Thesis (M.S.)--Oregon State University, 1984. / Typescript (photocopy). Includes bibliographical references (leaves 54-60). Also available on the World Wide Web.

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Plant hormone abscisic acid (ABA) plays a main role in coordinating various stress signals in plants. ABA regulates the expression of genes and activities of enzymes in response to various stress conditions. In the following studies we were able to study the ABA mediated regulation of enzymes in plants. Using in-gel activity analysis we identified that ABA regulates the activity of aspartate aminotransferase (AAT), an enzyme involved in nitrogen assimilation and carbohydrate metabolism. Our results indicate that phosphorylation of AAT by SnRK2.2 and 2.3 kinases results in down regulation of AAT2 and AAT3 isozyme activities in Arabidopsis. AAT was identified as a negative regulator of drought stress and aat mutant plants showed improved survival following drought conditions. Using in-gel staining method we were able to visualize sugar phosphatases like fructose 1-6 bisphosphatase family, sedoheptulase-1,7-bisphosphatase, inositol mono phosphatases; protein serine/threonine phosphatases, protein tyrosine phosphatases and studied their response to ABA and drought stress. Fructose-1-6 bisphosphatase family of phosphatases were identified to be induced by ABA in Arabidopsis and rice. N-acetylglucosamine (GlcNAc) is present on glycoproteins and as post translational modification (PTM) in cytoplasmic and nuclear proteins. N-acetylglucosamine is removed from target proteins by hexosaminidases. Little is known about the hexosaminidases in plants. Using in-gel activity analysis we were able to identify an ABA induced Beta-hexosaminidase with a neutral pH optimum in soybean. The nuclear DNA in chromatin is associated with basic proteins called histones. The N-terminal tails of histones contain different PTMs including methylation, phosphorylation, ubiquitination, acetylation, ADP-ribosylation and glycosylation. The histone lysine methylation can serve as a binding site or repel/disrupt the histone binding proteins. The effector/reader proteins specifically recognize the post translational modifications and responsible for the downstream process. Many histone methyl modification effector proteins have been characterized but very few proteins whose binding was disrupted by the presence of a PTM were identified. Using peptide pulldown analysis, far western analyses we identified a WD-40 domain containing histone binding (HB01) protein as direct interactor of unmodified histone. The presence of post translational modifications disrupts HB01 binding to histone H3.

Cuscuta or dodder is one of the best known higher plant parasite with around 158 species over 5 continents parasitising a wide variety of host plants (Yuncker,1932) Dodders are characterised by their interesting parasitic behaviour and extraordinary appearance among the obligate parasitic flowering plants (Kuijt, 1969)

Hormones control plant development by coordinating changes in the expression of numerous genes at crucial times in a tissue and organ-specific manner. They have been implicated in controlling various aspects of grape berry development, in particular, the important process of ripening and are used in some crops to control growth and ripening. Abscisic acid (ABA), is associated in grapevine with the response to water stress but may also have a role in berry ripening. We have shown over three seasons that ABA levels in Cabernet Sauvignon berries increase dramatically at veraison, consistent with it being involved either as a trigger for ripening or as a response to the increase in sugars that occurs at this time. Net ABA accumulation doesn't occur until veraison, the decrease in ABA concentration in the first phase of berry development being due to berry expansion. The decrease in ABA that occurs later in development is likely to be due to a combination of catabolism and sequestration into the bound form. The genes crucial to ABA synthesis, 9-cis-epoxycarotenoid dioxygenase (NCED) and zeaxanthin epoxidase (ZEP), were expressed throughout berry development and no clear correlation was found between their levels and that of ABA. Laboratory studies have shown that isolated berries respond to the presence of sucrose through an increase in ABA biosynthesis pathway gene expression (NCED and ZEP). This resulted in de novo synthesis of ABA as inhibition of the carotenoid synthesis pathway by a phytoene desaturase inhibitor prevented ABA accumulation. Replicated field trials clearly showed that ABA treatments can be effective in significantly enhancing ripening when applied in at or near the end of the first period of berry expansion. Colour accumulation in the skins commenced earlier in ABA-treated fruit as did the increase in sugar levels. ABA treatment also advanced the timing of the second phase of berry expansion as it appeared to eliminate the lag phase of berry growth. Taken together these data demonstrate that ABA is likely to play some part in the control of berry ripening and can be used to advance the timing of ripening. Further investigation into the characteristics of ABA-treated fruit will be needed to investigate the compositional character of treated fruit and to gauge its suitability for winemaking. An ability to control the timing of ripening may provide considerable benefits to the wine industry in terms of wine style/quality and for winery scheduling. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1278807 / Thesis (Ph.D.) - The University of Adelaide, School of Agriculture, Food & Wine, 2007.

Hormones control plant development by coordinating changes in the expression of numerous genes at crucial times in a tissue and organ-specific manner. They have been implicated in controlling various aspects of grape berry development, in particular, the important process of ripening and are used in some crops to control growth and ripening. Abscisic acid (ABA), is associated in grapevine with the response to water stress but may also have a role in berry ripening. We have shown over three seasons that ABA levels in Cabernet Sauvignon berries increase dramatically at veraison, consistent with it being involved either as a trigger for ripening or as a response to the increase in sugars that occurs at this time. Net ABA accumulation doesn't occur until veraison, the decrease in ABA concentration in the first phase of berry development being due to berry expansion. The decrease in ABA that occurs later in development is likely to be due to a combination of catabolism and sequestration into the bound form. The genes crucial to ABA synthesis, 9-cis-epoxycarotenoid dioxygenase (NCED) and zeaxanthin epoxidase (ZEP), were expressed throughout berry development and no clear correlation was found between their levels and that of ABA. Laboratory studies have shown that isolated berries respond to the presence of sucrose through an increase in ABA biosynthesis pathway gene expression (NCED and ZEP). This resulted in de novo synthesis of ABA as inhibition of the carotenoid synthesis pathway by a phytoene desaturase inhibitor prevented ABA accumulation. Replicated field trials clearly showed that ABA treatments can be effective in significantly enhancing ripening when applied in at or near the end of the first period of berry expansion. Colour accumulation in the skins commenced earlier in ABA-treated fruit as did the increase in sugar levels. ABA treatment also advanced the timing of the second phase of berry expansion as it appeared to eliminate the lag phase of berry growth. Taken together these data demonstrate that ABA is likely to play some part in the control of berry ripening and can be used to advance the timing of ripening. Further investigation into the characteristics of ABA-treated fruit will be needed to investigate the compositional character of treated fruit and to gauge its suitability for winemaking. An ability to control the timing of ripening may provide considerable benefits to the wine industry in terms of wine style/quality and for winery scheduling. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1278807 / Thesis (Ph.D.) - The University of Adelaide, School of Agriculture, Food & Wine, 2007.

Hormones control plant development by coordinating changes in the expression of numerous genes at crucial times in a tissue and organ-specific manner. They have been implicated in controlling various aspects of grape berry development, in particular, the important process of ripening and are used in some crops to control growth and ripening. Abscisic acid (ABA), is associated in grapevine with the response to water stress but may also have a role in berry ripening. We have shown over three seasons that ABA levels in Cabernet Sauvignon berries increase dramatically at veraison, consistent with it being involved either as a trigger for ripening or as a response to the increase in sugars that occurs at this time. Net ABA accumulation doesn't occur until veraison, the decrease in ABA concentration in the first phase of berry development being due to berry expansion. The decrease in ABA that occurs later in development is likely to be due to a combination of catabolism and sequestration into the bound form. The genes crucial to ABA synthesis, 9-cis-epoxycarotenoid dioxygenase (NCED) and zeaxanthin epoxidase (ZEP), were expressed throughout berry development and no clear correlation was found between their levels and that of ABA. Laboratory studies have shown that isolated berries respond to the presence of sucrose through an increase in ABA biosynthesis pathway gene expression (NCED and ZEP). This resulted in de novo synthesis of ABA as inhibition of the carotenoid synthesis pathway by a phytoene desaturase inhibitor prevented ABA accumulation. Replicated field trials clearly showed that ABA treatments can be effective in significantly enhancing ripening when applied in at or near the end of the first period of berry expansion. Colour accumulation in the skins commenced earlier in ABA-treated fruit as did the increase in sugar levels. ABA treatment also advanced the timing of the second phase of berry expansion as it appeared to eliminate the lag phase of berry growth. Taken together these data demonstrate that ABA is likely to play some part in the control of berry ripening and can be used to advance the timing of ripening. Further investigation into the characteristics of ABA-treated fruit will be needed to investigate the compositional character of treated fruit and to gauge its suitability for winemaking. An ability to control the timing of ripening may provide considerable benefits to the wine industry in terms of wine style/quality and for winery scheduling. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1278807 / Thesis (Ph.D.) - The University of Adelaide, School of Agriculture, Food & Wine, 2007.

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references. Also available in electronic version. Access restricted to campus users.

PhD by publication.

Thesis (Ph. D.)--University of Hong Kong, 2008. / Includes bibliographical references (leaf 190-207) Also available in print.