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Literature review and will block root development (PIERIK, 1997). Examples of cytokinins include kinetin, zeatin, 2-iP, BA and thidiazuron (PIERIK, 1997). Some new cytokinins, called topolins have been synthesised in the Laboratory of Growth Regulators, Palacký University and Institute of Experimental Botany AS CR, Czech Republic. These include MemT [6-(3-methoxybenzylamino)purine, MemTR [6-(3- methoxybenzylamino)-9-b-D-ribofuranosylpurine], mT [6-(3- hydroxybenzylamino)purine]and mTR [6-(3-hydroxybenzylamino)-9-b-D- ribofuranosylpurine] (BAIRU et al., 2007). A high concentration of cytokinins can cause many small shoots to initiate but fail to develop (GABA, 2004). Shoots are induced into forming roots by placing them in a regeneration medium, containing a high level of cytokinin, and then in a medium with no plant growth regulators (GABA, 2004). Cytokinins inhibit rooting and can be effectively removed from the plant material by placing shoots in a medium without plant growth regulators (GABA, 2004). Such a treatment can also be used to reduce endogenous cytokinin levels (GABA, 2004). 2.9.3.3 Gibberellins Gibberellins are, in most cases, non-essential for plant development in in vitro culture (PIERIK, 1997). In tissue culture, gibberellic acid (GA3) is used to stimulate either shoot elongation or the conversion of buds into shoots (PIERIK, 1997). Gibberellins reduce root formation and embryogenesis in vitro (PIERIK, 1997). Gibberellins are primarily used to stimulate cell elongation and to produce elongated shoots in plant tissue culture (GABA, 2004). Unwanted side effects caused by gibberellins include reduction in the number of buds produced, the elongation of leaf structures such as petioles and lamina, the excessive elongation of shoots and reduced root production (GABA, 2004). YASMIN et al. (2003) found that GA3 dissolved in 0.2% ethanol inhibited adventitious rooting of mungbean cuttings but when dissolved in water, GA3 promoted adventitious rooting at 10 -7 M and 10 -8 M (YASMIN et al., 2003). This indicates that ethanol suppresses the promoting effects of GA3 (YASMIN et al., 2003). 71
2.9.3.4 Abscisic acid Literature review Abscisic acid is rarely used in tissue culture protocols and has a negative effect on growth in most cases (PIERIK, 1997). It is mainly used in plant tissue culture to facilitate somatic embryo maturation (GABA, 2004) but may also be used in some regeneration processes and rarely used to produce somatic embryos (GABA, 2004). ABA induces the formation of essential LEA (late embryogenesis abundant) proteins found at late stages of embryogenesis in somatic and sexual embryos (GABA, 2004). LEA proteins are associated with tolerance to water stress resulting from desiccation and cold shock (GOYAL et al., 2005). 2.9.3.5 Ethylene Ethylene or physiological reactions similar to that caused by ethylene, is produced by certain plastic containers, plant tissue and as a result of fire (PIERIK, 1997). This is the only gaseous natural plant growth regulator and it is naturally produced by all plant tissues in a controlled fashion (GABA, 2004). Endogenously produced ethylene can accumulate in a closed vessel to levels that negatively affect plant growth and development (PIERIK, 1997). The biological effect of ethylene depends on how air- tight the vessel is and the sensitivity of the plant material (GABA, 2004). Ethylene is primarily known for its effects on fruit ripening (GABA, 2004). Exposure to ethylene also results in reduced stem length, restricted leaf growth, premature leaf senescence and may cause increased growth of axillary buds (GABA, 2004). An enhanced ethylene concentration can induce callus formation, while inhibiting bud and shoot regeneration (GABA, 2004). Low concentrations of ethylene stimulate somatic embryogenesis, while high concentrations of ethylene inhibit somatic embryogenesis (GABA, 2004). Explants need a low level of ethylene for correct biological functioning, but too high an ethylene concentration leads to symptoms of excess (GABA, 2004). Such symptoms of excess include stunted growth, a reduction in leaf size and leaf drop (PIERIK, 1997; NOWAK & PRUSKI, 2002). These plants do not acclimatise well to the in vivo environment and often desiccate shortly after being transferred to soil (NOWAK & PRUSKI, 2002). 72
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Propagation of Romulea species Pier
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Contents 2.7 GERMINATION PHYSIOLOGY
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Contents 5.3.1 Explants from seedli
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Abstract The suitability of various
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Declarations I Pierre André Swart,
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Declarations DETAILS OF CONTRIBUTIO
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Publications from this thesis ASCOU
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List of Figures Figure 2.13: Suther
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was significantly different from th
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List of Tables Table 2.1: Names of
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List of Abbreviations 2,4-D 2,4-Dic
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Die vlakhaas spits sy oor hy het di
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As die mens dan ook so sy dankbaarh
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Introduction where a great number o
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Introduction The subgenera Romulea
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2 Literature review Leef van daad e
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Literature review Figure 2.2: Life
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Literature review Figure 2.4: Life
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Literature review The plants are sh
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Literature review flowers (DE VOS,
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Literature review often found on cl
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Literature review flowers of R. lei
Page 45 and 46: Literature review flattened upper s
Page 47 and 48: 2.2.16 Romulea tabularis Literature
Page 49 and 50: Literature review extinct, R. papyr
Page 51 and 52: Literature review R. leipoldtii occ
Page 53 and 54: Literature review Figure 2.8: Calvi
Page 55 and 56: Literature review Figure 2.14: Fras
Page 57 and 58: Figure 2.20: Nieuwoudtville weather
Page 59 and 60: Literature review Figure 2.26: Grah
Page 61 and 62: Literature review Figure 2.29: Diag
Page 63 and 64: Literature review Figure 2.30: A te
Page 65 and 66: Literature review Macronutrients ca
Page 67 and 68: Literature review The soils of the
Page 69 and 70: Literature review The embryo is the
Page 71 and 72: Literature review Phase 2 is seen a
Page 73 and 74: Literature review endogenous gibber
Page 75 and 76: Literature review tolerable level (
Page 77 and 78: Literature review these channels pe
Page 79 and 80: Literature review 2.8.7 Seed dorman
Page 81 and 82: Literature review the embryo (COPEL
Page 83 and 84: Literature review germinated under
Page 85 and 86: Literature review (COPELAND, 1976).
Page 87 and 88: 2.9 BRIEF REVIEW OF IN VITRO CULTUR
Page 89 and 90: Literature review (DEBERGH, 1994).
Page 91 and 92: Literature review PIERIK (1997) sta
Page 93 and 94: Literature review The distinguishin
Page 95: Literature review The essential fun
Page 99 and 100: Table 2.6: Example of a matrix to e
Page 101 and 102: Literature review Young embryos req
Page 103 and 104: Literature review and the addition
Page 105 and 106: Literature review organ is then pro
Page 107 and 108: Literature review environmental str
Page 109 and 110: 2.11 IN VITRO FLOWERING Literature
Page 111 and 112: Literature review higher regenerati
Page 113 and 114: Subfamily Ixioideae (continued) Tri
Page 115 and 116: Literature review Table 2.8: Corm i
Page 117 and 118: 3 Investigation into the habitat of
Page 119 and 120: Soil sampling and analysis The firs
Page 121 and 122: Soil sampling and analysis Table 3.
Page 123 and 124: 4 Germination physiology 4.1 INTROD
Page 125 and 126: 4.2.2 Water content and imbibition
Page 127 and 128: Germination physiology (-N), phosph
Page 129 and 130: Germination physiology rosea seeds
Page 131 and 132: Germination physiology Figure 4.4:
Page 133 and 134: Germination (%) 50 40 30 20 10 0 77
Page 135 and 136: Germination (%) 100 80 60 40 20 0 c
Page 137 and 138: Germination physiology The relative
Page 139 and 140: Germination physiology seeds of R.
Page 141 and 142: 5.2 MATERIALS AND METHODS In vitro
Page 143 and 144: In vitro culture initiation and mul
Page 145 and 146: 5.2.3 Explant comparison In vitro c
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In vitro culture initiation and mul
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5.4 DISCUSSION In vitro culture ini
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6 In vitro corm formation and flowe
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In vitro corm formation and floweri
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6.3 RESULTS 6.3.1 Corm formation In
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Commercialization potential of Romu
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Commercialization potential of Romu
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BASKIN, C. C., and BASKIN, J. M. (1
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Literature cited DOWLING, P. M., CL
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Literature cited HILTON-TAYLOR, C.
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Literature cited KUMAR, A., SOOD, A
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Literature cited PIERIK, R. L. M. (
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Literature cited STEINITZ, B., COHE
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