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

Triticum aestivum (wheat) plants grown at a day:night temperature of 18:13 degreesC from anthesis were held as well watered controls, or subject to ei ther a mild (large pot volume) or a more severe (small pot volume) water st ress by withholding water from the time of anthesis. Extracts from the pedu ncle (enclosed by the flag leaf sheath) and the penultimate internode were prepared to determine the activities of fructan exohydrolase and acid inver tase and to assess the level of hexose sugars, sucrose and fructans. Measur ements were made of ear and individual grain grain eights and stem fresh we ight and dry weight. Plant water relations at the time of each sampling wer e determined as the flag leaf water potential and the water content of indi vidual organs. Water stress resulted in a shorter duration of kt mel fillin g, smaller kernels at maturity and an earlier loss of stem eight. 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 fructa n exohydrolase and acid invertase in the internodes of stressed plants. Thi s correlation suggests that the conversion of fructans to fructose might ha ve resulted from enzyme induction associated with water stress, but as this conversion occurs before the major export of reserves from the stern it mi ght be only indirectly related to changes in the demand for reserves.