1-Methylcyclopropene (1-MCP) treatment differentially mediated expression of vacuolar processing enzyme (VPE) genes and delayed programmed cell death (PCD) during ripening and senescence of apple fruit

The main purpose of this research was to evaluate the impacts of 1-methylcyclopropene (1-MCP) treatment on vacuolar processing enzyme (VPE) genes and programmed cell death (PCD) during ripening and senescence of apple fruit (Malus x domestica Borkh.). The ethylene antagonists 1-MCP (1 mu L L-1) was applied to apples after harvest. Both treated and control fruit were stored at 20 & PLUSMN; 2C. The data showed that 1-MCP treatment main-tained flesh firmness, delayed climacteric peaks of respiration and ethylene, reduced VPE activity, relative electrical conductivity (REC), malondialdehyde (MDA) content and reactive oxygen species (ROS) accumulation during ripening. Transmission electron microscopy (TEM) and DNA ladder assay revealed that 1-MCP delayed vacuolar-mediated PCD in ripening apple fruit. Generally, expression of MdVPE gamma 1, MdVPE gamma 2, MdVPE delta 4 and MdVPE delta 7 was down-regulated by 1-MCP treatment, while expression of MdVPE alpha 4 and MdVPE beta 2 was enhanced by it during ripening compared with controls. 1-MCP treatment differentially reduced expression of MdVPE alpha 1, MdVPE alpha 2 and MdVPE alpha 5 at the early ripening stage but promoted their expression at the late ripening stage, while it had the opposite effects on MdVPE beta 1, MdVPE beta 3 and MdVPE gamma 4 expression. After transient overexpression of MdERF2, MdVPEs displayed varying expression patterns, among which MdVPE alpha 2 transcripts increased greater than the other genes. Our results indicated that MdVPEs expression and vacuolar-mediated PCD were mediated by ethylene signal during ripening and senescence of apple fruit.