Comparative proteomic analysis reveals the roots response to low root-zone temperature in Malus baccata.

Soil temperature is known to affect plant growth and productivity. In this study we found that low root-zone temperature (LRT) inhibited the growth of apple (Malus baccata Borkh.) seedlings. To elucidate the molecular mechanism of LRT response, we performed comparative proteome analysis of the apple roots under LRT for 6 days. Total proteins of roots were extracted and separated by two-dimensional gel electrophoresis (2-DE) and 29 differentially accumulated proteins were successfully identified by MALDI-TOF/TOF mass spectrometry. They were involved in protein transport/processing/degradation (21%), glycometabolism (20%), response to stress (14%), oxidoreductase activity (14%), protein binding (7%), RNA metabolism (7%), amino acid biosynthesis (3%) and others (14%). The results revealed that LRT inhibited glycometabolism and RNA metabolism. The up-regulated proteins which were associated with oxidoreductase activity, protein metabolism and defense response, might be involved in protection mechanisms against LRT stress in the apple seedlings. Subsequently, 8 proteins were selected for the mRNA quantification analysis, and we found 6 of them were consistently regulated between protein and mRNA levels. In addition, the enzyme activities in ascorbate-glutathione (AsA-GSH) cycle were determined, and APX activity was increased and GR activity was decreased under LRT, in consistent with the protein levels. This study provides new insights into the molecular mechanisms of M. baccata in responding to LRT.

[The effect of exogenous H2O2 on mitochondrial membrane permeability and cell nuclear DNA in roots of Malus hupehensis].

To investigate the changes in mitochondrial permeability transition, DNA degradation and cell death, seedling roots of Malus hupehensis Rehd. were treated directly with exogenous H(2)O(2). The results showed that mitochondrial permeability increased obviously by 0.024% (V/V) H(2)O(2) treatment for 30 min and increased continuously during the time of H(2)O(2) treatment (Fig.1). At the time of mitochondrial permeability increasing, mitochondrial membrane potential (Delta psi m) decreased (Fig.2). In addition, the ratio of Cyt c/a became lower (Fig.3) when mitochondrial permeability increased and Delta psi m decreased. DNA fragments were detected at the 60 min of H(2)O(2) treatment, the number of fragments increased after 60 min of H(2)O(2) treatment (Fig.4). Granular nuclei stained irregularly were evident in root slices stained by acridine orange (Fig.5). This indicates H(2)O(2) can induce programmed cell death by increasing mitochondrial permeability and decreasing Delta psi m in the root of Malus hupehensis Rehd.