Control of plant development by light, CO2 and oligosaccharins in vitro with emphasis to strawberry (Fragaria x ananassa) 'Red Joy'

Miranda, John Hubert (2002). Control of plant development by light, CO2 and oligosaccharins in vitro with emphasis to strawberry (Fragaria x ananassa) 'Red Joy' PhD Thesis, School of Land, Crop and Food Sciences, The University of Queensland.

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Author Miranda, John Hubert
Thesis Title Control of plant development by light, CO2 and oligosaccharins in vitro with emphasis to strawberry (Fragaria x ananassa) 'Red Joy'
Formatted title

Control of plant development by light, CO2 and oligosaccharins in vitro with emphasis to strawberry (Fragaria x ananassa) 'Red Joy'

School, Centre or Institute School of Land, Crop and Food Sciences
Institution The University of Queensland
Publication date 2002-01-01
Thesis type PhD Thesis
Supervisor Prof Richard Williams
Dr. Allan Wearing
Total pages 227
Collection year 2002
Language eng
Subjects L
300302 Plant Growth and Development
620502 Horticultural crops
Formatted abstract
Plant phenotype is the end product of the interaction between the genotype and the environment. This interaction is 'mediated' by the physiology of the plant. These general statements are equally applicable to plant growth in vitro (plant tissue culture). However, traditionally the focus in vitro has been on the control of growth by manipulation of the culture medium, particularly the growth regulator component. There is potential to control plant development in vitro by manipulation of environmental factors. Our capacity to utilise this approach is limited by our lack of knowledge of the control of morphogenesis by environmental factors in vitro. This thesis addresses this problem by exploring the effects of CO2 and light quality on strawberry 'Red Joy' in vitro and investigates the subsequent regulatory influence of photosynthetic end product on morphogenesis.

Within the physical environment, light intensity, duration and quality or CO2 concentration, may influence in vitro plant culture development. There are only few reports on the influence of light quality compared to that of intensity. While responses to CO2 have frequently been investigated, the focus here is on the subsequent effects on morphogenesis rather than just growth (or just dry weight gain). This leads to consideration of the effects of oligosaccharins as products of the photosynthetic system and potential mediators of the effects of changes in photosynthetic efficiency on development. A brief account of new knowledge generated from the investigations is given below.

Evidence is provided for the first time, of significant developmental effects of light spectral quality and CO2 on strawberry 'Red Joy' in vitro. Short wavelength light (blue) increased total dry weight, leaf and stem dry weights and leaf area. Plant height decreased under blue light and increased with increasing wavelength. As the wavelength increased shoot number reduced.

CO2 enrichment increased total dry matter, leaf and stem dry matter, chlorophyll a/b ratio and carbon content but reduced fresh weight, the number of leaves and leaf size. The greater leaf area (number x size) in the closed (non-enriched) system appeared to be related to photorespiration. It is suggested that a limited CO2 supply triggers redirection of morphogenesis towards the production of more leaf area and hence a greater capacity to harvest the limited supply of CO2.

The lack of long light wavelengths limited leaf development. PS U photochemical efficiency was inhibited due to changes in the density of PS II components and/or alteration of the structural integrity of PS II.

Chlorophyll fluorescence studies provided the first evidence of the occurrence of photoinhibition of PS II of leaves developed and CO2 monitoring provided the first evidence of in vitro photorespiration of plants developed under low light intensity of conventional tissue culture system. Under CO2 depleted conditions photorespiration occurred. In a closed system under white light, photorespiration and photoinhibition occurred simultaneously. The reversible photoinhibition was affected by light spectral quality whereas irreversible photo damage appeared to have occurred in response to the prolonged limited supply of CO2 in the light. Increases in fresh weight, leaf number and leaf size resulted from limited CO2 availability and consequent increased photorespiration. Prolonged exposure to CO2 depletion altered the leaf anatomy considerably resulting in large intercellular spaces.

Blue light could substitute BAP for promoting the number of shoots. Sequential treatment with blue light for shoot induction, then red light for shoot growth could be superior to the conventional use of BAP for shoot multiplication. Endogenous sucrose accumulation increased under yellow light or in CO2 enriched systems. Light quality or CO2 regime did not affect fructose or glucose accumulation in vivo.

The differential response in in vivo sucrose accumulation due to CO2 regimes and light spectral qualities was significantly associated with important physiological and morphological characters of the in vitro whole plant. This association indicated that these in vivo compounds might have a possible regulatory role on morphogenesis of in vitro plants. A new oligosaccharide (unidentified) which was isolated from plants developed under short wavelength lights in vitro was indicative of the plant's ability to synthesise new oligosaccharins.

Oligosaccharin, oligogalacturonide fractions derived from polygalacturonic acid hydrolysis or polygalacturonase digestion, when added in the media at 100 µM concentration, altered morphogenic expression of strawberry plants in vitro. Oligogalacturonide fractions 14-18 increased fresh weight by 4 fold, root length by 5 times, root number by 10 times and leaf area by 4 times when compared with control (water). Oligogalacturonide fractions 9 - 1 3 and acid hydrolysis derived fraction induced almost similar responses for most of the characters, but was much different from that of fraction 14-18. Plant height decreased uniformly in all treatments due to the presence of these oligomers when compared with control. Galacturonic acid, the monomer of the above fractions, when added in the media also increased fresh weight, root number and length when compared with control, but the rate of increase was much lower than the effect of oligogalacturonide fractions 14 - 18. These responses may be due to the differences in the reductive potential of the oligomers and monomers. It is assumed that these oligomers might have acted endogenously to increase transcription rate, as well as exogenously to increase mobilisation of nutrients in the media because of its ability to change plasma membrane functions such as K+ efflux, Ca+ influx and alkalisation of the media.

Thus, this thesis has demonstrated that light quality, CO2 supply and exogenous oligosaccharins can be used to regulate the pattern of morphogenesis of strawberry plantlets in vitro. From the associations between endogenous or exogenous oligosaccharins and in vitro morphogenesis elucidated in different sections, it can be concluded that oligosaccharins had a major role in in vitro adaptation or development of strawberry plants. Some of the findings can help to avoid the detrimental effects of plant growth regulators and to eliminate acclimatisation protocols in a micropropagation system. It might also help to explain some of the hitherto inexplicable variations in in vitro culture performance where the significance of changes in environmental conditions has been overlooked.
Keyword Strawberries -- Effect of atmosheric carbon dioxide on
Strawberries -- Morphogenesis
Strawberries -- Micropropagation
Photosynthesis -- Regulation

Document type: Thesis
Collection: UQ Theses (RHD) - UQ staff and students only
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Created: Sat, 25 Aug 2007, 04:00:31 EST