| Touch has been shown to affect plant growth and development. Daily touch treatments often result in a reduction in plant height, an increase in stem diameter, a delay in flowering, and an acceleration of senescence in a variety of plant species. Ethylene has been shown to have similar effects and thought to cause touch responses. However, mechanisms in which touch is perceived, transduced, and used to activate other responses in plant systems remain unclear. Therefore, this study was initiated to better understand touch-induced responses in plants. Differential display PCR was used to identify touch-regulated genes from 3-week-light-grown ethylene insensitive etr1-3 Arabidopsis (Columbia ecotype) mutant plants. The ethylene insensitive etr1-3 Arabidopsis mutant was used to reduce ethylene effects and increase the chance of identifying touch-induced genes, which possibly were not regulated by ethylene. From the 24 combinations of primer sets used, 32 cDNA fragments were selected of which only 3 cDNA fragments (A8A, G5A, and G7F) were touch-inducible. The 3 cDNA fragments were activated 10 min following a 30 sec touch treatment. The fragments were then used to screen a cDNA library for a full-length or near full-length cDNA.; A 1.2 kb fragment for OPR3 was obtained from A8A screenings. This cDNA fragment encodes for 12-oxophytodienoate-10, 11-reductase (OPR), an enzyme in the jasmonic acid biosynthetic pathway. OPR3 was induced 10 min following a touch treatment, reaching a maximum level at 60 min, and declining by 120 min. Wounding also activated OPR3 with similar kinetics to touch treatment. In addition to touch and wounding, treatments with methyl jamonate clearly activated OPR3 expression, while ethylene had no effect. Treatment with NaCl as well as CaCl2 strongly increased OPR3 expression, whereas a slight induction was also observed from treatment with MgCl2. Darkness treatment, however, did not activate OPR3.; Effects of daily touch treatments on growth and development of jasmonic acid deficient opr3 Arabidopsis mutant plants were also observed. Preliminary results showed that daily touch treatments for 4 weeks had no significant effect on leaf area and inflorescence length of the opr3 plants, whereas smaller leaves and shorter inflorescences were observed from touch-treated wild-type Wassilewskija (WS) plants. However, leaves of touch-stimulated opr3 plants showed signs of stress, which were increased necrotic regions on the leaves. Plant fresh and dry weights of control and touch-stimulated groups were not significantly different in both wild-type and opr3 plants.; The cDNA library screenings with G5A fragment resulted in a 2 kb cDNA encoding for a calcium-dependent protein kinase (CDPK32). Northern analysis showed that CDPK32 expression was activated within 10 minutes, reaching a maximum level between 20–30 min, and declining to almost undetectable levels 60 min following a touch treatment. (Abstract shortened by UMI.)... |
