Phytochrome B Enhances Photosynthesis at the Expense of Water-Use Efficiency in Arabidopsis    

Abstract

In open places, plants are exposed to higher fluence rates of photosynthetically active radiation and to higher red to far-red ratios than under the shade of neighbor plants. High fluence rates are known to increase stomata density. Here we show that high, compared to low, red to far-red ratios also increase stomata density in Arabidopsis (Arabidopsis thaliana). High red to farred ratios increase the proportion of phytochrome B (phyB) in its active form and the phyB mutant exhibited a constitutively low stomata density. phyB increased the stomata index (the ratio between stomata and epidermal cells number) and the level of anphistomy (by increasing stomata density more intensively in the adaxial than in the abaxial face). phyB promoted the expression of FAMA and TOO MANY MOUTHS genes involved in the regulation of stomata development in young leaves. Increased stomata density resulted in increased transpiration per unit leaf area. However, phyB promoted photosynthesis rates only at high fluence rates of photosynthetically active radiation. In accordance to these observations, phyB reduced long-term water-use efficiency estimated by the analysis of isotopic discrimination against 13 CO 2 . We propose a model where active phyB promotes stomata differentiation in open places, allowing plants to take advantage of the higher irradiances at the expense of a reduction of water-use efficiency, which is compensated by a reduced leaf area.

Phototropins But Not Cryptochromes Mediate the Blue Light-Specific Promotion of Stomatal Conductance, While Both Enhance Photosynthesis and Transpiration under Full Sunlight

“…Conversely, both phyB (Boccalandro et al, 2009;Casson et al, 2009) and cry are involved in long-term changes that indirectly condition rapid stomatal responses. In the case of phyB, the effects on stomatal density (Boccalandro et al, 2009;Casson et al, 2009) are larger than the effects on stomatal aperture (Wang et al, 2010). In the case of cry, the effects on stomatal aperture are larger than the effects on stomatal density (this article).…”

“…High irradiances, typical of open places and seasons with clear skies, increase stomatal density (Willmer and Fricker, 1996;Lake et al, 2001;Thomas et al, 2004;Casson and Gray, 2008). The high red to farred ratios of open places also increase stomatal density compared to the low ratios of dense vegetation canopies (Boccalandro et al, 2009). These effects of irradiance (Casson et al, 2009) and red/far-red ratio (Boccalandro et al, 2009) are at least partially mediated by phytochrome B (phyB) perception of the light signals.…”

“…The high red to farred ratios of open places also increase stomatal density compared to the low ratios of dense vegetation canopies (Boccalandro et al, 2009). These effects of irradiance (Casson et al, 2009) and red/far-red ratio (Boccalandro et al, 2009) are at least partially mediated by phytochrome B (phyB) perception of the light signals. Cryptochrome 1 (cry1) and 2 (cry2) increase stomatal index ), i.e.…”

Atmospheric moisture controls far-red irradiation: a probable impact on the phytochrome

“…The mechanisms by which phytochrome influences water economy may be more or less complicated (Boccalandro et al, 2009;González et al, 2012;Sokolskaya et al, 2003). Some recent reports show that the phytochrome increases tolerance to high evaporative demand (Auge et al, 2012) and that phytochromes phyA and phyB can modulate drought stress responses (D' Amico-Damiāo et al, 2015).…”

Genetic suppression of plant development and chloroplast biogenesis via the Snowy Cotyledon 3 and Phytochrome B pathways

“…In the absence of functional PhyB, the PIF transcription factors are not degraded and thus continue to repress transcription of the essential genes required for chloroplast development and function (Chory et al 1989;Stephenson et al 2009). Loss of PhyB function not only impairs chloroplast development but also affects other processes such as shade avoidance, water use efficiency and flowering time (Reed et al 1993;Boccalandro et al 2009).…”