The interactive effects of light, temperature and CO[subscript 2]/O[subscript 2] ratios on photosynthesis in Coix lachryma-jobi L
- Mjwara, Jabulani M, Botha, Christiaan E J
- Authors: Mjwara, Jabulani M , Botha, Christiaan E J
- Date: 1993
- Language: English
- Type: Article
- Identifier: vital:6527 , http://hdl.handle.net/10962/d1005961
- Description: A portable infra-red gas analyzer was used to investigate the interactive effects of light, temperature, and CO[subscript 2]/O[subscript 2] ratios under controlled environmental conditions in an attempt to model gas exchange characteristics of Coix lachryma-jobi L. Plotting light response curves as a function of temperature (20, 25, 30 and 35 degrees C) revealed no sign of light saturation even at a photosynthetic photon flux density (PPFD) close to 2000 µmol m[superscript -2]s[superscript -1]. High net assimilation rates (A) of approximately 24 µmol CO[subscript 2] m[superscript -2]s[superscript -1] were realized at 30-35 degrees C. Assimilation (A) versus internal CO[subscript 2] partial pressure Ci curves showed a steep rise in A with increase in C[subscript i] but saturated at approximately 150 µl[superscript -1] and the effect was similar in either the absence or presence of O[subscript 2], under all temperature regimes. C. lachryma-jobi exhibited low CO[subscript 2] compensation points (Γ*) between 0 and 10 µl[superscript -1] at either 0 or 21% O[subscript 2]. The slopes of double reciprocal plots of 1/A versus 1/C[subscript i], were nearly identical and crossed the y-intercept at almost identical points under all O[subscript 2] concentrations. This data indicated that there was no apparent O[subscript 2] inhibition and that the apparent inhibitor constant (K[subscript i]) for O[subscript 2] at the site of carboxylation did not change with an increase in [O[subscript 2]] from 0 to 21%. These observations were further confirmed by results obtained from the analysis of apparent carboxylation efficiency where no inhibition of A with increase of [O[subscript 2]] occurred. These characteristics are thus consistent with typical features of C[subscript 4] photosynthesis.
- Full Text: false
- Authors: Mjwara, Jabulani M , Botha, Christiaan E J
- Date: 1993
- Language: English
- Type: Article
- Identifier: vital:6527 , http://hdl.handle.net/10962/d1005961
- Description: A portable infra-red gas analyzer was used to investigate the interactive effects of light, temperature, and CO[subscript 2]/O[subscript 2] ratios under controlled environmental conditions in an attempt to model gas exchange characteristics of Coix lachryma-jobi L. Plotting light response curves as a function of temperature (20, 25, 30 and 35 degrees C) revealed no sign of light saturation even at a photosynthetic photon flux density (PPFD) close to 2000 µmol m[superscript -2]s[superscript -1]. High net assimilation rates (A) of approximately 24 µmol CO[subscript 2] m[superscript -2]s[superscript -1] were realized at 30-35 degrees C. Assimilation (A) versus internal CO[subscript 2] partial pressure Ci curves showed a steep rise in A with increase in C[subscript i] but saturated at approximately 150 µl[superscript -1] and the effect was similar in either the absence or presence of O[subscript 2], under all temperature regimes. C. lachryma-jobi exhibited low CO[subscript 2] compensation points (Γ*) between 0 and 10 µl[superscript -1] at either 0 or 21% O[subscript 2]. The slopes of double reciprocal plots of 1/A versus 1/C[subscript i], were nearly identical and crossed the y-intercept at almost identical points under all O[subscript 2] concentrations. This data indicated that there was no apparent O[subscript 2] inhibition and that the apparent inhibitor constant (K[subscript i]) for O[subscript 2] at the site of carboxylation did not change with an increase in [O[subscript 2]] from 0 to 21%. These observations were further confirmed by results obtained from the analysis of apparent carboxylation efficiency where no inhibition of A with increase of [O[subscript 2]] occurred. These characteristics are thus consistent with typical features of C[subscript 4] photosynthesis.
- Full Text: false
The ultrastructure and computer-enhanced digital image analysis of plasmodesmata at the Kranz mesophyll-bundle sheath interface of Themeda triandra var. imberbis (Retz) A. Camus in conventionally-fixed leaf blades
- Botha, Christiaan E J, Hartley, B J, Cross, Robin H M
- Authors: Botha, Christiaan E J , Hartley, B J , Cross, Robin H M
- Date: 1993
- Language: English
- Type: Article
- Identifier: vital:6502 , http://hdl.handle.net/10962/d1005925
- Description: The ultrastructure of the plasmodesmata at the Kranz mesophyll-bundle sheath (KMS-BS) interface in Themeda triandra, and the substructures within the plasmodesmata were investigated, using conventionally fixed leaf-blade material, enhanced by the addition of 0.1% tannic acid to the primary fixative. Examination of high-resolution electronmicrographs, and computer-enhanced digital images suggests that these plasmodesmata are complex structures, comprised of helically-arranged particulate material. The electron-dense particles are between 2.5 and 3.0nm in diameter. These particles are specifically associated with the inner face of the inner plasmalemma membrane leaflet, and the outer region of the desmotubule wall. The electron-dense particles are presumably proteinaceous and embedded in a lipid matrix. In the constricted median portion of the KMS-BS plasmodesmata, the space between the desmotubule and the inner plasmalemma membrane leaflet and areas surrounding the proteinaceous particles thereof (the cytoplasmic sleeve) is about 3nm in cross-section, and constitutes what we believe to be the space through which intercellular transport takes place.
- Full Text: false
- Authors: Botha, Christiaan E J , Hartley, B J , Cross, Robin H M
- Date: 1993
- Language: English
- Type: Article
- Identifier: vital:6502 , http://hdl.handle.net/10962/d1005925
- Description: The ultrastructure of the plasmodesmata at the Kranz mesophyll-bundle sheath (KMS-BS) interface in Themeda triandra, and the substructures within the plasmodesmata were investigated, using conventionally fixed leaf-blade material, enhanced by the addition of 0.1% tannic acid to the primary fixative. Examination of high-resolution electronmicrographs, and computer-enhanced digital images suggests that these plasmodesmata are complex structures, comprised of helically-arranged particulate material. The electron-dense particles are between 2.5 and 3.0nm in diameter. These particles are specifically associated with the inner face of the inner plasmalemma membrane leaflet, and the outer region of the desmotubule wall. The electron-dense particles are presumably proteinaceous and embedded in a lipid matrix. In the constricted median portion of the KMS-BS plasmodesmata, the space between the desmotubule and the inner plasmalemma membrane leaflet and areas surrounding the proteinaceous particles thereof (the cytoplasmic sleeve) is about 3nm in cross-section, and constitutes what we believe to be the space through which intercellular transport takes place.
- Full Text: false
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