EFFECTS OF CHITOSAN AND O-80 CHITOSAN RESIDUE ON GROWTH, PHOTOSYNTHESIS, YIELD AND GENE EXPRESSION OF RICE Oryza sativa L.

Abstract

This research was aimed to increase rice production, using ‘Pathumthani1’ rice as a model, by the application of chitin/chitosan related products. For chitosan application, polymeric (P) and oligomeric (O) chitosan with 80% and 90% deacetylation in 1% (v/v) acetic acid at 5 – 80 mg/L were tested for the enhancement of seedling growth. It was found that all chitosan treatments inhibited seedling growth due to the negative effects of the chitosan solvent, acetic acid. Lactic acid was shown to have less toxicity to rice seedlings in comparison with acetic acid and citric acid. When lactic acid was used as chitosan solvent, 40 mg/L polymeric chitosan with 90% deacetylation (P90-40) was found to be the most appropriate plant growth stimulator. Based on these data, it should be noted that the appropriate chitosan types, concentration and solvent should be under consideration prior to agricultural application. For chitin rich material, three levels of shrimp shell (SS) or fermented chitin waste (FCW), 0.25, 0.5 and 1 % (w/w) were applied as soil supplement 7 days before seedling transplanting and rice growth, photosynthesis parameters and yield were investigated. Addition of either chemical or organic fertilizer was used as controls. It was found that SS and FCW application resulted in the increase of photosynthesis ability leading to the significantly higher tiller numbers, shoot biomass and grain yields. Particularly, addition of 1% SS or FCW led to the increase of grain weight/pot by 4.9 and 4.3 fold compared with the chemical fertilizer control. To investigate the SS and FCW effects at the molecular level, the genes involving in photosynthesis process, Oxygen-evolving enhancer protein 1 (OEE1), Chlorophyll a-b binding protein (PsbS1) and Ribulose bisphosphate carboxylase small chain (rbcS) were studied for gene expression after SS or FCW treatment. The gene expression levels of OEE1, and rbcS in the seedlings after FCW addition were found to be similar to the controls, while the gene expression levels of PsbS1 significantly increased on day 14 after treatment. Meanwhile in SS treatment, treated seedlings significantly had the lower level of rbcS gene expression but showed the similar level of OEE1 and PsbS1 gene expression, compared to the controls. These suggested that the rice seedling growth stimulation by SS and FCW resulted by different mechanisms. In conclusion, 40 mg/L of P90 chitosan in lactic acid had a potential to enhance ‘Pathumthani1’ rice seedling growth, while SS and FCW can be considered as rice seedling growth stimulants in order to develop chitin-rich residues for sustainable rice production.