Abstract
In order to understand the mechanisms underlying acquisition of tolerance to salinity, we recently produced callus tissues of tobacco and Medicago truncatula resistant to NaCl-induced salt stress following application of a step-up recurrent selection method. The effects of salinity on cell size are known, but those on cell morphometry including cell and nuclear surface area and position of nuclei within salt stress resistant cells were never studied before. This work fills that gap, using suspension cultured cells of M. truncatula A17 initiated from callus, and Nicotiana tabacum BY-2 cell line resistant to increasing NaCl concentrations up to 150 mM NaCl. The surface area of salinity resistant cells of M. truncatula A17 and N. tabacum BY2 and their nuclei, produced by step-up recurrent selection, were reduced, and cells elongated as NaCl increased, but these parameters proved to be unreliable in explaining cell survival and growth at high NaCl. Conversely, nuclei of resistant cells migrated from the center to the periphery of the cytoplasm close to the walls. Nuclear marginalization was for the first time observed as a result of salt stress in plant cells, and could be a novel helpful morphological marker of acquisition of salinity tolerance.
Highlights
Increased soil salinity is a world-wide problem, there is a need to develop more salinityresistant crop cultivars (Ochatt, 2015)
In vitro selection for salt tolerance has focused on cellular (Davenport et al, 2003) and genetic (Elmaghrabi et al, 2013) mechanisms involved in salt tolerance using selected NaCl-tolerant cell lines, while gene transfer has been successfully exploited very recently to generate salt (Confalonieri et al, 2019) and water stress (Confalonieri et al, 2014; Alcântara et al, 2015; Duque et al, 2016) tolerance in M. truncatula
In M. truncatula cell suspensions, the initial trend was an increase in cell and nuclear area following 60 days exposure to 50 mM NaCl these increases were not significant (P > 0.05)
Summary
Increased soil salinity is a world-wide problem, there is a need to develop more salinityresistant crop cultivars (Ochatt, 2015). In vitro selection for salt tolerance has focused on cellular (Davenport et al, 2003) and genetic (Elmaghrabi et al, 2013) mechanisms involved in salt tolerance using selected NaCl-tolerant cell lines, while gene transfer has been successfully exploited very recently to generate salt (Confalonieri et al, 2019) and water stress (Confalonieri et al, 2014; Alcântara et al, 2015; Duque et al, 2016) tolerance in M. truncatula. In a recent review, Gundersen and Worman (2013) examined the sparse knowledge and understanding of the reasons and effects of cell movement and of the position of their nuclei within the cytoplasm.
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