Acclimation of photosynthesis to increasing atmospheric CO2: The gas exchange perspective

The nature of photosynthetic acclimation to elevated CO₂ is evaluated from the results of over 40 studies focusing on the effect of long-term CO₂ enrichment on the short-term response of photosynthesis to intercellular CO₂ (the A/C_i response). The effect of CO₂ enrichment on the A/C_i response was dependent on growth conditions, with plants grown in small pots (< 5 L) or low nutrients usually exhibiting a reduction of A at a given C_i, while plants grown without nutrient deficiency in large pots or in the field tended to exhibit either little reduction or an enhancement of A at a given C_i following a doubling or tripling of atmospheric CO₂ during growth. Using theoretical interpretations of A/C_i curves to assess acclimation, it was found that when pot size or nutrient deficiency was not a factor, changes in the shape of A/C_i curves which are indicative of a reallocation of resources within the photosynthetic apparatus typically were not observed. Long-term CO₂ enrichment usually had little effect or increased the value of A at all C_i. However, a minority of species grown at elevated CO₂ exhibited gas exchange responses indicative of a reduced amount of Rubisco and an enhanced capacity to metabolize photosynthetic products. This type of response was considered beneficial because it enhanced both photosynthetic capacity at high CO₂ and reduced resource investment in excessive Rubisco capacity. The ratio of intercellular to ambient CO₂ (the C_i/C_a ratio) was used to evaluate stomatal acclimation. Except under water and humidity stress, C_i/C_a exhibited no consistent change in a variety of C₃ species, indicating no stomatal acclimation. Under drought or humidity stress, C_i/C_a declined in high-CO₂ grown plants, indicating stomata will become more conservative during stress episodes in future high CO₂ environments.Abbreviations A net CO₂ assimilation rate - C_i (C_a) intercellular (ambient) partial pressure of CO₂ - operational C_i intercellular partial pressure of CO₂ at a given ambient partial pressure of CO₂ - g_s stomatal conductance - normal CO₂ current atmospheric mole fraction of CO₂ (330 to 355 mol mol^–1) - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase     

Analysis of effector T cells against the murine syngeneic tumor MethA in mice orally administered antitumor polysaccharide SPR-901

The growth of MethA tumor was significantly inhibited by oral administration of the -glucan SPR-901 in BALB/c (+/+) mice but not in nude mice. Mice treated orally with SPR-901 exhibited an augmentation of antigen-specific resistance against rechallenge with the tumor cells. The tumor-neutralizing activity of regional lymph node cells from MethA-bearing mice against the tumor was augmented by oral administration of SPR-901. The tumor-neutralizing activity of lymph node cells from SPR-901-treated mice mainly appeared in Lyt2+cells. Furthermore, lymphokine-activated killer activity of these cells was enhanced by administration of SPR-901. The antitumor effect of SPR-901 was abrogated in mice depleted of either L3T4+ or Lyt2+ cells, and in cyclosporin-A-treated mice. These results suggest that Lyt2+ cells are important effector cells in MethA-bearing mice orally adminstered SPR-901 and that functional exertion of both Lyt2+ and L3T4+T cells is necessary for the antitumor effect of orally administered SPR-901 in vivo.     

生态交错带（Ecotone）理论研究进展

生态交错带（Ｅｃｏｔｏｎｅ）理论研究进展高洪文（东北师范大学草地研究所,长春１３００２４）ＡｄｖａｎｃｅｍｅｎｔｏｆＴｂｅｏｒｅｔｉｃａｌＲｅｓｅａｒｃｈｉｎＥｃｏｔｏｎｅ．￥ＧａｏＨｏｎｇｗｅｎ（ＩｎｓｔｉｔｕｔｅｏｆＧｒａｓｓｌａｎｄＲｅ－ｓｅａ...     

利用林木边行优势营造杨树速生丰产林的试验研究──林农复合生态经济系统的新模式

利用林木边行优势营造杨树速生丰产林的试验研究──林农复合生态经济系统的新模式许鸿儒,刘金声（辽宁省黑山县林业局,１２１４００）（辽宁省林业厅造林处,沈阳１１０００１）范学文（辽宁省锦西市林业局,１２１５００）ＰｌａｎｔｉｎｇｏｆＦａｓｔ－Ｇｒｏｗｉｎ...     

贺兰山主要森林水文作用的初步研究

贺兰山主要森林水文作用的初步研究徐万仁,张永庆（宁夏科委,银川７５０００１）（宁夏农学院,永宁７５０１０５）杜和平,李丽英（宁夏贺兰山自然保护区管理局,银川７５０００３）（宁夏惠农县林业局,７５３２００）ＰｒｅｌｉｍｉｎａｒｙＳｔｕｄｙｏｎＨｙｄｒｏ...     

Population fragmentation may reduce fertility to zero in Banksia goodii — a demonstration of the Allee effect

All individuals of all known populations of Banksia goodii were assessed for seed production. Small populations produced no or only a few seeds per unit canopy area. Effects of population size on seed production per unit area and seed production per plant were present over the whole range of population sizes, indicating that even in large populations seed production may still not be at its maximum. Resource differences could not explain this disproportionate decrease in seed production with decline in population size, because there were no differences in soil properties and understorey or overstorey cover between the small and large populations. Although plants in small and large populations were similar in size, seed production per plant was much lower in small populations. This was not because plants in small populations produced fewer cones but because the fraction of these cones that was fertile was much lower. Five of the nine smallest populations (<200 m²) produced no fertile cones over the last 10 years. The number of seeds per fertile cone did not depend on population size. The results are discussed in relation to pollination biology.     

Estimates of the residual nitrogen benefit of groundnut to maize in Northeast Thailand

Four cultivars of groundnut were grown in upland soil in Northeast Thailand to study the residual benefit of the stover to a subsequent maize crop. An N-balance estimate of the total residual N in the maize supplied by the groundnut was made. In addition three independent estimates were made of the residual benefits to maize when the groundnut stover was returned to the land and incorporated. The first estimate (Estimate 1) was an N-balance estimate. A dual labelling approach was used where ¹⁵N-labelled stover was added to unlabelled microplots (Estimate 2) or unlabelled stover was added to ¹⁵N-labelled soil microplots (Estimate 3). The nodulating groundnut cultivars fixed between 59–64% of their nitrogen (as estimated by the ¹⁵N isotope dilution method using non-nodulating groundnut as a non-fixing reference) producing between 100 and 130 kg N ha^-1 in their stover. Although the following maize crop suffered from drought stress, maize grain N and dry weights were up to 80% and 65% greater respectively in the plots where the stover was returned as compared with the plots where the stover was removed. These benefits were comparable with applications of 75 kg N ha^-1 nitrogen in the form of urea. The total residual N estimates of the contribution of the nodulated groundnut to the maize ranged from 16.4–27.5 kg N ha^-1. Estimates of the residual N supplied by the stover and fallen leaves ranged from 11.9–21.3 kg N ha^-1 using the N-balance method (Estimate 1), from 6.3–9.6 kg N ha^-1 with the labelled stover method (Estimate 2) and from 0–11.4 kg N ha^-1 with the labelled soil method. There was closest agreement between the two ¹⁵N based estimates suggesting that apparent added nitrogen interactions in these soils may not be important and that N balance estimates can overestimate the residual N in crops following legumes, even in very poor soils. This work also indicates the considerable ability of local groundnut cultivars to fix atmospheric nitrogen and the potential benefits from returning and incorporating legume residues to the soil in the upland cropping systems of Northeast Thailand. The applicability of the ¹⁵N methodology used here and possible reasons for the discrepancies between estimates 1, 2 and 3 are discussed.     

Isolation of a new paramutagenic allele of thesulfurea locus in the tomato cultivar Moneymaker following in vitro culture

A new allele, SC148, of thesulfurea locus inLycopersicon esculentum was detected in a line derived after repeated selfing of plants that had been regenerated from tissue culture. Like the originalsulf mutant, SC148 displayed two mutant phenotypes: green-yellow speckled plants in which thesulf ^vag allele is present and pure yellow plants homozygous for thesulf ^tpura allele. Although the mutant alleles are recessive to wild-type, an unpredictable number of variegated and pura plants appeared in F₁ progenies that had been derived from crosses between SC148 and wild-type tomato plants. The presence of the wild-typesulf ⁺ allele in these variegated heterozygotes was demonstrated using a cytological marker that is linked tosulf. It is concluded that the mutantsulf allele of SC148, imposes its variegated expression state on the wild-typesulf ⁺ allele present insulf ⁺/sulf^vag heterozygotes. This behaviour, known as paramutation, has also been described for the originalsulf allele. The SC148 allele, however, seems to induce changes at an earlier stage in development. The analogy of this paramutagenic system to dominant position effect variegation inDrosophila is discussed.     

The interaction of the vanadyl(IV) cation with phytic acid

The interactions of VO²⁺ with phytate to form both soluble and insoluble complexes, have been studied by electronic absorption spectroscopy. A soluble 1∶1 VO²⁺: phytate complex is formed at pH <1. At higher pH-values insoluble complexes are produced. Two different solid complexes, obtained respectively at pH=2 and 4, were isolated and characterized. The maximal bonding ratio of VO²⁺: phytate was found to be 4, on the basis of a pH binding profile.     

Thermoluminescence properties of the S2-state in chloride-depleted water oxidizing complexes after reconstituting treatments with various monovalent anions

Under conditions that assured rebinding of the extrinsic 17 and 23 kDa polypeptides, Cl^--depleted Photosystem II membranes isolated from spinach chloroplasts were subjected to reconstituting treatments in media containing NaF, NaCl, NaBr, NaI or NaNO₃, or they were kept in a medium without any added salt other than the buffer. After removing most of the unbound reconstituting anions by washing, the O₂-evolution activities and thermoluminescence properties of the membranes were compared. While the temperature of maximal thermoluminescence emission was lowest for membranes treated with Cl^-, no uniform correlation was evident between the temperature profile of the thermoluminescence emission and the apparent activating effectiveness of the anions in the membranes' water oxidizing machinery. However, the differences between the thermoluminescence features did conform to a trend according to which the emission temperatures were upshifted as the size of the activating anion increased, and its hydration energy decreased, i.e. Cl^-<Br^-<NO₃ ^-<I^-. The inactive F^- anions were not well retained by the membranes. To explain the experimental data it is suggested that the structural environment of the charge accumulating Mn-center is influenced by the ionic conditions encountered by the Photosystem II membranes after Cl^- removal, further enforced by the binding of compatible anions, and then stabilized by the 17 and 23 kDa extrinsic polypeptides. If, as some concepts imply, the anion binding sites are located at or near the functional Mn, only very exceptional characteristics of the water-oxidizing mechanism may account for the observation that the potentially electron-donating I^- anion can serve as activator and that it stabilizes rather than destabilizes the S₂-state.Abbreviations Chl chlorophyll - Hepes 4-(2-hydroxyethyl)-1-piperazine-ethane sulfonic acid - Mes 2-(N-morpholino)ethane sulfonic acid - Pheo the pheophytin a of the Photosystem II reaction center - PS photosystem