Thesis (PhD) -- Macquarie University, School of Biological Sciences, 1988. / Bibliography: leaves 112-121. / General introduction to seed priming -- Water relations of tomato seed germination -- Water relations to tomato seeds during priming -- Water relations of germinating primed tomato seeds -- Histological study of tomato seed germination and priming -- Endosperm weakening during germination and priming of tomato seeds -- General discussion -- References. / It is the aim of this thesis to examine hypotheses regarding the prevention of radicle emergence during priming and of the enhancement of germination following priming. This work should identify the control sites in the processes of radicle emergence and their modification during priming. -- For the most part these hypotheses are underlain by an analysis of germination as a special case of plant cell expansion. A study of cell expansion requires an understanding of the water relations of the tissues involved. Therefore, the sequence of events during the germination of tomato seeds was first examined through a water relations study then the changes caused by priming were examined. -- The study of the water relations of germinating tomato seeds revealed that the seeds came into Ψ equilibrium with the imbibitional solution, whereas, the embryo was measured at much lower Ψ. There was no evidence of a lowering of embryo Ψπ nor of an increase in embryo Ψp prior to radicle emergence. The embryo Ψ measurements need to be interpreted with caution for they are ex situ measurements and thus do not directly measure these properties in the seed. It is unlikely that a large ΔΨ could be maintained within the seed during imbibition. Thus the existence of a large seed to embryo Ψp can be inferred from these measurements. The moisture release isotherm of the excised embryo confirmed this inference. The endosperm tissue enclosing the embryo was found to restrict the hydration level of the embryo prior to its emergence. As the embryo was capable of expansive growth prior to radicle emergence, it was concluded that the weakening of the endosperm controlled radicle emergence in tomato seeds. -- During priming the tomato seeds were in Ψ equilibrium with the priming solution, but the embryo was not. As the embryo was capable of growth after 2 days of the 6 day priming treatment, it was concluded that radicle emergence was prevented by the maintenance of the endosperm restraint. Germinating primed seeds did not display a marked plateau during imbibition. Both seed and embryo water contents were higher than those of non-primed seeds. However, embryo Ψ and Ψπ were lower than those of embryos from non-primed seeds, eventhough embryo Ψπ measurements during priming had not revealed significant lowering. The relative growth rate of seedlings from primed seeds was higher than that of non-primed seeds for the first 12 h after radicle emergence. / The endosperm of tomato seeds consisted of two distinct cell types found in separate locations within the seed. At the micropylar end of the seed the endosperm cells had thin walls, whereas those in the rest of the seed had thickened walls. The outer walls of outermost endosperm cells in the rest of the seed had massively thickened walls whereas these were lacking from the outer cells of the micropylar region. -- All cells, except those of the root cap, contained protein bodies. The protein bodies of the micropylar region endosperm cells were seen to breakdown to form vacuoles prior to radicle emergence. The protein bodies in other cells did not appear to change prior to this time. During priming protein body breakdown was more extensive in the micropylar region endosperm cells and vacuole formation also occurred in the radicle. After radicle emergence the cells of the radicles from primed seeds were found to be about 50% larger than those of the radicles from non-primed seeds. -- Endosperm weakening preceded radicle emergence in tomato seeds. Slower germinating seeds within the population had higher values for endosperm resistance. Endosperm weakening during priming resulted in values for endosperm resistance which were lower than those measured from a population of germinating non-primed seeds. Germinating primed seeds had resistances which were similar to those of priming seeds. It was concluded that a final rapid endosperm weakening step may be necessary for radicle emergence to occur. -- These studies have shown that tomato seeds prime because the endosperm does not weaken sufficiently to permit expansion of the radicle. The mechanism by which some endosperm weakening was permitted, but the final weakening for radicle emergence was prevented was not identifiable. Priming advanced the timing of radicle emergence by improving the rate of water uptake by the seeds; by eliminating the time necessary for the loosening of embryo cell walls and by permitting the completion of the first step of the endosperm weakening process. Enbryos from primed seeds had improved cell wall extensibilities which permitted higher relative growth rates during the first 12 h after radicle emergence. / Mode of access: World Wide Web. / x, 121 leaves, 4 leaves of plates ill

The International Seed Testing Association and the Association of Official Seed analysts define seed vigour as the ability of a seed lot to perform during the germination process and crop stand establishment under a wide range of environmental conditions. There are many ways to determine seed vigour, but few satisfy the requirements of being simple, inexpensive and reproducible, among others, to permit the seed industry to adopt seed vigour as an indicator of seed quality when they sell seeds. Hence, the standard germination test, which is performed under uniform and favourable conditions, is generally used to indicate seed quality when seeds are marketed. The objective of this study was to determine the performance of tomato and pepper seeds in response to pre-germination hydration and dehydration relative humidities (12%, 49% and 75% RH). Before hydration, seeds were hydrated at three temperatures (10°C, 20°C and 30°C). Hydration was performed by imbibing pre-weighed pepper ('Santarini' and 'California Wonder'), Chilli and tomato ('Heinz', 'Marondera' and 'Roma') seeds for 2 h in 10 ml of distilled H(2)0 per 100 seeds at 10°C, 20°C and 30°C. Dehydration was performed by change in seed mass determined during a 72-hour dehydration at 12%, 49% and 75% RH. Seed performance in response to imbibition and dehydration was determined by leakage of electrolytes from seeds during imbibition, laboratory germination capacity and seedling emergence under simulated shadehouse nursery conditions. A pot experiment was conducted to determine the effects of seed treatments on yield. Seed mass increased by about 50% during the 2-hour of hydration. Dehydration was hastened by decreasing the RH, and 12% RH significantly (P < 0.05) reduced the post-imbibition seed moisture content compared with 49% and 75% RH. The latter two relative humidities reduced the seed moisture content to about 10% and 15%, respectively, for all cultivars, irrespective of imbibition temperature. Low imbibition temperature (10°C) significantly (P < 0.01) increased electrolyte leakage, compared with high imbibition temperatures (20°C and 30°C), which were not significantly different from each other. At all hydration temperatures, low RH (12%) caused a significant (P < 0.01) decrease in seed germination whereas 49% RH and 75% RH apparently had a priming effect on seeds. There was no significant difference between imbibition temperatures, with respect to seed germination, but 100G caused a significant decrease in germination index, a measure of seed vigour. Seedling emergence was significantly (P < 0.01) reduced by both low imbibition temperature (10oG) and low dehydration relative humidity (12% RH). The negative effects of low imbibition temperature and rapid dehydration at 12% RH were also observed as stunted seedling growth. Principal component analysis and linear regression were used to determine a statistical model to predict seedling emergence from germination percentage. The model predicted emergence consistently, but it overestimated it by about 2% to 3%. It is concluded that low imbibition temperature and rapid dehydration can be used to simulate stress to determine seed performance in pepper and tomato. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.