Patterns of pinitol accumulation in soybean plants and relationships to drought tolerance

Abstract

Previous studies indicate that methylated cyclitols are potentially important osmolytes in plants. In a search for genetic diversity for pinitol (D‐3‐O‐methyl‐chiro‐inositol) accumulation in soybean (Glycine max (L.) Merr.), two‐ to three‐fold differences in pinitol accumulation in leaf blades were found among Chinese plant introductions. Furthermore, it was found that genotypes that accumulated high concentrations of pinitol, when grown under well‐watered conditions, had been selected for performance in regions of China having low rainfall. Among the carbohydrates analysed, pinitol accumulation was uniquely associated with adaptation to dry areas of China. A detailed study of pinitol accumulation in the soybean plant showed two‐ to three‐fold gradients in pinitol concentration from the bottom to the top of the plant. The gradient shifted during plant development, with consistently higher concentrations of pinitol in the uppermost leaves. Pinitol accumulation was not correlated with activity of the key biosynthetic enzyme, inositol methyl transferase. This result and other lines of evidence indicated that shifting patterns of pinitol accumulation were due to translocation of the cyclitol from lower to upper nodes. Pinitol, proline, and sugars accumulated in leaf blades on soybean plants subjected to drought, but the molar concentration of pinitol in stressed plants was greater than the concentrations of proline or sugars. Although the mechanism by which pinitol participates in drought tolerance is not fully known, our results provide additional correlative evidence linking pinitol and drought tolerance in soybean.

Soluble Carbohydrates in Soybean

“…The free cyclitols myo-inositol, D-ononitol, D-pinitol, and D-chiro-inositol (Fig. 11) are present in soybean leaves (Streeter, 2001;Streeter et al, 2001). D-Ononitol is an intermediate in the conversion of myo-inositol to D-pinitol in leaves of legumes (Dittrich & Brandl, 1987).…”

“…11), cell wall components, membrane components and phytic acid (Loewus & Murthy, 2000;Raboy, 2009). D-Pinitol is synthesised in leaves (Dittrich & Brandl, 1987;Streeter, 2001;Streeter et al, 2001), transported to seeds, and unloaded by soybean seed coats into the apoplastic space surrounding immature embryos (Figs. 11 & 12;Gomes et al, 2005;Kosina et al, 2009Kosina et al, & 2010.…”

Arabidopsis INOSITOL TRANSPORTER2 Mediates H+ Symport of Different Inositol Epimers and Derivatives across the Plasma Membrane

“…Moreover, monomethylated inositols are found in all plants but are especially common in legumes. In leaves of unstressed soybean (Glycine max), for example, concentrations of pinitol (3-O-methyl-chiroinositol) can be 2-fold higher than the combined concentrations of Suc, all monosaccharides, and myoinositol (Smith and Phillips, 1982;Streeter et al, 2001). This already high concentration is further increased in droughtstressed plants, underlining the important role of unmethylated and methylated inositols as osmoprotectants (Thomas and Bohnert, 1993;Sheveleva et al, 1997;Nelson et al, 1998;Hasegawa et al, 2000;Streeter et al, 2001;Murakeö zy et al, 2003).…”

Nitrogen fixation is synchronized with carbon metabolism inLotus japonicusandMedicago truncatulanodules under salt stress

“…This sugar accumulation may be due to the substantial decline in sucrose synthase activity, which controls the flux of carbon and energy for the bacteroids (Arrese-Igor et al 1999), leading to the decrease in nitrogen fixation. A strong correlation between sugar accumulation and osmotic stress tolerance has been widely reported (Gilmour et al 2000;Streeter et al 2001;Taji et al 2002), which support a higher tolerance of L. japonicus nodules to salt stress. M. truncatula nodules did not show nodule carbohydrate accumulation; however, amino acids accumulated in these nodules by NaCl, which could be explained as a consequence of damage produced by saline stress, in accordance with results of Gordon et al (1997), Soussi et al (1998) and Khadri et al (2007) in nodules of soybean, chickpea and common bean, respectively.…”

“…It has been argued that the accumulation of sucrose under salinity, associated with inhibition of the sucrose hydrolytic enzyme sucrose synthase (Arrese-Igor et al 1999), induces a deficiency of carbon for bacteroids with the subsequent inhibition of nitrogenase activity (Hunt and Layzell 1993). A strong correlation between sugar accumulation and osmotic stress tolerance has been widely reported, including transgenic experiments (Gilmour et al 2000;Streeter et al 2001;Taji et al 2002).…”