African
Journals OnLine
|
| Issues Available | About the Journal |
South African Journal of Botany 67 (1) 2001, 1–9
©2001 NISC Pty Ltd,
Minireview
Regulation within the supracellular highway — plasmodesma are the key
CEJ Botha1* and RHM Cross2
1 Botany Department and 2 Electron Microscopy Unit, Rhodes University, Grahamstown 6140, South Africa
* Corresponding author, e-mail: [email protected]
Received 16 October 2000, accepted in revised form 19 October 2000
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 formation 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.
South African Journal of Botany 67 (1) 2001, 10–14
©2001 NISC Pty Ltd,
Reproductive biomass allocation in the dioecious perennial Acanthosicyos horrida
SM Eppley* and EH Wenk1
Center for Population Biology, University of California, Davis, California 95616, USA
1 Present address: Department of Integrative Biology, University of California, Berkeley, California 94720, USA
* Corresponding author, e-mail: [email protected]
Received 14 September 1999, accepted in revised form 22 September 2000
In a Namib population of the dioecious perennial Acanthosicyos horrida Welw. ex Hook. f. in which fruit production is declining, we investigated the effects of plant gender, plant size, and subpopulation elevation (a proxy of water availability) on a plant's biomass allocation to sexual reproduction. While males invested more heavily in buds and flowers than females, females allocated 10 times more total biomass to reproduction per m3 of vegetation than males during our survey period. Also, smaller plants, particularly females, allocated more biomass to reproduction per m3 of vegetation than larger plants. This result suggests that plant fecundity per m3 of vegetation decreases with plant size. Aging of the population could thus be a cause of the reduced fruit production; however, we found that the population was skewed towards the smallest size classes. On the other hand, the fact that plants in the subpopulation at higher elevation above the river were only six percent as productive as plants in the subpopulation at low elevation suggests that the depth of the water table may be critical to fruit production and that a reduced groundwater level caused by nearby urbanisation could have long term effects on harvests.
South African Journal of Botany 67 (1) 2001, 15–38
©2001 NISC Pty Ltd, www.nisc.co.za
The identification of Broad Habitat Units as biodiversity entities for systematic conservation planning in the Cape Floristic Region
RM Cowling1* and CE Heijnis
Institute for Plant Conservation, University of Cape Town, Rondebosch 7701 South Africa
1 Present Address: Terrestrial Ecology Research Unit, Department of Botany, University of Port Elizabeth, PO Box 1600, Port Elizabeth 6000 South Africa
* Corresponding author, e-mail: [email protected]
Received 22 November 1999, accepted in revised form 4 August 2000
Despite many decades of vegetation-related research, the globally significant Cape Floristic Region (CFR) lacks a system of land classes that can be used as surrogates for biodiversity in conservation planning at the region-wide scale. Here we present a system of Broad Habitat Units (BHUs), suitable for planning at the 1:250 000 scale or larger. The BHUs were derived by intersecting coverages of Homogeneous Climate Zones, geology and topography in a geographic information system. A vegetation type coverage (Low and Rebelo 1996) was used to guide the classification under certain circumstances. A total of 15 primary and 88 secondary BHUs were identified in the CFR (87 892 km2). Of the latter, 69 were included in the Fynbos biome, which covered 81.5% of the CFR. At the primary BHU level, the system is very similar to existing vegetation treatments. The system is a good surrogate for biodiversity pattern and process, and therefore has good potential to provide meaningful entities for systematic and strategic conservation planning in the region.
South African Journal of Botany 67 (1) 2001, 39–43
©2001 NISC Pty Ltd, www.nisc.co.za
Two new Phaeophleospora species associated with leaf spots of Proteaceae
JE Taylor1, PF Cannon2, JC David2 and PW Crous1*
1 Department of Plant Pathology, University of Stellenbosch, Bag X1, Stellenbosch 7602, South Africa
2 CABI Bioscience, Bakeham Lane, Egham, Surrey TW20 9TY, United Kingdom
* Corresponding author, e-mail: [email protected]
Received 28 March 2000, accepted in revised form 22 August 2000
Two new foliicolous species of Phaeophleospora Rangel are described from Proteaceae in Africa. Phaeophleospora concentrica sp. nov., which causes a distinctive leaf spot disease of Protea caffra Meisn. is described from Kenya. A further species, P. capensis sp. nov. is described from leaf spots on a species of Protea L. collected in South Africa.
South African Journal of Botany 67 (1) 2001, 44–46
©2001 NISC Pty Ltd, www.nisc.co.za
A new species of Polyxena (Hyacinthaceae, tribe Massonieae) from Komsberg, Northern Cape Province
AM van der Merwe and EM Marais*
Department of Botany, University of Stellenbosch, Bag X1, Matieland 7602, South Africa
* Corresponding author, e-mail: [email protected]
Received 15 November 1999, accepted in revised form 23 August 2000
Polyxena longituba AM vd Merwe, from Komsberg in the Northern Cape Province is described as a new species. It resembles P. corymbosa (L.) Jessop, with regard to flower shape and colour but is distinguished by its long perianth tube and involute, canaliculate leaves. The flowers close at night and the species is self-pollinating.
South African Journal of Botany 67 (1) 2001, 47–52
©2001 NISC Pty Ltd, www.nisc.co.za
The stigma and style of Lobostemon (Boraginaceae) and their systematic implications
MH Buys
AP Goossens Herbarium, School for Environmental Sciences and Development, Botany Division, Potchefstroom University for CHE, Potchefstroom 2520, South Africa
* corresponding authur, e-mail: [email protected]
Received 17 May 2000, accepted in revised form 11 September 2000
A study of the stigma and style of Lobostemon Lehm. (Boraginaceae, tribe Lithospermeae Bentham & Hooker) is presented. Lobostemon is endemic to the Cape fynbos region of South Africa and comprises about 29 species. Surface characters of the stigma as well as the indumentum of the styles are discussed. In this regard, Lobostemon is characterised by possessing dry, papillate, bilobed stigma branches. Glabrous styles are largely confined to the section Lobostemon. A transformation series of the stigmatic regions investigated is presented.
South African Journal of Botany 67 (1) 2001, 53–57
©2001 NISC Pty Ltd, www.nisc.co.za
The influence of water stress on non-structural carbohydrate concentration in Themeda triandra
IB Oosthuizen* and HA Snyman
Department of Grassland Science, PO Box 339, University of the Free State, Bloemfontein 9300, South Africa
* Corresponding author, e-mail: [email protected]
Received 2 May 2000, accepted in revised form 22 September 2000
The objective of this study was to determine the influence of four different watering treatments (T1 = 75-100%, T2 = 50-75%, T3 = 25-50% and T4= 0-25% of Field Water Capacity) on the concentration of total non-structural carbohydrates during three growth stages (vegetative, pipe and reproductive) and also in three plant parts (roots, stubble and leaves) of the indigenous C4 grass species Themeda triandra. The total non-structural carbohydrate concentration (TNCC) was higher in all the plant parts (P<0.05) as well as all the growth stages (P<0.05), in T4 than T1. The results confirm that total non-structural carbohydrates are allocated (as growth reserves) to certain plant parts with increased water stress, with the largest allocation to the stubble. Because a mid-summer drought is more the rule than the exception in semi-arid areas, severe defoliation of Themeda triandra in the pipe growth stage during these conditions will be extremely detrimental to the survival of this key forage plant.
South African Journal of Botany 67 (1) 2001, 58–64
©2001 NISC Pty Ltd, www.nisc.co.za
Vegetation ecology of the southern Free State: Vegetation of the drainage channels
PW Malan1*, HJT Venter2 and PJ du Preez2
1 Department of Biology, University of North West, Bag X2046, Mmabatho 2735, South Africa
2 Department of Botany and Genetics, University of the Free State, PO Box 339, Bloemfontein 9300, South Africa
* Corresponding author, e-mail: [email protected]
Received 1 February 2000, accepted in revised form 26 September 2000
Little information is available on the vegetation of the southern Free State. A phytosociological analysis of the riparian shrub communities of the southern Free State is presented. Relevés were compiled in 38 stratified random sample plots. A TWINSPAN classification, refined by Braun-Blanquet Procedures, resulted in 9 distinct vegetation units grouped as two major communities.
South African Journal of Botany 67 (1) 2001, 65–68
©2001 NISC Pty Ltd, www.nisc.co.za
Observations on hairs in the capitula of some southern African Asteraceae genera
PPJ Herman
National Botanical Institute, Bag X101, Pretoria 0001, South Africa
e-mail: [email protected]
Received 29 May 2000, accepted in revised form 26 September 2000
Septate hairs are recorded and described for the first time from the capitula of various southern African asteraceous genera. Such hairs are present on the paleae of Eriocephalus L., the cypselas of Tarchonanthus L., Lasiospermum Lag., Arctotis L. and Arctotheca JC Wendl. and the receptacle of Lidbeckia PJ Bergius. The basal coma of hairs on the cypselas of Ursinia Gaertn. subgenus Sphenogyne (R.Br.) Prassler also consists of septate hairs. The hairs in Eriocephalus, Tarchonanthus, Lasiospermum, Arctotis and Arctotheca have oblique cell walls while in Lidbeckia the hairs have perpendicular cell walls. In Ursinia subgenus Sphenogyne the septate hairs also have oblique cell walls and, in addition, spiral wall thickenings. Multicellular, biseriate hairs mixed with some septate hairs were observed in Arctotheca. The basal coma of the cypselas of Arctotis and Haplocarpha Less. consists of twin hairs. Septate hairs can be considered a generic characteristic of the genera Tarchonanthus and Arctotheca and possibly of the genera Eriocephalus, Lasiospermum, Lidbeckia and Ursinia subgenus Sphenogyne.
South African Journal of Botany 67 (1) 2001, 69–70
©2001 NISC Pty Ltd, www.nisc.co.za
Short Communication
Three cotyledons on Schinziophyton rautanenii seedlings
FP Graz
Polytechnic of Namibia, Department of Agriculture, Bag 13388, Windhoek, Namibia
e-mail: [email protected]
Received 24 June 2000, accepted in revised form 9 October 2000
During a study of seedling growth in Schinziophyton rautanenii (Schinz) Hutch. Ex Radcl.-Sm. some anomalous seedlings developed from a batch of seeds collected in the Rundu area of northern Namibia. These seedlings had three cotyledons instead of the usual two. This report of tricotyly in Euphorbiaceae is the first for the family.
South African Journal of Botany 67 (1) 2001, 71–73
©2001 NISC Pty Ltd, www.nisc.co.za
Short Communication
Isolation of the anti-bacterial vernodalin from traditionally used Vernonia colorata
KA Reid, AK Jäger and J van Staden*
Research Centre for Plant Growth and Development, School of Botany and Zoology, University of Natal Pietermaritzburg, Bag X01, Scottsville 3209, South Africa
* Corresponding author, e-mail: [email protected]
Received 5 August 2000, accepted 20 September 2000
Leaf extracts of Vernonia colorata were screened for anti-bacterial activity using the disc-diffusion assay. Micrococcus luteus, Klebsiella pneumoniae and Staphylococcus aureus were inhibited by ethyl acetate extracts, but not by hexane and water extracts. The ethyl acetate extract was fractionated by silica vacuum chromatography and a chromatron using hexane:ethyl acetate gradients. The presence of anti-bacterial activity was confirmed by bioautography. The major anti-bacterial compound in the ethyl acetate leaf extract was identified by NMR as vernodalin. The minimal inhibitory concentration of vernodalin against S. aureus was 100Ďg ml-1.
South African Journal of Botany 67 (1) 2001, 74–77
©2001 NISC Pty Ltd, www.nisc.co.za
Short Communication
Micropropagation of the River Lily, Crinum variabile (Amaryllidaceae)
CW Fennell1*, NR Crouch2 and J van Staden1
1 Research Centre for Plant Growth and Development, School of Botany and Zoology, University of Natal Pietermaritzburg, P/Bag X01 Scottsville 3209, South Africa
2 Ethnobotany Unit, National Botanical Institute, PO Box 52099, Berea Road, Durban 4007, South Africa
* Corresponding author, e-mail: [email protected]
Received 25 July 2000, accepted in revised form 5 October 2000
Crinum variabile (Jacq.) Herb. is restricted to the Namaqualand, Bokkeveld Mountains and western Karoo regions of South Africa. Although its potential as a horticultural subject has been recognised, factors relating to the biology of the plant limit large scale propagation. These include short-lived seed viability and vegetative offsets that are produced too slowly or infrequently. As an alternative to conventional methods, C. variabile was successfully propagated in vitro using twin-scale explants. Shoots developed in the axes of twin-scales when placed on a Murashige and Skoog (MS) medium. Plant growth regulators were not required for the induction of shoots but benzyladenine (BA), in the absence of naphthalene acetic acid (NAA), promoted their outgrowth. The inclusion of 5gl-1 activated charcoal improved development by increasing the bulblet size and frequency with which shoots formed bulblets. These bulblets were used to initiate further cultures by splitting them in half. Such a system provided for the continuous multiplication of C. variabile bulblets which readily transferred to the soil.