which completes former investigations (VAN DE VOOREN 1969a, b, 197 1 a, b).

High temperature

Plants under short day conditions at 32° C are induced to flower bud formation. A quantitative juvenility for 32° SI), interaction between 32° SD and L _20° , partial induction by 32° SD and desinduction of this partial induction in SD _20° exist in both strains, but E ₁ is more sensitive than L ₁ .

High temperature action on flower induction is maximal during the middle of a 16 h dark period for both E ₁ and L ₁ . Maximal action in E ₁ is more precisely 7 h after the onset of darkness, independent on the length of the dark period for 8-16 h photoperiods. There is no action for 20 and 24 h photoperiod.

No influence of temperatures on flower induction during SD is apparent in the range 10°-30°C and an increasing response in the range 35°-50° C.

Light

Light intensity is an important factor in flower induction. Increasing light intensities during SD or CL increase the flowering response. The optimal light intensity during CL is rather low in E ₁ and has not been reached in L ₁ in our experiments.

Photoperiodic response curves at 20° and 32° C for E ₁and L ₁

For photoperiods from 8 to 18 h more numbers of cycles necessary for 50% flowering are needed for 20° C than for 32° C. The curves run parallel for both E, and L, at photoperiods from 18 to 24 h. In this range E ₁ needs an equal number and L ₁ decreasing numbers of cycles.

Hypothesis

The mechanism of flower induction is a balance between two processes:
1. A deblocking process in high intensity light, increasing light intensities accelerating it with an optimum, temperature insensitive.
2. A reblocking process in darkness, starting about 4 h after the onset of darkness° reaching its maximum after 6-7 h and decreasing for about 5 h, temperature sensitive, temperatures higher than 30°-35° C slowing it down increasingly. Incandescent light postpones the onset of darkness and hence the reblocking.

When these 2 processes are out of balance and more deblocking than reblocking occurs, a critical level or disappearance of the block is reached and flower induction is completed.

Models

Models, based on the foregoing hypothesis, are presented for induction by LD _20° high intensity light, LD _20° - high+low intensity incandescent light, 32° SD. These models fit well and can be used to predict time of flowering under specific conditions.