Salt accumulation and ascorbate peroxidase activity and gene expression in genotypes of rice (Oryza sativa L.) contrasting in salinity tolerance

Date

10-2007

Degree

Bachelor of Science in Biology

College

College of Arts and Sciences (CAS)

Adviser/Committee Chair

Merlyn S. Mendioro

Co-adviser

Abdelbagi M. Ismail

Abstract

Three rice genotypes contrasting in salinity tolerance namely: IR 29 (salt-sensitive), IR 65192-4B-10-3 (IR 651) and FL 478 (salt-tolerant) were used to investigate the effects of salinity on the morphology, salt accumulation in plant tissue and activity and gene expression (OsAPx2 and OsAPx8) of ascorbate peroxidase (APX). Plant biomass as well as ion concentration in plant tissue were measured on the shoot and root of rice seedlings subjected to salt stress for 18 days. On the other hand, activity and gene expression of ascorbate peroxidase were analyzed at different time intervals after salinization. Salinity reduced the biomass (shoot and root dry weight) of the three genotypes. Biomass reduction was more evident in the roots and appeared to be more pronounced in the salt-sensitive cultivar, IR 29 (59%). Under salinity, IR 29 also showed a significantly higher shoot Na' (0.51 mg g"' dry wt.), and lower IC/Na* (0.92). On the other hand, tolerant genotypes, IR 651 and FL 478, maintained a higher shoot IC/Na* (1.50 and 1.29, respectively), lower shoot Na'(0.28 and 0.27 mg g' dry wt, respectively) and higher root Na' (1.39 and 0.98 mg dry wt, respectively) compared to IR 29. Transcript analyses of specific OsAP.r2 and OsAN8 genes were shown in both saline and nonsaline conditions at 7h, 24h, 72h, and 144h. OsAP.r8 expression was higher than OsAN2 and also under saline conditions suggesting an important role of this gene in salt stress. Total enzyme activity of APX clearly demonstrated difference between the tolerant and sensitive genotypes, and was evident starting at 144h saline treatment. A few mechanisms seem to underlie the tolerant genotypes under salt-stress; these include a shoot salt exclusion mechanism and an efficient antioxidant system.

Language

English

Location

UPLB Main Library Special Collections Section (USCS)

Call Number

Thesis

Document Type

Thesis

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