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
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
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
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
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
Xylem as well as phloem sustains severe damage due to feeding by the Russian wheat aphid
- Authors: Saheed, S A , Liu, Lin , Jonsson, L 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