Browsing by Author "Venter, T. L."
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- ItemStomatal density profiling in Vitis vinifera L. using non-destructive field microscopy(Stellenbosch : Stellenbosch University, 2015-12) Venter, T. L.; Strever, A. E.; Stellenbosch University. Faculty of Agrisciences. Dept. of Viticulture and Oenology.ENGLISH ABSTRACT: When plants began colonising land ca. 400 million years ago, they needed to adapt structurally to limit water loss from aerial parts. Thus, a waxy cuticle developed on these parts, particularly the leaves, in order to prevent transpiration from these surfaces. This layer is, however, impermeable to carbon dioxide (CO2) which is required as a substrate in photosynthesis. Therefore, the stomata evolved to allow for gaseous exchange to take place. The main function of stomata is to ensure that the amount of CO2 taken up by the plant is balanced with the amount of water available to it. Stomatal development and function has been studied extensively, but few of these studies have been done on Vitis vinifera L. Since the stomatal development process is complex and carefully guided, a lot of these past studies were conducted on the model plant Arabidopsis thaliana in order to attempt to ascertain which genes may be involved in this process, and how. Environmental stimuli have been found to affect both stomatal development and function. These effects can be short-term, in which case stomata will respond to a momentary change in conditions by opening or closing the stomatal pore (change in stomatal function), or long-term, by which the response is more permanent and affects stomatal density and/or size (change in stomatal development). Such factors which have been investigated include CO2 levels, relative humidity, both light quantity and quality, as well as limited water availability. It has been found that changes in response to water-stress are brought about by the increased production of the plant hormone, abscisic acid, in the roots, which is then transported to the leaves in the transpiration stream. For Vitis vinifera L. the effect of light (quantity and quality), CO2 concentration and water-stress on stomatal development and function have been investigated by other researchers. Various methods are used in stomatal research. The most common methods are light and scanning electron microscopy. These methods are both destructive and make use of intact leaf tissue, or epidermal peels and impressions. In this study an adapted microscopy technique was used in order to test whether it would be suitable for conducting stomatal investigations non-destructively over a period of time. Four Vitis vinifera L. cultivars were selected for this study and in-field stomatal investigations were carried out over the period between bunch closure and post-véraison. A portable digital microscope was used to capture images and these were then digitally analysed. The aim was to investigate whether stomatal density differs between cultivars, leaves of a single plant as well as between different positions on a single leaf. In general there were differences found between cultivars, but not all the differences were significant. Younger leaves displayed a higher stomatal density than more mature leaves and the degree of this also varied between cultivars. Little differences were noted over time and between on-leaf positions. The method was successful in conducting the relevant investigations, but it was not without problems and shortcomings. The resolution of the images produced was not sufficient to allow for the calculation of stomatal index and size, but stomatal density could be determined reliably. With the rate at which new technology becomes available, these issues may be minimised or eliminated in the near future, and the application of this method to stomatal investigations expanded.