A xylem retrieval pathway in rice leaf blades – evidence of a role for endocytosis?
- Botha, Christiaan E J, Aoki, N, Scofield, G N, Liu, Lin, Furbank, R T, White, R G
- Authors: Botha, Christiaan E J , Aoki, N , Scofield, G N , Liu, Lin , Furbank, R T , White, R G
- Date: 2008
- Language: English
- Type: Article
- Identifier: vital:6505 , http://hdl.handle.net/10962/d1005930 , http://dx.doi.org/10.1093/jxb/ern150
- Description: The structure and transport properties of pit membranes at the interface between the metaxylem and xylem parenchyma cells and the possible role of these pit membranes in solute transfer to the phloem was investigated. Electron microscopy revealed a fibrillar, almost tubular matrix within the pit membrane structure between the xylem vessels and xylem parenchyma of leaf blade bundles in rice (Oryza sativa). These pits are involved primarily with regulating water flux to the surrounding xylem parenchyma cells. Vascular parenchyma cells contain large mitochondrial populations, numerous dictyosomes, endomembrane complexes and vesicles in close proximity to the pit membrane. Taken collectively this suggests that endocytosis may occur at this interface. A weak solution of 5,6-carboxyfluorescein diacetate (5,6-CFDA) was applied to cut ends of leaves and after a minimum of 45 minutes, the distribution of the fluorescent cleavage product, 5,6-carboxyfluorescein (5,6-CF) was observed using confocal microscopy. Cleavage of 5,6-CFDA occurred within the xylem parenchyma cells and the non-polar 5,6-CF was then symplasmically transported to other parenchyma elements and ultimately, via numerous pore plasmodesmata, to adjacent thick-walled sieve tubes. Application of Lucifer Yellow, and, separately, Texas Red labelled dextran (10 kDa) to the transpiration stream, confirmed that these membrane-impermeant probes could only have been offloaded from the xylem via the xylem vessel-xylem parenchyma pit membranes, suggesting endocytotic transmembrane transfer of these membrane-impermeant fluorophores. Accumulation within the thick-walled sieve tubes, but not in thin-walled sieve tubes, confirms the presence of a symplasmic phloem loading pathway, via pore plasmodesmata between xylem parenchyma and thick-walled sieve tubes, but not thin-walled sieve tubes.
- Full Text:
- Date Issued: 2008
- Authors: Botha, Christiaan E J , Aoki, N , Scofield, G N , Liu, Lin , Furbank, R T , White, R G
- Date: 2008
- Language: English
- Type: Article
- Identifier: vital:6505 , http://hdl.handle.net/10962/d1005930 , http://dx.doi.org/10.1093/jxb/ern150
- Description: The structure and transport properties of pit membranes at the interface between the metaxylem and xylem parenchyma cells and the possible role of these pit membranes in solute transfer to the phloem was investigated. Electron microscopy revealed a fibrillar, almost tubular matrix within the pit membrane structure between the xylem vessels and xylem parenchyma of leaf blade bundles in rice (Oryza sativa). These pits are involved primarily with regulating water flux to the surrounding xylem parenchyma cells. Vascular parenchyma cells contain large mitochondrial populations, numerous dictyosomes, endomembrane complexes and vesicles in close proximity to the pit membrane. Taken collectively this suggests that endocytosis may occur at this interface. A weak solution of 5,6-carboxyfluorescein diacetate (5,6-CFDA) was applied to cut ends of leaves and after a minimum of 45 minutes, the distribution of the fluorescent cleavage product, 5,6-carboxyfluorescein (5,6-CF) was observed using confocal microscopy. Cleavage of 5,6-CFDA occurred within the xylem parenchyma cells and the non-polar 5,6-CF was then symplasmically transported to other parenchyma elements and ultimately, via numerous pore plasmodesmata, to adjacent thick-walled sieve tubes. Application of Lucifer Yellow, and, separately, Texas Red labelled dextran (10 kDa) to the transpiration stream, confirmed that these membrane-impermeant probes could only have been offloaded from the xylem via the xylem vessel-xylem parenchyma pit membranes, suggesting endocytotic transmembrane transfer of these membrane-impermeant fluorophores. Accumulation within the thick-walled sieve tubes, but not in thin-walled sieve tubes, confirms the presence of a symplasmic phloem loading pathway, via pore plasmodesmata between xylem parenchyma and thick-walled sieve tubes, but not thin-walled sieve tubes.
- Full Text:
- Date Issued: 2008
Using assessment and reflexive teaching practices to inform and guide changes to the teaching and learning activities in Introductory Accounting
- Authors: Bezuidenhout, L Peta
- Date: 2008
- Language: English
- Type: Conference paper
- Identifier: vital:6081 , http://hdl.handle.net/10962/d1008585
- Description: Teaching accounting to first year university students in higher education institutions is becoming increasingly complex as we deal with increasing class sizes, increasing diversity and a student body which appears to be less inclined to study without external motivating factors, while to be successful in studying accounting requires more than passive learning. Our aim was to make our students active participants in their accounting studies. After studying established research into assessment and approaches to student learning, changes were made to our course to ensure increased and active participation from our students. Critical to this change was guiding students in making the shift from a surface approach to learning, to a deep approach to learning where they would engage with the subject matter in a manner more likely to result in truly understanding the concepts and principles being taught. An important part of implementing these changes was asking our students to evaluate the innovations after they had taken place. Feedback received from our students resulted in the use of a new and unplanned innovation in the form of the setting of regular mini-tests. This was arguably the most successful of all the interventions introduced during the year and resulted in our journey being more exciting and less predictable than expected.
- Full Text:
- Date Issued: 2008
- Authors: Bezuidenhout, L Peta
- Date: 2008
- Language: English
- Type: Conference paper
- Identifier: vital:6081 , http://hdl.handle.net/10962/d1008585
- Description: Teaching accounting to first year university students in higher education institutions is becoming increasingly complex as we deal with increasing class sizes, increasing diversity and a student body which appears to be less inclined to study without external motivating factors, while to be successful in studying accounting requires more than passive learning. Our aim was to make our students active participants in their accounting studies. After studying established research into assessment and approaches to student learning, changes were made to our course to ensure increased and active participation from our students. Critical to this change was guiding students in making the shift from a surface approach to learning, to a deep approach to learning where they would engage with the subject matter in a manner more likely to result in truly understanding the concepts and principles being taught. An important part of implementing these changes was asking our students to evaluate the innovations after they had taken place. Feedback received from our students resulted in the use of a new and unplanned innovation in the form of the setting of regular mini-tests. This was arguably the most successful of all the interventions introduced during the year and resulted in our journey being more exciting and less predictable than expected.
- Full Text:
- Date Issued: 2008
- «
- ‹
- 1
- ›
- »