A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. August 2015. / iii ABSTRACT Global changes are likely to have negative impacts on many ecosystems including savannas. Semi-arid environments are notable for the wide range of seasonal patterns of leaf display in the tree communities. The environmental cues of leaf out and leaf drop are not consistent across species, and are not always directly linked to water availability, indicating that some species might be particularly sensitive to changes in climate. Strategies employed by trees which leaf early or drop their leaves late are likely to impact other aspects of their life-history and functioning so I expect particular plant functional types to be associated with particular vegetation functional traits. I assessed how variable savanna leafing strategies are among 28 species at a semi-arid savanna site at Nylsvley, and used this information to group species into plant functional types (PFTs). These PFTs were then assessed in terms of key vegetative traits to explore the life history consequences of different leafing strategies. Leaf phenology was monitored throughout one growing season and quantified using 8 key phenological metrics. The timing of leaf display tracks the timing of seasonal rainfall but with wide variation, with some species retaining their leaves throughout dry season. Other species loss some leaves throughout the growing season, some species only flushed their leaves after the first rains, and other flush before the first rains. I identified 4 clear PFTs using the MClust clustering integrated with subjective procedure. Four vegetative traits were measured: specific leaf area, leaf nitrogen, maximum stomatal conductance and wood density. I identified some clear trade-offs between vegetative traits and phenological strategies. There was also a positive relationship between degree of rain stimulated flushing metric and wood density. Using objective clustering methods to determine plant functional types has some clear advantages over more subjective methods but depends on good input data. Identifying plant functional types at Nylsvley has led to some insights into functioning of these savannas, but as there appear to be strong links between plant traits and particular leafing strategies it might be more appropriate to explore syndromes of vegetation functional traits when modelling responses to global change.

No description available.

Call number: LD2668 .T4 1939 K41 / Master of Science

The epidermis from a range of species from the genus Allium was peeled from the base, middle, and tip of the adaxial and abaxial surfaces of leaf material. Epidermal peels were water mounted after being peeled using forceps, and photographed using Nomarski microscopy. The epidermis is composed of rows of cells which run parallel to one another, and to the long axis of the leaf. Guard cells are present on both surfaces of the leaf in most species, but some species lack guard cells on either the abaxial or adaxial surface. Guard cells are sunken to varying degrees in all species surveyed. Subsidiary cells are lacking in all species surveyed. End walls of nonstomatal cells are either even or oblique. Micropapilae, striations, or trichomes are present in some species, but most species lack epidermal structures. Epidermal cells range in size from two to three times greater in length than width to greater than fifteen times longer than wide. The majority of parallel walls are either straight or diamond-shaped while others are wrinkled, wavy, or broadened. Allium is separated into three groups according to the structure of the parallel walls. Group one includes those species with typically straight parallel walls; group two those species with diamond-shaped parallel walls; and group three is comprised of those species with wavy parallel walls.

Fern classification is in a state of flux, the largest area of disagreement being the family Polypodiaceae (Wagner, 1959). This polyphyletic group (Eame, 1936) has been divided by several prominet workers into many families. Ching (1940) recognized thirty-two, Holttum (1947) five, and Copeland (1947) nine families. Munz and Keck (1959) divided the old famliy Polypodiaceae, as represented by the ferns of California, into five families. The classification of Munz and Keck is the most recent treatment in this paper. Historically, classification of the leptosporangiate ferns has been based on the sorus, but the last half century has seen greater use vegetative characters. Problems of phylogenetic relationships can only be solved by the study of a number of features from all aspects of the planet. The more characters considered and evaluated, the more accurate and valuable are the conclusions. This line of reasoning has been pursued fruitfully in other plant groups as exemplifed by Metcalfe (1960) in his work on the anatomy of the monocotyledons. In this work the microscopical characters of the lamina were taken as being of major importance because of eary availability and the fact that one does not have to have the plant in flower before investigations can proceed. Another important reason for studying vegetative characteristics is that they are often preserved in the fossil record. Black (1929), Odell (1932), Florin (1951), and Greguss (1961) have studied cutinized superficial leaf epidermis preserved as fossils. The work of Florin has been particularly important in clarifying the phylogeny of the living conifers The questions of the value of the epidermis in the study of the ferns still remains unsolved problem. Therefore, it is the intention of this paper to explore the possibility of using epidermal charaters as a basis for establishing patterns of morphological and taxonomic significance. Because of their easy availability, the native ferns of California were used for this study.

Abstract not available

TOOTH/MIR160A regulates leaf margin outgrowth in Arabidopsis thaliana Unlike animals, a striking aspect of the plant development is that they have evolved a flexible pattern of post embryonic development. This exposes them to the challenges of many biotic and abiotic signals throughout their life. So, plants have to evolve/regulate various mechanisms to modulate their growth and development for accomplishing a successful life cycle in the prevailing environmental conditions. Auxin is involved in the initiation of lateral organs at the meristem and serration development along the leaf margin (Bilsborough et al., 2011, Hay et al., 2006). These two developmental mechanisms share common molecular players. For example, CUC2 is required for the boundary formation at the SAM and also is shown to be essential for serration formation at the leaf margin. Similarly, tth shows increased leaf serration phenotype as well as defects in the positioning of flowers at the meristem. This demonstrates the functional significance of TTH-regulated ARFs in controlling auxin mediated developmental pathways. Leaves originate as small lumps of undifferentiated cells at the flanks of the shoot apical meristem which undergo several rounds division and expansion to generate the mature leaf with characteristic size, shape and leaf margin. Both, endogenous as well as environmental factors modulate the growth and development of a leaf. This is evident from the plasticity in leaf form, observed during the life time of a single plant, as well as from the diversity among closely related species living in different habitats. It is well known that pathways controlling leaf form are subjected to the effects of selection and adaptation. Leaf margin is a key feature of the final leaf shape and it contributes to the abundant diversity in leaf form. Leaf margin architecture varies quite significantly from smooth or entire margin to margins with large outgrowths (lobed margins). The evolution and ecological advantages of this diversity is a subject of intense investigation. It also provides a wonderful system to study the mechanistic details of iterative generation of repeated units, which is a common feature in producing many biological shapes. Recent advances in molecular technologies and the availability of genomic resources ushered the identification of new factors involved in leaf margin development. Our current knowledge of this developmental programme is that CUC2 establishes auxin maxima at the leaf margin by reorienting an auxin efflux carrier PIN1 which ultimately results in serration outgrowth (Bilsborough et al., 2011, Hay et al., 2006). A few missing links in this pathway are the mechanistic details of CUC2 function in reorienting PIN1 and the molecular details of auxin mediated serration outgrowth. Forward genetic screens have been valuable in characterizing a genetic pathway even in the post genomic era. An EMS mutagenesis screen was performed in this context to identify novel factors that can improve our understanding of this intricate mechanism. tooth was identified in the M2 population based on its increased leaf serration phenotype. Genetic analysis showed that tth phenotype is due to a monogenic recessive mutation. Along with increased leaf serration, tth also shows various developmental defects such as aberrant phyllotaxy, narrower cotyledons and narrower leaves. Positional cloning and sequencing analysis showed a G to A transition at the AT2G39175 locus which codes for MIR160A. The mutation is at the 7th base position of the mature miRNA sequence. Functional characterization of miRNAs by isolating mutations is hampered by their small genomic sizes. Till now, only a few miRNAs have been characterized by mutational analysis in plants (Allen et al., 2007, Baker et al., 2005, Cartolano et al., 2007, Chuck et al., 2007, Knauer et al., 2013, Nag et al., 2009, Nikovics et al., 2006). miR160-ARF10 regulatory module is shown to be required for leaf blade out growth and serration, but not leaf complexity in tomato (Hendelman et al., 2012). miR160 is coded by 3 loci in Arabidopsis, MIR160A, B and C. All three loci encode identical mature miRNA that targets 3 Auxin response factors, ARF10, 16 and 17. ARFs are the effector molecules of auxin mediated developmental programmes. Genetic analysis showed that enhanced serration outgrowth in tth is due to the up-regulation of its target genes. Here, we have identified a miRNA that negatively regulates serration outgrowth by repressing ARF10, 16 and 17 whose functional significance in regulating leaf margin development was not known previously. Extensive genetic interaction studies have shown that TTH acts in parallel to SAW-BP and MIR164-CUC pathways in regulating leaf margin development. We have also shown that CUC2 and PIN1 are absolutely essential for serration development in tth. CUC2 establishes a pattern required for the expression of ARF10 at the leaf margin. In the absence of CUC2, downstream effector molecules such as ARFs can not perform their function. arf10-2 arf16-2 could reduce, but not suppress serration outgrowth in various mutants suggesting their functional redundancy with other ARF family members. CUC2 establishes auxin maxima at the leaf margin that triggers the degradation of AUX/IAA repressors thereby relieving ARF proteins which mediate serration outgrowth. Whereas, TTH acts at the post transcriptional level for maintaining normal ARF transcript levels Role of SPYINDLY in Arabidopsis leaf margin development SPYNDLY encodes an O-linked N-acetyl glucosamine transferase that acts as a negative regulator of GA response. Consistent with its role in GA response, spy mutants show several GA dependent phenotypes such as early flowering and hyper branched trichomes. spy mutants also show several GA independent phenotypes such as aberrant phyllotaxy and smooth leaf margin. We have studied its role in regulating Arabidopsis leaf serration development. Reporter analysis of ARF10::GUS and CUC2::GUS in spy-3 revealed that SPY is not involved in establishing serration pattern. The spy-3 leaves did not show any defects during the early stages of serration development, but the mature leaves display smooth leaf margin indicating that SPY function is required for serration outgrowth. As shown in the present study, TTH regulated ARFs are also involved in serration outgrowth. Analysis of leaf margin phenotype in tth spy-3 showed that SPY activity is not required for ARF mediated serration outgrowth. Similar genetic interaction studies with SAW-BP pathway mutants showed that leaf margin out growth mediated by meristematic genes is not dependent on SPY function. Genetic interaction studies with MIR164-CUC pathway genes showed that SPY is required for serration outgrowth in these mutants. Interestingly, the cuc2-3 mutant is defective at both patterning and outgrowth of serration. The spy-3 could suppress serration out growth in cuc2-D suggesting that CUC2 mediated serration out growth is dependent on SPY activity. Protein-protein interaction studies between SPY and CUC2 are in progress to demonstrate whether SPY directly interacts with CUC2 or CUC2 derived signal to regulate serration out outgrowth. It is interesting to examine how mutations at SPY locus can abolish serration out growth mediated by CUC2, but does not affect the serration pattern, even though CUC2 is reported to be essential for both the patterning and outgrowth of serration.