Increase in the expression of an alpha-amylase gene and sugar accumulation induced during cold period reflects shoot elongation in hyacinth bulbs

The aim of this study was to investigate physiological and biochemical mechanisms of shoot elongation after cold period in hyacinth (Hyacinthus orientalis L. cv. Delft Blue). Hyacinth shoot rapidly elongated during hydro-culture period in cooled bulbs, but not in non-cooled bulbs. Alpha-amylase (EC 3.2.1.1.) is a key enzyme involved in starch hydrolysis. Alpha-amylase activity increased during the cold storage period and was low during rapid shoot elongation in hyacinth. In the non-cooled bulbs, its activity remained at the similar level. Sucrose content increased during the cold storage period in the shoot, but not in the scales. We, for the first time, isolated cDNA for cold-responsive alpha-amylase gene (HoAmy1A, accession No. AB198975) from hyacinth, and presented that HoAmy1A expression increased in the scale during the cold storage period, but the level was very low during shoot elongation. We also found that promoter region of HoAmy1A contained CArG element, which is related to the response to low temperature. In tulip (Tulipa genesriana L.), the most studied bulbous plant, dramatic increase in alpha-amylase activity and translocation of sugars from the scales to shoot occurred during the growth stage, following cold treatment (Komiyama et al., 1997; Lambrechts et al., 1994). Our results suggest that there are two types (tulip and hyacinth types) of sprouting mechanisms in bulbous plants.