Insights into the World of Pea Nodulation Using the Low Nodulator R50.

摘要

Cytokinin oxidase (CKX) is the enzyme responsible for the degradation of cytokinin, a class of adenine-based plant hormones that stimulate cell division, among other physiological processes. The pea mutant R50 is characterized by having a pale leaf phenotype, dwarf stature, few lateral roots, low nodule formation, and elevated levels of endogenous cytokinins in its shoots, roots and nodules. When compared to that of the wild-type Sparkle, total CKX activity is low but the transcript levels of PsCKX1 are significantly higher. In this study, I investigated the expression of PsCKX1 throughout the development of a nodule and the localization of PsCKX1 in the nodules of Sparkle and R50. To achieve this goal, a spot-inoculation technique was developed to capture different stages of nodule organogenesis. Sparkle nodules developed as expected. The nodules of R50, however, were delayed with root hairs exhibiting abnormal waving. Furthermore, an accumulation of starch grains was noticeable in the mature nodules which formed. Transcription of PsCKX1 was up-regulated upon inoculation, reaching a plateau for Sparkle but continuously increasing for R50. There were no differences in the localization of PsCKX1 between the two lines, but the immunofluorescence signal was much higher in the mutant. Finally, a protocol for the creation of composite plants was worked out with the goal of using the technique for later complementation of R50. All evidence allowed me to suggest that R50 produces a defective PsCKX1 protein which maybe the cause of abnormal nodulation.