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

• Published in: Plant physiology (Bethesda) Vol. 150; no. 2; pp. 1083 - 1092
• Main Authors: Boccalandro, Hernán E, Rugnone, Matías L, Moreno, Javier E, Ploschuk, Edmundo L, Serna, Laura, Yanovsky, Marcelo J, Casal, Jorge J
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Biologists 01.06.2009
• Subjects: Arabidopsis - physiology; Arabidopsis - radiation effects; Arabidopsis Proteins - metabolism; Biological and medical sciences; Epidermal cells; Fundamental and applied biological sciences. Psychology; Leaf area; Leaves; Light; Photoperiod; Photosynthesis; Photosynthesis - radiation effects; Photosynthetically active radiation; Phytochrome B - metabolism; Plant cells; Plant physiology and development; Plant Stomata - metabolism; Plant Stomata - radiation effects; Plant Transpiration - radiation effects; Plants; Signal Transduction - radiation effects; Transgenic plants; Transpiration; Water - physiology; Whole Plant and Ecophysiology; Arabidopsis thaliana; Plant physiology; Cruciferae; Dicotyledones; Angiospermae; Phytochrome; Spermatophyta; Water use efficiency; Experimental plant; Photosynthesis
• ISSN: 0032-0889; 1532-2548; 1532-2548
• DOI: 10.1104/pp.109.135509

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 ¹³CO₂. 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.