A comparative study of just cadmium （Cd） or heat and their combination treatments on some physiological parameters and the antioxidant systems in transgenic rice （Oryza sativa L. cv. Zhonghua No.11） carrying glutathione-S-transferase （GST, EC. 2.5.1.18） and catalasel （CAT1, EC. 1.11.1.6） and non-transgenics was conducted. The results revealed improved resistance in the transgenics to Cd and the combined Cd and heat stress than non-transgenics. Data showed that the activities of CAT, GST, superoxide dismutase （EC.1.15.1.1） and all components of the ascorbate-glutatbione cycle measured in the stressed transgenics shoots are significantly different from those of non-transgenics. Results indicated that co-expression of GST and CAT1 had an important effect on the antioxidant system, in particular, the whole ascorbate-glutathione cycle. The less oxidative damage induced by Cd and the stress combination in the transgenics resulted not only from the GST and CAT1 transgene but also from the coordination of the whole ascorbate-glutathione cycle.
[Objective] The aim was to study the relationship between urcrose, zinc and the root system growth in rice. [Method] Changes of root system growth, ROS generation and root system proton export ability were analyzed in rice （Oryza sativa L. cv Zhonghua No.11） treated with different concentrations of Zn （NO3）3 sucrose, com- bined sucrose and Zn （NO3）3 mannitol as well as mannitol plus Zn （NO3）2. [Result] The results showed that treatment with 1-3 mM Zn（NO3）2 resulted in significant increases in total root length /number and in accumulation of H202 and 02- but decreases in root system proton export ability. With the exception of shoot length, the length of primary, adventitious, and lateral roots, and the number of adventitious, and lateral roots on primary /adventitious roots were all influenced by different concentrations of sucrose. High concentrations of sucrose caused increases in H202 and O2-, starva- tion or high concentrations of sucrose reduced root system proton export ability after treating with or without Zn. However, at the same concentration of sucrose, different changes of these indicators were observed between Zn and non-Zn treatments. The regulation of root system growth induced by sucrose was marked different from that of mannitol at the same concentration of 5%, suggesting that these effects were caused by sugar signal but not by osmotic potential. [Conclusion] This study indicat- ed that both sucrose and Zn play important roles in the regulation of rice root system growth.
The link between root growth, H2O2, auxin signaling, and the ceil cycle in cadmium （Cd）-stressed rice （Oryza sativa L. cv. Zhonghua No. 11） was analyzed in this study. Exposure to Cd induced a significant accumulation of Cd, but caused a decrease in zinc （Zn） content which resulted from the decreased expression of OsHMA9 and OsZIP. Analysis using a Cd-specific probe showed that Cd was mainly localized in the meristematic zone and vascular tissues. Formation and elongation of the root system were significantly promoted by 3-amino-l,2,4-triazole （AT）, but were markedly inhibited by N,N＇. dimethylthiourea （DMTU） under Cd stress. The effect of H2O2 on Cd-stressed root growth was further confirmed by examining a gain-of-function rice mutant （carrying catalasel and glutathione-S-transferase） in the presence or absence of diphenylene iodonium. DR5-GUS staining revealed close associations between H2O2 and the concentration and distribution of auxin. H2O2 affected the expression of key genes, including OsYUCCA, OsPIN, OsARF, and OslAA, in the auxin signaling pathway in Cd-treated plants. These results suggest that H2O2 functions upstream of the auxin signaling pathway. Furthermore, H2O2 modified the expression of cell-cycle genes in Cd-treated roots. The effects of H2O2 on root system growth are therefore linked to auxin signal modification and to variations in the expression of cell-cycle genes in Cd-stressed rice. A working model for the effects of H2O2 on Cd-stressed root system growth is thus proposed and discussed in this paper.
Feng-Yun ZhaoMing-Ming HanShi-Yong ZhangKai WangCheng-Ren ZhangTao LiuWen Liu
Arabidopsis thaliana seedlings were cultivated in 0-500 μmol/L of extraneous cerium （Ce） for 7 d to investigate the toxicity, uptake and translocation of rare earth elements （REEs）. The results showed that Ce could be largely absorbed by the roots ofA. thaliana and translocated to the shoots. But the uptake rates of Ce by the roots were much higher than the translocation rates from roots to shoots. Ultrastructural analysis revealed that Ce was mainly distributed on the cell wall. At higher concentration, Ce could also enter cell, destroy the ultrastructure of cells and disturb the intrinsic balance of nutrient elements of A, thaliana, Addition of Ce （50-500 μmol/L） to the culture medium significantly inhibited the elongation of primary roots, decreased chlorophyll content, rosette diameter and fresh mass of plants. The damage increased with the increase of Ce concentration in culture medium, although primary root elongation, chlorophyll content, and rosette diameter were stimulated by relatively low concentration （0.5 μmol/L） of Ce. Thus, it is speculated that REEs may become a new type contamination if we don＇t well control the release of REEs into the environment.
