Annals of Botany 91: 195-204, 2003
© 2003 Annals of Botany Company
Assessment of Enzyme Induction and Aerenchyma Formation as Mechanisms for Flooding Tolerance in Trifolium subterraneum ‘Park’
1 Département de Biologie, Faculté des Sciences de Tunis, 1060 Tunis, Tunisia and 2 UMR de Physiologie et Biotechnologie Végétales, BP 83, 33883 Villenave d’Ornon Cedex, France
* For correspondence. Fax + 33 (0) 557 122541, e-mail ricard{at}bordeaux.inra.fr
Received: 29 June 2001; Returned for revision: 23 August 2001; Accepted 16 October 2001
The objective of this study was to evaluate the role of enzyme induction and aerenchyma formation in prolonged tolerance to soil flooding in a variety of underground clover (Trifolium subterraneum ‘Park’) previously selected for resistance. Seedlings were grown in hydroponic tanks, initially with aeration for 3 weeks and subsequently in the absence of aeration for up to 3 weeks. After 1 h in the absence of aeration, the oxygen concentration in the hydroponic medium had decreased to 1·5 %. During the 3 weeks of extreme oxygen deficiency, primary roots died and were replaced by considerable numbers of adventitious roots. Activities of many glycolytic and fermentative enzymes increased in adventitious roots. Excised adventitious roots were capable of immediate induction of ethanol in the absence of lactate production, in association with energy charge higher than that in excised roots of aerobically maintained controls. Energy charge was even higher when measured in adventitious roots in planta. Interestingly, haemoglobin protein could be correlated with energy charge. Aerenchyma was readily visualized in adventitious roots by optical microscopy of longitudinal and transverse sections. We conclude that avoidance of root anoxia via aerenchyma is the major mechanism for prolonged root tolerance in Trifolium subterraneum ‘Park’.
Key words: Trifolium subterraneum, clover, flooding, hypoxia, anoxia, acclimation, energy metabolism, aerenchyma, roots, haemoglobin, endopeptidases.
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