Programmed Cell Death and Aerenchyma Formation in Water-Logged Sunflower Stems and Its Promotion by Ethylene and ROS.

Previous studies have shown that waterlogging/ hypoxic conditions induce aerenchyma formation to facilitate gas exchange. Ethylene (ET) and reactive oxygen species (ROS), as regulatory signals, might also be involved in these adaptive responses. However, the interrelationships between these signals have seldom been reported. Herein, we showed that programmed cell death (PCD) was involved in aerenchyma formation in the stem of Helianthus annuus. Lysigenous aerenchyma formation in the stem was induced through waterlogging (WA), ethylene and ROS. Pre-treatment with the NADPH oxidase inhibitor diphenyleneiodonium (DPI) partially suppressed aerenchyma formation in the seedlings after treatment with WA, ET and 3-amino-1, 2, 4-triazole (AT, catalase inhibitor). In addition, pre-treatment with the ethylene perception inhibitor 1-methylcyclopropene (1-MCP) partially suppressed aerenchyma formation induced through WA and ET in the seedlings, but barely inhibited aerenchyma formation induced through ROS. These results revealed that ethylene-mediated ROS signaling plays a role in aerenchyma formation, and there is a causal and interdependent relationship during WA, ET and ROS in PCD, which regulates signal networks in the stem of H. annuus.

Programmed cell death during floral nectary senescence in Ipomoea purpurea.

The nectaries of Ipomoea purpurea wilt in the late flowering period. The senescence process of nectaries is frequently associated with cell lysis. In this paper, various techniques were used to investigate whether programmed cell death (PCD) was involved in the senescence process of nectaries in I. purpurea. Ultrastructural studies showed that nectary cells began to undergo structural distortion, chromatin condensation, mitochondrial membrane degradation, and vacuolar-membrane dissolution and rupture after bloom. 4',6-Diamidino-2-phenylindole (DAPI) and terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine-5'-triphosphate (dUTP) nick end-labeling (TUNEL) assay showed that nectary cell nuclear DNA began to degrade during the budding stage, and disappeared in the fruiting stage. DNA gel electrophoresis showed that degradation of DNA was random. Together, these results suggest that PCD participate in the senescence of the nectary in I. purpurea. PCD began during the budding period, followed by significant changes in nectary morphology and structure during the flowering period. During the fruiting stage, the PCD process is complete and the nectary degrades.