Enhanced Stomatal Conductance by a Spontaneous Arabidopsis Tetraploid, Me-0, Results from Increased Stomatal Size and Greater Stomatal Aperture.

Keina Monda,Hitoshi Sakakibara,Juntaro Negi,Mimi Hashimoto-Sugimoto,Ryo Akashi,Mikiko Kojima,Koh Iba,Genki Ishigaki,Hiromitsu Araki,Sho Takahashi,Nobuharu Goto,Satoru Kuhara

doi:10.1104/pp.15.01450

Abstract

The rate of gas exchange in plants is regulated mainly by stomatal size and density. Generally, higher densities of smaller stomata are advantageous for gas exchange; however, it is unclear what the effect of an extraordinary change in stomatal size might have on a plant's gas-exchange capacity. We investigated the stomatal responses to CO2 concentration changes among 374 Arabidopsis (Arabidopsis thaliana) ecotypes and discovered that Mechtshausen (Me-0), a natural tetraploid ecotype, has significantly larger stomata and can achieve a high stomatal conductance. We surmised that the cause of the increased stomatal conductance is tetraploidization; however, the stomatal conductance of another tetraploid accession, tetraploid Columbia (Col), was not as high as that in Me-0. One difference between these two accessions was the size of their stomatal apertures. Analyses of abscisic acid sensitivity, ion balance, and gene expression profiles suggested that physiological or genetic factors restrict the stomatal opening in tetraploid Col but not in Me-0. Our results show that Me-0 overcomes the handicap of stomatal opening that is typical for tetraploids and achieves higher stomatal conductance compared with the closely related tetraploid Col on account of larger stomatal apertures. This study provides evidence for whether larger stomatal size in tetraploids of higher plants can improve stomatal conductance.

Highlights

The rate of gas exchange in plants is regulated mainly by stomatal size and density
We identified 1,777 probes as upregulated and 1,706 probes as down-regulated differentially expressed genes (DEGs) in Me-0 compared with tetraploid Col
This study identified Me-0 as a unique Arabidopsis ecotype having large stomata and a high gs

Summary

Introduction

The rate of gas exchange in plants is regulated mainly by stomatal size and density. Generally, higher densities of smaller stomata are advantageous for gas exchange; it is unclear what the effect of an extraordinary change in stomatal size might have on a plant’s gas-exchange capacity. Given a constant total stomatal pore area, large stomata are generally disadvantageous for gas exchange compared with smaller stomata, because the greater pore depth in larger stomata increases the distance that gas molecules diffuse through. This increased distance is inversely proportional to gsmax (Franks and Beerling, 2009). In addition to the negative effects of large stomata on gas exchange (Franks et al, 2009), polyploids may have another disadvantage; del Pozo and Ramirez-Parra (2014) showed that artificially induced tetraploids of Arabidopsis have a reduced stomatal density (stomatal number per unit of leaf area) and a lower stomatal index (stomatal number per epidermal cell number). An increase in the ploidy level of Festuca arundinacea results in an increase in the CO2-exchange rate (Byrne et al, 1981); polyploids may not necessarily have a reduced gasexchange capacity

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Results

Conclusion