A tale of two neglected systems-structure and function of the thin- and thick-walled sieve tubes in monocotyledonous leaves
- Authors: Botha, Christiaan E J
- Date: 2013
- Language: English
- Type: Article , text
- Identifier: vital:6499 , http://hdl.handle.net/10962/d1004514 , http://dx.doi.org/10.3389/fpls.2013.00297
- Description: There is a large body of information relating to the ontogeny, development and the vasculature of eudicotyledonous leaves. However, there is less information available concerning the vascular anatomy of monocotyledonous leaves. This is surprising, given that there are two uniquely different phloem systems present in large groups such as grasses and sedges. Monocotyledonous leaves contain marginal, large, intermediate, and small longitudinal veins that are interconnected by numerous transverse veins. The longitudinal veins contain two metaphloem sieve tube types, which, based upon their ontogeny and position within the phloem, are termed early (thin-walled) and late (thick-walled) sieve tubes. Early metaphloem comprises sieve tubes, companion cells and vascular parenchyma (VP) cells, whilst the late metaphloem, contains thick-walled sieve tubes (TSTs) that lack companion cells. TSTs are generally adjacent to, or no more than one cell removed from the metaxylem. Unlike thin-walled sieve tube (ST) -companion cell complexes, TSTs are connected to parenchyma by pore-plasmodesma units and are generally symplasmically isolated from the STs. This paper addresses key structural and functional differences between thin- and thick-walled sieve tubes and explores the unique advantages of alternate transport strategies that this 5–7 million years old dual system may offer. It would seem that these two systems may enhance, add to, or play a significant role in increasing the efficiency of solute retrieval as well as of assimilate transfer.
- Full Text:
- Date Issued: 2013
- Authors: Botha, Christiaan E J
- Date: 2013
- Language: English
- Type: Article , text
- Identifier: vital:6499 , http://hdl.handle.net/10962/d1004514 , http://dx.doi.org/10.3389/fpls.2013.00297
- Description: There is a large body of information relating to the ontogeny, development and the vasculature of eudicotyledonous leaves. However, there is less information available concerning the vascular anatomy of monocotyledonous leaves. This is surprising, given that there are two uniquely different phloem systems present in large groups such as grasses and sedges. Monocotyledonous leaves contain marginal, large, intermediate, and small longitudinal veins that are interconnected by numerous transverse veins. The longitudinal veins contain two metaphloem sieve tube types, which, based upon their ontogeny and position within the phloem, are termed early (thin-walled) and late (thick-walled) sieve tubes. Early metaphloem comprises sieve tubes, companion cells and vascular parenchyma (VP) cells, whilst the late metaphloem, contains thick-walled sieve tubes (TSTs) that lack companion cells. TSTs are generally adjacent to, or no more than one cell removed from the metaxylem. Unlike thin-walled sieve tube (ST) -companion cell complexes, TSTs are connected to parenchyma by pore-plasmodesma units and are generally symplasmically isolated from the STs. This paper addresses key structural and functional differences between thin- and thick-walled sieve tubes and explores the unique advantages of alternate transport strategies that this 5–7 million years old dual system may offer. It would seem that these two systems may enhance, add to, or play a significant role in increasing the efficiency of solute retrieval as well as of assimilate transfer.
- Full Text:
- Date Issued: 2013
Russian wheat aphids: Breakfast, lunch, and supper. Feasting on small grains in South Africa
- Botha, Christiaan E J, Sacranie, S, Gallagher, Sean, Hill, Jaclyn M
- Authors: Botha, Christiaan E J , Sacranie, S , Gallagher, Sean , Hill, Jaclyn M
- Date: 2016
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/69031 , vital:29374 , https://doi.org/10.1016/j.sajb.2016.12.006
- Description: The Russian Wheat Aphid (Diuraphis noxia, RWA) negatively impacts commercially grown barley and wheat in South Africa. Climate change, the attendant rise in [CO2], and the appearance of new RWA biotypes have the potential to induce severe crop yield loss in agriculturally important wheat and barley cultivars. This study presents data showing changes in relative aphid population numbers, concurrently with assessments of plant damage under controlled environmental conditions, under ambient and elevated (450 ppm) [CO2]. Extensive structural damage to the vascular tissue and disruption to the transport systems were revealed using light, fluorescence and electron microscopy. This, coupled with biotype population studies, demonstrated that RWA has the capacity to inflict severe, potentially permanent damage to vegetative small grain plants. Furthermore, some currently ‘resistant’ cultivars may well lose resistance as a direct result of increasing atmospheric [CO2]. A small (50 ppm) increase in atmospheric [CO2] may result in increased aphid population numbers, potentially serious plant damage and, by implication, a potentially negative impact on yield, as increased aphid density per plant leads to an accelerated disruption of the assimilate and transpiration transport pathways. These outcomes pose a direct threat to the commercial small grain industry of South Africa and by extension, to other small grain production areas elsewhere.
- Full Text: false
- Date Issued: 2016
- Authors: Botha, Christiaan E J , Sacranie, S , Gallagher, Sean , Hill, Jaclyn M
- Date: 2016
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/69031 , vital:29374 , https://doi.org/10.1016/j.sajb.2016.12.006
- Description: The Russian Wheat Aphid (Diuraphis noxia, RWA) negatively impacts commercially grown barley and wheat in South Africa. Climate change, the attendant rise in [CO2], and the appearance of new RWA biotypes have the potential to induce severe crop yield loss in agriculturally important wheat and barley cultivars. This study presents data showing changes in relative aphid population numbers, concurrently with assessments of plant damage under controlled environmental conditions, under ambient and elevated (450 ppm) [CO2]. Extensive structural damage to the vascular tissue and disruption to the transport systems were revealed using light, fluorescence and electron microscopy. This, coupled with biotype population studies, demonstrated that RWA has the capacity to inflict severe, potentially permanent damage to vegetative small grain plants. Furthermore, some currently ‘resistant’ cultivars may well lose resistance as a direct result of increasing atmospheric [CO2]. A small (50 ppm) increase in atmospheric [CO2] may result in increased aphid population numbers, potentially serious plant damage and, by implication, a potentially negative impact on yield, as increased aphid density per plant leads to an accelerated disruption of the assimilate and transpiration transport pathways. These outcomes pose a direct threat to the commercial small grain industry of South Africa and by extension, to other small grain production areas elsewhere.
- Full Text: false
- Date Issued: 2016
A moderate elevation in [CO 2] results in potential hypervirulence on SABBIErica
- Gallagher, Sean, Hill, Jaclyn M, Murugan, N, Botha, Christiaan E J
- Authors: Gallagher, Sean , Hill, Jaclyn M , Murugan, N , Botha, Christiaan E J
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/68835 , vital:29329 , https://doi.org/10.1016/j.sajb.2017.10.010
- Description: The Russian Wheat Aphid (Diuraphis noxia Kurdjumov, 1913) (RWA) is a serious pest of grain crops and is of considerable concern in South Africa, particularly in terms of barley grown specifically for the brewing industry. This paper highlights the effect of a small (50 ppm) increase in [CO2] on the growth rate of the four South African RWA biotypes on the SABBIErica barley cultivar. Controlled environment experiments revealed that the colony growth rate for RWASA4 was significantly lower than SA1 under ambient conditions as well as significantly lower than SA1, SA2 or SA3 under elevated CO2 conditions. The unexpected difference suggested an atypical, non-preferential feeding habit on SABBIErica, for RWASA4. The small RWASA4 colonies inflicted similar morphological damage to the significantly larger RWASA1 – RWASA3 biotype populations — indicative of potential hypervirulence under elevated CO2. The continuous feeding of RWASA biotypes causes damage to the transport system as well as substantial, catastrophic damage to mesophyll chloroplasts as well as mitochondria within the host plant's leaves. The TEM study revealed evidence of sequential/systematic degeneration of chloroplasts and mitochondria with continued aphid feeding, which we suggest is an indication of potential emergent hypervirulence under elevated CO2 conditions.
- Full Text: false
- Date Issued: 2017
- Authors: Gallagher, Sean , Hill, Jaclyn M , Murugan, N , Botha, Christiaan E J
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/68835 , vital:29329 , https://doi.org/10.1016/j.sajb.2017.10.010
- Description: The Russian Wheat Aphid (Diuraphis noxia Kurdjumov, 1913) (RWA) is a serious pest of grain crops and is of considerable concern in South Africa, particularly in terms of barley grown specifically for the brewing industry. This paper highlights the effect of a small (50 ppm) increase in [CO2] on the growth rate of the four South African RWA biotypes on the SABBIErica barley cultivar. Controlled environment experiments revealed that the colony growth rate for RWASA4 was significantly lower than SA1 under ambient conditions as well as significantly lower than SA1, SA2 or SA3 under elevated CO2 conditions. The unexpected difference suggested an atypical, non-preferential feeding habit on SABBIErica, for RWASA4. The small RWASA4 colonies inflicted similar morphological damage to the significantly larger RWASA1 – RWASA3 biotype populations — indicative of potential hypervirulence under elevated CO2. The continuous feeding of RWASA biotypes causes damage to the transport system as well as substantial, catastrophic damage to mesophyll chloroplasts as well as mitochondria within the host plant's leaves. The TEM study revealed evidence of sequential/systematic degeneration of chloroplasts and mitochondria with continued aphid feeding, which we suggest is an indication of potential emergent hypervirulence under elevated CO2 conditions.
- Full Text: false
- Date Issued: 2017
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