Selection of a mutation conferring high NaCl tolerance to gametophytes of Ceratopteris

Abstract

Spores from a weakly salt tolerant strain of Ceratopteris richardii containing the mutation stl1 were irradiated and sown on nutrient medium supplemented with 200 mM NaCl. A single highly salt tolerant gametophyte was recovered and selfed to generate a homozygous sporophyte. Spores from this strain, 10α23, were used to document the sexual transmission of the trait and to monitor the inheritance of tolerance in crosses to both the wild type and to the parental salt tolerant strain. Genetic analysis showed the 10α23 strain to possess both the original stl1 mutation and an additional semi-dominant nuclear mutation, stl2, that individually conferred a high level of tolerance to gametophytes. In combination, both mutations had additive effects. Tolerance was also evident in sporophytes, but at a lower level than in gametophytes.

The Analysis of Genetically and Physiologically Complex Traits Using Ceratopteris: A Case Study of NaCl-Tolerant Mutants

“…Precordate gametophytes from each strain were transferred to control medium (3.7 mM K+ ), to medium supplemented with 200 mM NaCl, and to medium without added K+, i.e., trace K+. All strains examined exhibit co-segregation of stl2-type salt tolerance (Hickok et al 1991) and K+ sensitivity (Vogelien et al 1995). These data along with the genetic origin of the mutation in a completely homozygous line and subsequent genetic analyses lend further support for a single gene basis for the salt-tolerant phenotype and corresponding ion transport phenomena.…”

“…Segregation tests subsequently showed that 10a23 carried two unlinked mutations, stll and stl2 ( fig. 1; Hickok et al 1991). The new mutation, stl2, exhibited partial additivity with stll and independently conferred tolerance up to 275 mM NaCl.…”

“…In addition, once they are defined genetically, we refer to such strains merely I50 is the approximate concentration (mM) that gives 50% inhibition of gametophytic growth. Values were obtained from dose response curves in Hickok et al (1991), Vogelien (1993), and Vogelien et al (1995).…”

“…stl2 confers a high level of tolerance not only to Na+ (NaCl, Na2SO4) but also to Mg2+ salts (MgCl2, MgSO4) (table 1; Hickok et al 1991;Vogelien 1993;Vogelien et al 1995). Tolerance to mannitol was equivalent to stll, and higher tolerance than either wildtype or stll was evident with melibiose (table 1).…”

“…These efflux mechanisms ultimately utilize ATP either directly or indirectly by the action of a H+ -ATPase and result in ATP consumption that is reflected in growth sensitivity to K+. Alleviation of this sensitivity occurs when the external K+ concentration is reduced to near trace levels or by the addition of small amounts of other cations, such as Na+ (Hickok et al 1991). In this case, Na+ may interfere with high-velocity K+ influx and reduce it to levels more comparable with the wildtype.…”