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Review
. 2017 Jan;119(1):1-11.
doi: 10.1093/aob/mcw191. Epub 2016 Oct 5.

Evaluating physiological responses of plants to salinity stress

S Negrão  1 , S M Schmöckel  1 , M Tester  2
Affiliations
Review

Evaluating physiological responses of plants to salinity stress

S Negrão et al. Ann Bot. 2017 Jan.

Abstract

Background: Because soil salinity is a major abiotic constraint affecting crop yield, much research has been conducted to develop plants with improved salinity tolerance. Salinity stress impacts many aspects of a plant's physiology, making it difficult to study in toto Instead, it is more tractable to dissect the plant's response into traits that are hypothesized to be involved in the overall tolerance of the plant to salinity.

Scope and conclusions: We discuss how to quantify the impact of salinity on different traits, such as relative growth rate, water relations, transpiration, transpiration use efficiency, ionic relations, photosynthesis, senescence, yield and yield components. We also suggest some guidelines to assist with the selection of appropriate experimental systems, imposition of salinity stress, and obtaining and analysing relevant physiological data using appropriate indices. We illustrate how these indices can be used to identify relationships amongst the proposed traits to identify which traits are the most important contributors to salinity tolerance. Salinity tolerance is complex and involves many genes, but progress has been made in studying the mechanisms underlying a plant's response to salinity. Nevertheless, several previous studies on salinity tolerance could have benefited from improved experimental design. We hope that this paper will provide pertinent information to researchers on performing proficient assays and interpreting results from salinity tolerance experiments.

Keywords: Assessing salinity tolerance; analysing salinity data; osmotic stress; quantifying physiological traits; salt stress phenotyping; salt-imposition systems; tolerance indices.

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Figures

F<sc>ig</sc>. 1.
Fig. 1.
Salinity tolerance should be calculated by measuring the effects of salinity on plant growth during the time of stress imposition and not during the lifetime of the plant. Growth of two hypothetical genotypes is shown, before (T0 to T1) and after (T1 to T2) imposition of salinity stress. Genotype A grows faster than Genotype B under control conditions, but its growth is inhibited more by salinity. If growth were measured by biomass increase from T0 to T2, Genotype A would appear to be more salt tolerant. However, if growth were measured only from T1 to T2, then Genotype B would appear to be more salt tolerant.
F<sc>ig</sc>. 2.
Fig. 2.
Correlating the salt tolerance index (ST) with Na+ content. (A) A strong correlation is observed when plotting ST in relation to Na+ content in a number of genotypes of tetraploid wheat, indicating that the more tolerant genotypes accumulate less shoot Na+ (modified from Munns and James, 2003). (B) No correlation exists between ST and shoot Na+ content in 20 moderately stressed bread wheat varieties (modified from Genc et al., 2007). Although there is no obvious correlation, a decrease in Na+ content in shoots may still cause an increase in salinity tolerance, as indicated by the arrow. Note the different y-axes, because plants are different species of Triticum and were treated with different NaCl concentrations. Note also that values on the x-axes were obtained using different, although related, tissues. Genc et al. (2007) report a similar lack of correlation when using Na content of just the blade of leaf 3. (C) Data from A and B are plotted on the same axis. Figures used with permission of the publishers.
F<sc>ig</sc>. 3.
Fig. 3.
Correlation between salt tolerance index (ST) and the relative water fraction (RWF) in Arabidopsis thaliana ecotypes. Plants were grown in hydroponics for 4 weeks according to Conn et al. (2013), and subjected to 7 d of salt stress after increasing salinity to 125 mm NaCl over three increments separated by 12 h each. CaCl2 was added to the medium to maintain constant Ca2+ activity. Unpublished data of Dr David E. Jarvis.
F<sc>ig</sc>. 4.
Fig. 4.
Example of the use of principal component analysis (PCA) to assess the importance of traits contributing to salinity tolerance. The example traits used here are relative root mass ratio (RRMR), shoot dry mass (SDM), harvest index (HI), days to flowering (DF) and shoot Na+ content.
See this image and copyright information in PMC

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