Aerenchyma formation

Summary Aerenchyma – tissue containing enlarged gas spaces – occurs in many plants. It is formed either as part of normal development, or in response to stress (e.g. hypoxia). Two mechanisms of aerenchyma formation have been described; schizogeny, in which development results in the cell separation and lysigeny, in which cells die to create the gas space. While schizogenous aerenchyma provides a fascinating system for study and has been described in detail at a morphological and ultrastructural level, little is known about the molecular genetics of its formation. The ultrastructure and morphology of lysigenous aerenchyma has also been researched in detail, and considerable progress has been made in describing the cell death processes involved, particularly in relation to programmed cell death. Once again, the molecular genetics of the process are not well understood. Aerenchyma is of great importance in crop survival in waterlogging. It is also important in being a major pathway for the release of the global warming gas methane to the atmosphere in flooded soils. Understanding the regulation of its development is therefore a research priority. Contents Summary 35 I. Introduction 36 II. Schizogenous aerenchyma formation 36 III. Lysigenous aerenchyma formation 37 IV. Regulators of lysigenous aerenchyma formation 38 V. Key questions in lysigenous aerenchyma formation 38 VI. Sensing hypoxia; early events in aerenchyma formation 39 VII. Ultrastructural changes associated with lysigenous aerenchyma formation 39 VIII. Late events in cell death in aerenchyma formation 42 IX. Comparative evidence for programmed cell death in aerenchyma formation 43 X. Comparison with other abiotic initiators of cell death in plants 45 XI. Conclusions and future prospects 46 Acknowledgements 47 References 47