Abstract: * Gas spaces ( aerenchyma ) form as an adaptation to submergence to facilitate gas exchange .
In rice ( Oryza sativa ) , aerenchyma develop by cell death and lysis , which are poorly understood at the cellular level .
* Aerenchyma formation was studied in rice stems by light microscopy .
It was analyzed in response to submergence , ethylene and hydrogen peroxide ( H ( 2 ) O ( 2 ) ) treatment , and in the MT2b : : Tos17 mutant .
O ( 2 ) . ( - ) was detected with nitroblue tetrazolium and an epinephrine assay .
H ( 2 ) O ( 2 ) was detected with 3 , 3-diaminobenzidine .
* Aerenchyma develop constitutively in all internodes of the deep-water rice variety Pin Gaew 56 , but are absent from the nodes .
Constitutive aerenchyma formation was also observed in two lowland rice varieties , albeit to a lesser degree .
A larger number of aerenchyma are present in older internodes , and at the top of each internode , revealing developmental gradients .
Submergence or treatment with the ethylene-releasing compound ethephon promoted aerenchyma formation in all genotypes analyzed .
Pre-aerenchymal cells contain less starch , no chloroplasts , thinner cell walls and produce elevated levels of O ( 2 ) . ( - ) and H ( 2 ) O ( 2 ) compared with other parenchymal cells .
Ethephon promotes O ( 2 ) . ( - ) formation and H ( 2 ) O ( 2 ) promotes aerenchyma formation in a dose-dependent manner .
Further-more , genetic downregulation of the H ( 2 ) O ( 2 ) scavenger MT2b enhances aerenchyma formation .
* Aerenchyma formation is mediated by reactive oxygen species .
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