Browsing by Subject "plant growth regulator"
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Item Abscisic Acid-Regulated Growth Modulations and Its Application for Stress and Quality Management of Vegetable Transplants(2014-08-01) Agehara, ShinsukeThe goal of this study is to develop a management tool for producing high quality, more stress tolerant vegetable transplants and for prolonging transplant marketability. This study primarily involves physiological and morphological growth modulation by the stress hormone abscisic acid (ABA). The first part of this study evaluated the effects of ABA foliar spray on stress and quality management of vegetable transplants. In muskmelon seedlings subjected to water withholding, pre-stress treatment of ABA improved the maintenance of leaf relative water content by limiting transpirational water loss. Upon re-watering, the ABA-treated seedlings showed faster photosynthetic recovery and greater dry matter accumulation than the untreated seedlings. In jalape?o pepper, ABA applied at the cotyledon to 3-leaf stage improved transplant compactness with minimal negative side effects. Although this method induced undesirable growth modifications in bell pepper and watermelon, ABA applied immediately before the transplant maturity stage was effective in delaying excessive shoot growth of bell pepper seedlings. These results demonstrate three beneficial effects of ABA for vegetable transplants: stress control, height control, and extension of transplant marketability. The second part of this study examined the mechanisms of ABA-induced growth modulations in Arabidopsis: inhibition of leaf expansion, leaf chlorosis, and promotion of primary root elongation. Microscopic analysis of leaf epidermis revealed that ABA inhibits cell expansion, but not cell division or stomata formation, suggesting that the ABA-induced inhibition of leaf expansion is a mechanism to conserve water without limiting plant growth capacity. Leaf chlorosis induced by exogenous ABA occurred only in mature leaves and independently of ethylene synthesis. Tissue nitrogen (N) analysis with a ^(15)N-labeling technique indicated a role of ABA as a regulator of N distribution. A proposed new mechanism is that ABA limits distribution of N into non-growing mature leaves, thereby inducing leaf-age dependent chlorosis. Using scanning electron microscopy (SEM), dehydration-induced root damage was characterized by thickening and deformation of root tips. Although exogenous ABA did not alleviate this damage, it promoted primary elongation especially under water stress. These results suggest that the overall function of ABA in stress adaptation is to conserve water and nutrients to support new growth.Item Evaluation of organophosphate insecticides on performance of transgenic and conventional cotton(Texas A&M University, 2005-08-29) Hundley, Christopher AlanGenetically modified cotton (Gossypium hirsutum L.) acreage has increased dramatically over the last six years. Reports of variable results in fiber quality and yield have arisen in these cultivars. Some changes in production practices have occurred coincident with the introduction of transgenic technology, such as reduced use of broad-spectrum insecticides, including organophosphates (OP) that could potentially influence the growth and yield of cotton. One factor that might affect these parameters is the difference in the amount of foliarly-applied phosphorus (P) between an OP and non-phosphate (NP) insecticide regime. Therefore, a study was conducted to investigate selected growth characteristics, yield, and fiber quality of genetically modified and conventional cotton as influenced by OP and foliar phosphorus (FP) applications. A four replication strip-plot experimental design was utilized with cultivar serving as the whole plot and insecticide regime as the sub-plot. Three cultivars of the same recurrent parent (ST4892BR, ST4793R, and ST474) were planted in 2001 and 2002 under irrigated conditions in Burleson County, TX on a Weswood silty clay loam (fine-silty, mixed, thermic Fluventic Ustochrept). The insecticide regime consisted of NP, NP+FP, and OP treatments. The FP was applied at P2O5 weight equivalent to the P component in the concurrent OP application. ST4892BR had greater lint yield than ST4793R and ST474. The yield increase can be explained through plant mapping analysis which showed ST4892BR producing larger bolls and greater boll numbers. In addition, evaluation of fruiting distribution showed ST4892BR contained more lint on sympodial branches 6 through 10. The insecticide regime effect on lint yield resulted in higher yield (P=0.08) for the NP+FP regime. Examination of yield components revealed NP+FP increased second position bolls, predominantly at sympodial branches 6 through 10. Leaf tissue analysis revealed increased levels of P for the OP and NP+FP over that of the NP insecticide regime, which indicates a potential for plants to acquire P from OP insecticides. Furthermore, the considerable yield response to small amounts of FP is not clearly understood. While conclusive evidence exists regarding cultivar yield differences, this study does not provide sufficient evidence to conclude that OP insecticides influence growth, yield, or fiber quality characteristics of these cotton cultivars.