Submitted to: Subtropical Plant Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/1/2007
Publication Date: 12/31/2007
Citation: Showler, A., Cavazos, J.O., Moran, P.J. 2007. Dynamics of free amino acid accumulations in cotton leaves measured on different timelines after irrigation. Subtropical Plant Science. 59:38-55. Interpretive Summary: Although it is known that drought-stressed cotton leaves accumulate free amino acids, including some that are essential to herbivorous insect growth and development, the changes that occur while soil moisture declines over time are not known. To characterize their dynamics, free amino acids and water potentials were measured at three different time scales: minutes, hours, and days. Some free amino acids responded differently than others during the onset of water-deficit stress in each of the three time scales.
Technical Abstract: Accumulations of 16 free amino acids (FAAs) in cotton, Gossypium hirsutum L., leaves in potted greenhouse plants were recorded across three time scales following irrigation. The time scales, 15-minute, 12-hours, and daily sampling intervals, revealed the dynamic response of each FAA, and showed different trends in concentrations and percentages of total FAAs. Some, but not all, FAAs were correlated with changes in water potential after irrigation. The lack of correlation of some FAAs with water potential during each time scale suggests that metabolic, or biosynthetic, regulation is involved, not just dilution or concentration effects brought about by rehydration and dehydration. The 15-minutes scale revealed a decrease in levels of eight FAAs, and summed free essential amino acids, that occurred within the first 45-60 minutes after irrigation. The dilution of those FAAs indicates that physiological and chemical factors other than those that govern FAA synthesis or metabolism are responsible for the initial uptake of water. Despite an increase in water potential 48 hours after irrigation, three FAAs did not increase, but the other 13 FAAs accumulated in a pattern roughly similar to that of water potential over 48 h and 7 d. Only eight FAAs were correlated with water potential in the days scale (some that were not significantly correlated with water potential increased after a short lag). Irrigation and water-deficit stress, via their effects on summed FAAs that are essential to insect growth and development, were related to the leaf nutritional value of cotton for herbivorous arthropods. Our results have utility in predicting these stress status of cotton under variable irrigation regimes, and for understanding relationships between favorable host plant nutrition, pest herbivores, and to irrigation.