Studies On Genotypic Variation Of Coleoptile Elongation Rate And Its Mechanism In Paddy Rice (Oryza Sativa L.)

The genotypic variation of coleoptile elongation and the effects of temperature, aeration condition and soil moisture content on coleoptile elongation were studied in this paper using 85 rice genotypes under controlled conditions. The relationship between coleoptile length and some seed characteristics, and the effects of plant hormones on the growth of coleoptiles were also investigated. The main results derived from this study were as follows:There was great genotypic variation of rice coleoptile elongation. Generally, the coleoptile elongation could be classified into three types, i.e., fast, middle and slow. Correlation coefficient analysis showed the coleoptile length could be used as a reliable index for germplasm screening. Two genotypes, E26 with the fastest rate and Z99312 with the slowest rate of coleoptile enlogation, were selected in this study.Under water stress conditions, the varieties with longer coleoptiles had the ability to produce good quality seedlings. This result suggests that it is possible to select rice germplasms with characteristic of fast elongation of coleoptiles for direct seeding rice.There were significant effects of ecological factors such as temperature, aeration condition and soil moisture content on coleoptile elongation. Remarkable interactions were also found in temperature X genotype, aeration X genotype and soil moisture content X genotype. The effects of environmental factors on coleoptile elongation were greater than that of genotypic variation, the latter also had a significant role on coleoptile elongation.The significant, positive correlations between amylose content and a-amylase activity in endosperm and coleoptile length were found in this study, while there were no significant correlations between grain weight, endosperm weight, B-amylase activity of endorsperm and coleoptile length. The principal component analysis indicated that a -amylase activity of endorsperm could be the number one of major physiological factors which caused genotypic variation of coleoptile elongation.In this study we also found that there were no significant correlations between coleoptile length and IAA, ABA contents and B-glucanse activity of coleoptilesproduced from seeds soaked with IAA and ABA respectively. However, there were significant positive correlations between reduction of IAA content in coleoptile growth period and coleoptile length (r=0.82711, p = 0.0423), and between B -glucanse activity and IAA content (r=0.86116,B=0.0276). This result suggested that the B-glucanse activity might be regulated by IAA in coleoptiles.