Circadian regulation of sunflower heliotropism, floral orientation, and pollinator visits

Abstract

Young sunflower plants track the Sun from east to west during the day and then reorient during the night to face east in anticipation of dawn. In contrast, mature plants cease movement with their flower heads facing east. We show that circadian regulation of directional growth pathways accounts for both phenomena and leads to increased vegetative biomass and enhanced pollinator visits to flowers. Solar tracking movements are driven by antiphasic patterns of elongation on the east and west sides of the stem. Genes implicated in control of phototropic growth, but not clock genes, are differentially expressed on the opposite sides of solar tracking stems. Thus, interactions between environmental response pathways and the internal circadian oscillator coordinate physiological processes with predictable changes in the environment to influence growth and reproduction.

Biomimetic Engineering Analysis of Heliotropic Plants

“…Heliotropism is possible due to the growth of cells in a plant that are furthest from the light source. Phototropism and heliotropism are complex biological responses involving interactions of multiple photoreceptors and multiple signaling pathways that together combine to produce a growth gradient on the shady side of a plant [48]. According to Shell, the ability of a plant to receive sunlight is given by the variable I, irradiance.…”

“…Turgor pressure helps with growth, transport and movement of fluids within the plant [44]. Plant cells generate hydrostatic pressures known as turgor pressure.…”

“…The osmotic (π) and turgor pressure (P) of a cell are conveniently combined in the term water potential, which is a measure of the energy state of the water at any point [44]. Pritchard describes this equation as shown below in Eq.…”

“…The plant circadian clock influences a wide range of physiological and biochemical events, such as photosynthesis and the induction of flowering [17]. This clock helps prepare plants to receive all available energy resources to support plant growth and pollination [44], [45].…”

“…This growth promotes a directional growth towards the light source. Phototropism and heliotropism are complex biological responses involving interactions of multiple photoreceptors and multiple signaling pathways that together combine to produce a growth gradient on the shady side of a plant [48].…”