Characterization of summer dormancy in Narcissus tazetta var. Chinensis and the role of NtFTs in summer dormancy and flower differentiation

Abstract

Summer dormancy is critical for plant survival under unfavorable conditions. However, unlike winter dormancy, summer dormancy is relatively uncharacterized, especially in Narcissus tazetta var. Chinensis. The aim of the present study was to characterize the summer dormancy of N. tazetta var. Chinensis and to assess the role of NtFTs in summer dormancy and flower differentiation. Bulbs were obtained every 7 days between April 14 and July 14, 2012. Bulbs were weighed and measured. Morphology and amyloplast properties of the main bud and the fourth layer scale were assessed by hematoxylin staining and periodic acid Schiff reaction, respectively. Relative mRNA expressions of NtFTs were determined by real-time RT-PCR. Morphological observation and amyloplast changes in main buds and the fourth layer scale revealed that summer dormancy is separated in the early and late dormancy stages. NtFT1 expression was in opposition with NtFT2 and NtFT3 expressions during dormancy, which suggested that NtFTs, which are target genes of temperature-signal pathways, regulate the dormancy process. The expression levels of NtFT1 gradually increased while NtFT2 and NtFT3 decreased during the bulb swelling stage, in the dormancy period (from May 5 to July 7), the expression levels of NtFT1 changed with a inverse “V” pattern in the early dormancy stage, which is opposite with both the expression of NtFT2 and NtFT3; the expression levels of NtFT1 decreased while NtFT2 and NtFT3 showed an increasing pattern in the late dormancy stage. In conclusion, summer dormancy in N. tazetta var. Chinensis was separated in two distinct phases. NtFTs might be involved in summer dormancy of N. tazetta var. Chinensis.