Stress-Related Proteins Are Specifically Expressed under Non-Stress Conditions in the Overwinter Buds of the Gentian Plant Gentiana triflora

Abstract

The overwinter bud of the gentian plant, Gentiana triflora, is an organ that develops from the basal tuber in late spring and becomes dormant and freezing-tolerant for overwintering. Here, proteins specifically enriched in the overwinter buds were identified using two-dimensional polyacrylamide gel electrophoresis followed by amino acid sequencing. Enriched proteins included those so far identified as stress- and cold-inducible in other plants, i.e., two isoforms of ethylene-induced esterase, a dehydration-induced protein, glyoxalase I, thioredoxin peroxidase, two isoforms of ascorbate peroxidase and a membrane pore protein. Interestingly, the stress-related proteins had already accumulated in the overwinter buds under non-stress conditions in early summer. Accumulation of these proteins was also examined in a mutant gentian, which developed overwinter buds but lacked cold tolerance and died under conditions below 3°C. In this mutant, several proteins including one of the putative esterase, enolase and ascorbate peroxidase were absent or greatly decreased. Thus, it appears that these stress-related proteins are expressed under non-stress conditions to aquire cold tolerance before overwintering.