Studies On The Mechanism Of Plant Perception,Signal Transduction And Response To Gravity

In plants, the shoot and the root generally show negative and positive gravitropism, respectively. There are three steps involved in the process of gravitropism: gravity perception, signal transduction and differential growth.We isolated a novel mutant from the rice mutant pool constructed by efficient transformation technique mediated by Agrobacterium tumefaciens, which showed gravity-insensitive behavior in shoot growth but normal behavior in root growth. Morphological and Histological observation, effects of exogenous materials are involved in our research. We also map primarily the location of la gene using SSR and CAPS markers. By now we obtain the following results:1. According to the statistic report of segregation of mutant and crossbreed posterity, such as V136 / Zhonghua 11, V136 / Nipponbare, V136 / CP87, V136 / P21, this mutation was probably caused by a monogenic and recessive gene.2. The roots of mutant exhibit positive gravitropic responses, while sheathes are insensitive to gravity on earth. Sheathes of wild type and mutant growing in clinostat simulating microgravity are all agravitropism.3.The results of cyto-histological stain showed that there was no statistical difference in the number and size of amyloplasts in specialized cells of coleoptile and sheath between the gravity-insensitive rice mutant and the Wild type (Oryza sativa L.subsp.Japonica) ( Zhonghua 11 ), which all grew on the ground or clinostat respectively. Furthermore, in these cells of both seedlings grown on earth, amyloplasts were found sedimented at the distal end of each cell of the special starch sheath tissues. After inverting the seedlings, re-sedimentation of amyloplasts toward the direction of gravity was almost completed in 5 minutes. In these cells of the seedlings grown on clinostat, amyloplasts were dispersed in the starch sheath tissue.4.Results of treatments using exogenous Ca2+, EGTA and ATP suggested 1) lower concentration of Ca2+ (0.0005 , 0.005 和 0.05mmol/L) promote differently the bending of roots of wild type, 2) higher concentration of Ca2+(0.5 和 5.0mmol/L ) and EGTA (5.0 和 l0.0mmol/L) inhibit distinctly such bending of roots of wild type 3) 5.0 mol/L ATP inhibit the bending roots of mutant.5.Through linkage analysis of polymorphic SSR markers of chromosome 11 with la gene, which is recessive, two SSR markers ( RM536 and RM209) were found to have 10 cM and 5.9 cM with la, respectively, which is near the centromere.