Characterization of a Salt-Responsive 24-Kilodalton Glycoprotein in Mesembryanthemum crystallinum

Abstract

A concanavalin A (Con A)-binding polypeptide with a molecular mass of 24 k D (termed "SRgp24") was associated with the intercellular space of Mesembryanthemum crystallinum 1. callus. When callus was grown in medium containing between O and 100 mM NaCI, SRgp24 was deteded by Con A binding. lncreasing the NaCl concentration to 200 mM caused a reduction in the amount of SRgp24 within 3 d, and returning the callus to medium without salt resulted in an accumulation of SRgp24. lmmunoblot analysis showed that appreciable amounts of SRgp24 accumulated in the leaves when plants were grown under sodium-limiting conditions. Unlike most of the cell-wall Con A-binding proteins in M. crystallinum callus, the carbohydrate moiety of SRgp24 was resistant to endoglycosidase H digestion. After purification of SRgp24, the N terminus was sequenced and found to share 55 to 60% identity with the N terminus of osmotin, a group 5 pathogenesis-related protein (PR-5) that accumulates in salt-adapted tobacco cell suspension. lmmunocytochemical assays, with affinity-purified antibodies to SRgp24, indicated that SRgp24 preferentially accumulated in the cell-wall region. We conclude that SRgp24 is a salt-responsive glycoprotein related to the PR-5 family in M. crystallinum.CAM plants are well-adapted to arid habitats because of their ability to conserve water and to sustain COz fixation through periods of drought stress. Mesembryanfhemum crystallinum L., the common ice plant, is a halophyte with the capacity to induce CAM when water stressed (Winter, 1985; Bohnert et al., 1988). It is able to survive both drought and salt stress through unique stress-tolerance mechanisms. ABA also appears to have a role in regulating CAM induction, although its mechanism is not yet understood (Chu et al., 1990;McElwain et al., 1992).When M. crystallinum is exposed to high extemal salt, Pro (Heun et al., 1981) and pinitol (Paul and Cockbum, 1989) accumulate in the cytoplasm where they function as compatible solutes. Apparently this allows a physiological range of Na ions to be maintained in the cytosol while compartmentalizing excess NaCl in the vacuole or intercellular space. Preferential exclusion of Na+ from the cytosol requires transport across the plasma membrane or tonoplast. Because M. crystallinum adapts to drought stress and is a halophyte, it serves as a model system to study the mechanisms of plant adaptation to salt and water stress (Cushman et al., 1990). A major limitation of this system, however, is that both CAM and osmotic adjustment are induced concurrently after exposure of plants to high salt concentrations. The nature of these different adaptive mechanisms could be probed more efficiently if only one set of adaptive mechanisms were induced.A cell culture initiated from hypocotyls of M. crystallinum provides an amendatory approach to this problem. We found that Pro levels increased more than 13-fold when light-grown callus was transferred to 200 mM NaCl, whereas the activity of phosphoenolpyruvate carboxylase, the key enzyme for performi...

Antimicrobial Activity of Malting Barley Grain Thaumatin-Like Protein Isoforms, S and R

“…We have reported previously that malting barley TLPs isoforms are glycosylated with different sugar content, TLP-S being two fold higher and with the ability to bind concanavalin A 8 . It is worthy to note that the number of newly recognized glycoproteins among the TLPs family is growing 13,16,18,19,23,26,37 . We have demonstrated TLP-S has higher antifungal and antibacterial activity than TLP-R, regarding the IC 50 value.…”

Partial nitrate nutrition amends photosynthetic characteristics in rice (Oryza sativa L. var. japonica) differing in nitrogen use efficiency

“…N assimilation is a very important sink for redox equivalents from the photosynthetic electron flow (Raab and Terry 1994;Lasa et al 2002;Guo et al 2007c). Therefore, PNN may affect simultaneous CO 2 assimilation by influencing N assimilation.…”

“…than under NO 3 -in sugar beet, French bean and high-bush blueberry (Raab and Terry 1994;Claussen and Lenz 1999;Guo et al 2005); however, no marked differences have been observed in raspberry and strawberry (Claussen and Lenz 1999). Such contradictory observations might have occurred due to differences in plant species used or to variations in environmental conditions employed (Raab and Terry 1994;Guo et al 2007c).…”

“…Many plant species show growth depressions when NH 4 ? is supplied as the sole N-form (Feil 1994;Raab and Terry 1994;Claussen and Lenz 1999). The response to NH 4 ?…”

“…has a negative effect on leaf expansion as compared to those that received NO 3 -only (Walch-Liu et al 2000). In the presence of NO 3 -, higher ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) amount and activity, chlorophyll content and consequently higher photosynthetic capacity on the leaf area basis were reported (Raab and Terry 1994;Guo et al 2002Guo et al , 2005. CO 2 assimilation rate (A) based on leaf area is higher under NH 4…”