Responses of amino acid metabolizing enzymes from plants differing in salt tolerance to NaCl

Abstract

This paper reports the effects of NaCl on the in vivo activity of glutamate dehydrogenase (GDH) and glutamic-oxaloacetic transaminase (GOT) and on the in vitro activity of GDH, both enzymes having been isolated from plants differing in salt tolerance. The plants investigated were Vicia faba (salt-sensitive), Atriplex nitens and Atriplex calotheca (more or less salt-tolerant), and Atriplex halimus (halophyte) grown at various NaCl concentrations. GDH and GOT isolated from various salt-tolerant plants grown at low NaCl concentrations were inhibited in a similar way. At high NaCl concentrations, the enzyme activities remain at constant values only in the Atriplex species. GOT was more impaired by NaCl than GDH. In the case of GOT, the double reciprocal plot indicated the type of a noncompetitive inhibition. The in vitro effect of NaCl on the activity of GDH from the differentially salt-tolerant plants was of a different kind, i.e. GDH isolated from V. faba was clearly inhibited by NaCl, whereas NaCl stimulated the activity of GDH from all Atriplex species investigated. Kinetic analysis showed that substrate inhibition of GDH from A. nitens and A. calotheca grown at non-saline conditions could be removed by NaCl. Inhibition by high NaCl concentrations at low substrate concentrations was removable by increasing substrate concentrations. Moreover, the inhibition at low substrate concentrations was shown to be competitive. GDH lost this regulatory property when the plants were pretreated with 500 mM NaCl. GDH from A. halimus also possessed this control, but in contrast to A. nitens and A. calotheca, activity and control of GDH isolated from A. halimus were stimulated by pretreating the plants with 500 mM NaCl. The results showed that DDH isolated from the salt-tolerant Atriplex species was adapted to high NaCl concentrations of the tissue. Possible mechanisms of the interactions between GDH from salt-tolerant Atriplex species and NaCl are discussed.

Differences in salt tolerance of three sugar beet genotypes

“…However, this idea has been questioned recently (Flowers et al 1977). Under certain conditions in-vitro enzymes from salt tolerant species like Beta vulgaris (Kylin and Hansson 197L Flowers 1972b) or certain Atriplex species (Priebe and Jager 1978) can be stimulated by quite high NaCl concentrations.…”

The tolerance of Atriplex halimus L. to environmental stresses

“…Boughalleb et al (2009) related enhanced growth to improvements in stomatal conductance, transpiration and CO 2 assimilation at moderate external NaCl levels (< 300 mM); Khedr et al (2011) suggested that vacuolar Na + accumulation increases cell volume and the photoassimilatory surface area of the leaves, stimulating growth. Results indicating an adaptation of A. halimus glutamate dehydrogenase (EC 1.4.1.2) to high tissue NaCl levels were presented by Priebe and Jäger (1978). Sadder et al (2013) demonstrated that salt-exposed plants had increased expression of specific genes: those controlling the synthesis of acetohydroxy acid reductoisomerase (EC 1.1.1.86), early-responsive dehydration stress-related proteins and ER-lumenal protein.…”

Adaptations of Plants to Flooding with Salt Water

“…In addition to growth inhibition, salinity also induces symptoms of injury in salt-sensitive species. Atriplex halimus is more salt tolerant than A. calatheca, which in turn is more salt tolerant than A. nitens (Priebe and Jäger, 1978). In the middle of the continuum there is some degree of overlap in the salt tolerance of species normally regarded as halophytic (e.g., Puccinelliapeisonis) and those normally considered glycophytic (e.g., barley) (Greenway and Munns, 1980).…”