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Roles of Riboflavin-Mediated Reactive Oxygen Species and Callose Deposition in Plant Defense Response

Author: SunMaoWu
Tutor: DongHanSong
School: Nanjing Agricultural College
Course: Biochemistry and Molecular Biology
Keywords: Riboflavin Priming Defense response Hydrogen peroxide
CLC: S432.2
Type: Master's thesis
Year: 2009
Downloads: 97
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Abstract

Riboflavin (vitamin B2) biosynthetic and functional pathways affect plant growth, development, and defensive responses by multiple mechanisms. Riboflavin is involved in anti-oxidation and peroxidation. Both processes affect the production of reactive oxygen species (ROS) in oxidative burst. ROS are essential for the hypersensitive cell death, growth, and defense against pathogens and insects, as well as many other responses to environmental stress. Besides having a pivotal biological function as a component of coenzymes, riboflavin appears as an elicitor of systemic acquired resistance (SAR) in plants, but the underlying molecular mechanism remains unclear. SAR is associated with the ability to induce cellular defense responses more rapidly and to a greater degree than in non-induced plants, a process called priming.Callose is composed ofβ-1,3-D-glucan, and it plays an important role in regulating the sieve tube metabolism and development. In addition, its composition and discomposition have direct relation with the process of plant growth and metabolism. And, plants are affected by unpleasant environment or fierce stimulation, such as mechanical wound, high heat and etc, callose in sieve tube will instantly regulate the normal physiological process in feedback, which means that sieve tube molecules compose the callose in no time, which deposits on the surface or in the sieve pores to jam pores and maintains regular material transportation in other sieve tubes. In the same way, if the stimulation disappears, the callose mentioned above will discompose in accordance, to restore the transportation function. Fourthermore, callose has a close relation with aphid and disease resistance in addition to its participating in the process of normal growth and metabolism of plant. This thesis attempted to determine whether the extrinsic use of riboflavin to Arabidopsis thaliana could induce priming of defense response and whether callose deposition could play a role in the induction of Arabidopsis resistance to the green peach aphid.Evidence obtained in this study suggested that riboflavin-induced priming for pathogen responses in Arabidopsis required hydrogen peroxide and NPR1(non-expressor of PR genes), induced plant resistance toward infection with virulent Pseudomonas syringae pv. tomato DC3000 was mechanistically connected with the expression of defense response genes and cellular defensive events, including H2O2 burst, hypersensitive cell death (HCD) and callose deposition. Riboflavin treatment and inoculation of plants with P. syringae pv. tomato DC3000 were neither active but both synergized to induce priming events. The defense-priming process needed NPR1 (essential regulator of systemic acquired resistance) and maintenance of H2O2 burst but was independent of salicylic acid (SA), jasmonic acid (JA), ethylene (ET), and abscisic acid (ABA). Our results suggest that the role of riboflavin in priming defenses is subject to signaling process distinct from the known pathways of hormone signal transduction.It was shown that riboflavin-induced priming was related with defense signal transduction in Arabidopsis. To explore whether the disturbed redox homeostasis also functions in the exogenous riboflavin-induced priming, we detected the ROS accumulation in plants from the beginning of riboflavin sprayed till 5 days post treatment (dpt). The results showed that riboflavin triggered ROS accumulation in plants during the period tested and the levels of ROS reach the highest at 2 hours post treatment (hpt), but restore to the original level at 5 dpt. Meanwhile, the riboflavin-treated plants are more sensitive to the extra oxidative stresses, generated by paraquat, suggesting that the plants have escalated oxidative state. Combined with catalase and P. syringae pv. tomato DC3000 inoculation, we analyzed the cellular and molecular defense responses. Catalase, which infiltrated at 30min after riboflavin treatment, nullifies the escalated oxidative state and the augmented ROS accumulation when infected by P. syringae pv. tomato DC3000. Moreover, the disease resistance is also abolished in riboflavin pretreated but catalase treated plants, which suggests that the disrupted redox homeostasis is required in riboflavin-induced priming. However, the disrupted redox homeostasis is independent of NPRI.Further evidence indicated that harpin-induced callose deposition affected Arabidopsis resistance to the green peach aphid. With regard to the reports of property of callose and harpin, we wondered whether protein harpin impacted the aphid-resistance through bringing the callose deposition in plants and whether the quantity of callose in Arabidopsis was connected with the aphid-resistance. Starting with this aim, we successively examined the capacity of aphid resistance of wild type Col-0 and three mutants (atlg05570, at2g13680, at1g06490),the difference of aphid resistance between the control plant and those treated with harpin, the callose deposition of the plant treated with harpin, and the expression status of these three genes related with the composition of callose (At1G05570, At2G13680, At1G06490). As a result, we found that harpin induced the increasing deposition of callose to enhance the aphid-resistance, and the quantity of callose deposition was positively related to the capacity of aphid-resistance in Arabidopsis.

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CLC: > Agricultural Sciences > Plant Protection > Pest and Disease Control > Plant diseases and their prevention > Plant immunology
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