Long-term anoxia tolerance in leaves of Acorus calamus L. and Iris pseudacorus L.

Mature green leaves of Acorus calamus and Iris pseudacorus have been shown to survive at least 28 d of total anoxia in the dark during the growing sea son, increasing up to 75 d and 60 d in overwintering leaves in A. calamus a nd I. pseudacorus, respectively. During the period of anaerobic incubation the glycolytic rate is reduced, carbohydrate reserves are conserved and eth anol levels in the tissues reached an equilibrium. Prolonged anoxia signifi cantly suppressed leaf capacity for respiration and photosynthesis. After 2 8 d of anoxia, respiratory capacity was reduced in A. calamus and I. pseuda corus by 80% and 90%, respectively. The photosynthetic capacity of leaves d ecreased by 83% in A. calamus and by 97% in I. pseudacorus after 28 d of an oxia. This reduction in photosynthetic capacity was accompanied by a modifi cation of the chlorophyll fluorescence pattern indicating damage to the PSI I reaction centre and subsequent electron transport. Chlorophyll content wa s only slightly reduced after 28 d under anoxia and darkness in A. calamus, whereas there was a 50% reduction in I. pseudacorus. On return to air A. c alamus leaves that endured 28 d of anoxia recovered full photosynthetic act ivity within 7 d while those of I. pseudacorus had a lag phase of 3-10 d. T his well-developed ability to endure prolonged periods of oxygen deprivatio n in both these species is associated with a down-regulation in metabolic a ctivity in response to the imposition of anaerobiosis. It is suggested that when leaf damage eventually does take place in these species after protrac ted oxygen deprivation, it is anoxic rather than postanoxic stress that is responsible.