The effects of boron and 24- epibrassinolid treatments on expression levels of some genes related to cell wall in Arabidopsis thaliana (L.) Heynh

Deficiency or high concentration of boron in soil could be an important abiotic stress factor affecting the plant cell wall. It has been determined that, Brassinosteroids (BR) even at very low concentrations, are efficient in enhancing the tolerance to environmental stress, and also regulatory functions in plant growth and development such as cell division, elongation and enlargement. At the same time, there are not many studies concerning to understand the mechanisms of how BRs increase the tolerance to stresses. The aim of this thesis study is to search in molecular level in Arabidopsis thaliana, as a model plant, (a) the effects of boron deficiency and boron toxicity on cell wall in plants and (b) effects of 24-Epibrassnolid (EBL) on boron stress taken place in plants in leaf and root cell wall. Arabidopsis thaliana (L.) Heynh plants were grown in hydroponic environment for five weeks and ten weeks and incubated for 24 hours in environments excluding boric acid (BA) (-BA, 0 µM) or including high concentration of BA (+BA, 3000 µM) and/or 1 µM EBL hormone. In rosette leaf and root samples of applied plants (five and ten week-plants) expression levels of some cellulose synthase genes playing role in cell wall synthesis (CESA1, CESA4, CESA6, CESA8 and CSLB5), genes coding xyloglucan endotransglycosylase/hydrolase proteins (XTH16, XTH21 and XTH23), expansin genes (EXPA5, EXP8 and EXP14), pectin methyl esterase genes (PME2 and PME41) and genes coding cell wall protein (SEB1) were determined by Real-Time PCR analysis. In leaf samples of five weeks and ten weeks plants, generally similar expression profiles were shown in CESA1 with CESA6 and CESA4 with CESA8. In leaf samples of five weeks plants, the application of high concentration BA increases the expression of CESA4, CESA8 and CSLB5 genes, while in ten weeks plants expression of CESA4, CESA6 and CESA8 genes increased in either 0 µM and 3000 µM BA application. In five weeks and ten weeks plants, expression of EXP8 gene was decreased in result of 0 and 3000 µM BA application; EBL application together with BA increased the expression significantly (P ˂ 0.01). mRNA level of EXP14 gene is decreased in consequence of 0 µM BA application in five weeks plants, while in ten weeks plants application of 3000 µM BA increased the mRNA level. The expression of XTH16 gene decreased in result of alone EBL or BA applications in five plants, however application of EBL and BA together was more decreased the expression. Expression of XTH23 gene has increased significantly in EBL together with 0 and 3000 µM BA applications in leaf tissues of samples of both two plant groups (P ˂ 0.01). PME2 and PME41 genes has shown similar expression profiles in five weeks and ten weeks plants and additional EBL hormone to BA applications has provided to increase the expressions dramatically. In ten weeks plants expression of SEB1 gene has increased in all treatments comparing to the control (P ˂ 0.01). Within the concept of surveyed genes, EBL hormone formed specific responses to leaf and root tissues. In root samples of five weeks plants, EBL applications alone or with BA generally decreased the expressions of surveyed genes (except XTH23 gene) while in ten weeks plants expressions of only CSLB5, EXP14, XTH16 and PME2 genes decreased. In root samples of five weeks plants all applications decreased the expression of CESA1 (except 0 µM BA application) and CESA4 genes according to control. In root tissues of ten weeks plants, 0 µM BA application did not change the expression of EXPA5 gene but when applied with EBL hormone, expression increased. Transcript level of EXP14 gene in five weeks plants significantly decreased in alone EBL hormone or EBL with 3000 µM BA application, while in ten weeks plants 0 µM BA application caused the decrease of expression. In ten weeks plants expression of XTH23 gene increased with alone EBL application, on the other hand, in five weeks plants EBL application increased the expression in 0 µM BA application which normally did not show expression change according to control and in 3000 µM BA application which normally showed a significant decrease. mRNA level of XTH21 gene showed a significant decrease according to control as a result of 3000 µM BA together with EBL application. Expression of PME2 gene showed significant decreases in five weeks and ten weeks group plant root cells in consequence of EBL and BA applications. As for the expression of SEB1 gene showed different expression profiles in five weeks and ten weeks plants root cells. Consequently, thesis study is the first study in terms of conducing og boron-brassinosteroid interaction in plant cell wall. With the study, along with the effects of boron deficiency and toxicity in cell wall, changes that brassinosteroids generated in cell wall in response to stress has been determined in molecular level comprehensively.