Foliar micromorphology of Arctotis arctotoides (L.F.) O. Hoffm
South African Journal of Botany
created by the flood served as a template for establishment by immigrants and regeneration of existing species, which consequently resulted in a patch mosaic. This study aims to identify spatial and temporal riparian vegetation change, and to establish a long-term study to monitor the direction of change following a large infrequent disturbance. Thirty eight preselected pre-flood plots of 1991 were re-sampled in 2003 and 2006. Spatial and temporal vegetation change could be detected from
... etected from results obtained from Correspondence Analysis (CA) in the CANOCO package. The clusters represent unstable states and the direction of change is still unclear, although it is envisaged that data to be collected in 2010 will show the direction more clearly. Additional to plot data, pre-selected belt transects will be re-sampled for further support findings on vegetation dynamics following the 2000 flood. Importance values of selected species are compared to strengthen ecological interpretations of vegetation and floristic change. Vegetation and floristic change has a direct effect on riparian ecosystem function and therefore has an immediate consequence for the KNP's adaptive management approach. Arctotis arctotoides is a perennial herb used for the treatment of various diseases. Several secondary metabolites have been isolated from the plant, some of which are very effective as antimicrobial agents. Scanning electron microscopical examination of the foliar appendages of the plant revealed that its leaf surfaces are characterised by anisocytic stomata, glandular and non-glandular trichomes. The stomata and glandular trichomes are more abundant on the abaxial than the adaxial surfaces of the leaves. Crystal deposits were also observed around the stomata and near the glandular trichomes. Energy dispersive X-ray spectroscopy showed that Al, K, Fe, Ca, Na and Si were the major constituents of the crystals. Naturally, distinct morphological variations exist among the ultra structures on the leaf surfaces of the plant. The distributions of the stomata and the two types of trichomes on both surfaces also differ both in shape and in structure. We postulate that the various bioactive metabolites produced by this herb are from the glandular trichomes found on the leaf surfaces. Changes in tissue cytokinin (CK) profiles and their physiological implications in micropropagated Harpagophytum procumbens in relation to shoot-tip necrosis (STN) and CK treatments were studied. Total CK content was quantified in benzyladenine (BA)-treated necrotic and normal samples and in samples treated with the CKs BA, meta-topolin (mT) and metatopolin riboside (mTR) with and without the auxin indole-3acetic acid (IAA). Generally necrotic shoots yielded more total CK compared to normal shoots. Cytokinin accumulation was higher at the basal section (basal N middle N top). Further analysis of the CKs based on structural and functional forms revealed excessive accumulation of 9-glucosides (deactivation products-toxic metabolites) and limited amounts of O-glucosides (storage forms-re-utilisable) on necrotic and BA-treated shoots compared to the normal and topolin-treated cultures. The addition of IAA enhanced the formation of 9-glucosides in BAtreated cultures but reduced it in topolin-treated cultures. The symptom of STN could therefore be attributed to CK deficiency and/or unavailability due to conversion to other forms such as 9glucosides which are neither active nor convertible to active forms. These lower levels of active CKs cause cessation of cell division and death of meristematic tissues resulting in STN.