Browsing by Subject "phytohormones"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Effects of Drought-Stress on Cotton (Gossypium hirsutum L.) and Host-Plant Resistance to Western Flower Thrips (Frankliniella Occidentalis Pergande)(2012-11-05) Fiene, Justin G. 1983-Herbivory by Western Flower Thrips (Frankliniella occidentalis Pergande) (WFT) and drought-stress due to limited water availability are currently two major factors that can severely impact cotton (Gossypium hirsutum L.) production. This dissertation examines the effects of drought-stress on cotton and host-plant resistance (HPR) to WFT in laboratory conditions, and seeks to identify the physiological and morphological mechanisms that underlie drought-tolerance and HPR. A life-history systems-approach was developed that provides a new level of detail for understanding how environmental variation impacts adult female WFT. The approach was illustrated by investigating the combined effects of cotton genotype, periodic drought-stress, and prey availability on the adult female omnivorous thrips using a factorial design. Three treatment conditions were significantly different, none of which were predicted based on prevailing ecological-hypotheses. At the same time, the approach produced three novel insights about WFT life-history and reproductive strategy. The roles of negative photo-taxis and leaf biomechanical properties were investigated as potential mechanisms that influence WFT foraging-decisions on individual cotyledons. Results showed that WFT foraging-decisions could be considered adaptive, but there was limited support for either of the mechanisms investigated. The physiological responses to drought stress and drought recovery were investigated for three transgenic cotton cultivars and an untransformed wild-type (WT). At peak drought, ABA levels, stomatal area, and stomatal apertures in the transgenic isolone, AtRAV1-1 were 48% lower, 27.7%, and 16.3% smaller than WT. These results suggest that AtRAV1-1 was the most drought-tolerant and support the hypothesis that changes in stomatal morphology may have functionally contributed to drought-tolerance. Lastly, I investigated whether changes in phytohormone concentrations associated with periodic-drought stress in four cotton cultivars (three transgenic and WT) were correlated with WFT feeding, fitness and state-dependent reproductive responses (i.e., the relationship between initial weight and reproduction). Results showed that JA-Ile and JA were positively correlated with state-dependent egg viability and fecundity, respectively, and negatively correlated with total egg viability and fecundity, respectively, supporting the hypothesis that JA and JA-Ile underlie the negative effects on WFT reproduction and the associated shift to state-dependent reproduction.Item Phytochrome B Controls Shoot Architecture by Regulating Phytochrome Interacting Factors and Phytohormones(2014-04-30) Holalu, Srinidhi VPlant architectural responses to changes in the ratio of red light to far-red light (R: FR) are mediated by phytochromes (phy), especially phyB. phyB function is transduced through interactions with the PHYTOCHROME INTERACTING FACTORS (PIFs) family of transcription factors. This study assessed the roles of Arabidopsis thaliana PIF4, PIF5 and PIF7 in mediating shoot architectural responses to high and low R:FR. The genetic interactions between various PIFs and phyB were also examined. The results indicated that PIF4/PIF5 and PIF7 are required for suppression of branch outgrowth under low R:FR, or with the loss of functional phyB. Compared to wild-type, lower levels of axillary bud abscisic acid (ABA) were detected in the pif7 and pif4pif5 mutants under low R:FR. The loss of functional phyB elevated axillary bud sensitivity to exogenous ABA. It was also demonstrated that the abscisic acid biosynthetic enzyme NCED3 was essential for aspects of phyB mediated regulation of branching. The analysis of transcript abundances of a panel of auxin-responsive genes in pif and phyB mutants in the study suggested that PIF4/PIF5 may mediate branching responses by regulating the transcription of auxin-signaling genes. PIF7 mediated effects on bud outgrowth may involve regulation of both ABA abundances and sensitivity in buds. In summary, PIF4/PIF5 and PIF7 affect branching by regulating auxin-signaling in shoots, ABA biosynthesis and sensitivity in buds in response to the R:FR in coordination with phyB. Assessment of the kinetics of axillary bud outgrowth and ABA levels in buds revealed a significant change in bud ABA levels as early as 1 h after alteration of the R:FR. This indicates that buds are able to rapidly respond to variations in the R:FR. Ethylene is known to mediate plant responses to variation in the R:FR. The assessment of plant architectural changes in the ethylene insensitive mutants ein2-1 and etr1-2 revealed a minor contribution of ethylene in mediating branch outgrowth responses to the R:FR. EIN2 and ETR1 were shown to regulate normal gravitropic responses in rosette branches.