Senescence and protein remobilisation in leaves of maturing wheat plants grown on waterlogged soil

The influence of waterlogging on leaf senescence and protein remobilisation was investigated in winter wheat (Triticum aestivum L., cv.Arina), which was grown in large pots embedded in the field in spring. The soil of intact pots was flooded permanently from anthesis to maturity, while in perforated control pots the soil was well aerated throughout the maturation period. No major effects of waterlogging were observed in the third leaf from the top, which was already senescing when the treatment was started. The degradation of proteins and chlorophyll was accelerated slightly in the second leaf from the top and considerably in the flag leaf. The contents of free amino acids in the uppermost leaf blades were lower on waterlogged soil than on control pots. Furthermore, amino acids in the blades did not accumulate during the earlier protein remobilisation observed on flooded soil, indicating that the export of amino acids via the phloem was fully functional. The loss of leaf proteins and the changes in the pattern of peptide hydrolases during senescence were similar in treated and control plants. Endopeptidase activities increased in an early phase of senescence at pH 5 and later also at pH 9, while aminopeptidase activities decreased. Therefore, nitrogen remobilisation was accelerated on flooded soil, but the senescence-related changes were very similar to those observed in control plants.