Plant Responses to the Environment

This Special Focus Issue (Vol. 57, Issue 4) of Plant and Cell Physiology is co-organised and guest edited by Gwyneth Ingram and Toru Fujiwara, and showcases some of the current research by French and Japanese laboratories into understanding how plants are able to respond in a variety of ways to environmental stresses, such as temperature, salinity and metal ions.

Editorial: Special Focus Issue on Plant Responses to the Environment
Gwyneth Ingram and Toru Fujiwara
In this special focus issue, Ingram and Fujiwara discuss the 4 featured reviews and 6 research articles that elegantly illustrate how plants, despite their sessile nature, can effectively handle abiotic environmental stresses thanks to a wide range of diverse physiological and genetic /epigenetic mechanisms. Most of the articles contributed here form part of a Japan-France network established to promote the exchange and collaboration of plant scientists between both countries.

Staying Alive: Molecular Aspects of Seed Longevity
Naoto Sano, Loïc Rajjou, Helen M. North, Isabelle Debeaujon, Annie Marion-Poll and Mitsunori Seo
Seed longevity, the period over which seed remains viable, is an important trait not only for plant survival under changing environments but also for agriculture. This review summarizes the molecular bases for seed longevity by mainly focusing on four aspects: protection, repair, hormonal/developmental regulation in relation to dormancy, and maternal effects. Understanding these mechanisms will contribute to the improvement of seed quality and hence to the efficient production of crops in future.

Asparagine Metabolic Pathways in Arabidopsis
Laure Gaufichon, Steven J Rothstein and Akira Suzuki
In this review, we describe the current information on asparagine metabolic pathways that are involved in physiologically important processes in plants. The structure of genes and their expression profiles in response to biological signals are assessed with regards to the regulation of the encoded enzymes involved in asparagine synthesis and the utilisation of amide- and amino-nitrogen from asparagine. These data sets underline the important interactions between asparagine and carbon metabolism in different tissues and at different developmental stages.

Performance and Limitations of Phosphate Quantification: Guidelines for Plant Biologists
*FREE: Editor-in-Chief's Choice Article*
Satomi Kanno, Laura Cuyas, Hélène Javot, Richard Bligny, Elisabeth Gout, Thibault Dartevelle, Mohamed Hanchi, Tomoko M. Nakanishi, Marie-Christine Thibaud and Laurent Nussaume
Phosphate (Pi) is an essential plant macronutrient and its cellular homeostasis is a highly regulated and complex process that has yet to be fully elucidated. Recent advances in molecular-genetic, biochemical and physiological methodologies, as well as imaging technologies, have aided our understanding of the dynamics of Pi uptake, its inter- and intra-cellular movement, and effects on gene expression in plants. This review discusses the potential uses and limitations of the current methods for tracing and quantifying Pi in plants and the future outlook for Pi research.

Plant Nitrogen Acquisition Under Low Availability: Regulation of Uptake and Root Architecture
*FREE: Open Access Article*
Takatoshi Kiba and Anne Krapp
Nitrogen nutrients are important for plant growth and productivity, however they are scarce in natural soils. To adapt to such challenging conditions plants have optimized ways to efficiently acquire nitrogen under low nitrogen availability. This review provides an update on the molecular determinants of nitrogen acquisition efficiency, such as uptake activity and root architecture with special reference to the regulation of these determinants by nitrogen supply at both the transcriptional and post-transcriptional level.

Highly Sprouting Tolerant Wheat Grain Exhibits Extreme Dormancy and Cold Imbibition Resistant Accumulation of Abscisic Acid
Yu-ichi Kashiwakura, Daisuke Kobayashi, Yusuke Jikumaru, Yumiko Takebayashi, Eiji Nambara, Mitsunori Seo, Yuji Kamiya, Tetsuo Kushiro and Naoto Kawakami
Low temperatures during seed imbibition break dormancy in many plant species, but the mechanism underlying this process has not been clarified. Here, pre-harvest sprouting wheat varieties were studied for dormancy breakage and maintenance. The results indicate that low temperatures induce expression of ABA catabolism genes and decrease ABA levels in dormant embryos, while in extremely dormant lines ABA biosynthesis genes are induced and ABA catabolism genes suppressed. Thus the regulation of ABA metabolism genes may be critical for dormancy maintenance and breakage at low temperatures.

Dual Regulation of Root Hydraulic Conductivity and Plasma Membrane Aquaporins by Plant Nitrate Accumulation and High-Affinity Nitrate Transporter NRT2.1
Guowei Li, Pascal Tillard, Alain Gojon and Christophe Maurel
This study addresses the profound interplay that exists between external nitrate availability and water absorption by plant roots. A reverse genetic approach in Arabidopsis revealed that nitrate signaling, rather than nitrogen assimilation products, and the high affinity nitrate transporter, NRT2.1, govern the root water transport capacity. The molecular mechanisms underlying this new mode of regulation are yet to be fully elucidated, but involve aquaporins.

Visualization of Mineral Elements Uptake and the Dynamics of Photosynthates in Arabidopsis by a Newly Developed Real-Time Radioisotope Imaging System (RRIS)
*FREE: Open Access Article*
Ryohei Sugita, Natsuko I Kobayashi, Atsushi Hirose, Takayuki Saito, Ren Iwata, Keitaro Tanoi, and Tomoko M Nakanishi
The variety of tools available for the non-destructive analysis of nutrient transport in living plants is currently limited. Here, the long-distance transport modes of 8 ions and photosynthetically fixed carbon were visualized over a 24 hour period in Arabidopsis thaliana using a newly developed real-time radioisotope imaging system (RRIS). The results revealed several characteristic transport properties including the occurrence of ion-specific transport systems along the inflorescence, and the switching of source/sink organs during the development of lateral stems. Thus, radiotracer experiments coupled with RRIS can be considered a powerful and effective tool to investigate long-distance transport systems in plants, which is central to many physiological phenomena including growth regulation and stress response.

The Arabidopsis Mg Transporter, MRS2-4, is Essential for Mg Homeostasis Under Both Low- and High-Mg Conditions
Koshiro Oda, Takehiro Kamiya, Yusuke Shikanai, Shuji Shigenobu, Katsushi Yamaguchi and Toru Fujiwara
Mg is a macronutrient required for a number of enzymatic reactions and it is also a component of chlorophyll, which makes its homeostasis important. In this paper, Oda et al. identified an ER-localized Mg transporter, MRS2-4, through the screening for mutants sensitive to low Mg conditions. The mutant also showed growth defects under high Mg conditions, indicating that MRS2-4 is essential for the adaptation to both low and high Mg levels.

Characterization of the Chloride Channel-like, AtCLCg , Involved in Chloride Tolerance in Arabidopsis thaliana
Chi Tam Nguyen, Astrid Agorio, Mathieu Jossier, Sylvain Depre?, Se?bastien Thomine and Sophie Filleur
The compartmentalization of toxic ions into vacuoles is a tolerance strategy for plants in response to NaCl stress. Here we show in Arabidopsis that AtCLCg , which is part of the CLC channel/exchanger family, has a role in cytosolic Cl- homeostasis as previously shown for AtCLCc . Interestingly, although these two proteins are not redundant, the expression of AtCLCg and AtCLCc are mutually dependent. Collectively, these findings highlight a complex network underlying compartmentalization of Cl-.

Ky-2, a Histone Deacetylase Inhibitor, Enhances High-Salinity Stress Tolerance in Arabidopsis thaliana
Kaori Sako, Jong-Myong Kim, Akihiro Matsui, Kotaro Nakamura, Maho Tanaka, Makoto Kobayashi, Kazuki Saito, Norikazu Nishino, Miyako Kusano, Teruaki Taji, Minoru Yoshida, and Motoaki Seki
Chromatin regulation is essential for plants to adapt to environmental changes by regulating genes and genome activities. In this work, the histone deacetylase inhibitor Ky-2 strengthens salinity stress tolerance caused by increasing transcription of AtSOS1 , which encodes a Na+/H+ antiporter, and enhancing SOS1-dependent Na+ efflux. This finding opens up the possibility of developing a spray that would induce resistance to salinity stress and increase crop yields on farmlands prone to salt damage.