Batch cultures of the marine diatom, Thalassiosira pseudonana were grown in the defined medium Aquil without EDTA and with varying concentrations of added iron (Fe). The response of cultures to Fe depletion was more rapid and dramatic when in vivo fluorescence (a correlate of cellular chlorophyll a) was used as a measure of biomass instead of cell density. In vivo fluorescence and in vivo fluorescence per unit cell density were found to be more sensitive and reliable measures of Fe limitation than cell density alone. Because the physiology of nutrient-limited cells changes rapidly in batch culture, a chemostat was designed and constructed to grow axenic cultures of T. pseudonana under constant degrees of Fe limitation. Fe-limited chemostat cultures grown in Aquil without EDTA were also partly limited by silicate. Despite growing to higher cell densities, Fe-replete batch cultures were not silicate limited. It thus appears that Fe-stress contributes to increased silicate quotas in this organism. Doubling the silicate concentration of the medium alleviated silicate limitation and cells responded to Fe limitation by continuing cell division for a time while in vivo fluorescence remained constant. Measured quotas of cellular Fe were 370 attomoles⋅cell⁻¹ (1 attomole is 1 X 10⁻⁸ moles) for an Fe-replete culture and ranged from 50 to 100 attomoles⋅cell⁻¹ for Fe-deplete batch and chemostat cultures. Fe associated with the cell surface was not detected in cells grown in a batch culture which received no added Fe or in an Fe-limited chemostat culture. As a comparison, the dinoflagellate, Protogonyaulax tamarensis Clone D-255 grown in Fe-limited batch culture was found to have an Fe quota of 116 femtomoles⋅cell⁻¹ which, however, was in close agreement with T. pseudonana when Fe quotas were calculated on a per unit volume basis. A method for the measurement of Fe uptake by ⁵⁵Fe .labelling was developed which estimated an uptake rate of 90B attomoles⋅cell⁻¹⋅hr⁻¹ over a 10 min exposure to 450 nM Fe. Many of the methods developed and tested in this study should prove valuable in future study of the iron requirement of phytoplankton and their adaptations to low-Fe stress. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Eleven zoysiagrass genotypes with known reactions to Fe-stress were grown under either growth chamber or greenhouse conditions in a series of four separate experiments. Genotypes grown in the growth chamber studies were subjected to three temperature ranges (18-12(DEGREES)C, 30-21(DEGREES)C, a

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The influence of iron nutrition on patterns of photosynthetic behavior, nitrogen metabolism, and fixed-carbon allocation is reported for a common freshwater green alga. Cultures of Scenedesmus quadricauda were grown in Fraquil medium in which iron concentrations ranged from 1.0 μM to 0.01 μM (log 10-6 to 10-8 M, respectively). Carbon 14 and nitrogen uptake experiments were conducted at photosynthetically saturating and subsaturating photon flux densities.

Bermudagrass (<i>Cynodon</i> spp.), when cultured at the northern limit of adaptation for semitropical grasses, is exposed seasonally to temperatures low enough to limit growth and turf quality. Research was conducted to investigate the influence of foliar iron and cytokinin applications on bermudagrass growth during fall and spring. The relationship of photosynthesis, respiration, and nonstructural carbohydrate composition to chilling temperatures was also studied. Foliar applications of Fe in late-summer and fall extended bermudagrass performance during low temperature periods of fall. Frequent Fe applications aided the retention of green bermudagrass turf during prolonged exposure to chilling temperatures. Iron applied the previous season stimulated post-dormancy recovery. Benzyladenine (BA) applied alone was not as effective as Fe for promoting green bermudagrass color retention during fall and BA had few effects on spring growth when applied the previous season. Applications of BA in conjunction with Fe were beneficial for retention of green bermudagrass color during late fall when clear plastic covers were used to prevent frost injury. A 6- to 8-week longer bermudagrass growing season occurred when clear plastic covers were used to prevent frost injury. Iron and BA did not significantly affect the total nonstructural carbohydrate (TNC) levels in Midiron bermudagrass rhizomes and stolons at the onset of dormancy in field studies. Midiron bermudagrass had higher photosynthetic and respiration rates than Tifgreen bermudagrass after 4 days exposure to chilling (10/7°C day/night) temperatures in controlled environment studies. Midiron recovered higher photosynthetic rates than Tifgreen when returned to a warm (30°C) environment after exposure to chilling temperatures. The TNC in leaves of Midiron and Tifgreen increased 88 and 160%, respectively, during 5 days at chilling temperatures. The inability to transport carbohydrate from and the subsequent accumulation of high photoassimilate levels in leaves was associated with the inability of bermudagrass to fully recover high photosynthetic rates following chilling. Reduced respiratory activity was apparently responsible for the accumulation of high TNC levels in leaves. In contrast to photosynthesis, respiration was reversibly inhibited by short term exposure of bermudagrass to chilling temperatures. Rapid recovery of high respiratory activity may be important for maintenance of aesthetically pleasing bermudagrass turf following chilling. Foliar applied Fe or BA generally caused darker green Midiron and Tifgreen turf after exposure to chilling temperatures in a controlled environment, although the enhancement of physiological activity differed with chemical applied and cultivar. Iron stimulated recovery of photosynthetic and respiratory activity in both cultivars after exposure to chilling temperatures. However, during chilling Midiron CO₂ exchange was more responsive to Fe applications. Benzyladenine increased photosynthesis in Tifgreen but not in Midiron and did not significantly affect respiration in either cultivar. Neither Fe nor BA had a consistent effect on TNC levels in bermudagrass leaves, rhizomes, or stolons. These investigations indicate that cultivar selection may play a major role in determining turf quality at chilling temperatures. Iron may modify bermudagrass physiology and enhance performance of bermudagrass exposed to chilling temperatures. / Ph. D. / incomplete_metadata