No abstract

A grape-bud-oriented genomic platform was produced for a large-scale comparative analysis of bud responses to two stimuli of grape-bud dormancy release, hydrogen cyanamide (HC) and heat shock (HS). The results suggested considerable similarity in bud response to the stimuli, both in the repertoire of responding genes and in the temporary nature of the transcriptome reprogramming. Nevertheless, the bud response to HC was delayed, more condensed and stronger, as reflected by a higher number of regulated genes and a higher intensity of regulation compared to the response to HS. Integrating the changes occurring in response to both stimuli suggested perturbation of mitochondrial activity, development of oxidative stress and establishment of a situation that resembles hypoxia, which coincides with induction of glycolysis and fermentation, as well as changes in the interplay between ABA and ethylene metabolism. The latter is known to induce various growth responses in submerged plants and the possibility of a similar mechanism operating in the bud meristem during dormancy release is raised. The new link suggested between sub lethal stress, mitochondrial activity, hypoxic conditions, ethylene metabolism and cell enlargement during bud dormancy release may be instrumental in understanding the dormancy-release mechanism. Temporary increase of acetaldehyde, ethanol and ethylene in response to dormancy release stimuli demonstrated the predictive power of the working model, and its relevance to dormancy release was demonstrated by enhancement of bud break by exogenous ethylene and its inhibition by an ethylene signal inhibitor.

The detection of genes having similar expression profiles following the application of different stimuli that trigger bud break may constitute potent tools for the identification of pathways with a central role in dormancy release. We compared the effects of heat shock (HS) and hydrogen cyanamide (HC) and demonstrated that HS leads to earlier and higher bud-break levels. Changes in transcript levels of catalase, alcohol dehydrogenase and pyruvate decarboxylase were induced following both treatments. However, timing and extent of changes in transcript level differed. Changes occurred earlier in HS-treated buds and were more intense in HC-treated buds. The changes in transcript levels after both treatments were temporary. The rapid and short-lasting changes in gene expression following HS treatment correlated with the faster and higher level of bud-break that this treatment exerted. This correlation may propose that the reported molecular events are mechanistically involved in dormancy release. To test the hypothesis that temporary oxidative stress is part of the mechanism inducing dormancy release, we analyzed the effect of HS and HC treatments on the expression of ascorbate peroxidase, glutathione reductase, thioredoxin h, glutathione S-transferase and sucrose synthase genes and found that they were induced by both treatments in a similar pattern. Taken together, these findings propose that similar cellular processes might be triggered by different stimuli that lead to dormancy release, and are consistent with the hypothesis that temporary oxidative stress and respiratory stress might be part of the mechanism that leads to bud break.