Asparagine synthesis and localization of transcripts for asparagine synthetase in tips of harvested asparagus spears

Asparagine (Asn) accumulated markedly in the tips of harvested asparagus (Asparagus officinalis L,.; King et al., 1930) shortly after the harvest-induced accumulation of-asparagine synthetase (AS) transcripts (Davies and King, 1993). Supplying harvested asparagus spears with 1 mmol . L(-1) phosphinothricin (PPT a specific inhibitor of glutamine synthetase) markedly reduced glutamine (Gin) content, increased the ammonium content, and prevented Asn formation in spear tips from 6 to 12 h after harvest. AS transcripts accumulated to high levels in spears supplied with either PPT or water from 6 h after harvest. The data provide evidence that: the in vivo activity of AS is strictly Gin-dependent. In situ localization of AS transcripts demonstrated tissue-specific responses by cells of the spear tip to harvest. We propose that Asn accumulation effectively acts as a nitrogen storage mechanism in the tips of harvested asparagus spears.