Abstract
Epidermal fragments enriched in guard cells (GCs) were isolated from the halophyte quinoa (Chenopodium quinoa Wild.) species, and the response at the proteome level was studied after salinity treatment of 300 mM NaCl for 3 weeks. In total, 2147 proteins were identified, of which 36% were differentially expressed in response to salinity stress in GCs. Up and downregulated proteins included signaling molecules, enzyme modulators, transcription factors and oxidoreductases. The most abundant proteins induced by salt treatment were desiccation-responsive protein 29B (50-fold), osmotin-like protein OSML13 (13-fold), polycystin-1, lipoxygenase, alpha-toxin, and triacylglycerol lipase (PLAT) domain-containing protein 3-like (eight-fold), and dehydrin early responsive to dehydration (ERD14) (eight-fold). Ten proteins related to the gene ontology term “response to ABA” were upregulated in quinoa GC; this included aspartic protease, phospholipase D and plastid-lipid-associated protein. Additionally, seven proteins in the sucrose–starch pathway were upregulated in the GC in response to salinity stress, and accumulation of tryptophan synthase and L-methionine synthase (enzymes involved in the amino acid biosynthesis) was observed. Exogenous application of sucrose and tryptophan, L-methionine resulted in reduction in stomatal aperture and conductance, which could be advantageous for plants under salt stress. Eight aspartic proteinase proteins were highly upregulated in GCs of quinoa, and exogenous application of pepstatin A (an inhibitor of aspartic proteinase) was accompanied by higher oxidative stress and extremely low stomatal aperture and conductance, suggesting a possible role of aspartic proteinase in mitigating oxidative stress induced by saline conditions.
Highlights
Photosynthesis, the most important biochemical reaction in the world, will not occur in plants unless carbon dioxide is allowed to enter the leaves through stomatal pores, the apertures of which are controlled by guard cell (GC) movements
Quinoa plants were treated with 300 mM NaCl for three weeks
Lower levels of catalase may be necessary in the guard cells in saline conditions as H2O2 functions as a signaling molecule in the guard cell and induces saline conditions as functions as a signaling molecule in the guard cell and induces stomatal closure in response to high salinity stress
Summary
Photosynthesis, the most important biochemical reaction in the world, will not occur in plants unless carbon dioxide is allowed to enter the leaves through stomatal pores, the apertures of which are controlled by guard cell (GC) movements. The stomatal pore area may be only as much as 1% of total leaf surface, but diffusion rates from the leaf could be 95% as much evaporation as from the stomata [1]. Massive amounts of water and CO2 are passing through stomata of plant leaves each year [2], and changes in stomatal aperture in response to environmental factors impact on the flux of both carbon dioxide and water at a global level [3]. Salinity stress is one of the most detrimental environmental stresses that affects water balance through stomatal conductance. Salinity affects 20% of arable land [4]
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