A Ca(2+)-dependent cysteine protease is associated with anoxia-induced root tip death in maize.
Imposition of anoxia on maize (Zea mays cv. B73) seedlings for 48 h or longer led to the death of the root tip. The necrosis extended into the root axis during postanoxic treatment, leading to the mortality of 30-50% of the seedlings. Using zymography, protease profiles in the root tissues of anoxic seedlings were studied. O2 deprivation for 24 h or longer repressed pre-existing protease activities and induced a novel soluble enzyme in the roots. The anoxia-induced protease (AIP) activity was predominant in the root apex at 24 h of anoxia and, subsequently, became the most abundant soluble activity in the root axis as well. The induction of AIP and its in vitro renaturation were Ca(2+)-dependent. Inhibitor sensitivity studies indicated that AIP is a cysteine protease. In SDS-acrylamide gels, the enzyme activity migrated as a 23.5 kDa polypeptide. The anoxic induction of the activity was repressed by cycloheximide treatment, suggesting that new protein synthesis was required for the AIP appearance. Excision of the root tip (de-tipping) before anoxia led to a superior recovery of seedlings from stress injury. De-tipped seedlings showed lesser root damage and an increased production of lateral roots compared to intact seedlings. Furthermore, the superior anoxia tolerance of de-tipped seedlings was associated with a decreased AIP activity. Thus, the appearance of AIP activity in the root tip at 24 h of anoxia was spatially and temporally associated with the root tissue death. These studies further indicate that the root tip elimination early during anoxia may provide an adaptive advantage.
Subbaiah
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Department of Crop Sciences, University of Illinois, Urbana 61801-4730, USA. subbaiah@uiuc.edu
Kollipara
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KP
Sachs
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MM
D000693:Anaerobiosis; D002118:Calcium / Q000378:metabolism; D003546:Cysteine Endopeptidases / Q000096:biosynthesis* / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D018519:Meristem / Q000378:metabolism / Q000502:physiology; D009336:Necrosis; D010100:Oxygen / Q000378:metabolism*; D018517:Plant Roots / Q000378:metabolism / Q000502:physiology*; D003313:Zea mays / Q000378:metabolism / Q000502:physiology*
D003546:Cysteine Endopeptidases; D010100:Oxygen; D002118:Calcium