Planting date, storage and gibberellic acid affect dormancy of Zantedeschia Spreng. hybrids : a thesis presented in partial fulfilment of the requirements for the degree of Masters in Applied Science, Massey University, Palmerston North, New Zealand

To match the supply of Zantedeschia cut flowers and tubers to the demands of the international market, crops have to be timed to a schedule, which requires control of the growth cycle and, in particular, dormancy. In order to improve the predictability and accuracy of timing of Zantedeschia, the effect of different planting seasons and two dormancy-breaking treatments were tested on cultivars 'Black Magic' and 'Treasure', which were known to have a contrasting level of dormancy. Tissue-cultured plants were ex-flasked in July and November 1999, and grown for 180 days in a heated glasshouse (first cycle). Between 120 and 180 days of growth, plants were harvested at 15 days intervals, and tubers cured. Subsequently, tubers were stored for 0 or 3 weeks (10 ± 1°C; 70-80% RH) and dipped in 100 mg.L -1 gibberellic acid plus surfactant or water plus surfactant, prior to planting for dormancy assessment (second cycle). Growing the plants with four months difference in planting date did not cause major alteration in the occurrence of dormancy. Dormancy was brought forward by up to 10 days after the November date of ex-flask, but this was most likely to be due to higher temperatures during that period. In contrast, depth of dormancy varied between cultivars, with 'Black Magic' taking in average 16 days longer to emerge than 'Treasure'. Storage partially released bud dormancy of the tubers. It increased emergence to over 80% regardless of the time of harvest in the first cycle and cultivar, but reduced time to emergence mostly after harvests at 180 days. Furthermore, following storage, time to emergence was reduced to over 50 and 30 days for 'Black Magic' and 'Treasure', respectively, which exceeded the commercially acceptable period to emerge. Gibberellic acid also broke bud dormancy, improving emergence to over 80%, and reduced time to emergence to between 29 and 57 days, irrespective of the time of harvest in the first cycle and cultivar. The effectiveness of gibberellic acid at any time following harvest during the first cycle, may imply that dormancy of Zantedeschia is not as deep as in temperate woody plants. Cessation of leaf emergence in the first cycle was found not to be directly related to the occurrence of dormancy. Degree-days, on the other hand, presented a possible alternative to predict this process. It was estimated that deepest dormancy of 'Black Magic' occurred between 2614 and 2732 °C-days after planting, while deepest dormancy of 'Treasure' occurred between 2681 and 2839 °C-days after planting. The present study presents storage and gibberellic acid as possible options to control dormancy, and the use of degree-days to predict the occurrence of this process. Further research is necessary to develop these options as commercially applicable practices, and to further clarify the process of dormancy in Zantedeschia

Long Term Effects of Chronic Variable Stress Administered during Different Developmental Stages in Mice

A number of studies have suggested that the occurrence of past trauma can increase an individual\u27s chance of developing PTSD from a new traumatic experience later in life. Trauma that occurs during childhood appears to have a particularly strong effect on this risk increase. Furthermore, conditioned fear responses have been shown to incubate over extended periods of time in animal models. To further investigate the role these phenomena play in the development of PTSD, this study exposed juvenile and adult mice to 7 days of chronic variable stress (CVS). One month later, a Pavlovian delay fear conditioning procedure was used to assess fear learning behavior, and anxiety levels were assessed with an Elevated Plus-Maze (EPM). It was hypothesized that mice who experienced CVS exposure as juveniles would show greater long-term levels of anxiety and long-term sensitization to later fear learning than mice who experienced CVS as adults. Furthermore, mice exposed to CVS, regardless of age, were hypothesized to show significantly enhanced anxiety and fear conditioning relative to control mice. Surprisingly, it was found that stress induced sensitization of fear conditioning deteriorated over the 30-day incubation period for both juvenile and adult mice, leading to no differences between groups, including controls, in fear learning behaviors. Adult stressed mice showed significantly greater anxiety levels than adult controls, while juvenile stressed and control mice showed no difference in anxiety. These results suggest possible neurological differences between juvenile and adult mice in regions involved in fear learning, such as the hippocampus, the central nucleus of the amygdale, and the bed nucleus of the stria terminalis. Alternative interpretations of the data are discussed. Despite failing to support the proposed hypotheses, this study suggests that a successful animal model of PTSD should consider the differential dynamics of associative and non-associative fear learning processes. Furthermore, the moderating effects of developmental stages on the effects of chronic stress should also be acknowledged and investigated further

Dissecting accretion and outflows in accreting white dwarf binaries

This is a White Paper in support of the mission concept of the Large Observatory for X-ray Timing (LOFT), proposed as a medium-sized ESA mission. We discuss the potential of LOFT for the study of accreting white dwarfs. For a summary, we refer to the paper.Comment: White Paper in Support of the Mission Concept of the Large Observatory for X-ray Timin