Investigating the effect of Glomus etunicatum colonization on structure and phloem transport in roots of Eragrostis curvula (Umgeni)
- Authors: Skinner, Amy
- Date: 2007
- Subjects: Glomus (Fungi) , Phloem , Plant translocation , Weeping lovegrass , Vesicular-arbuscular mycorrhizas , Mycorrhizal fungi , Mycorrhizas
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4227 , http://hdl.handle.net/10962/d1003796 , Glomus (Fungi) , Phloem , Plant translocation , Weeping lovegrass , Vesicular-arbuscular mycorrhizas , Mycorrhizal fungi , Mycorrhizas
- Description: The symbiotic unit of an arbuscular mycorrhizal fungus and its host is able toachieve and maintain far higher inflow of nutrients than non-mycorrhizal roots. The colonization strategy of the mycobiont within the plant is intrinsic to the symbiosis with respect to both structural adaptations and nutrient exchange. An investigation into the effect of Glomus etunicatum colonization on the structure and phloem transport in Eragrostis curvula (Umgeni) allowed for greater insight into the dynamic of the symbiosis. The combined use of stains (such as Trypan Blue, Chlorazol Black, Safranin and Fast Green), and techniques, (such as freeze-microtome transverse sectioning and permanent slide preparations) contributed to a successful general observation of an intermediate colonization strategy using light microscopy methods. However, clarity into structural detail of mycorrhizal forms required electron microscopy studies. The SEM method used with freeze fracture was a relatively quick and simple method allowing for the observation of surface and internal features. The TEM method allowed for highresolution images providing insight into the variations in the apoplasmic compartmental form, and how this may relate to the function of the symbiosis with regard to fungal coils or arbuscules. The apoplasmic nature of mycorrhizas was substantiated and no symplasmic connections were found between symbionts. Fluorescence studies demonstrated that 5,6-carboxyfluorescein was transported through the phloem into the roots of E. curvula, but remained predominantly in the root phloem. Unloading only occurred in optimal nutrient exchange areas of meristimatic lateral or apical growth regions. It was not possible, using fluorescence techniques and related equipment available, to conclusively establish if there were symplasmic connections between the mycobiont and its host or if bidirectional transfer of nutrients occurred at the same interface.
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- Date Issued: 2007
Confirmation of a slow symplasmic loading and unloading pathway in barley (Hordeum Vulgare L.) source and sink leaves
- Authors: Buwa, Lisa Valencia
- Date: 2003
- Subjects: Phloem , Plant translocation , Barley -- Metabolism
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4253 , http://hdl.handle.net/10962/d1007804
- Description: Visualization of the transport pathway in barley (Hordeum vulgare) leaves was carried out using a combination of aniline blue and a symplasmically transported fluorochrome, 5,6 carboxyfluorescein (5,6-CF). When applied to a source leaf, basipetal movement of 5,6-CF was observed after 3 h and the fluorochrome front was observed about 3-4cm away from the point of application. The fluorochrome was taken up into the symplasm of the mesophyll and was loaded into the bundle sheath cells and then subsequently the vascular parenchyma and finally into the sieve tubes. In sink leaves, acropetal movement was observed after 3 h and the fluorochrome had moved approximately 3 cm away from the point of application. Unloading of 5,6-CF occurred from all classes of longitudinal veins. Studies on solute retrieval showed that 5,6 CF-diacetate was transferred to xylem parenchyma where it was metabolized. 5,6-CF was then transferred from the xylem parenchyma to the vascular parenchyma cells, and it would appear that thick-walled sieve tubes were the first to show 5,6-CF labeling. Counterstaining with aniline blue demonstrates the presence of plasmodesmata and this suggests a potential symplasmic pathway from the mesophyll to the sieve tubes. Application of 5,6 CF-diacetate revealed a slow symplasmic pathway, which involved transfer of 5,6-CF, which was effected via plasmodesma.
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- Date Issued: 2003
Symplasmic pathway in phloem loading and unloading in source and sink leaves of Zea mays L. as evidenced under normal and elevated CO₂ conditions
- Authors: Nogemane, Noluyolo
- Date: 2003
- Subjects: Phloem , Plant translocation , Plant cells and tissues , Corn -- Metabolsim
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4254 , http://hdl.handle.net/10962/d1007813
- Description: Zea mays plants kept at ambient (ca 375ppm) and elevated CO₂ (ca 650 to 700ppm) were used to examine the possibility of a symplasmic loading, unloading and transport pathway in dark-adapted and illuminated (200μmolm⁻²sec⁻¹ ) sink and source leaves. 5,6-carboxyfluorescein diacetate was introduced into the mesophyll cells and symplasmic transfer observed 3h after application. In sink and source leaves exposed to ambient CO₂ and illuminated at 200 molm-2sec-1, the fluorescence front was observed approximately 3cm from the point of application, while in dark-adapted plants, the fluorescence front was observed approximately 1cm from the point of application. Under elevated CO₂ conditions the fluorescence front in illuminated plants appeared to transport faster moving approximately 5cm from the point of application, and in dark-adapted plants, only 3cm from the point of application. Based on the increase in 5,6-CF accumulation under elevated CO₂ conditions, the present study suggests that there was an increase in capacity for assimilate loading and transport under elevated CO₂ conditions. In source leaves, 5,6-CFDA was taken up into the mesophyll cells, loaded symplasmically and transported basipetally. In sink leaves 5,6- CFDA was taken up from basal mesophyll and after symplasmic loading, was transported acropetally where it was offloaded into the younger immature sink region. Transport in the sieve tubes was confirmed by using aniline blue, which was applied 3h after 5,6-CF transport. Aniline blue coupled with 5,6-CF transport studies showed that the sieve tubes of both cross and longitudinal veins are involved in symplasmic unloading, loading and transport processes in sink and source leaves. Apoplasmic uptake of 5,6-CFDA by cut leaves showed that after apoplasmic transport via the transpiration stream, 5,6-CFDA was offioaded to the xylem parenchyma where it was metabolically cleaved , releasing fluorescent 5,6-CF into the xylem parenchyma. Transverse sections cut after 3h of uptake were observed after 120 and 180 min suggesting that a retrieval of solutes occurs from the xylem to the xylem parenchyma, bundle sheath, phloem parenchyma and to the th in-walled sieve tubes. It was not possible to determine if the thick-walled sieve tubes were involved or if they took up 5,6-CF. Given the available data on loading and offioading of assimilates in sink and source leaves respectively, this study demonstrated that a slow symplasmic pathway exists from the mesophyll to the phloem, and that offloading from the phloem in sink leaves can occur via a symplasmic route.
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- Date Issued: 2003
Observations of selective feeding of the aphid, Sitobion yakini (eastop) on leaf blades of barley (Hordeum vulgare L)
- Authors: Matsiliza, Babalwa
- Date: 2000
- Subjects: Aphids , Phloem , Barley
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4212 , http://hdl.handle.net/10962/d1003781 , Aphids , Phloem , Barley
- Description: Penetration of leaves of barley (Hordeum vulgare L.) plants grown under normal conditions and those exposed to physiological stress, by the aphid, Sitobion yakini was investigated using light and electron microscope techniques. This was carried out to determine if there was evidence of preferential feeding on either thin- or thick-walled sieve tubes in the barley leaf. Under both stress and non-stress conditions, preliminary results of an electron microscope investigation showed that penetration of the epidermis and mesophyll was largely intercellular, becoming partly intercellular and in part intracellular inside the vascular bundle. A total of 317 stylets and stylet tracks were encountered during the examination of 2000 serial sections. In non-stressed plant material, 293 (92%) terminated in thin-walled sieve tubes and only 24 (8%) in thick-walled sieve tubes. Investigation of 1000 serial sections using stressed plant material showed, that 84 of 89 (94%) stylets and stylet tracks encountered terminated in thin-walled sieve tubes. Furthermore, 90 of 94 (96%) stylets and stylet tracks encountered in 1000 serial sections from the second experiment of control non-stressed plant material (control) terminated in thin-walled sieve tubes. The thin-walled sieve tubes were significantly more visited (probed) by the aphid than the thick-walled sieve tubes. Under stress conditions, 50 of 89 (56%) stylets and stylet tracks which terminated in thin-walled sieve tubes were associated with the small longitudinal bundles. Under normal conditions, 65 of 94 (69%) stylets and stylet tracks which terminated in thin-walled sieve tubes were associated with the small longitudinal bundles. There were no significant differences on the number of probes of sieve elements between the two treatments. These data suggest that the aphid S. yakini feeds preferentially on the thin-walled sieve tubes of the small longitudinal vascular bundles in plants grown under normal conditions and those exposed to physiological stress, such as water stress. This further suggests that the thin-walled sieve tubes in barley leaf blades are more attractive to the aphid and are probably most functional in terms of phloem loading and transport.
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- Date Issued: 2000