Experiments were conducted with a Blue M "Vapor-Temp" controlled environment apparatus to show the effect of temperature, light intensity, relative humidity and age upon the rate of CO₂ exchange for twelve barley varieties. All varieties showed an increase in CO₂ uptake with an increase in temperature to a certain optimum, varying with variety. When the temperature was raised above this point, the rate of CO₂ uptake decreased. In all varieties tested the rate of CO₂ uptake increased as light intensity was increased up to 2400 ft. candles. Three out of four varieties tested showed significant changes in rate of CO₂ uptake with changes in relative humidity. All varieties tested showed an initial decrease in rate of CO₂ uptake per unit leaf area as the plants aged from 15 to 30 days. Above this age there was little change in rate of CO₂ exchange. Experiments were also conducted in photoperiod chambers to determine the developmental response of different barley varieties to different photoperiods. It was found that the varieties differed in overall response to photoperiod. Within a variety there was a difference in rate of development between plants subjected to different photoperiods. The optimal photoperiod for head differentiation and for head appearance was 21 or 24 hours for all varieties. / Land and Food Systems, Faculty of / Graduate

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Photosynthesis, photorespiration and differences in their interactions among species were studied. In the first of two parts of the investigation, the CO₂ compensation concentration of members of the Gramineae and other plants was determined with an infrared CO₂ analyzer. In some cases the Initial products of ¹⁴C0₂ fixation and leaf anatomy were also examined. In plants with low compensation values (lacking photo-respiration) the initial products of photosynthesis were formed by the C₄-dlcarboxylic acid pathway. High compensation plants (with photorespiration) produced compounds typical of the Calvin cycle. The leaf veins of low compensation species were surrounded by a specialized parenchyma bundle sheath containing a high concentration of chloroplasts with large quantities of starch. Low compensation members of the Gramineae belonged to the arlstidoid, chloridoid-eragrostoid and panicoid lines of evolution. Of the genera confined to these phylogenetic lines, Panlcum was found to differ in photosynthetlc physiology and bundle sheath characteristics at the subgeneric level. This type of photosynthetlc diversity also occurred within Cyperus (Cyperaceae), Atriplex and Bassia (Chenopodiaceae). Despite these differences, the correlation between type of photosynthetlc pathway, compensation value and leaf anatomy was consistent. The literature indicates that low compensation grasses have photosynthetic rates that are about double those of plants with photorespiration correlated with a temperature optimum for photosynthesis of about 35°. Species with photorespiration have optima within the range 10-25°. Some simple assay procedures proposed on the basis of these correlations allow rapid determination of the physiological and biochemical status of plants with respect to photosynthesis. In the second part of the investigation, some published studies of photorespiration and glycolate oxidation were reexamined and correlated by infrared CO₂ analysis. Photosynthetic rate data at different O₂ tensions for wheat, oat and corn seedlings fed 3-(3,4-dichlorophenyl)-l, 1 dimethyl urea (DCMU) indicated that dark respiration continued in the light when photosynthesis was completely inhibited. Photorespiration was also inhibited. The O₂ sensitivity of glycolate-stimulated CO₂ production was found to be compatible with the proposal that glycolate is a substrate of photorespiration. Both 'in vivo' and 'in vitro' studies of the alga Nitella flexilis revealed a pathway of glycolate oxidation resembling that of higher plants. DCMU inhibition of photosynthesis by Nitella gave results similar to those for the monocotyledons tested. Under very low light intensity, CO₂ compensation in corn was measurable but was not sensitive to high O₂ concentration. It appears that the lack of photorespiration in this plant is not the end result of efficient internal recycling of CO₂ to photosynthesis. / Science, Faculty of / Botany, Department of / Graduate

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Bibliography: leaves 102-107 / 107 leaves : ill ; 31 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Agronomy, Waite Agricultural Research Institute, 1984

Two varieties of Pisum sativum, L, Jade and Olympic, were grown for a period of four weeks from seeding, under constant light intensity and diurnally fluctuating temperatures, while being subjected to varying-artificially induced-degrees of nutrient stress. Net carbon dioxide exchange rates were measured in order to determine the influence of excess or deficient nitrogen and phosphorus concentrations within the nutrient medium. Carbon dioxide assimilation rates, under various degrees of nutrient stress were highly variable, both within the same variety and between varieties tested. Microchemical determinations of chlorophylls a and b, and of inorganic phosphate, nitrate and nitrite were carried out in order to determine the relationship of some physiological aspects of mineral deficiency to carbon dioxide assimilation. Investigations as to changes in stomatal index (I) as a result of nutrient stress also showed a large amount of variation. Results obtained indicated that variety Jade was very sensitive to nitrogen deficiency within the rooting medium, as evidenced by a large increase in stomatal index values with nitrogen deficiency. Olympic showed a greater sensitivity to phosphorus deficiency than did Jade. Neither total chlorophyll content, nor chlorophyll a/b ratio appeared to exert any deciding influence upon net carbon dioxide assimilation. A relationship appeared to exist between CO₂ assimilation and quantities of nitrate and/or nitrite present within the photosynthetic tissues of plants tested. This experiment was unable to fully explain the reason(s) for the great degree of variability of net CO₂ exchange rates extant even between plant specimens growing in the same nutrient medium. Some technical improvements applicable to the present experiments as well as some alternative experimental procedures are discussed. / Land and Food Systems, Faculty of / Graduate

Call number: LD2668 .T4 1985 B63 / Master of Science

Graduation date: 2006

No description available.