Mechanism Of Gibberellin In A Quick Development Mutant Of Winter Wheat

Gibberellin is one of the important hormones regulating plant height development. In this study, a wheat quick development mutant(qd) obtained from mutagenesis by 7Li ion beam irradiation to wheat variety Lunxuan 987 was used to reveal its plant height development and gibberellin sensitivity. Quantitative real-time PCR and enzyme-linked immunosorbent assays were used to analyze the related gene expression and content of gibberellin. The main results are as following:1. No phenotypic differences between qd and wild type plants were observed at the seedling stage in the field. From the jointing stage to the heading stage, qd plants were taller than wild type plants due to their cells being longer. However, wild type plants and qd plants were the same height once at the heading stage.2. Measurement of plant heights of 10-day-old seedlings of qd and wild type with or without GA showed that the height of qd was equivalent to that of wild type seedlings when both were grown without GA. However, qd seedlings were significantly taller than wild type seedlings when both were cultivated in a solution containing 17 μM GA, while the height of wild type seedling was not increased by GA treatment, indicating the mutant qd was sensitive to GA. In wild type seedlings, the expression levels of both Rht-A1 and Rht-B1 genes were not affected by GA treatment, while expression of Rht-D1 gene was slightly increased. In qd seedlings grown with GA stimulation, the expression level of all three Rht alleles was lower than that of the control samples.3. Sequence of the DELLA protein coding gene Rht for both qd and wild type plants showed that the wild type seedlings carry the Rht-B1 b allele. Nucleotide 190 in the corresponding qd gene was mutated from thymine(T) to cytosine(C), which eliminated a stop codon and resulted in the Rht-B1 a type allele. The stop codon in the Rht-B1 b allele was transformed into a normal codon in the Rht-B1 a allele, which encodes glutamine(Q). This gene mutation caused the qd plants to be sensitive to exogenous GA.4. Under field conditions, continuous gibberellin treatment significantly increased plant height of qd, while it didn’t show obvious effects on wild type plant height.5. It was showed that the expression levels of Ta KAO, which encodes an enzyme that catalyzes an early step of GA biosynthesis, were the same in qd and wild type plants at the first two weeks after jointing. At the third and fourth week after jointing, the Ta KAO expression level was higher in qd plants than in wild type plants. Henceforth, the expression level of this gene decreased, becoming significantly lower in qd than in wild type plants at the sixth week after jointing. During the first four weeks after the plants reached the jointing stage, the expression levels of the Ta GA20 ox gene, which encodes an enzyme involved in the last step of bioactive GA biosynthesis of qd and wild type plants did not differ. However, at the fifth and sixth week after jointing, the expression level of this gene was significantly lower in qd plants than in wild type plants.6. We also measured the endogenous GA levels of qd and wild type plants at the jointing, booting, and heading stages. The GA1+3 level was higher in qd plants than in wild type plants at both the jointing and booting stages, whereas it was lower in the qd at the heading stage. However, the difference of the GA4+7 content between the qd and wild type plants was not significant at any of these three stages. The internode number and plant height was the same between qd and wild type at mature stage. Consistent with the variations in GA contents, the lengths of the first three basal internodes were longer, and the lengths of the last two internodes were shorter in qd plants than in wild type plants.7. The differences in stem, spike, and seed were found in the qd plants and wild type plants with continuous treatment of gibberellin and paclobutrazol.