Effects of drying rate on dehydration sensitivity of excised wheat seedling shoots as related to sucrose metabolism and antioxidant enzyme activities

In the present study we investigated the possible involvement of sucrose metabolism and enzymatic antioxidant defences in dehydration tolerance of wheat shoots excised from 2- or 3-day old seedlings and dried in the presence of silica gel (fast drying) or in an atmosphere at 85% relative humidity (slow drying). Slowly dried shoots lost water to 0.45 g H2O g(-1) dry weight (DW) and 80-85% of them remained viable. When fast dried, 60% of shoots died at 0.40 g H2O g(-1) DW and all of them were dead at 0.14 g H2O g(-1) DW. Dehydration induced an increase in sucrose content which was much more marked in slowly dried shoots than in fast dried ones. The accumulation of sucrose was associated with an increase in sucrose synthase activity. After a small increase, sucrose phosphate synthase activity declined and became nil in completely dehydrated shoots. Shoot water loss also resulted in accumulation in H2O2 and malondialdehyde, the latter being about twice higher in shoots fast dried than in those slowly dried. Superoxide dismutase and catalase activities increased continuously during shoot dehydration. Glutathione reductase activity increased only during the first 0.5-1 h of dehydration and then decreased. The involvement of sucrose metabolism and enzymatic antioxidant defences in drought shoot tolerance is discussed. (C) 2004 Elsevier Ireland Ltd. All rights reserved.