Salt Responses of Enzymes from Species Differing in Salt Tolerance

Abstract

Enzymes which are affected by the addition of inorganic salts during in vitro assay were extracted from salt-sensitive Phaseolus vulgaris, salt-tolerant Atriplex spongiosa, and Salicornia australis and tested for sensitivity to NaCl. In each case malate dehydrogenase, aspartate transaminase, glucose 6-phosphate dehydrogenase, and isocitrate dehydrogenase showed NaCl responses similar to those found for commercially available crystalline enzymes from other organisms. Enzymes extracted from plants grown in saline cultures showed no important changes in specific activity or salt sensitivity. Interaction of pH optima and NaCl concentrations suggests that enzymes may differ in the way they respond to salt treatment.

Salinity-Induced Effects in the Halophyte Suaeda salsa Using NMR-based Metabolomics

“…Betaine can be biosynthesized by cells for the protection against osmotic stresses, such as drought, high salinity, and high temperature in biological systems including both plants and animals (especially marine invertebrates; Moghaieb et al 2004;Zhang et al 2011a, b;Liu et al 2011c, d, e). The pathway of betaine biosynthesis in S. salsa is straightforward: choline monooxygenase (CMO) converts choline to betaine aldehyde that can then be converted to betaine by betaine aldehyde dehydrogenase (BADH; Lee et al 2004;Peel et al 2010;Greenway and Osmond 1972;Bao et al 2011). As an alkaloid, betaine is a key secondary metabolite involved in osmotic balance in halophyte (Peel et al 2010;Greenway and Osmond 1972).…”

Sodium as nutrient and toxicant

“…Less of an extreme gradient was found by Carden et al (2003) in barley seedlings exposed to 200 mM NaCl, but here too the cytosolic Na + activity value was low, maximally, 29 mM. Interestingly, these are levels at which little enzyme inhibition occurs (Greenway and Osmond 1972;Munns and Tester 2008), so mechanisms of Na + -specific toxicity may need to be sought elsewhere. Of additional importance is the conundrum that these low values, relative to CATE and other methods, suggest that either unidirectional Na + fluxes reported across the membrane using tracers (Britto and Kronzucker 2009), or exchange half-times for cytosolic Na + pools (Essah et al 2003), have been substantially overestimated.…”

“…For other, nonosmotic functions of K + , replacement by Na + may, however, not be as easily achieved. From the perspective of biochemical functions, such as in the cytoplasm, poorly characterized as it remains (Cheeseman 2013), there is believed to be a rather strict requirement for K + , and a strong maintenance of its concentration ; indeed, K + is considered essential for protein synthesis (Hall and Flowers 1973;Wyn Jones et al 1979) and oxidative phosphorylation (Flowers 1974), both of which are equally inhibited by Na + in glycophytes and halophytes (Greenway and Osmond 1972). More generally, K + is considered essential for the functioning of 50-60 enzymes (Leigh and Wyn-Jones 1986).…”

Toxicological effects of environmentally relevant lead and zinc in halophyte Suaeda salsa by NMR-based metabolomics

“…(For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) (BADH) (Greenway and Osmond, 1972). In this work, the decrease of choline meant the promotion of betaine synthesis which was confirmed by the elevation of betaine in the above-ground part of S. salsa seedlings.…”