A moderate elevation in [CO 2] results in potential hypervirulence on SABBIErica
- 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
Russian wheat aphids: Breakfast, lunch, and supper. Feasting on small grains in South Africa
- 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 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
Stronger induction of callose deposition in barley by Russian wheat aphid than bird cherry-oat aphid is not associated with differences in callose synthase or ≤-1,3-glucanase expression
- Authors: Saheed, Sefiu A , Cierlik, Izabela , Larsson, Kristina A E , Delp, Gabriele , Bradley, Graeme , Jonsson, Lisbeth M V , Botha, Christiaan E J
- Date: 2009
- Language: English
- Type: Article
- Identifier: vital:6542 , http://hdl.handle.net/10962/d1005984
- Description: The effects of infestation by the bird cherry-oat aphid (BCA), (Rhopalosiphum padi L) and the Russian wheat aphid (RWA) (Diuraphis noxia Mordvilko) on callose deposition and gene expression related to callose accumulation were investigated in barley (Hordeum vulgare L. cv. Clipper). The BCA, which gives no visible symptoms, induced very limited callose deposition, even after 14 days of infestation. In contrast, RWA, which causes chlorosis, white and yellow streaking and leaf rolling, induced callose accumulation already after 24h in longitudinal leaf veins. The deposition was pronounced after 72 h, progressing during 7 and 14 days of infestation. In RWA-infested source leaves, callose was also induced in longitudinal veins basipetal to the aphid-infested tissue, whereas in sink leaves, more callose deposition was found above the feeding sites. Nine putative callose synthase genes were identified in a data base search, of which eight were expressed in the leaves, but with similar level of expression in control and aphid-infested tissue. Four out of 12 examined β-1,3-glucanases were expressed in the leaves, and three of them were up-regulated in aphid-infested tissue. They were all more strongly induced by RWA than BCA. The results suggest that callose accumulation may be partly responsible for the symptoms resulting from RWA feeding and that a callose-inducing signal may be transported in the phloem. Furthermore it is concluded that the absence of callose deposition in BCA-infested leaves is not due to a stronger induction of callose-degrading β-1,3-glucanases in this tissue, as compared to RWA-infested leaves.
- Full Text:
- Date Issued: 2009
A xylem retrieval pathway in rice leaf blades – evidence of a role for endocytosis?
- 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
Resistance or tolerance: an examination of aphid (Sitobion yakini) phloem feeding on Betta and Betta-Dn wheat (Triticum aestivum)
- Authors: De Wet, L R , Botha, Christiaan E J
- Date: 2007
- Language: English
- Type: Article
- Identifier: vital:6517 , http://hdl.handle.net/10962/d1005945
- Description: Engineering pest resistance into crops is important. However, the mechanisms of resistance are not clearly understood. In this study, we examined the effects of aphid feeding on Russian wheat aphid-resistant and -susceptible cultivars of wheat (Triticum aestivum L.); Betta-Dn and Betta, respectively, by the grass aphid, Sitobion yakini (Eastop). These cultivars were grown with or without aphid colonies. In each case, we examined the plants specifically for the formation of wound callose associated with the phloem, using aniline blue and fluorescence microscopy. We observed that aphid feeding stimulated the formation of wound callose in the susceptible cultivar, but that callose was comparatively reduced in the resistant cultivar of wheat. In a separate series of experiments, the xenobiotic, 5, 6-carboxyfluorescein diacetate was applied to attached sink leaves, distal to feeding aphids. When leaf segments were examined four hours after application, little evidence of phloem transport of the fluorescent cleavage product, 5, 6-carboxyfluorescein (5, 6-CF), was evident below known aphid-probed sieve tubes. Low levels or absence of 5, 6-CF indicates that either the aphids have successfully redirected sap to themselves, or that the phloem is no longer functional. In contrast, 5, 6-CF transport was evident below sites of aphid probing in Betta-Dn, suggesting that the phloem was still capable of long-distance transport. In addition, callose deposition was reduced in Betta-Dn leaf phloem and it is surmised that transport was not as affected by aphid feeding in the resistant cultivar. This indicates that the ‘resistant’ wheat cultivar may in fact be tolerant to aphid feeding by successfully overcoming the nutrient drain that feeding aphids imposed on the phloem transport system.
- Full Text:
- Date Issued: 2007
Xylem as well as phloem sustains severe damage due to feeding by the Russian wheat aphid
- Authors: Saheed, S A , Liu, Lin , Jonsson, Lisbeth M V , Botha, Christiaan E J
- Date: 2007
- Language: English
- Type: Article
- Identifier: vital:6541 , http://hdl.handle.net/10962/d1005983
- Description: Investigation of comparative effects of feeding damage by the Russian wheat aphid (RWA, biotype SA1, Diuraphis noxia Mordvilko) on leaf blades of susceptible and resistant wheat cultivars (Triticum aestivum L. var Betta and Betta-Dn1 respectively) were carried out to establish the level of ultrastructural damage caused by this aphid and the possible limitation of damage induced which could be ascribed to the resistance gene Dn1 over the susceptible cultivar. Ultrastructurally, Betta-Dn1 sustained less damage to the vascular tissue as well as to the mesophyll during the experimental period. Both inter- and intracellular probes resulted in considerable saliva deposition as the aphids probed for suitable feeding sites. Salivary tracks were observed between and within mesophyll, bundle sheath cells as well as the vascular tissue, including the xylem. Disruption of organelles and cytoplasm resulted from cell probing and sheath deposition. Cell and organelle damage was more evident in the non-resistant Betta cultivar. The aphids probed for and fed from thin-walled sieve tubes preferentially. Few thick-walled sieve tubes showed evidence of either aphid probing or feeding-related damage. Saliva was deposited when the aphids probed inter- and intracellularly for feeding sites. The aphids appeared preferentially to probe for and feed from thin-walled sieve tubes, as few thick-walled sieve tubes showed evidence of damage. Vessels, apparently probed for water, contained watery saliva that encased the secondary walls and sealed pit membranes between probed vessels and xylem parenchyma. The xylem probed by the RWA was rendered non-functional, probably contributing to symptoms of leaf roll, chlorosis and necrosis, which were observed within two weeks of infestation in the susceptible Betta cultivar. This damage was limited in the resistant Betta-Dn1 cultivar during the same time frame.
- Full Text:
- Date Issued: 2007
What does the movement of the Phloem-mobile symplastic tracer, 5,6-carboxyfluorescein in shoots of Pisum Sativum L. Indicate - the existence of a symplastic transport system? - a bid to answer some puzzling questions
- Authors: Ade-Ademilua, Omobolanle Elizabeth , Botha, Christiaan E J
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:6492 , http://hdl.handle.net/10962/d1004475 , http://dx.doi.org/10.3923/ajpp.2006.127.131
- Description: Like other members of the Fabaceae, the minor veins of Pisum are categorized as a closed system termed type 2 minor vein configuration due to the presence of few or no plasmodesmal connections between the sieve element-transfer cell complex (SE-TCC) and the adjacent cells (Gamalei, 1989; van Bel and Gamalei, 1991) Pisum is classified further into the category of type 2 b minor vein configuration due to the presence of transfer cells with the characteristic wall ingrowths in the minor vein phloem (Gamalei, 1989). According to van Bel et al. (1992), there is a correlation between minor vein configuration and phloem loading. However, by reason of low plasmodesmal frequency, the pathway of the flow of assimilates in plants with type 2 minor vein configuration is considered to be apoplasmic (Gamalei, 1989; van Bel and Gamalei, 1991). Therefore, present reports on the movement of phloem-mobile 5,6-carboxyfluorescein, a known symplamically transported compound between pea leaflets raises some doubts on the accession that transport within the phloem in pea is strictly apoplasmic. In this study we look at different points of arguments and try to offer our explanation and conclusions on the transport pathways that are likely to exist in Pisum.
- Full Text: false
- Date Issued: 2006
A re-evaluation of plastochron index determination in peas - a case for using leaflet length
- Authors: Ade-Ademilua, Omobolanle Elizabeth , Botha, Christiaan E J
- Date: 2005
- Language: English
- Type: Article
- Identifier: vital:6491 , http://hdl.handle.net/10962/d1004472
- Description: The plastochron index (PI) is a measure of plant growth reports our findings on PI using the average length of and can be used to determine growth rate, based upon the first pair of leaflets on each node. Early leaflet appearance of successive leaves on the axis of the growth in peas occurs exponentially and the early plant. PI should under ideal growth conditions be a stages of growth of successive pairs of leaflets occur at regular event and should be predictable with a relatively the same relative growth rate. Given that growth of small error of a few hours. PI has been variously leaflets during early development can be measured calculated in peas, and each method reported has had successfully, we propose the use of leaflet growth as a with it a number of problems that do not allow for measure of the plastochron index in peas. Our results reasonable prediction of PI. Internode length varies suggest that plant age is best expressed using the greatly and is dependent upon the variety, which may be plastochron index, which is a measure of the time short- or long-stemmed; thus this parameter is not ideal interval between the initiations of successive events — for determining growth rate or plant age. This paper in the case of peas, of successive pairs of leaflets.
- Full Text:
- Date Issued: 2005
Reduction in transport in wheat (Triticum aestivum) is caused by sustained phloem feeding by the Russian wheat aphid (Diuraphis noxia)
- Authors: Botha, Christiaan E J , Matsiliza, Babalwa
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6498 , http://hdl.handle.net/10962/d1004498
- Description: The Russian wheat aphid (Diuraphis noxia) feeds preferentially from the phloem of longitudinal veins of nonresistant wheat leaves. The xenobiotic, 5,6-CFDA was applied to exposed leaf blade mesophyll cells in control and aphid-infested plants. In control plants, the fluorophore moved approximately 5–6cm from the point of application of 5,6-CFDA within 3h of application. The fluorochrome was transported in the sieve tube companion cell complex, including those in the numerous interconnecting transverse veins. Leaf blades on which the Russian wheat aphid had been feeding demonstrated a marked decrease in 5,6-CF transport. Aphids feeding on the leaves formed local sinks and redirected the fluorophore (and presumably associated assimilate) to the aphids’ gut, with little longitudinal translocation of 5,6-CF below inserted stylets or aphid feeding areas. Aniline blue staining revealed massive deposits of wound and reaction callose caused by the aphids, with callose associated with the sieve plates, pore-plasmodesma between the companion cells and their associated sieve tubes, as well as with plasmodesmal aggregates in parenchymatous elements within the vascular bundles. Leaves that had been colonised by aphids but from which the aphids were removed, showed extensive wound callose deposits, which persisted for up to 48h after removal of aphid colonies, suggesting that the damage caused by aphid feeding is a long-term, non-transient event in non-resistant plants.
- Full Text:
- Date Issued: 2004
The microstructure of plasmodesmata in internodal stem tissue of the Saccharum hybrid var. NCo376 : evidence for an apoplasmic loading pathway
- Authors: Botha, Christiaan E J , Cross, Robin H M , Gerber, Jacques
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6494 , http://hdl.handle.net/10962/d1004487
- Description: The distribution, structure and functional state of plasmodesmata were investigated to gain a clearer understanding of the sucrose transport pathway to the storage parenchyma cells in stem tissue in Saccharum officinarum var. NCo376. Evidence from structural studies on sugarcane stems by electron microscopy indicated that there are numerous plasmodesmata from the vascular bundles through to the storage parenchyma cells in mature stem tissue. Our studies, supported by fluorescence microscopy and iontophoresis, indicate that there are functional plasmodesmata in the phloemunloading pathway from transport phloem tissue to the bundle sheath in Saccharum, which could support symplasmic transport; plasmodesmata outside of the sheath cells in the storage parenchyma appear to be constricted by sphincter-like structures within their neck regions. Staining with Aniline Blue revealed evidence of large callose deposits, which co-localized with plasmodesmatal aggregates in the walls of the storage parenchyma cells. This suggests that the sucrose transport into, and accumulation by, storage parenchyma of mature stem tissue is under apoplasmic control.
- Full Text:
- Date Issued: 2004
Aphid (Sitobion yakini) investigation shows thin-walled sieve tubes in barley (Hordeum vulgare L) to be more functional than thick-walled sieve tubes
- Authors: Matsiliza, Balbalwa , Botha, Christiaan E J
- Date: 2002
- Language: English
- Type: Article
- Identifier: vital:6526 , http://hdl.handle.net/10962/d1005960
- Description: Barley, like most other grasses that have been studied, contains two kinds of sieve tube. The first formed are called thinwalled sieve tubes because of their thin wall compared to the late-formed, and are associated with companion cells. The late-formed are thick-walled sieve tubes, which differentiate next to the metaxylem vessels and lack companion cells. Aphid (Sitobion yakini (Eastop) feeding was studied using light microscopy to determine if they preferentially feed from thin- or thick-walled sieve tubes in the barley leaf. Penetration of the stylets through the leaf epidermis and mesophyll was largely intercellular, becoming partly intercellular and, partly, intracellular inside the vascular bundle. Sixteen of 19 pairs of stylets (84%), and 293 of 317 (92%) stylet tracks terminated at the thin-walled sieve tubes, suggesting that Sitobion yakini feeds preferentially on the thin-walled sieve tubes which seem to be more attractive to the aphid. These thin-walled sieve tubes are thus probably the most functional in terms of phloem loading and transport.
- Full Text:
- Date Issued: 2002
Regulation within the supracellular highway - plasmodesma are the key
- Authors: Botha, Christiaan E J , Cross, Robin H M
- Date: 2001
- Language: English
- Type: Article
- Identifier: vital:6500 , http://hdl.handle.net/10962/d1005918
- Description: Plasmodesmal connections are unique, highly dynamic intercellular structures that are lined by the plasmamembrane. They are believed to be a vital intercellular communication channel between living cells, linking numbers of living cells into interconnected, highly specialised cellular domains, thus enabling the plant to act as an integrated organism. Their evolution in the higher plant was inevitable. It is accepted that cell heterogeneity rather than cell divergence pressurised developing plant systems along a route that led to the development of intercellular passages and connections. With time these connections have evolved to allow some degree of regulation and traffic control. This paper explores some of the structure/function relationships in plasmodesmata. Attention is focused on the potential role of the neck region of these remarkable structures and discusses models which may explain the processes involved in regulating the movement of substances from cell to cell.
- Full Text: false
- Date Issued: 2001
Phloem loading in the sucrose-export-defective (SXD-1) mutant maize is limited by callose deposition at plasmodesmata in bundle sheath-vascular parenchyma interface
- Authors: Botha, Christiaan E J , Cross, Robin H M , Van Bel, A J E , Peter, Craig I
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6503 , http://hdl.handle.net/10962/d1005926
- Description: Using Lucifer Yellow we have demonstrated that the phloem-loading pathway from the mesophyll to the bundle sheath-vascular parenchyma interface in Zea mays source leaves follows a symplasmic route in small and intermediate vascular bundles in control as well as in the green sections of mutant sucrose-export-defective (SXD-1) plants. In the anthocyanin-rich mutant leaf sections, Lucifer Yellow transport was prohibited along the same path, at the bundle sheath-vascular parenchyma interface in particular. Plasmodesmata at the latter interface in SXD-1 anthocyanin-rich leaf sections appear to be structurally altered through callose deposition at the plasmodesmal orifices. We suggest that a transport bottleneck at the bundle sheath-vascular parenchyma interface is thus orchestrated and regulated through callose formation, preventing symplasmic transport across this important loading interface.
- Full Text:
- Date Issued: 2000
Towards reconciliation of structure with function in plasmodesmata—who is the gatekeeper?
- Authors: Botha, Christiaan E J , Cross, Robin H M
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6497 , http://hdl.handle.net/10962/d1004493
- Description: Whilst the structure of higher plant plasmodesmata was first described by Robards (1963. Desmotubule—a plasmodesmatal substructure. Nature 218, 784), and despite many subsequent intensive investigations, there is still much that remains unclear relating to their ultrastructure and functioning in higher plants. We have examined chemically fixed plant material, and suggest that the conformational changes seen in plasmodesmatal substructure, particularly the deposition of electron-dense extra-plasmodesmal material, is linked to either manipulation of the hormonal balance (as in Avocado fruit), or of osmotic potential in leaf blade material. These changes result in the deposition of β 1,3-glucan (callose) at the neck region of these plasmodesmata. This electron-dense material is deposited at the neck region of plasmodesmata, and forms a collar-like structure. The formation of a collar is shown to be coupled with loss of lucence within the cytoplasmic sleeve. The formation of a collar at the plasmodesmatal orifice thus results in encapsulation and closure of the plasmodesmatal orifice. Closure of the orifice coincides with a loss of electron-lucence and a lack of resolution of the desmotubule. These ultrastructural changes are potentially significant and could contribute to, result in, or assist in the down-regulation of cell to cell trafficking via plasmodesmata.
- Full Text:
- Date Issued: 2000
Symplastic solute transport and avocado fruit development : a decline in cytokinin/ABA ratio is related to appearance of the Hass small fruit variant
- Authors: Moore-Gordon, Clive S , Cowan, Keith A , Bertling, Isa , Botha, Christiaan E J , Cross, Robin H M
- Date: 1998
- Language: English
- Type: Article
- Identifier: vital:6525 , http://hdl.handle.net/10962/d1005959
- Description: Studies on the effect of fruit size on endogenous ABA and isopentenyladenine (iP) in developing avocado (Persea americana Mill. cv. Hass) fruit revealed that ABA content was negatively correlated with fruit size whilst the iP/ABA ratio showed a linear relationship with increasing size of fruit harvested 226 d after full bloom. The effect of this change in hormone balance on the relationship between symplastic solute transport and appearance of the small fruit variant was examined following manipulation of the endogenous cytokinin (CK)/ABA ratio. Application of ABA caused seed coat senescence and retarded fruit growth but these effects were absent in fruit treated with equal amounts of ABA plus iP. Thus, the underlying physiological mechanisms associated with ABA-induced retardation of Hass avocado fruit growth appeared to be inextricably linked to a decline in CK content and included: diminution of mesocarp and seed coat plasmodesmatal branching, gating of mesocarp and seed coat plasmodesmata by deposition of electron dense material in the neck region, abolishment of the electrochemical gradient between mesocarp and seed coat parenchyma, and arrest of cell-to-cell chemical communication.
- Full Text:
- Date Issued: 1998
Comparative ultrastructure of plasmodesmata of Chara and selected bryophytes: towards an elucidation of the evolutionary origin of plant plasmodesmata
- Authors: Cook, Martha E , Graham, Linda E , Botha, Christiaan E J , Lavin, Colleen A
- Date: 1997
- Language: English
- Type: Article
- Identifier: vital:6506 , http://hdl.handle.net/10962/d1005933 , http://www.amjbot.org/cgi/reprint/84/9/1169
- Description: We have used transmission electron microscopy to examine plasmodesmata of the charophycean green alga Chara zeylanica, and of the putatively early divergent bryophytes Monoclea gottschei (liverwort), Notothylas orbicularis (hornwort), and Sphagnum fimbriatum (moss), in an attempt to learn when seed plant plasmodesmata may have originated. The three bryophytes examined have desmotubules. In addition, Monoclea was found to have branched plasmodesmata, and plasmodesmata of Sphagnum displayed densely staining regions around the neck region, as well as ring-like wall specializations. In Chara, longitudinal sections revealed endoplasmic reticulum (ER) that sometimes appeared to be associated with plasmodesmata, but this was rare, despite abundant ER at the cell periphery. Across all three fixation methods, cross-sectional views showed an internal central structure, which in some cases appeared to be connected to the plasma membrane via spoke-like structures. Plasmodesmata were present even in the incompletely formed reticulum of forming cell plates, from which we conclude that primary plasmodesmata are formed at cytokinesis in Chara zeylanica. Based on these results it appears that plasmodesmata of Chara may be less specialized than those of seed plants, and that complex plasmodesmata probably evolved in the ancestor of land plants before extant lineages of bryophytes diverged.
- Full Text:
- Date Issued: 1997
Plasmodesmatal frequency in relation to short-distance transport and phloem loading in leaves of barley (Hordeum vulgare). Phloem is not loaded directly from the symplast
- Authors: Botha, Christiaan E J , Cross, Robin H M
- Date: 1997
- Language: English
- Type: Article
- Identifier: vital:6504 , http://hdl.handle.net/10962/d1005928
- Description: We investigated the phloem loading pathway in barley, by determining plasmodesmatal frequencies at the electron microscope level for both intermediate and small blade bundles of mature barley leaves. Lucifer yellow was injected intercellularly into bundle sheath, vascular parenchyma, and thin-walled sieve tubes. Passage of this symplastically transported dye was monitored with an epifluorescence microscope under blue light. Low plasmodesmatal frequencies endarch to the bundle sheath cells are relatively low for most interfaces terminating at the thin- and thick-walled sieve tubes within this C3 species. Lack of connections between vascular parenchyma and sieve tubes, and low frequencies (0.5% plasmodesmata per μm cell wall interface) of connections between vascular parenchyma and companion cells, as well as the very low frequency of pore-plasmodesmatal connections between companion cells and sieve tubes in small bundles (0.2% plasmodesmata per μm cell wall interface), suggest that the companion cell-sieve tube complex is symplastically isolated from other vascular parenchyma cells in small bundles. The degree of cellular connectivity and the potential isolation of the companion cell-sieve tube complex was determined electrophysiologically, using an electrometer coupled to microcapillary electrodes. The less negative cell potential {average -52 mV) from mesophyll to the vascular parenchyma cells contrasted sharply with the more negative potential (-122.5 mV) recorded for the companion cell-thin-walled sieve tube complex. Although intercellular injection of lucifer yellow clearly demonstrated rapid (0.75 μm s-1) longitudinal and radial transport in the bundle sheath-vascular parenchyma complex, as well as from the bundle sheath through transverse veins to adjacent longitudinal veins, we were neither able to detect nor present unequivocal evidence in support of the symplastic connectivity of the sieve tubes to the vascular parenchyma. Injection of the companion cell-sieve tube complex, did not demonstrate backward connectivity to the bundle sheath. We conclude that the low plasmodesmatal frequencies, coupled with a two-domain electropotential zonation configuration, and the negative transport experiments using lucifer yellow, precludes symplastic phloem loading in barley leaves.
- Full Text:
- Date Issued: 1997
The effect of fluctuating substrate salinity on the yield and flag leaf photosynthesis of wheat
- Authors: Beckett, R P , Drennan, P M , Botha, Christiaan E J
- Date: 1995
- Language: English
- Type: Article
- Identifier: vital:6501 , http://hdl.handle.net/10962/d1005922
- Description: The effects of constant and fluctuating substrate salinity on flag leaf photosynthesis and grain yield of wheat were investigated. Plants exposed to salinity fluctuating around a mean integrated value of 25 mol m-3 NaCl (0-50 mol m-3) and around 50 mol m-3 NaCl (25-75 mol m-3) had yields 36 and 38% higher, respectively, than those receiving the corresponding constant salinity. Plants treated with salinity fluctuating from 50-100 mol m-3 NaCl had a 14% lower yield than those receiving 75 mol m-3 NaCl. Flag leaf photosynthesis did not vary between treatments and during salinity fluctuations, suggesting that differences in flag leaf longevity caused the observed differences in yield. Results suggest plants grown under constant salinity are unlikely to behave as those in field situations, where fluctuating rather than constant salinity occurs.
- Full Text: false
- Date Issued: 1995
The interactive effects of light, temperature and CO[subscript 2]/O[subscript 2] ratios on photosynthesis in Coix lachryma-jobi L
- 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
- Date Issued: 1993