EFFECT OF SALINITY ON ACCUMULATION OF CHIRO-INOSITOL AND OTHER NON-STRUCTURAL CARBOHYDRATES IN LIMONIUM

Authors: Liu, Xuan; Wilson, Clyde; Grieve, Catherine

Submitted to: Proceedings of the International Salinity Forum
Publication Type: Proceedings
Publication Acceptance Date: 4/11/2005
Publication Date: 4/25/2005
Citation: Liu, X., Wilson, C., Grieve, C.M. 2005. Effect of salinity on accumulation of chiro-inositol and other non-structural carbohydrates in limonium. In: Proceedings of the International Salinity Forum, Managing Saline Soils and Water: Science, Technology, and Soil Issues. April 25-27, 2005. Riverside, CA pp:93-96.

Interpretive Summary: High soil salinity or salt stress is a worldwide environmental factor seriously limiting crop growth and yield. The salt-affected land amounts to more than 900 million hectares. Because irrigating water is rarely salt-free, irrigation adds salts into 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. Furthermore, most crops are salt sensitive but global human population continues to increase and maybe will increase by 50% by 2050. Obviously, salinity is a 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, they exhibit great diversity in their salt tolerance but little is known on their most growth-related physiological processes in response to salinity. In this study, we focused on two species of flower crops, Limonium (L.) perezii and L. sinuatum, popular members of USA floral industries, and examined their sugar and starch accumulation under different saline conditions. The unique sugar alcohol, chiro-inositol, was identified in both L. species. To our best knowledge, this is the first example of the presence of this compound in these two L. species. More important finding is that their leaf chiro-inositol level increased dramatically as salinity increased, which can contribute significantly to alleviation of salt stress impact. The enhanced accumulation of chiro-inositol by salt stress appears an important physiological process for L. plants to adapt to salt stress. This work also provides new information for gene target search in transformation via biotechnology for enhanced crop slat tolerance.

Technical Abstract: Limonium (L.) perezii cv. 'Blue Seas' and L. sinuatum, cv. 'American Beauty' were grown in greenhouse sand tanks and their carbohydrate accumulation in response to salinity was studied. Seven salinities with electrical conductivity ranging from 2.5 up to 30 dS/m were constructed based on San Joaquin Valley drainage water of California and Colorado River water salt compositions, and imposed through irrigating water on seedlings or germinating seeds for 4-13 week duration upon sampling. In addition to myo-inositol, another cyclitol, chiro-inositol, was for the first time identified to occur in the two L. species. More important finding is that their leaf chiro-inositol concentration increased significantly from 6.4 to 52.8 (L. perezii) and from 2.6 to 72.9 (L. sinuatum) µmol/g dry weight as salinity increased from 2.5 to 30 dS/m, which can contribute significantly to osmotic adjustment for stressed plants. The seedlings prior to salt treatment contained little chiro-inositol, indicating that the increase in chiro-inositol level with salinity did not come from its pre-accumulation but was a salt-induced response of more chiro-inositol synthesis per unit of biomass formation. This response accounted for a carbon partitioning change between soluble sugars, observed in the increase in the ratio of chiro-inositol over the sum of fructose, glucose and sucrose, from 0.034 to 0.29 (L. perezii) and from 0.012 to 0.32 (L. sinuatum) as salinity increased from 2.5 to 30 dS/m. Meanwhile, leaf myo-inositol concentration remained low and showed no significant response to salinity. Such a preference of more chiro-inositol accumulation over the rest of other soluble sugars in stressed plants did not affect starch accumulation and did not appear to cause carbohydrate limitation. Because the stressed plants showed no any visual stress injury through their life cycle, the increased chiro-inositol accumulation might be inevitably involved in protecting plants from salt-stress damages via some known cyclitol protective functions. The two salt compositions (different in Na+, sulfate and chloride ion proportions) resulted in no significant difference in leaf non-structural carbohydrate accumulation in L. species.