Pepper plants (Capsicum annuum L.) were grown in field and a greenhouse in Arizona to determine the effects of water stress, root temperature, and exogenously applied growth regulators on cytokinin production and the resulting growth. Research showed that vegetative plants were significantly higher in cytokinin activity and growth parameters than fruiting plants. Also, in root-pruned fruiting plants, cytokinin activity was less than that of intact fruiting plants. In vegetative plants, the competition between removed sinks and the rest of the shoot was reduced and, hence, more cytokinin came from the roots to the shoots. Besides, additional carbohydrates were available and recycled to the roots. In respect to temperature effect, elevating temperature from 15 to 30°C had a pronounced effect of increasing the growth rate and cytokinin activity. The measured parameters declined when temperature exceeded 30°C. Temperatures between 25 and 30°C were found to be optimum. Under experimental conditions, growth regulators (Cytex® and Burst®) applied to the soil or foliage had no significant effect on growth rates or cytokinin activity in roots. Also, applying Burst® or kinetin to the nutrient medium had inconsistent and statistically nonsignificant effects on photosynthesis and transpiration.

No description available.

No description available.

Typescript (photocopy) / xxiv, 183 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Physiology, 1982?

Call number: LD2668 .T4 1986 X8 / Master of Science / Horticulture, Forestry, and Recreation Resources

Tomato plants (Lycopersicon esculentum Mill.) were grown in the greenhouse and in the field during 1979 and 1980. The inflorescences were treated with gibberellin (GA4/7) and/or benzyladenine (BA). Root exudate was collected at various stages of growth and development for the estimation of the levels of cytokinins in the plant. Soluble sugars and starch were determined in inflorescences at different stages of development. Partitioning of dry matter between the different plant portions was studied to evaluate growth of tomato plants in two different conditions. The application of GA4/7 and BA to tomato inflorescences promoted the development and increased the number of flowers. These growth regulators substantially increased fruit set and yield of tomatoes in both greehouse and field experiments. Determinations of carbohydrates in inflorescences treated with growth regulators showed higher amounts of soluble sugars and starch over a considerable period of development. The level of cytokinins in root exudate was higher during early phase of vegetative growth. At the time of bud formation and anthesis, the level of cytokinins declined. The quantity of translocated cytokinins in the greenhouse was 4 to 5 times higher than under high temperatures in the field. The low levels of cytokinins were associated with poor flower development. Field grown tomato plants produced more vegetative growth and fewer inflorescences than plants in the greenhouse. Allocation of assimilates to newly developed leaves and low level of growth regulators in buds and inflorescences might contribute towards more vegetative growth but poor flowering under high temperatures.

Bibliography: leaves 216-237 / vii, 327 leaves, [31] leaves of plates : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Physiology, 1985

M.Sc. / Field grown plants are constantly challenged with a variety of stressful factors, such as high temperatures, drought and pathogen infection that adversely affect crop production and quality. These stresses seldom occur as single entities in plants and in warm climates, heat stress is often a common dominator in combinatorial stress. The heat shock (HS) response in plants has priority over other stress responses, including the pathogen-induced stress response. Activation of the HS response prevents the normal plant defence strategy, leaving the plant vulnerable to pathogen attack. However, prior exposure to elevated temperatures confers protection from subsequent, otherwise lethal, temperatures (thermotolerance) and a variety of other stress conditions including heavy-metals, chilling injury and certain pathogens (cross tolerance). In general, litterature supports a central role for heat shock proteins (HSP), in particular the 70 kDa HSP (Hsp70), in thermotolerance. Incompatible host-pathogen interactions lead to the activation of an array of defence mechanisms, including the promotion of phenylpropanoid metabolism. Phenylalanine ammonia-lyase is a key regulator of this metabolic pathway, influencing the production of salicylic acid, lignin and phytoalexins among other essential defence products. In this study it was hypothesised that prior exposure to non-lethal HS confers protection from subsequent heat-related suppression of the phenylpropanoid pathway, induced as a defence mechanism during an incompatible plant-pathogen interaction. This hypothesis was verified by analysing the effect of thermotolerance on pathogen-related stimulation of PAL promoter activity, enzyme activity and lignin deposition. The tomato, Lycopersicon esculentum cultivar UC82B and Ralstonia solanacearum, the causative agent of bacterial wilt, were used as host-pathogen model. Specific objectives in the study were: (1) Development of PAL promoter-GUS reporter transformed Lycopersicon esculentum. (2) Establishment of a thermotolerance protocol that ensures optimal Hsp70 levels at subsequent HS. (3) Evaluation of the influence of prior heat treatment on phenylpropanoid metabolism after exposure to HS in combination with Ralstonia solanacearum. Results obtained support the hypothesis indicating that thermotolerance protects phenylpropanoid metabolism, in particular PAL promoter and enzyme activity, and to a certain extent lignin production, induced by avirulent Ralstonia solanacearum during a second severe HS. In contrast, HS without a prior heat treatment, suppressed phenylpropanoid metabolism. The protective potential of prior heat treatment during subsequent infection under hyperthermic conditions support the application of HSP in the development of novel plant protection strategies.

Ph.D. / In plants, salicylic acid (SA) is a signaling molecule that regulates disease resistance responses such as systemic acquired resistance (SAR) and the hypersensitive response (HR), and has been implicated in both basal and acquired thermotolerance. It has also been shown that SA enhances heat-induced Hsp/Hsc70 accumulation in plants. In this study, temperature studies revealed that heat shock (HS) at 40 °C for 30 min significantly induced Hsp/Hsc70 accumulation in 3-week old tomato (UC82B) seedlings. Time- and dose-responsive studies showed that 0.1 mM SA for 17 hrs was unable to induce Hsp/Hsc70 but in combination with HS significantly (P > 0.001) potentiated this response. To investigate the mechanism of SA-mediated, heat-induced Hsp/Hsc70 potentiation, tomato seedlings were treated with either SA alone, HS or both, before analyses of hsp70 mRNA, Hsf DNA-binding and gene expression of hsp70, hsfAl, hsfA2 and hsfEll. SA alone established Hsf DNA-binding, but was not accompanied by increased Hsp70 accumulation or expression of hsp70 mRNA. SA had no significant effect on hsfA2 and hsf81 gene expression, but increased the basal levels of hsfAl. In heat-shocked plants, Hsf DNA-binding was enhanced, and increased hsfAl, hsfA2 and hsfB1 expression preceded accumulation of Hsp70. The combined treatment of SA and HS resulted in potentiated Hsf DNA-binding, enhanced expression of hsp70, hsfAl, hsfA2 and hsfB1, leading to potentiated levels of Hsp/Hsc70. Since increased hsp70 and hsf gene expression coincided with increased levels of Hsp70 accumulation, it is likely that the SA-mediated potentiation of Hsp70 is due to the ability of SA to regulate Hsfs during HS. This study therefore proposes a mechanism for the potentiation of Hsp70 by SA in the presence of heat, which might contribute to our understanding of the role SA plays in the heat shock response and thermotolerance.

Phenomenological models are presented which predicts transpiration rates (E) of individual leaves of Scaevola plumieri, an indigenous dune pioneer, and Ammophila arenaria, an exotic grass species introduced to stabilise mobile sand. In both cases E is predictably related to atmospheric vapour pressure deficit (VPD). VPD is calculated from measurements of ambient temperature and humidity, hence, where these two environmental variables are known, E can be calculated. Possible physiological reasons for the relationships of E to VPD in both species are discussed. Scaling from measurements of E at the leaf level to the canopy level is achieved by summing the leaf area of the canopy in question. E is predicted for the entire canopy leaf area by extrapolation to this larger leaf area. Predicted transpiration rates of individual shoot within the canopy were tested gravimetrically and shown to be accurate in the case of S. plumieri, but less so in the case of A. arenaria. Using this model, the amount of water used by a known area of sand dune is shown to be less than the rainfall input in the case of S. plumieri in wet and dry years. The water use of A. arenaria exceeds rainfall in the low-rainfall year of 1995, while in 1998 rainfall input is slightly higher than water extraction by the plants. Using a geographic information system (GIS), regional maps (surfaces) of transpiration were calculated from surfaces of mean monthly temperature and mean monthly relative humidity. Monthly surfaces of transpiration were subtracted from the monthly median rainfall to produce a surface of mean monthly water deficit. Areas of water surpluses along the coast correspond with the recorded distribution of both species in the seasons that the plants are most actively growing and reproducing. This suggests that unfavourable water availability during these two species growth periods limit their distributions along the coast. In addition to unfavourable water deficits, additional climatic variables that may be important in limiting the distribution of these two species were investigated using a discriminant function analysis.