Abstract: [Objective] Cold-induced flowering in Phalaenopsis, originated in tropical region, was the restrictions of commercially production because of their costing waste. Doritaenopsis, a hybridization of Doritis and Phalanopsis, became the most popular potted flowering crops. Experiments were performed to understand the fluctuation of vegetative growth and gene expression response to relative low temperature, and further to describe this unique inflorescence initiation. [Method] A Doritaenopsis hybrid ‘Tinny Tender’( Doritaenopsis Happy smile ×Happy valentine) was incubated in 22℃/18℃(day/night), with 30℃/25℃ as control, to induce the floral transition. Changes of starch, sucrose, reducing sugar, leaf area, ratio of Fv/Fm and Fv/Fo, and mRNA transcripts levels of 2 genes, annotated as DhSUT1 (Sucrose Transporter) and DhST1 (Sugar Transporter), isolated from the suppression subtractive hybridization (SSH) library of ‘Tinny Tender’. [Result] Slower increasing of leaf area and reducing of Fv/Fm and Fv/Fo were observed under 22℃/18℃ for 28d. Quick degradation of starch, continuous accumulation of reducing sugar and increase to peak at 28d cold-incubation then decrease of sucrose were determined. The mRNA transcripts of DhST1 rose up to the peak at 28d cold-induced, while those of DhSUT1 were decreased. [Conclusion] These results indicated that during cold-induced floral initiation, vegetative growth and photosynthesis capacity of were slow down, and sharp changes in carbohydrates were consist with up-regulated of DhST1 and down-regulated of DhSUT1 expression. In addition, sugar transporter genes performed differently under cold-induced, suggesting those candidate genes were responsible for the unique flowering induction of Doritaenopsis .

Key words: orchid (Doritaenopsis hybrid), ‘cold-sensitive’, carbohydrates, chlorophyll fluorescence, sugar transporter