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Literature review have the potential to develop into whole plants in a way analogous to zygote embryos, from somatic tissues (SLATER et al., 2003). Plant regeneration by somatic embryogenesis was first observed in carrot in 1958 (PHILLIPS et al., 1995). These somatic embryos can be produced either directly or indirectly. In direct somatic embryogenesis, the embryo is formed directly from a cell or a small group of cells without the production of an intervening callus (FINER, 1995). Direct somatic embryogenesis is however rare and only common in reproductive tissues (SLATER et al., 2003). In indirect somatic embryogenesis, a callus is first produced from the explant before embryos are produced. Synthetic auxins, especially 2,4-D, are most often used in protocols involving somatic embryogenesis (GRAY, 2005). Somatic embryogenesis usually proceeds in two distinct stages. In the initial stage (embryo initiation), a high concentration of 2,4-D is used (FINER, 1995). In the second stage (embryo production) embryos are produced in a medium with no or little 2,4-D (SLATER et al., 2003). Auxins activate pathways that induce the formation of embryogenic cells (GRAY, 2005). Auxins promote division, while suppressing differentiation and growth of embryogenic cells (GRAY, 2005). When using embryogenic cells as an explant, auxins are often not required as there is no need for an induction step (GRAY, 2005). In many dicotyledonous species cytokinins are also required to induce embryogenesis (GRAY, 2005). BA is the cytokinin most often used in embryogenesis (GRAY, 2005). Other cytokinins that have been used include TDZ, kinetin and zeatin (GRAY, 2005). Somatic and microspore embryogenesis has been reported in Tulipa sp., Gladiolus sp. and Nerine sp. (ZIV, 1997). 2.9.9 Hardening Micropropagation of a species is in some cases restricted due to unsuccessful ex vitro acclimatization, leading to a low survival rate of cultured plants (HUYLENBROECK et al., 2000). During this period of ex vitro acclimatization, plants must acquire the morphological and physiological features required by the in vivo environment and develop new patterns of resource allocation (HUYLENBROECK et al., 2000). In vivo cultured plants will otherwise not be able to cope with the 81
Literature review environmental stresses of the post-propagation environment (HUYLENBROECK et al., 2000). During acclimatization there is a switch to autotrophy and changes in stomatal functioning and cuticular composition (HUYLENBROECK et al., 2000). Water is rapidly lost from the in vitro cultured plantlet because of the failure of the stomata to respond to stimuli that would normally induce their closure (ROBERTS et al., 1990). The poorly developed cuticle results in a rapid loss of water (ROBERTS et al., 1990). Vitrified plants do not acclimatise well to in vivo conditions. Vitrified plants are common where liquid media and low agar concentrations are used (PIERIK, 1997). In vitrified plantlets there is a reduced deposition of cellulose and lignin, leading to an increase in water uptake by the cells and resulting in glassy swollen leaves and stems (ROBERTS et al., 1990). Because of this, and the low rates of photosynthesis sustained by the in vitro cultured plants, they easily suffer from photoinhibition and water stress; leading to the production of reactive oxygen species (HUYLENBROECK et al., 2000). It has been demonstrated that micropropagated plants develop antioxidant mechanisms during acclimatization (HUYLENBROECK et al., 1998). In vitro grown leaves are the only source of nutrition to cover metabolic demands and to sustain plant adaptation and regrowth during the first days after transplanting micropropagated plants to greenhouse conditions (HUYLENBROECK et al., 1998). The good and sustainable health of leaves is therefore essential to the acclimatization and survival of the plant (HUYLENBROECK et al., 1998). Plant hardening is usually carried out under greenhouse conditions to increase the chance of survival (AHLOOWALIA & PRAKASH, 2002). A commonly used greenhouse is the Quonset type. This consists of movable or fixed benches with hardening tunnels on them (AHLOOWALIA & PRAKASH, 2002). It is also advantageous to acclimatise plants to lower humidities while they are still under in vitro conditions (AHLOOWALIA et al., 2002). In this way, plants grown in strongly 82
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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
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Literature review flattened upper s
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2.2.16 Romulea tabularis Literature
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Literature review extinct, R. papyr
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Literature review R. leipoldtii occ
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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 and 96: Literature review The essential fun
Page 97 and 98: 2.9.3.4 Abscisic acid Literature re
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: Literature review organ is then pro
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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In vitro culture initiation and mul
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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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