Differential Role for Trehalose Metabolism in Salt-Stressed Maize

Abstract

Little is known about how salt impacts primary metabolic pathways of C 4 plants, particularly related to kernel development and seed set. Osmotic stress was applied to maize (Zea mays) B73 by irrigation with increasing concentrations of NaCl from the initiation of floral organs until 3 d after pollination. At silking, photosynthesis was reduced to only 2% of control plants. Salt treatment was found to reduce spikelet growth, silk growth, and kernel set. Osmotic stress resulted in higher concentrations of sucrose (Suc) and hexose sugars in leaf, cob, and kernels at silking, pollination, and 3 d after pollination. Citric acid cycle intermediates were lower in salt-treated tissues, indicating that these sugars were unavailable for use in respiration. The sugar-signaling metabolite trehalose-6-phosphate was elevated in leaf, cob, and kernels at silking as a consequence of salt treatment but decreased thereafter even as Suc levels continued to rise. Interestingly, the transcripts of trehalose pathway genes were most affected by salt treatment in leaf tissue. On the other hand, transcripts of the SUCROSE NONFERMENTING-RELATED KINASE1 (SnRK1) marker genes were most affected in reproductive tissue. Overall, both source and sink strength are reduced by salt, and the data indicate that trehalose-6-phosphate and SnRK1 may have different roles in source and sink tissues. Kernel abortion resulting from osmotic stress is not from a lack of carbohydrate reserves but from the inability to utilize these energy reserves.

Is change in ovary carbon status a cause or a consequence of maize ovary abortion in water deficit during flowering?

“…The latter is involved in cell and tissue expansion in numerous studies (Morris and Arthur, 1984;Sturm and Tang, 1999;Tang et al, 1999;Kohorn et al, 2006;Wang et al, 2010;Ma et al, 2014). WD reduced expansive growth without altering the carbon status of ovaries and silks as measured on a fresh weight basis; in particular, it induced soluble sugar accumulation and starch synthesis in all reproductive organs, as did an osmotic stress due to salt (Henry et al, 2015). This is confirmed by results concerning the trehalose biosynthetic pathway in reproductive tissues of maize plants subjected to osmotic stress.…”

“…This is confirmed by results concerning the trehalose biosynthetic pathway in reproductive tissues of maize plants subjected to osmotic stress. Trehalose-6-phosphate (T6P) functions as a signaling intermediate for reporting the cellular Suc status (Lunn et al, 2006;Yadav et al, 2014), and its content is increased in maize ovaries during salt stress (Henry et al, 2015) and WD (Nuccio et al, 2015). The reduction of transcript abundance of TPP, the enzyme converting T6P to trehalose, observed in silks of WD1 plants in this study (Fig.…”

A Tale of Two Sugars: Trehalose 6-Phosphate and Sucrose

“…Salt tolerance in Arabidopsis is dependent on expression of AtTPPD, a redox-sensitive, chloroplastic isoform of TPP, suggesting that trehalose accumulation in chloroplasts could help to preserve their functionality under salt stress (Krasensky et al, 2014). In maize, salt stress induced changes in expression of several genes encoding enzymes and transporters involved in trehalose and Suc metabolism (Henry et al, 2015). The levels of many of the intermediates of sugar metabolism, glycolysis, and the tricarboxylic acid cycle were also affected, with a 2-to 4-fold increase in Tre6P levels in leaves, kernels, and cobs being observed at the silking stage.…”

“…shoot apices) than in source leaves . The ratio also varies with the developmental stage of sink organs, such as developing grape (Vitis vinifera) berries (Dai et al, 2013) and developing wheat and maize seeds (Martínez-Barajas et al, 2011;Henry et al, 2015). Environmental conditions can also affect the Tre6P:Suc ratio.…”

Identification and characterization of the BZR transcription factor family and its expression in response to abiotic stresses in Zea mays L.

“…Hypoxic stress conditions were achieved by not bubbling air through the liquid solution for the entire experiment. For salt stress, a 100 mM NaCl concentration, which corresponds to severe salt stress in maize (Farooq et al 2015;Henry et al 2015;Zörb et al 2015), was employed. Finally, an intense heat stress, generally greater than 4 °C above optimum that in the case of maize is 25 °C (Hatfield and Prueger 2015), was performed by growing seedlings in a day/night cycle at 35/30 °C air temperature.…”