Rubisco content and photosynthesis of leaves at different positions in transgenic rice with an overexpression of RBCS

As ribulose 1·5-bisphosphate carboxylase/oxygenase (Rubisco) activity limits light-saturated photosynthesis under present atmospheric condition, the effects of an overexpression of RBCS on Rubisco content and photosynthesis were examined in the leaves at different positions in rice ( Oryza sativa L.). Rubisco content in the transformant was significantly greater in the uppermost, fully expanded leaves but decreased to levels similar to those in wild-type plants in the lower leaves. The mRNA levels of total RBCS and rbcL in these leaves were much less than those in the expanding leaves, where Rubisco synthesis is active, suggesting commensurately low level of synthesis. Although the activation state of Rubisco was lower in the uppermost, fully expanded leaves of the transformant, it recovered to its full level in the lower leaves. As a result, the photosynthetic rate did not differ in leaves at the same position between the transformant and the wild type. Similarly, whole plant biomass did not differ between these genotypes. Thus, we conclude that although the overexpression of RBCS led to an enhancement of Rubisco protein content in the uppermost, fully expanded leaves, it does not result in increased photosynthetic rates or plant biomass, because of an apparent down-regulation in its activation state.     

Plasticity in maximum stomatal conductance constrained by negative correlation between stomatal size and density: an analysis using Eucalyptus globulus

Maximum stomatal conductance to water vapour and CO₂ ( g _wmax, g _cmax, respectively), which are set at the time of leaf maturity, are determined predominantly by stomatal size ( S ) and density ( D ). In theory, many combinations of S and D yield the same g _wmax and g _cmax, so there is no inherent correlation between S and D , or between S , D and maximum stomatal conductance. However, using basic equations for gas diffusion through stomata of different sizes, we show that a negative correlation between S and D offers several advantages, including plasticity in g _wmax and g _cmax with minimal change in epidermal area allocation to stomata. Examination of the relationship between S and D in Eucalyptus globulus seedlings and coppice shoots growing in the field under high and low rainfall revealed a strong negative relationship between S and D , whereby S decreased with increasing D according to a negative power function. The results provide evidence that plasticity in maximum stomatal conductance may be constrained by a negative S versus D relationship, with higher maximum stomatal conductance characterized by smaller S and higher D , and a tendency to minimize change in epidermal space allocation to stomata as S and D vary.     

Metabolome analysis of photosynthesis and the related primary metabolites in the leaves of transgenic rice plants with increased or decreased Rubisco content

Because the comprehensive effects on metabolism by genetic manipulation of leaf Rubisco content are unknown, metabolome analysis was carried out on transgenic rice plants with increased or decreased Rubisco content using the capillary electrophoresis-time-of-flight mass spectrometry (CE-TOFMS) technique. In RBCS-sense plants, an increase in Rubisco content did not improve light-saturated photosynthesis. Glyceraldehyde 3-phosphate and sedoheputulose 7-phosphate levels increased, but ribulose bisphosphate (RuBP), ATP and ADP levels were not affected. It is considered from these results that RuBP regeneration independent of ATP supply became a bottleneck for photosynthesis. In RBCS-antisense plants, a decline in Rubisco content decreased photosynthesis with a substantial accumulation of RuBP. ATP and ADP levels also increased and were associated with increases in the diphosphate and triphosphate compounds of other nucleosides. These results imply that a decline in Rubisco content slowed down the Calvin cycle and that the resultant excess energy of ATP was transferred to other nucleoside diphosphates and triphosphates. The levels of amino acids tended to decline in RBCS-sense plants and increase in RBCS-antisense plants, probably reflecting the demand for Rubisco synthesis. Starch and carbohydrate levels decreased only in RBCS-antisense plants. Thus, genetic manipulation of Rubisco contents widely affected C and N metabolism in rice.     

Photosynthetic parameters in seedlings of Eucalyptus grandis as affected by rate of nitrogen supply

Seedlings of Eucalyptus grandis were grown at five different rates of nitrogen supply. Once steady‐state growth rates were established, a detailed set of CO₂ and water vapour exchange measurements were made to investigate the effects of leaf nitrogen content (N), as determined by nitrogen supply rate, on leaf structural, photosynthetic, respiratory and stomatal properties. Gas exchange data were used to parametrize the Farquhar–von Caemmerer photosynthesis model. Leaf mass per area (LMA) was negatively correlated to N. A positive correlation was observed between both day (R_d) and night respiration (R_n) and N when they were expressed on a leaf mass basis, but no correlation was found on a leaf area basis. An R_d/R_n ratio of 0·59 indicated a significant inhibition of dark respiration by light. The maximum net CO₂ assimilation rate at ambient CO₂ concentration (A_max), the maximum rate of potential electron transport (J_max) and the maximum rate of carboxylation (V_cmax) significantly increased with N, particularly when expressed on a mass basis. Although the maximum stomatal conductance to CO₂ (g_scmax) was positively correlated with A_max, there was no relationship between g_scmax and N. Leaf N content influenced the allocation of nitrogen to photosynthetic processes, resulting in a decrease of the J_max/V_cmax ratio with increasing N. It was concluded that leaf nitrogen concentration is a major determinant of photosynthetic capacity in Eucalyptus grandis seedlings and, to a lesser extent, of leaf respiration and nitrogen partitioning among photosynthetic processes, but not of stomatal conductance.     

Characterization of juvenile and adult leaves of Eucalyptus globulus showing distinct heteroblastic development: photosynthesis and volatile isoprenoids

Heteroblastic Eucalyptus (Eucalyptus globulus L.) leaves were characterized for their functional diversity examining photosynthesis and photosynthesis limitations, transpiration, and the emission of isoprene and monoterpenes. In vivo and combined analyses of gas-exchange, chlorophyll fluorescence, and light absorbance at 830 nm were made on the adaxial and abaxial sides of juvenile and adult leaves. When adult leaves were reversed to illuminate the abaxial side, photosynthesis and isoprene emission were significantly lower than when the adaxial side was illuminated. Monoterpene emission, however, was independent on the side illuminated and similarly partitioned between the two leaf sides. The abaxial side of adult leaves showed less diffusive resistance to CO(2) acquisition by chloroplasts, but also lower ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity, than the adaxial leaf side. In juvenile leaves, photosynthesis, isoprene, and monoterpene emissions were similar when the adaxial or abaxial side was directly illuminated. In the abaxial side of juvenile leaves, photosynthesis did not match the rates attained by the other leaf types when exposed to elevated CO(2), which suggests the occurrence of a limitation of photosynthesis by ribulose bisphosphate (RuBP) regeneration. Accordingly, a reduced efficiency of both photosystems and a high non-radiative dissipation of energy was observed in the abaxial side of juvenile leaves. During light induction, the adaxial side of juvenile leaves also showed a reduced efficiency of photosystem II and a large non-radiative energy dissipation. Our report reveals distinct functional properties in Eucalyptus leaves. Juvenile leaves invest more carbon in isoprene, but not in monoterpenes, and have a lower water use efficiency than adult leaves. Under steady-state conditions, in adult leaves the isobilateral anatomy does not correspond to an equal functionality of the two sides, while in juvenile leaves the dorsiventral anatomy does not result in functional differences in primary or secondary metabolism in the two sides. However, photochemical limitations may reduce the efficiency of carbon fixation in the light, especially in the abaxial side of juvenile leaves.     

Ontogenetic differences in mesophyll structure and chlorophyll distribution in Eucalyptus globulus ssp. globulus

Mesophyll structure has been associated with the photosynthetic performance of leaves via the regulation of internal light and CO(2) profiles. Differences in mesophyll structure and chlorophyll distribution within three ontogenetically different leaf types of Eucalyptus globulus ssp. globulus were investigated. Juvenile leaves are blue-grey in color, dorsiventral (adaxial palisade layer only), hypostomatous, and approximately horizontal in orientation. In contrast, adult leaves are dark green in color, isobilateral (adaxial and abaxial palisade), amphistomatous, and nearly vertical in orientation. The transitional leaf type has structural features that appear intermediate between the juvenile and adult leaves. The ratio of mesophyll cell surface area per unit leaf surface area (A(mes)/A) of juvenile leaves was maximum at the base of a single, adaxial palisade layer and declined through the spongy mesophyll. Chlorophyll a + b content showed a coincident pattern, while the chlorophyll a:b ratio declined linearly from the adaxial to abaxial epidermis. In comparison, the mesophyll of adult leaves had a bimodal distribution of A(mes)/A, with maxima occurring beneath both the adaxial and abaxial surfaces within the first layer of multiple palisade layers. The distribution of chlorophyll a + b content had a similar pattern, although the maximum ratio of chlorophyll a:b occurred immediately beneath the adaxial and abaxial epidermis. The matching distributions of A(mes)/A and chlorophyll provide further evidence that mesophyll structure may act to influence photosynthetic performance. These changes in internal leaf structure at different life stages of E. globulus may be an adaptation for increased xeromorphy under increasing light exposure experienced from the seedling to adult tree, similar to the characteristics reported for different species according to sunlight exposure and water availability within their native habitats.     

Leaf and root growth dynamics in Eucalyptus globulus seedlings grown in drying soil

Summary Seedlings of Eucalyptus globulus growing in soil columns were subjected to a 24 day soil drying treatment. Water and solute potentials of both young expanding and fully expanded leaves declined under reduced soil water availability, while slightly higher turgor was sustained by the fully expanded leaves. Although leaf area of unwatered seedlings was smaller, the corresponding leaf dry weight was quite similar to that of well-watered seedlings. Soon after rewatering, leaf area of plants experiencing water shortage was comparable to that of well-watered plants. It seems that a difference in wall properties between juvenile and mature leaves allows for an effective pattern of water use by eucalypt plants growing in drying soil. Some stomatal opening is sustained and therefore, presumably, some carbon may be fixed, keeping the carbon balance of the whole plant positive, and allowing a continuous cell division despite the limited water supply. The highest root density of both well-watered and unwatered plants was found in the upper soil layers. However, root growth of unwatered seedlings was gradually increased in the deeper soil layers, where thicker root apices and higher soil water depletion rates per unit root length were recorded. As a consequence, root absorbing surface area was as large in unwatered plants as in well-watered plants.     

夏玉米三叶期持续干旱下不同叶位叶片含水量变化及其与光合作用的关系

植物干物质的累积依赖于群体光合速率,而群体光合速率又与单叶的光合能力密切有关。叶片光合作用与其含水量密切相关,目前关于不同叶位叶片含水量对持续干旱的响应及其与光合作用的关系还未见报道。以华北夏玉米郑单958为材料,设置6个不同灌水处理,模拟不同灌溉量下持续干旱对夏玉米不同叶位叶片生理特性的影响,分析夏玉米顶部开始的第一、三、五叶位叶片的水分变化及其与净光合速率的关系。结果表明:夏玉米不同叶位的叶片最大含水量不同,且随干旱进程的推进叶片含水量的变化速率也不同,第一叶的叶片含水量下降速率高于第三、第五叶,第一叶的最大含水量高于第三、五叶,且可进行光合产物积累的叶片含水量下限随叶位的增加而增大。同时,第一叶的叶片含水量与土壤水分呈显著相关,且与净光合速率的相关性也非常强。第一叶可进行光合产物积累的叶片水分下限(净光合速率为零时的叶片含水量)最小,表明其耐旱性最强,对干旱具有指导意义。研究结果可为提高冠层光合作用模拟的准确性及夏玉米干旱发生发展的监测预警提供参考。     

Root and shoot elongation of rhizotron-grown seedlings of Eucalyptus nitens and Eucalyptus globulus in relation to temperature

Information on the growth response of a crop plant in relation to temperature can be helpful in selecting genotypes to suit local environments, scheduling favourable time of planting and forecasting growth and yield. To determine the effects of varying temperature on root and shoot elongation of eucalypt seedlings, elongation rates of roots and shoots were measured in rhizotrons for two species (Eucalyptus nitens (Deane and Maiden) Maiden, and Eucalyptus globulus Labill.) at a temperature range of 5–23 °C. Within this range of temperatures, elongation rates of roots and shoots of both species increased with an increase in temperature. Roots of E. globulus were more sensitive and shoots less sensitive to temperature than those of E. nitens. However, the threshold temperature corresponding with zero elongation rate predicted from the regression of elongation rate against temperature was similar for the roots (∼5 °C) and shoots (∼0 °C) of both species. Hysteresis did not appear to have a significant influence on root or shoot elongation of both species during warming compared with cooling. Results are discussed highlighting the importance of the interaction between development and growth of plant components.     

蒙古栎不同冠层部位叶片养分动态

以长白山原始针阔叶混交林优势树种蒙古栎为对象,研究了6-10月生长季不同冠层叶片单位叶面积质量(LMA)、单位质量和单位叶面积的C、N、P含量变化,以及N、P的再吸收效率与利用效率.结果表明:在生长季,蒙古栎冠层上、下部叶片的LMA和单位叶面积C含量(Carea)表现出明显的月动态变化;单位叶面积N、P含量(Narea、Parea)的月变化趋势与单位质量N、P含量(Nmass、Pmass)相似,而用单位叶面积与单位质量表示的N、P再吸收效率无明显差异.冠层位置对N的再吸收效率和利用效率无明显影响,但冠层上部P的再吸收效率和利用效率显著高于冠层下部.在未来气候变化情景下,蒙古栎较高的生存力和竞争力有助于促进生态系统的养分循环.     

Leachates of Eucalyptus globulus in Intermittent Streams Affect Water Parameters and Invertebrates

Low order streams running through Eucalyptus globulus plantations in Central Portugal are frequently reduced to isolated permanent or temporary summer pools with darkly stained water due to leaf leachates. Here we assess the toxicity of such leachates to the shredder Sericostoma vittatum. Leachates resulted in deoxygenated and more acid water, and increased its phenolic content and conductivity. S. vittatum exposed to high concentrations of leachates failed to grow and died within 30 days even in the presence of high quality food. Larvae in water with half the leachate concentration, consumed less leaf material, had lower growth rates, did not pupate and died within 100 days. Eucalypt leachates per se may affect the viability and ecology of macroinvertebrates in Portuguese streams. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Increased Rubisco content in maize mitigates chilling stress and speeds recovery

Many C₄ plants, including maize, perform poorly under chilling conditions. This phenomenon has been linked in part to decreased Rubisco abundance at lower temperatures. An exception to this is chilling‐tolerant Miscanthus, which is able to maintain Rubisco protein content under such conditions. The goal of this study was to investigate whether increasing Rubisco content in maize could improve performance during or following chilling stress. Here, we demonstrate that transgenic lines overexpressing Rubisco large and small subunits and the Rubisco assembly factor RAF1 (RAF1‐LSSS), which have increased Rubisco content and growth under control conditions, maintain increased Rubisco content and growth during chilling stress. RAF1‐LSSS plants exhibited 12% higher CO₂ assimilation relative to nontransgenic controls under control growth conditions, and a 17% differential after 2 weeks of chilling stress, although assimilation rates of all genotypes were ~50% lower in chilling conditions. Chlorophyll fluorescence measurements showed RAF1‐LSSS and WT plants had similar rates of photochemical quenching during chilling, suggesting Rubisco may not be the primary limiting factor that leads to poor performance in maize under chilling conditions. In contrast, RAF1‐LSSS had improved photochemical quenching before and after chilling stress, suggesting that increased Rubisco may help plants recover faster from chilling conditions. Relatively increased leaf area, dry weight and plant height observed before chilling in RAF1‐LSSS were also maintained during chilling. Together, these results demonstrate that an increase in Rubisco content allows maize plants to better cope with chilling stress and also improves their subsequent recovery, yet additional modifications are required to engineer chilling tolerance in maize.     

巨桉凋落叶分解初期对菊苣生长和光合特性的影响

采用盆栽试验,于2010年3-5月在四川农业大学教学科研园区内研究了巨桉凋落叶分解初期对受体植物菊苣幼苗生长和光合特性的影响.试验设置CK (0 g·pot-1)、A1(30 g·pot-1)、A2(60 g·pot-1)和A3 (90 g·pot-1)4个凋落叶施用水平,将各处理的凋落叶分别与12 kg土壤混合后装盆,播种菊苣,分别在播种30、45、60和75 d测定菊苣生长指标,待凋落叶量的最高处理组A3植株第3片真叶完全展开后,测定菊苣叶片的光合生理指标.结果表明:在各测定时间下,不同巨桉凋落叶施用水平的菊苣生物量积累和叶面积增长受到显著抑制;在凋落叶分解初期,菊苣幼苗叶片光合色素合成受到明显抑制,且随着凋落叶施用量增加抑制作用加大,各处理幼苗的光合速率日变化均呈午休双峰型曲线,气孔导度和水分利用效率的变化趋势与净光合速率相同,日光合总量表现为CK＞A1 ＞A2 ＞A3.经GC-MS定期检测,凋落叶中有33种小分子化合物随着凋落叶的分解而逐步释放,以具有化感作用的萜类物质为主.     

Calcium and oxalate content of the leaves of Phaseolus vulgaris at different calcium supply in relation to calcium oxalate crystal formation

Soluble and insoluble oxalate and insoluble calcium were measured in the leaves of Phaseolus vulgaris. The plants were grown in nutrient solutions with two different concentrations of calcium. Two developmental stages of the leaves were studied. Although the content of insoluble calcium differs widely according to leaf age and growth conditions, the percentage bound in crystals is nearly the same in all cases. In the growing leaves, concentrations of total oxalate are independent of calcium supply, thus, showing that the known rise in numbers of crystals, and of cells containing them, is not induced via oxalate biosynthesis. Fully expanded leaves contain more oxalate when grown in a nutrient solution with higher calcium concentration. Amounts of oxalate in percent of dry weight are similar to those given in the literature for other legume leaves.     

滤光膜对喜树幼苗叶片生长和喜树碱含量的影响

喜树 (Camptotheca acuminata)为中国特有树种 ,因其次生代谢产物喜树碱具有抗癌作用而闻名。通过用黄色、红色、蓝色 3种滤光膜对温室栽培的喜树幼苗进行遮光处理 ,研究了不同光照环境下喜树幼苗叶片生物量、叶绿素含量、光合作用和喜树碱含量的差异。结果表明在 30 d的遮光过程中 ,红膜和蓝膜遮光明显导致幼苗叶片生物量降低 ,黄膜遮光下幼苗叶片生物量在处理后 2 5 d才表现明显降低。不同滤光膜下幼苗叶片叶绿素含量先降低然后升高 ,遮光幼苗的叶绿素 a/ b明显低于日光幼苗。幼苗日最大净光合速率的顺序是 :日光 >黄膜 >红膜 >蓝膜。处理后第 2 0天 ,不同滤光膜下幼苗的光饱和光合速率 (Amax)、光饱和点 (Is)、光补偿点 (Ic)、最大表观量子效率 (AQYmax)都不同程度的低于日光幼苗。处理后第 10天至第 30天 ,遮光幼苗叶片喜树碱含量均显著高于日光下幼苗 ,以蓝膜下幼苗的喜树碱含量最高。蓝膜和黄膜下幼苗的喜树碱产量在后期处理中显著高于日光下幼苗 ,蓝膜下幼苗喜树碱产量在第 30天最高 ,是日光下幼苗的 2 .4 9倍。红膜下幼苗的喜树碱产量在第 10天后与日光下幼苗差异不显著。通过滤光膜遮光促进喜树碱在幼苗叶片中的积累 ,提高了叶片喜树碱产量 ,对喜树碱的生产实践有一定的意义     

Changes in the turnover of Rubisco and levels of mRNAs of rbcL and rbcS in rice leaves from emergence to senescence

Changes in the amount of ribulose 1,5‐bisphosphate carboxylase/oxygenase (Rubisco; EC 4·1·1·39) synthesized and degraded and the levels of rbcL and rbcS mRNAs were examined in the eighth leaf blades of rice from emergence to senescence. Synthesis of Rubisco was very active during leaf expansion, became quite low at the time of full expansion and then declined further during senescence. The changes in the levels of rbcL and rbcS mRNAs co‐ordinated approximately with those in the amount of Rubisco synthesized. Thus, it is suggested that the amount of Rubisco synthesized is determined primarily by the levels of rbcL and rbcS mRNAs during the life span of the leaves. Degradation of Rubisco started just before the time of full expansion and became far more active than its synthesis during senescence. Since the synthesis of Rubisco during senescence scarcely contributed to its amount, it can be concluded that the degradation of Rubisco is the major determinant for the amount of Rubisco in senescent leaves. The decline in the level of rbcL mRNA occurred much earlier in the developmental stage and proceeded at a much faster rate than that of rbcL DNA, indicating that the level of rbcL DNA is not a major determinant for the level of rbcL mRNA in senescent leaves of rice.     

Low stomatal and internal conductance to CO2 versus Rubisco deactivation as determinants of the photosynthetic decline of ageing evergreen leaves

A novel A-Ci curve (net CO2 assimilation rate of a leaf -An- as a function of its intercellular CO2 concentration -Ci) analysis method (Plant, Cell & Environment 27, 137-153, 2004) was used to estimate the CO2 transfer conductance (gi) and the maximal carboxylation (Vcmax) and electron transport (Jmax) potentials of ageing, non-senescing Pseudotsuga menziesii leaves in relation to their nitrogen (N) content and protein and pigment composition. Both gi and the stomatal conductance (gsc) of leaves were closely coupled to Vcmax, Jmax and An with all variables decreasing with increasing leaf age. Consequently, both Ci and Cc (chloroplastic CO2 concentration) remained largely conserved through successive growing seasons. The N content of leaves, as well as the amount of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and other sodium dodecyl sulfate-soluble proteins, increased during the first three growing seasons, then stabilized or decreased only slightly afterwards. Thus, the age-related photosynthetic nitrogen use efficiency (PNUE) decline of leaves was not a consequence of decreased allocation of N towards Rubisco and other proteins involved in bioenergetics and light harvesting. Rather, loss of photosynthetic capacity was the result of the decreased activation state of Rubisco and proportional down-regulation of electron transport towards the photosynthetic carbon reduction (PCR) and photorespiratory (PCO) cycles in response to a reduction of CO2 supply to the chloroplasts' stroma. This study emphasizes the regulatory potential and homeostaticity of Cc- rather than photosynthetic metabolites or Ci- in relation to the commonly observed correlation between photosynthesis and gsc.