No abstract

Mechanisms regulating flower senescence are not fully understood in any species and are particularly complex in composite flowers. Dahlia (Dahlia pinnata Cav.) florets develop sequentially, hence each composite flower head includes florets of different developmental stages as the whole flower head ages. Moreover, the wide range of available cultivars enables assessment of intraspecific variation. Transcriptomes were compared amongst inner (younger) and outer (older) florets of two flower head ages to assess the effect of floret vs. flower head ageing. More gene expression, including ethylene and cytokinin pathway expression changed between inner and outer florets of older flower heads than between inner florets of younger and older flower heads. Additionally, based on Arabidopsis network analysis, different patterns of co-expressed ethylene response genes were elicited. This suggests that changes occur in young inner florets as the whole flower head ages that are different to ageing florets within a flower head. In some species floral senescence is orchestrated by the plant growth regulator ethylene. However, there is both inter and intra-species variation in its importance. There is a lack of conclusive data regarding ethylene sensitivity in dahlia. Speed of senescence progression, effects of ethylene signalling perturbation, and patterns of ethylene biosynthesis gene expression differed across three dahlia cultivars (‘Sylvia’, ‘Karma Prospero’ and ‘Onesta’) suggesting differences in the role of ethylene in their floral senescence, while effects of exogenous cytokinin were less cultivar-specific.

Roses are highly valued as cut flowers worldwide but have limited vase life. Peduncle bending “bent neck” or “necking” is a major cause of reduced vase life, especially in some cultivars. Necking is thought to be caused by either an air embolism or accumulation of microorganisms at or within the stem end, blocking the xylem vessels and preventing water uptake. However, the underlying mechanisms of necking are poorly understood. Here, RNAseq analysis was applied to compare gene expression across three stages of peduncle necking (straight, <90°, and >90°), in the necking-susceptible Rosa hybrida cultivar H30. Most gene expression change was later in bending and there was, overall, more downregulation than upregulation of gene expression during necking. Photosynthetic, starch, and lignin biosynthesis genes were all downregulated, while genes associated with galactose metabolism, producing raffinose and trehalose that are both related to osmoprotection, were upregulated. Genes associated with starch breakdown, autophagy, and senescence were also upregulated, as were most of the NAC and WRKY transcription factors, involved in stress and senescence regulation. Microscopy showed a cellular collapse in the peduncle. These data support a possible mechanism, whereby a reduction in water transport leads to a cellular collapse in the peduncle, accompanied by upregulation of senescence and drought responses.

The dahlia is popular as an ornamental garden plant in the UK, however its value as a cut flower has been undermined by its short vase life. The vase life of dahlias is often no more than 5 days, whereas 10-14 days are required by the cut flower industry due to the supply chain involved in transporting cut flowers from growers to retailers, sufficient time in store, and still guaranteeing 5 days vase life to a consumer. The current study has considered ethylene sensitivity and how phytohormones interact with one another during the senescence process. In conjunction with these traditional methods RNA sequencing and de-novo assembly of the dahlia transcriptome in the cultivar 'Sylvia' has been carried out resulting in an assembly of over 20 000 genes, many of which change in expression during floret senescence.

The IBM Correcting Selectric typewriter was introduced 1 April 1973. It was a new dimension in typewriter history and a product that many wished had been conceived of years ago. The Correcting Selectric uses two types of ribbon systems: a Correctable Film ribbon with lift-off tape and a Tech III ribbon with cover-up tape. This paper is concerned with the former ribbon system because of the unique manner by which a typewriting error is corrected. The mechanical operation of the machine remains the same with both ribbon systems.