Interaction of plant growth regulators and reactive oxygen species to regulate petal senescence in wallflowers (Erysimum linifolium)

Background In many species floral senescence is coordinated by ethylene. Endogenous levels rise, and exogenous application accelerates senescence. Furthermore, floral senescence is often associated with increased reactive oxygen species, and is delayed by exogenously applied cytokinin. However, how these processes are linked remains largely unresolved. Erysimum linifolium (wallflower) provides an excellent model for understanding these interactions due to its easily staged flowers and close taxonomic relationship to Arabidopsis. This has facilitated microarray analysis of gene expression during petal senescence and provided gene markers for following the effects of treatments on different regulatory pathways. Results In detached Erysimum linifolium (wallflower) flowers ethylene production peaks in open flowers. Furthermore senescence is delayed by treatments with the ethylene signalling inhibitor silver thiosulphate, and accelerated with ethylene released by 2-chloroethylphosphonic acid. Both treatments with exogenous cytokinin, or 6-methyl purine (which is an inhibitor of cytokinin oxidase), delay petal senescence. However, treatment with cytokinin also increases ethylene biosynthesis. Despite the similar effects on senescence, transcript abundance of gene markers is affected differentially by the treatments. A significant rise in transcript abundance of WLS73 (a putative aminocyclopropanecarboxylate oxidase) was abolished by cytokinin or 6-methyl purine treatments. In contrast, WFSAG12 transcript (a senescence marker) continued to accumulate significantly, albeit at a reduced rate. Silver thiosulphate suppressed the increase in transcript abundance both of WFSAG12 and WLS73. Activity of reactive oxygen species scavenging enzymes changed during senescence. Treatments that increased cytokinin levels, or inhibited ethylene action, reduced accumulation of hydrogen peroxide. Furthermore, although auxin levels rose with senescence, treatments that delayed early senescence did not affect transcript abundance of WPS46, an auxin-induced gene. Conclusions A model for the interaction between cytokinins, ethylene, reactive oxygen species and auxin in the regulation of floral senescence in wallflowers is proposed. The combined increase in ethylene and reduction in cytokinin triggers the initiation of senescence and these two plant growth regulators directly or indirectly result in increased reactive oxygen species levels. A fall in conjugated auxin and/or the total auxin pool eventually triggers abscission

A simple non-destructive method for laboratory evaluation of fruit firmness

Devices which offer simple, inexpensive, reliable and non-destructive objective measurement of fruit firmness assist in the monitoring of quality. For the present study, the Analogue CSIRO Tomato Firmness Meter (AFM), which measures fruit deformation under a 500 g load applied for 30 s was modified by replacing the analogue displacement gauge with a digital gauge and by using a laboratory jack for positioning the fruit in the vertical dimension. Non-destructive measurements of tomato fruit softening during ripening and determined with the Digital Firmness Meter (DFM) were strongly correlated with both firmness measured with the AFM (r(2) = 0.96, n = 19) and with firmness determined subjectively by hand pressure (r(2) = 0.93, n = 19). Similarly, mango fruit softening during ripening was monitored and DFM and hand firmness measurements were well correlated (r(2) = 0.95, n = 10). The firmness of individual fruit could be measured around 20% faster with the DFM than with the AFM, and displacement was easier to read from the digital than from the analogue display. The DFM proved to be a suitable device for measuring fruit firmness in postharvest laboratory studies and warrants evaluation under commercial packing and handling conditions

Responses of banana fruit to treatment with 1-methylcyclopropene

Experiments were conducted to determine levels of 1-methylcyclopropene (1-MCP) exposure needed to prevent ethylene-stimulated banana fruit ripening, characterise responses of ethylene-treated fruit to subsequent treatment with 1-MCP, and to test effects of subsequent ethylene treatment on 1-MCP-treated fruit softening. Fruit softening was measured at 20 degrees C and 90% relative humidity. One hour exposure at 20 degrees C to 1000 nl 1-MCP/l essentially eliminated ethylene-stimulated ripening effects. Exposure for 12 h at 20 degrees C to just 50 nl 1-MCP/l was similarly effective. Fruit ripening initiated by ethylene treatment could also be delayed with subsequent 1-MCP treatment. However, 1-MCP treatment only slowed down ripening of ethylene-treated fruit when applied at 1 day after ethylene and was ineffective when applied 3 or 5 days after ethylene treatment. The ripening response of fruit treated with 1-MCP and subsequently treated with ethylene varied with interval time between 1-MCP and ethylene treatments. As time increased, the response of 1-MCP-treated fruit to ethylene was enhanced. Responses to 0.1, 1, 10 or 100 mu l ethylene/l concentrations were similar. Enzyme kinetic analysis applied to 1-MCP effects on ethylene-induced softening of banana fruit suggested that 1-MCP inhibition is by noncompetitive antagonism of ethylene binding

Responses of native Australian cut flowers to treatment with 1-methylcyclopropene and ethylene

Postharvest longevity of some cut flowers is shortened by exposure to ethylene gas. Adverse effects of ethylene may be prevented by treatment with 1-methylcyclopropene (1-MCP) gas. Responses of 14 different native Australian cut powers to 1-MCP and ethylene applied at concentrations of 10 nL.L-1 and 10 mu L.L-1, respectively, were examined. Each gas was applied alone for 12 hours at 20 degrees C and they were also applied in series. Vase lives of Ceratopetalum gummiferum, Chamelaucium uncinatum, Grevillea 'Kay Williams' and 'Misty Pink', Leptospermum petersonii, Telopea 'Shady Lady', and Verticordia nitens were reduced by ethylene treatment. Treatment with 1-MCP generally protected these cut flowers against subsequent exposure to ethylene. The 1-MCP treatment usually did not extend their vase lives in the absence of exogenous ethylene

The influence of relative humidity on disease caused by Botrytis cinerea in non-harvested versus harvested waxflower flowers

Waxflower (Chamelaucium) is an Australian native plant cultivated for cut flowers. The major problem during postharvest handling and transport of cut waxflower stems is floral abscission caused by Botrytis cinerea. To investigate infection of waxflower flowers by this fungal pathogen, experiments were conducted encompassing various environmental conditions in the laboratory, greenhouse and field with two waxflower cvs. Mullering Brook and My Sweet Sixteen. Under laboratory conditions at 20A degrees C and > 95% RH in moistened bags, flowers of both cultivars either harvested or non-harvested showed similar susceptibility to B. cinerea. For inoculated and non-inoculated sprigs at 11 days after treatment, disease incidence on cvs. Mullering Brook and My Sweet Sixteen flowers ranged between 99.0-99.2% and 88.4-88.9%, respectively. Corresponding floral abscission ranges were 98.5-100% and 88.4-92.9%, respectively. Under greenhouse conditions and > 95% RH, floral abscission ranges for inoculated flowers of both cultivars were 69.1-71.1% and 46.0-73.0%, respectively. Corresponding disease incidence ranges were 54.9-55.8% and 28.8-43.4%, respectively. Under field conditions and > 95% RH, cv. My Sweet Sixteen flowers were more resistant to B. cinerea infection (3.0-3.1% in year 1; 0.9-2.0% in year 2) than were cv. Mullering Brook flowers (33.1-51.9% in year 1; 44.0-57.1% in year 2). Under all experimental conditions, inoculated flowers that were not covered with moistened bags showed significantly (P < 0.05) lower levels of disease incidence (0-11.9%) and floral abscission (2.4-37.8%). This observation is consistent with quiescence of the fungus in the field, and activation of infection by favourable temperature and humidity conditions after harvest leading to floral abscission

An Eye for an Eye: Proportionality and Surveillance

It is often claimed that surveillance should be proportionate, but it is rarely made clear exactly what proportionate surveillance would look like beyond an intuitive sense of an act being excessive. I argue that surveillance should indeed be proportionate and draw on Thomas Hurka’s work on proportionality in war to inform the debate on surveillance. After distinguishing between the proportionality of surveillance per se, and surveillance as a particular act, I deal with objections to using proportionality as a legitimate ethical measure. From there I argue that only certain benefits and harms should be counted in any determination of proportionality. Finally I look at how context can affect the proportionality of a particular method of surveillance. In conclusion, I hold that proportionality is not only a morally relevant criterion by which to assess surveillance, but that it is a necessary criterion. Furthermore, while granting that it is difficult to assess, that difficulty should not prevent our trying to do so