The differences of glucose-6P dehydrogenase (G6PDH) activity and freezing resistance induced by freezing acclima-tion between cuttings of freezing-sensitive P. tomentosa and freezing-resistant P. suaveolens were compared for exploring the role ofG6PDH on the enhancement of freezing resistance induced by freezing acclimation. After 5 d of freezing acclimation at -3 ℃, thcLT50 of P. tomentosa has decreased from -6.2 ℃ in control cuttings to -14.3 ℃ in freezing acclimated ones, and the increase ofG6PDH activity was observed in freezing acclimated cuttings as compared with control ones. Whereas, when P. suaveolens wasfreezing acclimated at -20℃ for 5 d, the LT50 has decreased from -27. 1℃ in control cuttings to -43.5 ℃ in freezing acclimated ones,and the activity of G6PDH increased considerably. In addition, the increase of LT50 and the decrease of G6PDH activity resultingfrom 2 d of deacclimation at 25 ℃ were found in two kinds of freezing acclimated cuttings. It is concluded that the increase in theactivity of G6PDH may associate with the inherited freezing resistance of species and the enhancement of freezing resistance of cut-tings, and may play an important role in the antifreeze process under freezing temperature, which would provide the basis for thestudy on the molecular mechanism of freezing resistance in P. suaveolens and the cloning of gene associated with freezing resistance.
Lin Shanzhi Zhang Zhiyi Lin YuanzhenCollege of Biological Sciences and Biotechnology, Beijing Forestry University, Beijing 100083, P. R. China
To explore the physiological and biochemical mechanism of the occurrence of vitrified shoots of Populus suaveolens in tissue culture, the changes in water, chlorphyll, lignin, H2O2, phenylalanine ammonialyase (PAL), malonaldehyde (MDA), protective enzymatic systems, and some key enzymes involved in the ascorbate- glutathione cycle were comparatively studied in both normal and vitrified shoots of P. suaveolens. The results show that the lower activities of peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), glutathione reductase (GR) and PAL, and the less contents of chlorphyll, lignin, ascorbate (ASA) and reduced glutathione (GSH) as well as the lower ratios of ASA / DHA and GSH / GSSG are observed in vitrified shoots than in normal ones during the whole culture period. While in comparison with normal shoots, the higher activity of superoxide dismutase (SOD) and the more concentrations of water, H2O2, MDA, dehydroascorbate (DHA) and oxidized glutathione (GSSG) are found in vitrified shoots. Statistical analysis indicates that the enhanced activity of SOD and the decreased activities of CAT and POD as well as some enzymes involved in the ascorbate-glutathione cycle might be closely correlated to the accumulation of H2O2. The less regeneration of ASA and GSH and the lower capacity of the ascorbate-glutathione cycle observed in vitrified shoots might be due to a significant decrease in APX, MDAR, DHAR and GR activities and a decline in redox status of ASA and GSH. The decreases in chlorphyll content might result in a decline in photosynthesis. The lower activities of POD and PAL could result in the decrease of lignin synthesis and cell wall ligination, which might be the key factor leading to the increase in water content. It is concluded that the deficiency of detoxification capacity caused by the lower capacity of the ascorbate-glutathione pathway and the decreased activity of protective enzymatic system might lead to the large accumulation of H2O2 and the enhancement o
Total RNA was isolated from shoots regenerated in vitro of Populus suaveolens by the modified method of CTAB, and two clear bands of rRNA (28S and 18S) were observed in agarose electrophoresis. In addition, the values of OD260/OD280 and OD260/OD230 of extracted RNA were 2.12 and 2.23 respectively. The results show that RNA is little decomposed and the purity of RNA is high. Moreover, RNA isolated by the modified method of CTAB reagent had been successfully used for reverse transcription of P. suaveolens cDNAs and ideal special band was observed.
