M.Sc. (Botany) / Senescence of carnation flowers is accompanied by an increase in the sensitivity of the petals to ethylene. It appears that ethylene sensitivity during normal senescence and under stress conditions is induced by the production of short-chain saturated fatty acids ranging in chain-length from C7-C10 during the early stages. During pollination-induced senescence these acids are synthesized in the styles as a result of wounding and transported to the corolla where they induce an increase in ethylene sensitivity of the petals to ethylene, causing an advancement in the timing of the climacteric peak in ethylene production. It appears that the cell membrane is the site' of action for short-chain fatty acids in their regulation of ethylene sensitivity in plant tissues. These acids cause an increase "in the ability of the tissue to bind ethylene by affecting the physical properties of the cell membranes. Treatment with STS results in a suppression of ethylene sensitivity by stabilizing the cell membranes, thereby decreasing the ability of ethylene to bind to its receptor sites in the cell membranes. Treatment with short-chain fatty acids overrides this stabilizing effect to a great extent by increasing the permeability of cellular membranes and thus the sensitivity of the carnation petal tissue to ethylene.

No description available.

D.Sc. (Botany) / Senescence of Petunia hybrida petals is characterized by a typical climacteric respiration pattern. Pollination enhanced the rate of senescence and the start of the climacteric rise in respiration of the, corolla. Treatment with ethylene for a period of 6 hours had no effect on the rate of senescence, but increased the respiration rate. A ten hour treatment with ethylene increased the rates of both senescence and respiration. Initiation of the climacteric rise in respiration was also advanced. The cytochrome electron transport path was active throughout normal senescence and was the most important contributor to the total oxygen consumption by the petals during the pre- climacteric phase, while the contribution of the alternative pathway was minor. The contribution of the alternative pathway to oxygen consumption during the climacteric rise in respiration increased considerably, while the contribution of the cytochrome pathway decreased correspondingly. This suggests that the climacteric rise in respiration is due to an increase in the activity of the alternative pathway. Treatment with ethylene increased the contribution of the cytochrome pathway during the climacteric phase. Ethylene did not cause any significant increase in the activities of the processes of respiration preceding electron transport nor did it affect the availability of respiratory substrates. The results of this study suggest that the influence of ethylene on the electron transport system may be due to the effects of this hormone on the physical properties of the mitochondrial membranes.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Physiological characteristics of three cotton genotypes were evaluated for their responses to plant aging under high and low planting density (HPD and LPD) treatments. In addition, the relationship of these physiological characteristics to fruit production were determined. Two genotypes are sympodia producing, "Pima S-6" (Gossypium barbadense L.) and "Deltapine 90" (DPL-90) (G. hirustum L.). The third, a "Cluster Selection" (G. barbadense L.) does not produce sympodia. These genotypes were grown on a Gila sandy loam soil at Tucson, Arizona in 1984 and 1985. Plant physiological characteristics were measured under field conditions at 5 intervals. Leaf physiological characteristics were determined at 7 different leaf ages. LPD treatment significantly reduced total dry weight (TDW), fruit dry weight (FDW), and leaf area index (LAI) in each genotype, but reductions were more pronounced in Pima S-6 and Cluster Selection in both seasons. However, LPD treatment significantly increased plant leaf area, but had no effect on specific leaf weight (SLW), petiole nitrate-nitrogen (Petiole NO₃-N) concentration, leaf area ratio (LAR), and fruiting index (FI), for all genotypes in both seasons. The aging patterns of all physiological characteristics were similar in both planting density treatments, regardless of genotype or season. Regression analyses showed that photosynthetic rate was curvilinearly correlated with leaf age (r² = 0.65 to 0.77, P < 0.01). However, petiole NO₃-N concentration decreased linearly with increasing leaf age (r² = 0.90 to 0.91, P < 0.01). Photosynthetic rate increased curvilinearly with increasing petiole NO₃-N concentration (r² = 0.61 to 0.79, P < 0.01). SLW was not correlated with leaf age, or other leaf physiological characteristics regardless of planting density treatment in 1985. TDW, FI, and LAI were directly related, while petiole NO₃-N concentration and LAR were inversely related to fruit production for all genotypes in both seasons. Multiple regression analyses showed that excluding planting density treatment effect, TDW, FI, and LAI were the most important variables incorporated for fruit prediction in both seasons.

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M.Sc. / Please refer to full text to view abstract

Aging of ray parenchyma cells from the young sap-wood to recently formed heartwood was studied in single stems of Pinus banksiana Lamb., Picea mariana (Mill.) B.S.P., Abies balsamea (L.) Mill, and Populus tremuloides Michx. Season, radial location of cell within sapwood, and cell location vertically within a ray at a given radius were considered as factors which might influence the aging process. A 12 mm increment core was extracted at breast height, from the north aspect of a tree of each species in May and July for moisture content determination. Another set of cores from the south aspect of the same trees was collected in May, June, July, August, October, and November or December. These cores were used to investigate the physiological and cytological properties of living sapwood ray parenchyma cells. Qualitative and quantitative observations were made of the status of ray cells both with light and transmission electron microscopy in order to draw inferences concerning the sapwood/heartwood transformation from the aging of sapwood ray parenchyma cells. The sapwood moisture content of the three conifers studied was higher than that of heartwood, whereas in Populus tremuloides it was lower than that of heartwood. The sapwood moisture content in May was consistently greater than in July. Vitality of the sapwood ray parenchyma cells expressed by a new nuclear elongation index decreased from the outer sapwood towards the heartwood. The survival rate of the cells decreased curvilinearly from the middle sapwood towards the heartwood. At a given sapwood increment, a greater percentage of dead ray parenchyma cells was found among the marginal cells than among the central cells of a ray. No statistically significant difference was found between the vitality of the marginal and central cells, nor between any two contiguous sampling periods with exceptions in Pinus banksiana and Picea mariana between two contiguous sampling periods from July to December. No typical pattern for the distribution of lipid content was found. The pattern of starch distribution displayed significant species, radial, vertical and seasonal variation and showed two general patterns across the sapwood. Pattern A described a decreasing trend from the outer sapwood towards the inner sapwood. Pattern B was characterized by a relatively low starch content both in the outer as well as the inner sapwood. The starch content in Populus tremuloides and the lipid content in Pinus banksiana and Picea mariana displayed no statistically significant difference between marginal and central ray cells. The majority of ray parenchyma cells showed a statistically significant difference between two contiguous sampling periods in starch and lipid contents. There was no inverse relationship between the starch and lipid content over the growing season studied. Young ray parenchyma cells were rich in chromatin and cytoplasm which contained numerous cell organelles. These cells were characterized by amyloplasts which possessed one or more elongated starch granules with thylakoids and osmiophilic globuli, numerous small lipid droplets and mostly rod-like mitochondria. In contrast, aged ray parenchyma cells featured an aggregated, dense nucleus and cytoplasm which contained few cell organelles. These aged cells possessed enlarged swollen starch granules, large lipid droplets or lumps with two staining densities, round shaped mitochondria with inconspicuous cristae and a rough/broken plasmalemma. Some heartwood substances originated from the lipid lumps which appeared frequently in dying ray cells. Based on microscopic observations and measurements of the loss of vitality of ray parenchyma cells, a declining survival rate, the disintegration of cell organelles and the origin of heartwood substances from lipid lumps, it can be concluded that heartwood formation is largely associated with the death of sapwood ray parenchyma cells. The death of these cells is due to the passage of time. / Forestry, Faculty of / Graduate

Call number: LD2668 .T4 1985 K87 / Master of Science / Agronomy

Adequate nutrient supply to the medium solution of container-grown crops is a major concern to container plant production practices. The extent to which nutrients are removed by the plant from the medium solution of a container, however, has never been demonstrated. Mariogold, Tagetes erecta ‘Inca’ seeds were glasshouse-grown in 500 cc plastic pots containing 1 peat: 1 perlite (v/v) medium and fertilized daily with 200 ppm N as ammonium nitrate. Thirty, 35, 40, 45 and 50 day old plants were subjected to either 20, SO, 80 or 110 ppm N. Medium solutions were tested at hour 0 and 6, and analyzed for N, P and K. Nitrogen removal from the medium solution was greatest by 45 and 50 day old plants at the higher N treatments. Phosphorous and K removal also increased with plant age. Medium solutions were tested and analyzed again, 10 days later. Nitrogen removal, 10 days later, was greatest for 50, 55 and 60 day old plants at the higher N treatments. Phosphorus removal was greatest by 55 and 60 day old plants whereas K removal increased up to day 60 through all age groups. Total N, P and K in the tissue reflected nutrient removal rates; however, no differences in dry weight due to N treatment were detected. In a second experiment, to determine the age at which dry weight is affected by N treatment, plants of one age group were treated with either 10, 30, 50 or 70 ppm N. Shoot dry weights did not differ until day 27 when plants grown at 10 ppm were smaller than for other treatments. As plants aged, higher levels of N were required to prevent growth reduction. These results indicate that age influences the N removal rate from the medium solution of container-grown plants. This relationship affects the amount of N applied to the medium solution to satisfy plant N requirement. / M.S.