Seasonal changes in temperature response of photosynthesis and its contribution to annual carbon gain in Daphniphyllum humile, an evergreen understorey shrub.

We evaluated seasonal variation in photosynthetic temperature dependence and its contribution to annual carbon gain in an evergreen understorey shrub, Daphniphyllum humile Maxim, growing at the forest border and in the understorey of a deciduous forest. Plants at both sites exhibited similar optimal temperatures for photosynthesis (T(opt)). The activation energy for ribulose-1,5-bisphosphate (RuBP) carboxylation (HaV) at both sites tended to be higher in summer than in spring or autumn, suggesting that HaV may be the controlling factor in the T(opt) shift in D. humile. In contrast to the seasonal changes in T(opt ), the maximum photosynthetic rate at the optimal temperature (P(opt)) differed between the two sites: it was lower in autumn than in summer at the forest border, but was the same in summer and autumn in the understorey. In the understorey plants, nitrogen content (Narea) increased in autumn, but this was not the case for forest border plants. In addition, Rubisco content increased significantly in autumn in the understorey leaves but decreased distinctly in forest border leaves. Increased Narea and Rubisco in understorey leaves resulted in increased in photosynthesis in autumn. Annual carbon gain was 30.8 mol · m(-2) in forest border leaves and 5.8 mol · m(-2) in understorey leaves. Carbon gain in understorey leaves during the short period after overstorey leaf fall and before snow accumulation was approximately 49% of annual carbon gain. Furthermore, autumn carbon gain calculated using activation energy of summer with autumn photosynthetic parameters underestimated the autumn carbon gain by as much as 31%. In conclusion, photosynthetic temperature acclimation may be a key factor in increasing annual carbon gain in understorey D. humile.

Regulation of drought tolerance by gene manipulation of 9-cis-epoxycarotenoid dioxygenase, a key enzyme in abscisic acid biosynthesis in Arabidopsis.

Abscisic acid (ABA), a plant hormone, is involved in responses to environmental stresses such as drought and high salinity, and is required for stress tolerance. ABA is synthesized de novo in response to dehydration. 9-cis-epoxycarotenoid dioxygenase (NCED) is thought to be a key enzyme in ABA biosynthesis. Here we demonstrate that the expression of an NCED gene of Arabidopsis, AtNCED3, is induced by drought stress and controls the level of endogenous ABA under drought-stressed conditions. Overexpression of AtNCED3 in transgenic Arabidopsis caused an increase in endogenous ABA level, and promoted transcription of drought- and ABA-inducible genes. Plants overexpressing AtNCED3 showed a reduction in transpiration rate from leaves and an improvement in drought tolerance. By contrast, antisense suppression and disruption of AtNCED3 gave a drought-sensitive phenotype. These results indicate that the expression of AtNCED3 plays a key role in ABA biosynthesis under drought-stressed conditions in Arabidopsis. We improved drought tolerance by gene manipulation of AtNCED3 causing the accumulation of endogenous ABA.

Antisense suppression of proline degradation improves tolerance to freezing and salinity in Arabidopsis thaliana.

Synthesis, degradation, and transport of proline (Pro) are thought to cooperatively control its endogenous levels in higher plants in response to environmental conditions. To evaluate the function of Pro degradation in the regulation of the levels of Pro and to elucidate roles of Pro in stress tolerance, we generated antisense transgenic Arabidopsis plants with an AtProDH cDNA encoding proline dehydrogenase (ProDH), which catalyzes Pro degradation. Several transgenic lines accumulated Pro at higher levels than wild-type plants, providing evidence for a key role of ProDH in Pro degradation in Arabidopsis. These antisense transgenics were more tolerant to freezing and high salinity than wild-type plants, showing a positive correlation between Pro accumulation and stress tolerance in plants.

Biological functions of proline in morphogenesis and osmotolerance revealed in antisense transgenic Arabidopsis thaliana.

Many organisms, including higher plants, accumulate free proline (Pro) in response to osmotic stress. Although various studies have focused on the ability of Pro as a compatible osmolyte involved in osmotolerance, its specific role throughout plant growth is still unclear. It has been reported that Pro is synthesized from Glu catalyzed by a key enzyme, delta 1-pyrroline-5-carboxylate synthetase (P5CS), in plants. To elucidate essential roles of Pro, we generated antisense transgenic Arabidopsis plants with a P5CS cDNA. Several transgenics accumulated Pro at a significantly lower level than wild-type plants, providing direct evidence for a key role of P5CS in Pro production in Arabidopsis. These antisense transgenics showed morphological alterations in leaves and a defect in elongation of inflorescences. Furthermore, transgenic leaves were hypersensitive to osmotic stress. Microscopic analysis of transgenic leaves, in which the mutated phenotype clearly occurred, showed morphological abnormalities of epidermal and parenchymatous cells and retardation of differentiation of vascular systems. These phenotypes were suppressed by exogenous L-Pro but not by D-Pro or other Pro analogues. In addition, Pro deficiency did not broadly affect all proteins but specifically affected structural proteins of cell walls in the antisense transgenic plants. These results indicate that Pro is not just an osmoregulator in stressed plants but has a unique function involved in osmotolerance as well as in morphogenesis as a major constituent of cell wall structural proteins in plants.

Hemodynamic changes during hemodialysis.

35 patients with chronic renal failure were examined during the first 2 h of hemodialysis by invasive and non-invasive methods. The cardiac output was determined by the dye dilution technique in 11 of these patients and by Swan-Ganz catheterization in 5. In the patients without severe myocardial damage, the cardiac output during hemodialysis showed a significant increase (p less than 0.05), accompanied by a significant decrease of both mean blood pressure (p less than 0.05) and total peripheral resistance (p less than 0.05). Mean pulmonary artery pressure and pulmonary artery wedge pressure were reduced in all cases during hemodialysis. The increase in cardiac output during hemodialysis in patients with chronic renal failure may be attributed to the decrease in afterload.

Evaluation of myocardial contractility by the non-invasive method.

In evaluation of cardiac function by the non-invasive method, the possibility of separation of cardiac muscle performance from cardiac pump performance was studied. Among the non-invasive values, SV/ET, SV/(AO/EO), Pd/ICT, Pd/PEP, 1/ICT2, ET/PEP, and ET/ICT were considered as parameters for myocardial contractility. This research especially focused on Pd/ICT and ET/PEP. In auricular fibrillation it was possible to draw Starling-like curves and 3 dimensional coordinates to estimate a Vmax-like value. However this method could not be used in sinus rhythm. Whereas, in hypertension with abnormal afterload and uremia with abnormal preload, myocardial contractility was expressed by Pd/ICT under the influence of almost pure preload and ET/PEP under the influence of both preload and afterload. Therefore Pd/ICT was corrected with preload (AO/EO) and (Pd/ICT)/(AO/EO) may be used as the index for myocardial contractility.