Changes in the reduction state of ascorbate and glutathione, protein oxidation and hydrolysis leading to the development of dehydration intolerance in Triticum aestivum L. seedlings

Abstract

The present work demonstrates that the transition of wheat (Triticum aestivum L.) seedlings from dehydration tolerance to intolerance on the fifth day following imbibition is associated with a disturbance in cellular redox homeostasis. During germination the ratio of reduced (AsA) to oxidized ascorbate (DHA) was lower in the tolerant 4-day-old seedlings compared to the sensitive 6-day-old seedlings because of the lower ascorbate content in the former. The reduced glutathione (GSH) and total glutathione (GSH + GSSG) pools were higher in tolerant seedlings and remained higher upon dehydration. The development of dehydration intolerance with a seedling age coincided with a 50 % loss of the total glutathione pool and a shift of GSH/GSSG to a more oxidized state. Activities of ascorbate peroxidase and glutathione reductase increased with water deficiency in both tolerant and sensitive seedlings but the three new activity bands appeared only in sensitive seedlings. The stable ratio of GSH/GSSG and a higher AsA/DHA ratio in sensitive seedlings did not prevent the enhanced production of H2O2 and the peroxidation of lipids with dehydration. As a result, an increase in the protein carbonyl group and a significant decrease in the thiol groups were observed in dehydrated sensitive seedlings. Water deficiency enhanced the total azocaseinolytic activity, mainly in sensitive seedlings. The highest increase in protein carbonylation and lowest azocaseinolytic activity was observed at the beginning of seedling dehydration (15–25 % WSD) being in a sensitive phase of growth. The presented results indicate that the development of dehydration intolerance during the transition of wheat seedlings from heterotrophic to autotrophic growth is associated with an alterations in protein oxidation.