Accumulation of Chiro-inositol and Other Non-structural Carbohydrates in Limonium Species in Response to Saline Irrigation Waters

Abstract

Two statice cultivars, Limonium perezii cv. Blue Seas and L. sinuatum cv. American Beauty, were grown in greenhouse sand tanks to determine the effect of salt stress on carbohydrate accumulation and partitioning. For the first experiment, irrigation waters were prepared to simulate typical saline-sodic drainage effluent in the San Joaquin Valley of California with electrical conductivities of 2.5, 7, 11, 15, 20, 25, and 30 dS·m−1. A second experiment compared responses to two types of irrigation waters with salinity levels of 2.5, 6, 8, 10, 12, 16, and 20 dS·m−1: 1) San Joaquin Valley drainage waters, and 2) solutions mimicking concentrations of Colorado River water, a major irrigation water source for southern California. In addition to the presence of myo-inositol and three common sugars (fructose, glucose, and sucrose), chiro-inositol was for the first time isolated and identified in leaf and root tissues of both Limonium species. As salinity increased from 2.5 to 30 dS·m−1, leaf chiro-inositol concentration increased from 6.4 to 52.8 and from 2.6 to 72.9 μmol·g−1 dry weight for L. perezii and L. sinuatum, respectively, suggesting that chiro-inositol contributes substantially to osmotic adjustment in the stressed plants. Meanwhile, leaf myo-inositol concentration remained low in both species and showed little response to salinity. Before salt stress, the seedlings contained little chiro-inositol, indicating that salt enhanced chiro-inositol synthesis per unit of biomass formation. Significant (P ≤ 0.05) increasing trends for fructose and glucose and a decreasing trend for sucrose with increasing salinity were observed in the leaves of L. perezii but not L. sinuatum. As a result, the leaves of L. perezii had higher glucose and fructose but lower sucrose levels than that of L. sinuatum. However, no significant (P > 0.05) salt effect was found on the sum of the three common sugar concentrations in either species. Therefore, the accumulation of chiro-inositol resulted in a change in carbon partitioning among the soluble carbohydrates (i.e., the ratio of leaf chiro-inositol over a sum of the three common sugars rose from 0.034 to 0.29 dS·m−1 and from 0.012 to 0.32 dS·m−1 for L. perezii and L. sinuatum, respectively, as salinity increased from 2.5 to 30 dS·m−1). Salt stress did not affect starch accumulation and caused no carbon reserve deficiency. Furthermore, it was observed that salinity increased chiro-inositol phloem transport. The chiro-inositol response might be a physiological process for Limonium salt adaptation. The types of saline irrigation waters (i.e., sodium sulfate-dominated waters vs. a sodium chloride system) appear to have little effect on carbohydrate accumulation and partitioning in L. perezii.