Plant Strategies for Enhancing Access to Sunlight

Abstract

Light is a vital resource for plants, which compete for it particularly in dense communities. Plants have multiple photosensory receptors to detect the presence of competitors and thereby adjust their growth and developmental strategies accordingly. Broadly speaking, plants fall into two categories depending on their response to shading by leaves: shade tolerant or shade avoiding. Here, we describe the photoperception mechanisms and the growth responses elicited by the neighboring vegetation in shade-avoiding plants, focusing on Arabidopsis thaliana, where these responses are best understood. The type of response depends on plant density, ranging from neighbor detection modulating growth in anticipation of future shading to the response to canopy shade where light resources are limiting. These diverse environments are sensed by various photoreceptors, and we will describe our current understanding of signal integration triggered by distinct light cues in diverse light conditions.

Seedling Establishment: A Dimmer Switch-Regulated Process between Dark and Light Signaling

“…The low R:FR light signal inactivates PhyB, and thus will keep the main PIFs acting in SAS (PIF4, PIF5, and PIF7) active Li et al, 2012) and the production of growth-promoting hormones such as auxin, BR, GA, and ET high Bou-Torrent et al, 2014). In young seedlings, the SAS consists of a delay of some aspects of photomorphogenesis (hypocotyl growth arrest, cotyledon expansion, root development, pigment accumulation), and promotes cotyledon petiole elongation and upward cotyledon positioning (for review, see Ballaré and Pierik, 2017;Fiorucci and Fankhauser, 2017). In dense canopies, the emission of all kinds of volatile compounds increases, and they accumulate due to reduced airflow (Kegge et al, 2013).…”

Blue/green light-responsive cyanobacteriochromes are cell shade sensors in red-light replete niches

“…In other words, blue/teal-green CBCRs may be superior to red/far-red phytochromes for the shade detection in the upper region of the cyanobacterial layer of microbial mats (Figure 4B) because blue and teal-green light are less penetrating than red and far-red light, respectively, in thermophilic cyanobacterial mats [15, 26]. Red/far-red phytochromes, which are well known as a shade detector for shade avoidance of land plants, are distributed in various organisms, such as plants, algae, fungi, and bacteria [3, 27], suggesting that phytochromes may be the ancestor of the related but cyanobacteria-specific photoreceptors CBCRs. The blue/green variant is one of the most prevailing features among CBCRs but is missing in any other type of photoreceptor [4, 5].…”

In Arabidopsis, low blue light enhances phototropism by releasing cryptochrome 1-mediated inhibition ofPIF4expression

“…Plants detect neighbors by sensing the low red (R) to far red (FR) ratio (abbreviated as LRFR), which is a consequence of FR reflection by leaves. If the vegetation becomes denser a canopy filters sunlight, creating an environment with LRFR and reduced blue light, red light and Photosynthetic Active Radiation (PAR) (Fiorucci and Fankhauser, 2017). Enhanced hypocotyl elongation and leaf elevation, reduction of branching and flowering acceleration are some of the mechanisms that have evolved to optimize light capture and increase the fitness in response to vegetational shade (Ballare and Pierik, 2017).…”

“…Natural canopies are not uniform and gaps allow unfiltered light to create light gradients (Fiorucci and Fankhauser, 2017). Thus, when canopy shade is combined with a directional blue light gradient, plants reorient stem growth to position their photosynthetic organs towards blue light, in a process called phototropism (Ballare et al, 1992; Fiorucci and Fankhauser, 2017).…”

“…Natural canopies are not uniform and gaps allow unfiltered light to create light gradients (Fiorucci and Fankhauser, 2017). Thus, when canopy shade is combined with a directional blue light gradient, plants reorient stem growth to position their photosynthetic organs towards blue light, in a process called phototropism (Ballare et al, 1992; Fiorucci and Fankhauser, 2017). Phototropism is mainly controlled by the phototropin blue light receptors (phot1 and phot2 in A. thaliana ), which trigger a number of physiological responses including hypocotyl re-orientation towards directional blue light (Liscum and Briggs, 1995; Sakai et al, 2001).…”