Mobilization of fructan reserves and changes in enzyme activities in wheat stems correlate with water stress during kernel filling

Abstract

Triticum aestivum (wheat) plants grown at a day : night temperature of 18 : 13mC from anthesis were held as well watered controls, or subject to either a mild (large pot volume) or a more severe (small pot volume) water stress by withholding water from the time of anthesis. Extracts from the peduncle (enclosed by the flag leaf sheath) and the penultimate internode were prepared to determine the activities of fructan exohydrolase and acid invertase and to assess the level of hexose sugars, sucrose and fructans. Measurements were made of ear and individual grain weights and stem fresh weight and dry weight. Plant water relations at the time of each sampling were determined as the flag leaf water potential and the water content of individual organs. Water stress resulted in a shorter duration of kernel filling, smaller kernels at maturity and an earlier loss of stem weight. There was an increase in stem fructose and a fall in fructan level that preceded the loss of dry matter associated with water stress. Coincident with the early fall in fructan content under water stress there was a rise in both fructan exohydrolase and acid invertase in the internodes of stressed plants. This correlation suggests that the conversion of fructans to fructose might have resulted from enzyme induction associated with water stress, but as this conversion occurs before the major export of reserves from the stem it might be only indirectly related to changes in the demand for reserves.

The role of sucrose metabolizing proteins in hyperosmotic stress tolerance in sweet sorghum (Sorghum bicolor L. Moench)

“…Invertase activity of ICSV213 was higher under stress compared to ICSB338. These observations are supported by findings made by Wardlaw and Willenbrink (2000) and Trouverie et al, (2003) in wheat and maize plants respectively, where an increase in hexose accumulation in response to water stress was accompanied by a rise in invertase activity. The observed higher invertase activity compared to SPS in both varieties under stress was an indication that although SPS activity was increased by stress, its activity was below a threshold level necessary for sucrose to accumulate significantly.…”

Differential response of wild and cultivated wheats to water deficits during grain development: changes in soluble carbohydrates and invertases

“…Probably, it had exhausted its carbohydrate reserves in its quest to effectively translocate sugars for optimum grain development. Furthermore, enhanced mobilization of stem reserves in drought conditions is directly linked to an increased demand for these reserves by the ear (Wardlaw and Willenbrink 2000). C-306, on the other hand, was found to maintain highest WSC reserves under both the environment 30 days post-anthesis, indicating that C-306 might have a longer grain-filling period relative to other accessions.…”

Effects of Drought and Shading on Non-structural Carbohydrate Stored in the Stem of Potato (Solanum tuberosumL.)

“…The contribution of NSC stored in the stem to the grain yield of cereal crops can be more than 50% under stress conditions, but it is 5-33% in non-stress conditions (Hirano et al, 1998;Wardlaw and Willenbrink, 2000). These results suggest that stem reserves might act as a short-term buffer to maintain the supply of photosynthate to developing organs when the supply of photosynthate from source leaves can not satisfy the requirement of sinks (Takahashi et al, 1994;Wardlaw and Willenbrink, 2000).…”

“…Non-structural carbohydrate (NSC) can be stored in crop stems (Wardlaw and Willenbrink, 2000). Much of this NSC can be remobilized and transported to developing organs to increase their growth and yield (Setter et al, 1998).…”

“…In wheat stem, larger storage polymers (fructans) are decomposed to smaller polymers under drought conditions (Virgona and Barlow, 1991), and total NSC concentration decreases when the daily radiation is lower than 16.6 MJ m -2 day -1 during the mid-milk ripe stage (Takahashi et al, 1993). The contribution of NSC stored in the stem to the grain yield of cereal crops can be more than 50% under stress conditions, but it is 5-33% in non-stress conditions (Hirano et al, 1998;Wardlaw and Willenbrink, 2000). These results suggest that stem reserves might act as a short-term buffer to maintain the supply of photosynthate to developing organs when the supply of photosynthate from source leaves can not satisfy the requirement of sinks (Takahashi et al, 1994;Wardlaw and Willenbrink, 2000).…”