Submitted to: American Society of Plant Physiologists Meeting
Publication Type: Abstract Only
Publication Acceptance Date: July 28, 1999
Publication Date: N/A
Technical Abstract: Modified desiccation-tolerant plants, e.g., Sporobolus stapfianus, survive desiccation mainly by a drying induced cellular protection mechanism. Fully desiccation-tolerant plants, e.g., Tortula ruralis, rely on a constitutive protection system coupled to a rehydration induced recovery mechanism. In order to assess the relative effectiveness of these two tolerance strategies we are investigating the effect of desiccation on protein turnover via the ubiquitin-26S proteasome pathway in both S. stapfianus and T. ruralis. A full length ubiquitin cDNA was isolated from S. stapfianus and characterized. Northern analysis revealed two ubiquitin transcripts of 1.4 and 1.2 Kb in S. stapfianus. Both transcripts accumulated in the early stages of drying (the 1.4 kB transcript more so) but were reduced in dried tissues. The levels of both transcripts increased upon rehydration. Only the 1.4 Kb transcript was evident in the desiccation sensitive Sporobolus pyramidalis and also increased during drying. Similar analysis of T. ruralis gametophyte revealed three transcripts of 1.9, 1.3 and 0.65 Kb. Only the 1.3 Kb transcript levels varied in response to desiccation and rehydration. Rapid-drying was more effective in increasing the 1.3 Kb ubiquitin transcript which is consistent with the increase in cellular damage as a result of this treatment. Western analysis indicated that conjugated ubiquitin formed during drying in both species and was lost following rehydration. These results demonstrate that cellular damage, as measured by ubiquitin transcript/protein accumulation, does occur during drying in both fully and modified desiccation-tolerant plants. The extent and timing of the ubiquitin response can be used to differentiate between the two tolerance mechanisms.