The Importance of Non-Diffusional Factors in Determining Photosynthesis of Two Contrasting Quinoa Ecotypes (Chenopodium quinoa Willd.) Subjected to Salinity Conditions.

José Delatorre-Herrera,Karina B Ruiz,Manuel Pinto

doi:10.3390/plants10050927

José Delatorre-Herrera, Karina B Ruiz + Show 1 more

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https://doi.org/10.3390/plants10050927

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Abstract

The broad distribution of quinoa in saline and non-saline environments is reflected in variations in the photosynthesis-associated mechanisms of different ecotypes. The aim of this study was to characterize the photosynthetic response to high salinity (0.4 M NaCl) of two contrasting Chilean genotypes, Amarilla (salt-tolerant, salares ecotype) and Hueque (salt-sensitive, coastal ecotype). Our results show that saline stress induced a significant decrease in the K+/Na+ ratio in roots and an increase in glycine betaine in leaves, particularly in the sensitive genotype (Hueque). Measurement of the photosynthesis-related parameters showed that maximum CO2 assimilation (Amax) in control plants was comparable between genotypes (ca. 9–10 μmol CO2 m−2 s−1). However, salt treatment produced different responses, with Amax values decreasing by 65.1% in the sensitive ecotype and 37.7% in the tolerant one. Although both genotypes maintained mesophyll conductance when stomatal restrictions were removed, the biochemical components of Amarilla were impaired to a lesser extent under salt stress conditions: for example, the maximum rate of ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO; Vcmax) was not as affected in Amarilla, revealing that this enzyme has a higher affinity for its substrate in this genotype and, thus, a better carboxylation efficiency. The present results show that the higher salinity tolerance of Amarilla was also due to its ability to control non-diffusional components, indicating its superior photosynthetic capacity compared to Hueque, particularly under salt stress conditions.

Highlights

At present, about one-third of the world’s irrigated land [1] is affected by salinity, which reduces plant growth and crop yield [2]
When comparing the control plants of the two ecotypes, Hueque had a higher concentration of Glycine Betaine (GB) in the roots
The leaf/root ratio of GB content in Amarilla control plants was 3.64, while in stressed plants, it rose slightly to 4.34, which could indicate that this ecotype is not severely stressed by high salinity

Summary

Introduction

About one-third of the world’s irrigated land [1] is affected by salinity, which reduces plant growth and crop yield [2]. The salinity of soils is predominantly caused by salt transported by irrigation water [4]. An increase in the soil concentration of Na+ and other ions, such as Ca2+, Cl−, and K+, causes a decrease in the soil water potential, which limits the water absorbed by roots and induces water stress [8]. The accumulation of injurious ions may inhibit photosynthesis and protein synthesis, inactivate enzymes, and damage chloroplasts and other organelles [9]. Overaccumulation of Na+ in the cytosol inhibits protein synthesis, enzyme activity [1], and many photosynthetic processes [11,12]. Maintaining its water supply and excluding Na+ from photosynthetic organs are crucial mechanisms used by tolerant plants to ensure an adequate rate of carbon fixation under salt stress [13]. It is well known that a reduction in stomatal conductance negatively affects the CO2 assimilation rate as well as the water balance in leaves [3,14]

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