Onset of Phloem Export from Senescent Petals of Daylily

Abstract

~~During senescence, petals of attached daylily (Hemerocallis hybrid cv Cradle Song) flowers lost 95% sugar and 65% dry weight over the first 24 h, with 30% of dry weight loss coming from nonsugar components. Detaching flowers did not delay senescence, but halted loss of carbohydrate and amino acid, suggesting that loss in the intact state was due to phloem export. Peta1 autolysis occurred mainly in the interveinal parenchyma, causing vascular strands to begin separating from the petal mass. Such vascular strands still stained with tetrazolium and accumulated sucrose, indicating a retained viability. Their sucrose accumulation rates were high in comparison with those of other plant tissues, and the accumulated product was mainly sucrose. Sucrose synthesis took place in the senescent petal, and sucrose was the principal sugar in phloem exudate, whereas hydroxyproline and glutamine were the main transport amino acids. ['4ClSucrose applied t o attached senescent flowers was rapidly translocated t o other parts of the plant, particularly developing flower buds. Thus, onset of phloem export allowed most of the soluble carbohydrate and amino acid in the senescing flower t o be retrieved by the plant. Additional salvaged material came from proteins and possibly from structural carbohydrate. Over a 12-h period, the flower switched from acting as a strong carbohydrate sink during expansion t o become a strong source during senescence. This rapid reversal offers potential for phloem transport studies.The daylily, Hemerocallis hybrid cv Cradle Song, has been useful for studying development and senescence processes in flowers. First, its ephemeral flower has been shown to have severa1 features of senescence common to other, slower-declining plant tissues . When the first physical signs of senescence begin to appear (wilting, then onset of autolysis in the petal tips, later extending over the whole petal), there is a small but well-defined respiration climacteric, an increase in apparent free space, an increase in efflux of sugars and ions, and a change in the phospholipid pattern. Rather surprisingly, the ability of petals to accumulate phosphate and to maintain phosphate ester synthesis (along with a high energy charge) survives well into senescence. Second, the daylily does not respond to ethylene nor to ethylene inhibitors in its senescence and produces only traces of ethylene, leading to the conclusion

A Comparison of Leaf and Petal Senescence in Wallflower Reveals Common and Distinct Patterns of Gene Expression and Physiology

“…Both in leaves and petals, a key feature of senescence is remobilization of resources; in both organs, this has been demonstrated experimentally using isotope labeling (Nichols and Ho, 1975;Mae et al, 1985;Bieleski, 1995) or pigment transport (Erdelská and Ovečka, 2004). This is reflected in some of the major classes of genes whose expression is up-regulated in both these tissues during senescence.…”

Diurnal variations of polar organic tracers in summer forest aerosols: A case study of a Quercus and Picea mixed forest in Hokkaido, Japan

“…Graham et al (2003) reported that fructose, sucrose and glucose showed higher daytime concentrations, which were explained by the specific daytime release of pollen, fern spores and other "giant" bioaerosols. Sucrose is the predominant sugar in the phloem of plants and is important in developing flower buds (Bieleski, 1995). Pashynska et al (2002) reported that the atmospheric levels of inositol and sucrose and their contributions to OC were highest in early summer (June) owing to the developing leaves.…”

Sugars as source indicators of biogenic organic carbon in aerosols collected above the Howland Experimental Forest, Maine

“…3a). This disaccharide is the predominant sugar in the phloem of plants and is particularly important in developing flower buds (Bieleski, 1995).…”