Cytoplasmic Ca2+ Changes in Nematode Treated Lotus japonicus Root Hairs

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Title: Cytoplasmic Ca2+ Changes in Nematode Treated Lotus japonicus Root Hairs
Author: Sumanasinghe, Polwatta Gallage Shantha Ramani
Advisors: Dr. Wendy F. Boss, Committee Member
Dr. Nina Stromgren Allen, Committee Chair
Dr. David McK. Bird, Committee Member
Abstract: Nitrogen fixation by Rhizobia and phosphorous extraction by Mycorrhiza, are specific plant microbe interactions that are of paramount economical and ecological importance. Of similar impact to the economy and ecology is the interaction between endoparasitic nematodes and plant roots that leads to major losses in crop production. While Nod factor induced signaling events have been a research focus for many years, the nature of the early responses induced by nematode invasion are just beginning to emerge. Recent reports provide morphological as well as physiological and genetic evidence that symbiotic rhizobia and parasitic nematodes use common signaling pathways in the host plant during induction of feeding sites. One of the earliest physiological responses to Nod factors comprises calcium influx at the tip of the root hair and elevation of cytosolic calcium followed after 10 min by calcium spiking over the nucleus. It was therefore of particular interest to investigate whether similar calcium changes occur after treatment with nematodes. I used the ratiometric cytosolic calcium indicator Indo-1, in conjunction with confocal laser scanning microscopy, to monitor calcium changes in L. japonicus root hairs in space and time before and after treatment with RKN Meloidogyne incognita. The results were compared with those I obtained in parallel experiments after Nod factor application under the same experimental conditions. I showed that treatment with nematodes increases cytoplasmic calcium at the root hair tip by about 263 nM. The response starts about 2 min after RKN were introduced to the chamber and calcium elevation was sustained over a period of at least 20 min. The calcium concentration also increased over the nuclear area by about 183 nM showing a similar time course, however, calcium spiking was not observed. These results indicate that RKN and Nod factors induce a similar elevation of cytoplasmic calcium levels at the root and provide further evidence of the existence of a common signaling pathway between symbiotic rhizobia, mycorrhiza and parasitic nematodes.
Date: 2006-08-09
Degree: MS
Discipline: Botany

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