Phosphorus (P) acquisition through extensive root growth and P allocation to different plant organs through efficient remobilization are important for acclimation of crop plants to P-limited environments. This study elucidated changes in rice root growth and leaf P-remobilization and their influence on grain yield under P deficiency.
Methods
Two pot experiments were conducted with (P100) and without (P0) inorganic P supply using two Japanese rice cultivars: Akamai (Yamagata) and Koshihikari. Multiple harvests were made until the panicle initiation stage. Root and shoot growth response, P acquisition, and temporal leaf P-remobilization efficiency were measured. A separate experiment ascertained the final yield and grain P status.
Results
The Akamai rice cultivar showed enhanced root growth and more acquired soil P. The Akamai root dry weight was 66% greater than that of Koshihikari under P0. Confronting P deficiency, Akamai remobilized some P from its lower mature leaves to upper younger leaves starting from early growth. The remobilized P fraction increased to 72% at panicle initiation under P0. Under P0, Akamai exhibited two-fold higher leaf P-remobilization efficiency than under P100.
Conclusions
Enhanced root growth that facilitates acquisition of more soil P through better soil exploration coupled with efficient leaf P remobilization from the early growth stage improves adaptation of Akamai rice cultivar to P-limited environments. Nevertheless, P-starvation responses did not facilitate higher grain yields in P-limited conditions.
It is generally considered that stress causes decreased immune function in fish. In this study we examined in Atlantic salmon (Salmo salar Linnaeus) the effects of both short- (a single 15s out of water) and long-term (4 weeks of daily handling 15s out of water) stress on plasma cortisol (free and total) and glucose levels, expression of interleukin-1beta (IL-1beta) and survival of head kidney (HK) macrophages under culture with Aeromonas salmonicida. In the short-term study, samples were collected prior to the application of the stressor, and at 1, 3, 6, 12 and 24h post stress. Free and total plasma cortisol levels and the percentage of free cortisol increased significantly in the stressed group at 1 and 3h post stress. Plasma glucose levels were significantly higher than those of control fish at 1, 3 and 6h post stress. Constitutive expression of IL-1beta in macrophages isolated from head kidneys in stressed fish was significantly higher at 1 and 3h post stress. However, lipopolysaccharide (LPS) stimulated expression of IL-1beta in HK macrophages, exhibited significantly higher fold increases in unstressed fish compared to stressed fish. In the long-term study, with the exception of an increase in plasma glucose levels at 1 week, there were no significant differences in stress parameters between groups. There was a significantly higher constitutive IL-1beta expression in macrophages isolated from stressed fish over the first 2 weeks. At weeks 1, 2 and 3 the magnitude of IL-1beta response of isolated HK macrophages to LPS stimulation was reduced in >90% of the stressed fish. At 4 weeks there was no significant difference in inducible IL-1beta expression between the groups. Macrophages isolated from stressed fish also showed significantly decreased survival when exposed to A. salmonicida. This study shows a clear pattern from repeated handling stress, whereby effects on immune cells begin with increased constitutive expression of IL-1beta, followed by decreased stimulation of leucocytes by extracellular antigen, and finally decreased leukocyte survival when exposed to A. salmonicida. The implications of these changes in the immune system will be discussed with respect to the use of classical indicators of stress to predict possible effects on the immune system of fish. 相似文献
An Antarctic psychrotrophic bacterium, Shewanella livingstonensis Ac10, produces cis-5,8,11,14,17-eicosapentaenoic acid (EPA), a long-chain polyunsaturated fatty acid (LPUFA), as a component of membrane phospholipids
at low temperatures. The EPA-less mutant generated by disruption of the EPA synthesis gene becomes cold-sensitive. We studied
whether the cold sensitivity could be suppressed by supplementation of various LPUFAs. The EPA-less mutant was cultured at
6°C in the presence of synthetic phosphatidylethanolamines (PEs) that contained oleic acid at the sn-1 position and various C20 fatty acids with different numbers of double bonds from zero to five or cis-4,7,10,13,16,19-docosahexaenoic acid (DHA) at the sn-2 position. Mass spectrometric analyses revealed that all these fatty acids became components of various PE and phosphatidylglycerol
species together with shorter partner fatty acids, indicating that large-scale remodeling followed the incorporation of synthetic
PEs. As the number of double bonds in the sn-2 acyl chain decreased, the growth rate decreased and the cells became filamentous. The growth was restored to the wild-type
level only when the medium was supplemented with phospholipids containing EPA or DHA. We found that about a half of DHA was
converted into EPA. The results suggest that intact EPA is best required for cold adaptation of this bacterium. 相似文献
Mouse embryonic stem (ES) cells with the C57BL/6 genetic background allow the generation of knockout mice without the need to backcross to C57BL/6. However, C57BL/6 ES cells whose pluripotency after homologous recombination has been confirmed are not yet available from public cell banks. To facilitate the use of ES cells derived from C57BL/6 sublines in both biologic and medical research, we demonstrated that the use of knockout serum replacement as a medium supplement and 8-cell blastomeres as recipient embryos allowed establishment of ES cells and production of germline chimeric mice, respectively. Under effective conditions, a large number of ES cell lines were established from C57BL/6J and C57BL/6N blastocysts. The majority of ES cells in many cell lines obtained from both strains showed a normal chromosome number. Germline chimeric mice were generated from C57BL/6J and C57BL/6N ES cells. Finally, the ES cell line B6J-S1UTR, derived from C57BL/6J, was used for successful production of gene knockout mice. C57BL/6J ES (B6J-S1UTR and B6J-23UTR) and C57BL/6N ES (B6N-22UTR) cells are available from the cell bank of the BioResource Center at RIKEN Tsukuba Institute (http://www.brc.riken.jp/lab/cell/english/). 相似文献
Neoheterobothriumhirame is a blood feeding monogenean of olive flounder Paralichthys olivaceus. The parasite was first reported in the mid-1990s from the Sea of Japan and became epidemic within cultured and wild flounder populations after several years. Infected fish often suffer from severe anaemia and thus the parasite is thought to have played an important role in the recent depletion of flounder populations in some areas of Japan. However, the causal mechanism underlying the parasite epidemic and decreases in host populations is unclear because apparently N. hirame infection is not fatal to the host. Here, we tested the hypothesis that N. hirame indirectly reduces the survival of wild juvenile flounder by altering their behaviour and making them more susceptible to predation. We conducted a series of experiments to compare behaviours and predation susceptibility between experimentally infected juvenile P. olivaceus and uninfected fish. Results showed that N. hirame infection increases the activity level, alters diel activity and has negative effects on burrowing performance and swimming endurance. When juvenile flounder cohabitated with predators, the survival rate of infected juveniles was approximately 25% less than that of uninfected fish. We believe this is the first empirical evidence linking N. hirame infection to death of the host through predation. Consequences of N. hirame-induced behavioural change for the survival of juvenile flounder in the wild are discussed. We conclude that recent outbreaks of N. hirame are likely to have been a key factor in the decline of flounder populations in Japan. 相似文献