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

Authors: Liu, Xuan; Grieve, Catherine

Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/13/2009
Publication Date: 1/5/2009
Citation: Liu, X., Grieve, C.M. 2009. Accumulation of Chiro-inositol and Other Non-structural Carbohydrates in Limonium Species in Response to Saline Irrigation Waters. Journal of the American Society for Horticultural Science. 134(3):329–336.

Interpretive Summary: High soil salinity or salt stress severely limits crop growth and yield worldwide. It is estimated that salt-affected lands cover more than 900 million hectares. Because irrigation water is rarely salt-free, irrigation adds salts to soil and keeps turning more acreage into saline land. However, about half of the world’s land surface is dryland, which can only be made more productive by irrigation. This exacerbates the problem because most crops are salt sensitive and the growth in world population requires increasing use of irrigated lands. Clearly then, salinity is a serious threat to agricultural productivity. Thus, reducing the impact of salinity and improving crop production through increasing crop salt tolerance are important global goals. Floral crops exhibit great diversity in their salt tolerance but little is known about the response of their growth-related physiological processes to salinity. In this study, we focused on two species of floral crops, Limonium perezii and L. sinuatum, popular plants in USA floral industry with about 20 billion dollar yearly sales (Annual sale of Limonium species is 1.5 million dollars). We examined their sugar and starch accumulation under different saline conditions and found that the unique sugar alcohol, chiro-inositol, existed in the both species. More importantly, their leaf chiro-inositol level increased dramatically as salinity increased, which might contribute significantly to osmotic adjustment and alleviation of salt stress. This work also provides new information for gene to be used in transformation via biotechnology for enhanced crop salt tolerance.

Technical Abstract: Two statice cultivars, Limonium perezii (Stapf) F. T. Hubb cv. ‘Blue Seas’ and L. sinuatum (L.) Mill ‘American Beauty’, were grown in greenhouse sand tanks to determine the effect of salt stress on carbohydrate accumulation and partitioning. Irrigation waters were prepared to simulate typical saline-sodic drainage effluent in the San Joaquin Valley (SJV) of California with electrical conductivities (EC) of 2.5, 7, 11, 15, 20, 25 and 30 dS·m-1 for the first experiment. A second experiment compared the response to two types of irrigation waters with isoelectric salinity levels of 2.5, 6, 8, 10, 12, 16 and 20 dS·m-1: (1) SJV drainage waters, and (2) solutions mimicking concentrations of Colorado River (CCR) 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 wt) 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. Prior to 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 and from 0.012 to 0.32 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.