Influence of NaCl on Growth, Proline, and Phosphoenolpyruvate Carboxylase Levels in Mesembryanthemum crystallinum Suspension Cultures

Abstract

The facultative halophyte Mesembryanthemum crystallinum responds to salt stress by increasing the levels of phosphoenolpyruvate carboxylase (PEPCase) and other enzymes associated with Crassulacean acid metabolism. A more common response to salt stress in sensitive and tolerant species, including M. crystallinum, is the accumulation of proline. We have established M. crystallinum suspension cultures to investigate whether both these salt-induced responses occur at the cellular level. Leafand root-derived cultures maintain 5% of the total soluble amino acids as proline. Cell culture growth slows upon addition of 400 millimolar NaCI, and proline levels increase to 40% of the total soluble amino acids. These results suggest a functional saltstress and response program in Mesembryanthemum cells. Suspension cultures grown with or without 400 millimolar NaCI have PEPCase levels that compare with those from roots and unstressed leaves. The predominant protein cross-reacting with an anti-PEPCase antibody corresponds to 105 kilodaltons (apparent molecular mass), whereas a second species of approximately 110 kilodaitons is present at low levels. In salt-stressed leaves, the 110 kilodalton protein is more prevalent. Levels of mRNA for both ppcl (salt stress induced in leaves) and ppc2 (constitutive) genes in sait-treated suspensions cultures are equal to unstressed leaves, and only twice the levels found in untreated suspension cultures. Whereas cells accumulate proline in response to NaCI, PEPCase protein amounts remain similar in salttreated and untreated cultures. The induction upon salt stress of the 110 kilodalton PEPCase protein and other Crassulacean acid metabolism enzymes in organized tissues is not observed in cell culture and may depend on tissue-dependent or photoautotrophydependent programs.

Pathways of ROS homeostasis regulation in Mesembryanthemum crystallinum L. calli exhibiting differences in rhizogenesis

“…Measurements of proline concentration (Table 2) confirmed the results of previous studies (Thomas et al 1992;Kuźniak et al 2011), suggesting that salinity stress corresponded with a high level of proline in the tissue of M. crystallinum L. M. crystallinum callus grown in the presence of NaCl also responded to salt treatment by way of high proline accumulation. Proline, induced by stress conditions (Kuznetsov and Shevyakova 1999), in addition to its function in the plant cell's response to environmental stresses, plays also an important role in regulating cell morphology and differentiation as well as developmental transitions (Hare et al 2001).…”

Growth and development of Mesembryanthemum crystallinum (Aizoaceae)

“…Salt stress of suspension-cultured (non-adapted) cells leads to slow growth, although the cells remain viable, and proline concentrations increase dramatically (Thomas, DeArmond & Bohnert, 1992 a). Such unadapted cells will, however, show no pinitol increases and, thus, these cells must be considered glycophytic ; hence M. crystallinum is a halophyte only when organized tissues are present.…”

Exogenous application of mannitol and thiourea regulates plant growth and oxidative stress responses in salt-stressed maize (Zea maysL.)

“…However, different types of plants show different responses to these salt-induced injurious effects (Ashraf & Foolad 2007;Ashraf 2009). One of the premier responses of plants to salinity is the synthesis and accumulation of compatible organic substances including amino acids, especially proline (Thomas et al 1992;Ashraf & Foolad 2007;Ashrafijou et al 2010), quaternary ammonium compounds (Ashraf & Foolad 2007;Geng et al 2011), organic acids (Chen et al 2009;Farouk 2011), and polyols such as sorbitol and mannitol (Stoop et al 1996;Mitoi et al 2009). All these osmotically active organic solutes play a key role in osmotic adjustment, a phenomenon which has been widely reported to play an active role in maintaining cell turgor (Galinski 1995;Siringam et al 2011).…”