Little is known of the physiological and biochemical mechanisms underlying competitive interactions between alien invasive grasses and native taxa, and how these are affected by resource supply. Consequently, this study compared photosystem II (PS II) function, photosynthetic gas and water exchange, enzyme and pigment concentrations, flowering and biomass accumulation in an indigenous geophyte, Tritonia crocata (L.) Ker. Gawl., grown in monoculture and admixed with the alien grass, Lolium multiflorum Lam., at different levels of water and nutrient supply. Diminished stomatal conductances were the primary cause of reduced net C02 assimilation rates, and consequent biomass accumulation in T. crocata admixed with L. multiflorum at all levels of water and nutrient supply with one exception. These corresponded with decreased soil water contents induced presumably by more efficient competition for water by L. multiflorum, whose biomass was inversely correlated with soil water content. Biochemical impairments to photosynthesis were also apparent in T. crocata admixed with L. multiflorum at low levels of water and nutrient supply. These included a decline in the density of working photosystems (reaction center per chlorophyll RC/ABS), which corresponded with a decreased leaf chlorophyll a content and a decreased efficiency of conversion of excitation energy to electron transport (¥0 / l-^o), pointing to a reduction in electron transport capacity beyond QA~, a decline in apparent carboxylation efficiency and Rubisco content. At low nutrient levels but high water supply, non-stomatal induced biochemical impairments to photosynthesis (decreased RC/ABS, chlorophyll a and Rubisco content) were apparent in T. crocata admixed with L. multiflorum. These attributed to a reallocation of fixed carbohydrate reserves to floral production which increased significantly in T. crocata under these conditions only and associated with a corresponding reduction in the mass of its underground storage organ (bulb). The results of this study did not support the hypothesis that under conditions of low water and low nutrient supply invasive annual grasses would have a lesser impact on the growth and physiology of native geophytes than under resource enriched conditions that favor growth of these grasses. Unresolved is whether resource limitation and allelopathic mechanisms functioned simultaneously in the inhibition of the native geophyte by the alien grass. / Thesis (M. Environmental Science (Ecological Remediation and Sustainable Utilisation))--North-West University, Potchefstroom Campus, 2008.

GLK1 and GLK2 transcription factors have been suggested to be involved in the regulation of chloroplast development, organic nitrogen signaling, disease resistance and circadian rhythmicity (Waters et al. 2009; Gutiérrez et al. 2008; Savitch et al. 2007; Sprott et al. 2010). This implies that multiple factors may play roles in regulation of GLK genes. In the present study, transcriptional regulation of GLK1 and GLK2 in Arabidopsis by various endogenous and environmental stimuli was investigated with the objective of elucidating the primary signalling pathway affecting expression of these two genes. Collectively, results of GLK1 and GLK2 expression in response to the experimental treatments of Arabidopsis point to the regulation of the two genes by changes in photosynthetic metabolism and reactive oxygen species (ROS) levels, and by organic nitrogen signalling. Changes in ROS levels and organic nitrogen signalling may also affect the two genes indirectly by interfering with or altering photosynthetic metabolism.

The introduction of dwarfing genes in wheat and rice enabled significant yield improvements and was later termed the “Green-Revolution”. Dwarfing genes in sorghum have not been accompanied by such increases in grain production. On the contrary, some of the commercially employed dwarfing genes in sorghum have been associated with negative effects on grain yield. A positive correlation between plant height and grain yield was also observed in trial data for a diverse range of hybrids tested within the Queensland Department of Primary Industries and Fisheries Sorghum Breeding Program in north-eastern Australia. No attempts have previously been made to examine the physiological basis of the relationship between plant height and grain yield in sorghum. The dwarfing genes that are commercially used in wheat, Rht-B1 and Rht-D1 (formerly known as Rht1 and Rht2, respectively), on the other hand, have been studied extensively. They have been shown to have substantial and positive effects on grain number and harvest index, while not considerably reducing plant biomass, increasing grain yield. Our objective in this study was to examine the effect of height on the physiological and genetic determinants of growth and yield in sorghum to determine whether there was scope to improve yield by increasing the height of sorghum. A positive correlation between plant height and yield was observed in a population that was fixed for the major dwarfing genes, but showed variation in peduncle and panicle length, which are under control of minor dwarfing genes. To study the effects of a single major dwarfing gene (dw3) on biomass production and grain yield, 2- and 3-dwarf isogenic contrasts were developed in three different genetic backgrounds (R931945-2-2, R955343-1, R955637). In some cases, dw3 led to a significant reduction in plant biomass, which was not sufficiently offset by increase in harvest index to avoid yield reduction. This is contrary to the situation in wheat. The observed reductions in plant biomass in sorghum were associated with reduced tiller number and a reduction in radiation use efficiency (RUE) in the short types. Subsequent experiments suggested that an increase in allocation of biomass to the roots, rather than differences in photosynthetic capacity or respiration, was the main cause for the apparent reduction in RUE. However, due to plant-to-plant variability and the difficulty in accurately measuring root-total biomass ratio, studies with greater replication are required to confirm this hypothesis. It was also found that interactions with genetic background (and environment) moderated the effects of dw3, resulting in smaller height, biomass and grain yield reductions in some isogenic pairs. The effects of dwarfing genes on grain yield therefore need to be assessed separately for different genetic backgrounds. As lodging may be controlled by means other than height reduction (e.g. stay-green), we suggest that yield of standard sorghum types used in industrialised countries may benefit from moderate increases in plant height.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniversitet, 2005. / Härtill 5 uppsatser.

Thesis (Ph.D.)--University of Western Australia, 2007.

Thesis (Ph.D.)--Australian National University, 2002.

Thesis (M.Sc. Biological Sciences)--University of Waikato, 2007. / Title from PDF cover (viewed March 17, 2009) Includes bibliographical references (leaves 107-115)

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 60-64). Also available via the Internet.

Thesis (Ph. D.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 272-288).

Mémoire (M.Ress.Renouv.)--Université du Québec à Chicoutimi, 1997. / Document électronique également accessible en format PDF. CaQCU