Phenotypic and molecular changes in cassava (Manihot esculenta Crantz.) genotypes as a response to water-deficit stress

Abstract

Three local Indonesian cassava (Manihot esculenta Crantz) genotypes, Adira 4, Roti, and Ubi Kuning retained their growth under a water deficit environment. To understand the physiological and molecular responses of cassava plants under such stress, we observed leaf stomata characteristics, i.e. stomata dimension (width and length) and density, and molecular expression of aquaporin (AQP) gene, respectively. The observation was performed on all genotypes on day 26 and 45 after water-deficit treatment. Quantification of gene expression was performed by comparing the threshold cycle (Ct) values of AQP with Ct values β-tubulin for each genotype. Results showed that water deficit treatment significantly affected both stomata density, length and width in all genotypes. On day 26 after treatment, the density of stomata in Roti and Ubi Kuning increased two times higher than the stomata density in plants under well-watered supply. Stomata length of Roti and Adira 4 under water stress was 0.4 times shorter than those under normal water supply. Relative expression of AQP, encoding AQP PIP2 proteins, in the Roti genotype showed that the gene transcripts have no significant elevation after experiencing water stress. In Adira 4, the expressions of AQP increased two-times at day 26 under water-deficit treatment compared with AQP expressions in well-watered treatment and continued to elevate up to three times higher at day 45 than those of expressed in Adira 4 plants under well-water treatment. In addition to stomata phenotypic changes, Ubi Kuning may regulate its water channel proteins AQP PIP2 to control turgor pressure in the beginning phase of water stress conditions. These results showed that three cassava genotypes responded differently under water deficit stress and these may serve as basic knowledge for further analysis.