Concentrations of Non-Structural Carbohydrates in Tissues of Low, Medium, and High Vigor Cotton Seedlings.

Stand establishment and early growth are very important for a successful cotton growing season.  Rapid early growth enhances the chances that cotton seedlings can outgrow damage by biotic stress factors, and may also improve their ability to tolerate abiotic stress conditions.  However, our understanding of the genetic and physiological mechanisms governing early vigor in cotton is very limited.  Previously, we screened a large number of cotton genotypes for differences in early growth.  Based on this screen, we have identified three genotypes with low, medium, and high vigor and have paired these genotypes with a commercial cultivar for further examination of the mechanisms contributing to the observed differences.  Non-structure carbohydrates (fructose, glucose, sucrose and starch) were analyzed by HPLC separately for the upper-most fully expanded leaf, first true leaf, cotyledon, stem and root tissue collected from four genotypes grown in pots in the greenhouse, outdoors in pots, and in the field.   Tissue samples were collected during a period of 15 to 60 days after planting.  Total non-structural carbohydrates (TNC) in cotyledon tissue increased quickly early stage and dropped as in cotyledons aged. During the same period, only slight increases in TNC were found in stem and root tissues. Glucose concentrations dropped early but then remained relatively stable in all tissues.  Fructose concentrations were low in all tissues and all environments throughout development. Sucrose concentrations in true leaves, cotyledons, stems and roots followed tended to increase first and then either stabilized or declined.  In general, sucrose concentrations in stems and roots were greater than in cotyledons and other true leaves. Starch concentrations of first true leaves increased in early stage and stabilized as the plants developed.  While starch concentrations in stems and roots tended to increase as the plants developed, they were, for the most part, lower than in cotyledons and true leaves. Significant differences in glucose concentration were found among the genotypes for the upper-most fully expanded leaf, first true leaf and cotyledons for early samplings, but not for most other sugars and later samplings.  Considerable differences in non-structural carbohydrate concentrations of different tissues were found during early cotton growth and may have implications relative to seedling vigor which need to be investigated further.