Takanori Horibe

Genotype of FLOWERING LOCUS T homologue contributes to flowering time differences in wild and cultivated roses.

Rose flowers have long delighted humans as ornamental plants. To improve the ornamental value of roses it is necessary to understand the regulatory mechanisms of flowering. We previously found that flowering time is controlled by three minor quantitative trait loci (QTLs) and a major QTL co-localised with RoFT. In this study, we isolated three RoFT alleles encoding completely identical amino acid sequences from the parents of a mapping population. Correlation analysis of the RoFT genotypes and flowering time phenotypes in the mapping population showed that the RoFT_f and RoFT_g alleles contribute to the early-flowering phenotype, while the RoFT_e allele contributes to the late-flowering phenotype. We developed two novel cleaved amplified polymorphic sequence (CAPS) markers based on the genomic sequences of the RoFT alleles and clearly showed that the relationship between RoFT genotype and flowering time was applicable to 12 of 13 cultivated roses grown at the Higashiyama Botanical Gardens, Japan. Allele-specific expression analysis using a reverse transcription CAPS assay suggested that these RoFT alleles are regulated differentially at the transcription level. Furthermore, transgenic Arabidopsis thaliana plants ectopically expressing the RoFT gene showed an early-flowering phenotype. Conversely, in roses, RoFT was continuously expressed after floral bud formation, and RoFT transcript accumulation reached its peak after that of the floral meristem identity gene RoAP1b. These data suggest that RoFT may be essential not only for floral transition but also for normal floral development and flowering in roses.

Leaves Of Cut Rose Flower Convert Exogenously Applied Glucose To Sucrose And Translocate It To Petals

Abstract To understand the role that the leaves play in the translocation of soluble carbohydrates in cut rose flowers, we first evaluated the effect of leaf removal on flower quality and the sugar content in petals. Cut rose flowers with leaves had higher soluble sugar content in petals compared with cut flower without leaves. Next, we treated cut flowers with radioactive glucose to clarify translocation routes of exogenously applied sugar. There was no significant difference between the specific radioactivity of sucrose and glucose in leaves, but specific radioactivity of sucrose in petals was much higher than that of glucose. These results suggested that most of the exogenously applied glucose first moved to the leaves, where it was converted into sucrose and then the synthesised sucrose was translocated to the petals. Our results showed that the leaves of cut rose flowers play an important role in the metabolism and transportation of exogenously applied soluble carbohydrates toward the petals, thus contributing to sustaining the post-harvest quality.

Approach towards the control of rose flower opening by light environment

The opening of a flower is a phenomenon where sugars and water accumulate in the petals (a sink organ), causing the petal cells to swell dramatically in response. Cell division in the rose petals ends early, during the bud stage, and any later growth is caused by hypertrophy of individual petal cells.4–6 Rose petals are also hypothesized to show differences in cellular structure and mechanical strength which lead to different growth rates in adaxial and abaxial epithelial cells, causing the petals to bend outward.7,8 In addition, cellular hypertrophy is thought to occur through the accumulation of sugars in vacuoles within the cell, which raises the osmotic pressure inside the cell relative to outside, and through increased distensibility of the cell wall.9–11 Together, these changes cause water to flow into the cell. Even in cut flowers, there is a correlation between ease of opening after harvest and the soluble sugar content of the bud: varieties with high sugar content at the bud stage open well after cutting even without sugar supplementation, while those with low sugar content are arrested in a partially open state unless they are given sugar.12,13 This example clearly shows that sugars have a large impact on flower opening. Previous research in flower petals has shown that the sugar-metabolizing invertase enzymes are involved in sugar accumulation in vacuoles,14 while cell wall proteins such as expansins and endotransglycosylase/hydrolase (XTH) are involved in cell wall distensibility.15–18 In addition, it was shown that flower opening in tulips is caused by reversible phosphorylation of aquaporins, a family of water-permeable channels.19–21 Aquaporins are presumably involved in the flow of water into rose petal cells as well. Thus, hypertrophy of petal cells is thought to require 1) increased osmotic pressure within the cell, 2) relaxation of the cell wall, and 3) the flow of water into the cell (Figure 1).22 Figure 1 Flower opening and cell enlargement of rose petal cell. A: Roseflower opening is a process of irreversible petal growth and reflection in which existing cells expand and fresh and dry weights increase; B: Sugar accumulation in vacuole, cell wall loosening, and subsequent water flow into cell are thought

Petal Growth Physiology of Cut Rose Flowers: Progress and Future Prospects

Abstract Roses are the most important crop in the floriculture industry and attract both pollinators and human admirers. Until now, a lot of research focusing on postharvest physiology including flower senescence has been conducted, leading to improvement in vase life. However, few studies have focused on the physiology of petal growth, the perception of light by petals, and the relationship between petal growth and environmental conditions. Regarding roses, whose ornamental value lies in the process of blooming from buds, it is also important to understand their flowering mechanisms and establish methods to control such mechanisms, as well as focus on slowing the aging process, in order to achieve high quality of postharvest cut roses. Elucidation of the mechanisms of rose flower opening would contribute to enhanced quality and commercial production of floricultural crops as well as greatly advance basic scientific knowledge regarding plant biology. In this review, we describe the progress and future prospects in the study of petal growth physiology of cut roses.