Novel plant growth regulator effects on yield, senescence and cytokinin homeostasis in wheat, barley and rapid cycling Brassica rapa. (2018)
Type of ContentTheses / Dissertations
Thesis DisciplinePlant Biotechnology
Degree NameDoctor of Philosophy
PublisherUniversity of Canterbury
Two novel plant growth regulators (PGRs), INCYDE and TDZ-K, were tested to verify the claims made for each of them. INCYDE is reported to inhibit cytokinin oxidase/dehydrogenase (CKX) and to enhance yield and growth in Arabidopsis thaliana and Brassica napus L., and to increase plant resistance to abiotic stress. TDZ-K is reported to delay senescence in wheat leaves by blocking the degradation of photosynthetic complexes within photosystem II. The effect and efficacy of INCYDE and TDZ-K was determined by application to rapid cycling Brassica rapa (RCBr) in controlled growth rooms, and by spray application to wheat and barley cultivars in both field and pot trials. Following harvest, the effect of each PGR on growth and yield components was determined. Leaf samples were used to analyse the content of chlorophyll. Wheat and barley grain samples were freeze dried and analysed by LC-MS/MS to determine the content of endogenous cytokinins. Wheat grains and leaves from wheat and RCBr were sampled to analyse the expression of cytokinin-associated genes, including isopentenyltransferases (IPTs) and cytokinin oxidase/dehydrogenases (CKXs), using RT-qPCR.
INCYDE enhanced seed yield in RCBr when applied multiple times before flowering and under specific nitrogen conditions in growth room experiments, but neither INCYDE nor TDZ-K caused significant enhancement of yield following application to either wheat or barley in the field or in pot trials. However, INCYDE delayed senescence in barley in the pot trials. LC-MS/MS analyses revealed a strong peak in tZ cytokinins at four days after anthesis in wheat and barley, and an increase in the concentration of cZOG following INCYDE treatment. Changes in expression of cytokinin biosynthesis (IPT) and degradation (CKX) gene family members occurred following INCYDE and TDZ-K treatment of both RCBr and wheat.
The enhancement in yield in RCBr following multiple INCYDE applications led to a feedback response model, which involved RCBr normalising cytokinin levels in response to changes in cytokinin homeostasis. The efficacy of the PGRs under optimal conditions in the field was minimal. Nonetheless, INCYDE showed an ability to delay senescence under conditions of imposed stress in the pot trials, and it was shown that the PGRs were able to affect cytokinin homeostasis by altering the expression of genes associated with cytokinin biosynthesis and degradation in both wheat and RCBr.
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