Carbonhydrate Content and Root Growth in Seeds Germinated Under Salt Stress: Implications for Seed Conditioning

Authors: LEATHERWOOD, W - NC STATE UNIVERSITY; PHARR, D - NC STATE UNIVERSITY; Dean, Lisa; WILLIAMSON, JOHN - NC STATE UNIVERSITY

Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/10/2007
Publication Date: 6/1/2007
Citation: Leatherwood, W.R., Pharr, D.M., Dean, L.L., Williamson, J.D. 2007. Carbonhydrate Content and Root Growth in Seeds Germinated Under Salt Stress: Implications for Seed Conditioning. Journal of the American Society for Horticultural Science v. 132 (6) 876-882.

Interpretive Summary: Seeds from both salt tolerant and non salt tolerant plants were germinated in absence and presence of a range of salt concentrations. Soluble carbohydrates were measured after germination. Percent germination was measured over the course of 11 days. It was found that protective mechanisms against salinity vary among species and at different developmental stages.

Technical Abstract: Sugars and sugar alcohols have well documented roles in salt tolerance in whole plants and maturing seeds. Less is known, however, about possible effects of these compounds during germination. Seeds from mannitol-accumulating salt-tolerant celery [Apium graveloens L. var. dulce (P. Mill.) DC], non-mannitol-accumulating salt-tolerant cabbage [Brassica oleracea L. var. capitata 'Golden Acre'], and salt-sensitive non-mannitol-accumulating tobacco [Nicotiana tabacum L.] and arabidopsis [Arabidopsis thaliana (L.) Heynh.] were germinated on vertical phytagel plates containing 0 to 300 mM NaCl/L and their germination percentage root elongation and the carbohydrate content of seeds and seedlings were assessed. With the exception of cabbage, there was no positive correlation between the ability to germinate in the presence of salt and the salt tolerance of the mature plant. For instance, while cabbage seeds germinated in 300 mM NaCl, seed germination of two celery cultivars was inhibited completely by 150 mM NaCl. In contrast, seeds from salt-sensitive tobacco and Arabidopsis germinated in 200 mM NaCl. There was also no obvious relationship between salt tolerance and total soluble carbohydrates in either unimbibed seeds or in seedlings germinated in the presence of salt. For example, the most salt tolerant species, cabbage, had by far the highest seed and seedling carbohydrate content, while the next most tolerant, arabidopsis, had the lowest. Both, however, contained significant amounts of the osmoprotective polysaccharides raffinose or stachyose. Further, although celery seedling mannitol content initially increased at low NaCl concentrations (50 mM), germination and mannitol content decreased at higher NaCl concentrations (100 mM). Finally, the broadest correlation observed was a large increase in sucrose in seedlings at the lowest salt concentration significantly inhibited germination. Although most seeds did not germinate at these NaCl concentrations, they were still metabolically active as indicated by the fact that sucrose content was two to eight times higher than in unimbibed seeds, suggesting a possible role for sucrose in salt-stressed germinating seeds. These results not only suggest that plants use different mechanisms to provide salt tolerance in mature plants and germinating seeds, but that even when the same mechanism is employed in seeds it may be less effective.