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Under natural conditions, day and night lengths configure a 24-hour cycle of light and darkness.
In theory, a plant might determine the length of a crucial day by observing how long it is either light or dark.
Much experimental work in the early studies of photoperiodism was devoted to establishing which part of the light–dark cycle is the controlling factor in flowering.
Photoperiodism is the response to changes in daylength that enables plants to adapt to seasonal changes in their environment.
Although blooming is the most well-studied manifestation of photoperiodism in plants, additional reactions to daylength include bud dormancy and bulb or tuber initiation.
Seasonal flowering in response to daylength aids in species' habitat adaptation and flowering synchronization for optimal pollination effectiveness.
While the reaction happens elsewhere in the plant, leaves sense the duration of the day. The FT protein, which is produced in leaf vascular tissue in response to CO and whose expression is controlled by photoreceptors and the circadian clock functioning through an external coincidence mechanism, is involved in blooming.
FT travels through the phloem to the apex, where it binds to FD and starts the formation of the floral organ.
Similar functions for FT proteins are played during tuberization and bulb initiation.
A feature that underscores the importance of the dark period is that it can be made ineffective by interruption with a short exposure to light, called a night break.
Many SDPs (Short-Day Plants), such as Xanthium and Pharbitis, can be prevented from blooming by night-break treatments lasting only a few minutes, however LDPs (Long day Plants) sometimes need considerably longer exposures to encourage flowering.
For both LDPs and SDPs, a night break was found to be most effective when given near the middle of a dark period of 16 hours.
The identification of the night-break effect and its temporal dependency had a number of significant ramifications. It confirmed the pivotal significance of the dark period and offered a useful test for researching photoperiodic timekeeping.
It became feasible to analyses the function and identity of the photoreceptor without the interference of photosynthesis and other non-photoperiodic activities since only modest quantities of light are required.
"Photoperiodism” is defined as “The response to changes in daylength that enables plants (or any other living organisms) to adapt to seasonal changes in their environment.”
Plants monitor day length by Measuring the Length of the Night.
By K H AKHIL SRINIVAS.
(KHAS)
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