Phytochrome B enhances photosynthesis at the expense of water-use efficiency in Arabidopsis.

HernáN E Boccalandro,MatíAs L Rugnone,Edmundo L Ploschuk,Javier E Moreno,Jorge J Casal,Marcelo J Yanovsky,Laura Serna

doi:10.1104/pp.109.135509

HernáN E Boccalandro, MatíAs L Rugnone + Show 5 more

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https://doi.org/10.1104/pp.109.135509

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Journal: Plant Physiology	Publication Date: Apr 10, 2009
Citations: 159	License type: CC BY 4.0

Affiliation: University of Buenos Aires

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 far-red 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.

Highlights

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
Plants of Arabidopsis of the wild-type Landsberg erecta (Ler) and of the phytochrome B (phyB)-4 and phyB-5 mutants were grown under white-light photoperiods (12 h) terminated with or without a pulse of far-red light (FR) (+FR)
The +FR treatment and the phyB mutation increased the leaf area per plant (Fig. 1A) and reduced the rate of transpiration per unit leaf area (Fig. 1B), compared to wild-type plants grown under the high R/FR ratio control conditions

Summary

Introduction

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. In the latter species, prolonged FR added to a white-light background promotes stomatal conductance but this effect cannot be ascribed to phytochrome (Holmes et al, 1986) In addition to this rapid adjustment of the CO2 and water vapor fluxes to daily fluctuations in light levels via the regulation of the stomatal pore aperture, plants acclimate to the prevailing PAR conditions by changing stomatal density (number of stomata per unit area) and stomatal index (the ratio between the number of stomata in a given area and the total number of stomata and other epidermal cells in that same area). There is no correlation between photosynthetic rate and stomatal index in poplar (Populus spp.; Miyazawa et al, 2006) and transgenic anti-small subunit of Rubisco tobacco (Nicotiana tabacum) plants, show reduced photosynthesis and normal responses of stomatal density and stomatal index to PAR, suggesting that other photoreceptors could be involved in this regulation (Baroli et al, 2008)

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