Blue light and phytochrome-mediated stomatal opening in the npq1 and phot1 phot2 mutants of Arabidopsis

Recent studies have shown that blue light-specific stomatal opening is reversed by green light and that far-red light can be used to probe phytochrome-dependent stomatal movements. Here, blue-green reversibility and far-red light were used to probe the stomatal responses of the npq1 mutant and the phot1 phot2 double mutant of Arabidopsis. In plants grown at 50 micromol m-2 s-1, red light (photosynthetic)-mediated opening in isolated stomata from wild type (WT) and both mutants saturated at 100 micromol m-2 s-1. Higher fluence rates caused stomatal closing, most likely due to photo-inhibition. Blue light-specific opening, probed by adding blue light (10 micromol m-2 s-1) to a 100 micromol m-2 s-1 red background, was found in WT, but not in npq1 or phot1 phot2 double mutant stomata. Under 50 micromol m-2 s-1 red light, 10 micromol m-2 s-1 blue light opened stomata in both WT and npq1 mutant stomata but not in the phot1 phot2 double mutant. In npq1, blue light-stimulated opening was reversed by far-red but not green light, indicating that npq1 has a phytochrome-mediated response and lacks a blue light-specific response. Stomata of the phot1 phot2 double mutant opened in response to 20 to 50 micromol m-2 s-1 blue light. This opening was green light reversible and far-red light insensitive, indicating that stomata of the phot1 phot2 double mutant have a detectable blue light-specific response.     

Low irradiances affect abscisic acid, indole-3-acidic acid, and cytokinin levels of wheat (Triticum aestivum L.) tissues.

Wheat (Triticum aestivum L.) plants were grown under four irradiance levels: 1,400, 400, 200, and 100 micromol m-2 s-1. Leaves and roots were sampled before, during, and after the boot stage, and levels of abscisic acid (ABA), indole-3-acetic acid (IAA), zeatin, zeatin riboside, dihydrozeatin, dihydrozeatin riboside, isopentenyl adenine, and isopentenyl adenosine were quantified using noncompetitive indirect ELISA systems. Levels of IAA in leaves and roots of plants exposed to 100 micromol m-2 s-1 of irradiance were 0.7 and 2.9 micromol kg-1 dry mass (DM), respectively. These levels were 0.2 and 1.0 micromol kg-1 DM, respectively, when plants were exposed to 1,400 micromol m-2 s-1. Levels of ABA in leaves and roots of plants exposed to 100 micromol m-2 s-1 were 0.65 and 0.55 micromol kg-1 DM, respectively. They were 0.24 micromol kg-1 DM (both leaves and roots) when plants were exposed to 1,400 micromol m-2 s-1. Levels of isopentenyl adenosine in leaves (24.3 nmol kg-1 DM) and roots (29.9 nmol kg-1 DM) were not affected by differences in the irradiance regime. Similar values were obtained in a second experiment. Other cytokinins could not be detected (<10 nmol kg 1 DM) in either experiment with the sample sizes used (150-600 mg DM for roots and shoots, respectively).     

Phytochrome modulation of blue light-induced chloroplast movements in Arabidopsis

Photometric analysis of chloroplast movements in various phytochrome (phy) mutants of Arabidopsis showed that phyA, B, and D are not required for chloroplast movements because blue light (BL)-dependent chloroplast migration still occurs in these mutants. However, mutants lacking phyA or phyB showed an enhanced response at fluence rates of BL above 10 micromol m-2 s-1. Overexpression of phyA or phyB resulted in an enhancement of the low-light response. Analysis of chloroplast movements within the range of BL intensities in which the transition between the low- and high-light responses occur (1.5-15 micromol m-2 s-1) revealed a transient increase in light transmittance through leaves, indicative of the high-light response, followed by a decrease in transmittance to a value below that measured before the BL treatment, indicative of the low-light response. A biphasic response was not observed for phyABD leaves exposed to the same fluence rate of BL, suggesting that phys play a role in modulating the transition between the low- and high-light chloroplast movement responses of Arabidopsis.     

铁皮石斛叶片光合作用的碳代谢途径

 利用LI-6400光合测定系统测定了不同天气条件下铁皮石斛（Dendrobium officinale）叶片24h CO2吸收的动态以及CO2吸收对光强和温度的响应。晴天的白天和夜间铁皮石斛都能吸收CO2,中午CO2吸收速率为负值, CO2的交换方式具景天酸代谢途径(CAM)的特点。阴雨天,只有白天吸收CO2,夜间表现为暗呼吸,光合作用碳代谢的途径为C3途径。在多云的天气条件下,白天吸收CO2,并持续至日落后。夜间21∶00仍有CO2吸收,23∶00以后至次日凌晨处于暗呼吸状态。在500 μmol·m-2·s-1光照件下,20℃出现最大CO2吸收值。在夜间,25℃时CO2的吸收速率最高。有光和无光条件下,低温或高温引起CO2吸收速率下降均为非气孔因素所致。晴天上午,铁皮石斛叶片的表观量子产额为0.035,光合补偿点为2.9μmol·m-2·s-1,饱和光强为500μmol·m-2·s-1,强光下出现光抑制现象。叶片受到强光预先照射后,即使光照减弱光抑制效应仍保持一段时间,致使光合补偿点升高,表观量子产额下降,相同光强下的CO2吸收效率降低。结果表明：铁皮石斛为兼性CAM植物,随着环境条件的变化,其光合作用在景天酸代谢途径(CAM)与C3途径间变化。     

Determination of the site of CO₂ sensing in poplar: is the area-based N content and anatomy of new leaves determined by their immediate CO₂ environment or by the CO₂ environment of mature leaves?

Exposure to an elevated CO(2) concentration ([CO(2)]) generally decreases leaf N content per unit area (N(area)) and stomatal density, and increases leaf thickness. Mature leaves can 'sense' elevated [CO(2)] and this regulates stomatal development of expanding leaves (systemic regulation). It is unclear if systemic regulation is involved in determination of leaf thickness and N(area)-traits that are significantly correlated with photosynthetic capacity. A cuvette system was used whereby [CO(2)] around mature leaves was controlled separately from that around expanding leaves. Expanding leaves of poplar (Populus trichocarpa×P. deltoides) seedlings were exposed to elevated [CO(2)] (720 μmol mol(-1)) while the remaining mature leaves inside the cuvette were under ambient [CO(2)] of 360 μmol mol(-1). Reverse treatments were performed. Exposure of newly developing leaves to elevated [CO(2)] increased their thickness, but when mature leaves were exposed to elevated [CO(2)] the increase in thickness of new leaves was less pronounced. The largest response to [CO(2)] was reflected in the palisade tissue thickness (as opposed to the spongy tissue) of new leaves. The N(area) of new leaves was unaffected by the local [CO(2)] where the new leaves developed, but decreased following the exposure of mature leaves to elevated [CO(2)]. The volume fraction of mesophyll cells compared with total leaf and the mesophyll cell density changed in a manner similar to the response of N(area). These results suggest that N(area) is controlled independently of the leaf thickness, and suggest that N(area) is under systemic regulation by [CO(2)] signals from mature leaves that control mesophyll cell division.     

Separate localization of light signal perception for sun or shade type chloroplast and palisade tissue differentiation in Chenopodium album.

Physiological and ecological characteristics of sun and shade leaves have been compared in detail, but their developmental processes, in particular their light sensory mechanisms, are still unknown. This study compares the development of sun and shade leaves of Chenopodium album L., paying special attention to the light sensory site. We hypothesized that mature leaves sense the light environment, and that this information determines anatomy of new leaves. To examine this hypothesis, we shaded plants partially. In the low-light apex treatment (LA), the shoot apex with developing leaves was covered by a cap made of a shading screen and received photosynthetically active photon flux density (PPFD) of 60 micromol m(-2 )s(-1), while the remaining mature leaves were exposed to 360 micromol m(-2 )s(-1). In the high-light apex treatment (HA), the apex was exposed while the mature leaves were covered by a shade screen. After these treatments for 6 d, we analyzed leaf anatomy and chloroplast ultrastructure. The anatomy of LA leaves with a two-layered palisade tissue was similar to that of sun leaves, while their chloroplasts were shade-type with thick grana. The anatomy of HA leaves and shade leaves was similar and both had one-layered palisade tissue, while chloroplasts of HA leaves were sun-type having thin grana. These results clearly demonstrate that new leaves differentiate depending on the light environment of mature leaves, while chloroplasts differentiate depending on the local light environment.     

Elevated CO2 induces physiological, biochemical and structural changes in leaves of Arabidopsis thaliana

Leaves of Arabidopsis thaliana grown under elevated or ambient CO2 (700 or 370 micromol mol(-1), respectively) were examined for physiological, biochemical and structural changes. Stomatal characters, carbohydrate and mineral nutrient concentrations, leaf ultrastructure and plant hormone content were investigated using atomic absorption spectrophotometry, transmission electron microscopy and enzyme-linked immunosorbent assay (ELISA). Elevated CO2 reduced the stomatal density and stomatal index of leaves, and also reduced stomatal conductance and transpiration rate. Elevated CO2 increased chloroplast number, width and profile area, and starch grain size and number, but reduced the number of grana thylakoid membranes. Under elevated CO2, the concentrations of carbohydrates and plant hormones, with the exception of abscisic acid, increased whereas mineral nutrient concentrations declined. These results suggest that the changes in chloroplast ultrastructure may primarily be a consequence of increased starch accumulation. Accelerated A. thaliana growth and development in elevated CO2 could in part be attributed to increased foliar concentrations of plant hormones. The reductions in mineral nutrient concentrations may be a result of dilution by increased concentrations of carbohydrates and also of decreases in stomatal conductance and transpiration rate.     

10个秋菊品种的光合特性及净光合速率与部分生理生态因子的相关性分析

用CIRAS-2便携式光合测定系统测定了9月至10月10个秋菊[Dendranthema morifolium (Ramat.) Tvzel.]品种叶片的光合特征参数;在此基础上,对叶片光响应参数和CO2响应参数以及部分光合特征参数的日变化进行了比较分析;此外,还对净光合速率(Pn)与部分生理生态因子的相关性进行了分析.结果表明:10个秋菊品种的光补偿点(LCP)为92.83～167.37 μmol·m-2·s-1,光饱和点(LSP)为962.51～1 077.53 μmol·m-2·s-1,说明它们均为喜光植物;10个秋菊品种的CO2饱和点为1 060.46 ～1 485.48μmol·mol-1,CO2补偿点为77.62 ～ 133.16μmo1·mol-1,远大于一般的C3植物;各品种Pn的日变化呈典型的双峰型曲线,首峰(11～19μmol·m-2·s-1)出现在10:00左右,次峰出现在16:00左右,有明显的“午休”现象.相关分析结果表明:10个品种的Pn与气孔导度呈极显著正相关,与蒸腾速率呈显著或极显著正相关(品种‘关东新侠’、‘云龙凤舞’和‘日本黄’除外),与胞间CO2浓度呈显著或极显著负相关,与光合有效辐射强度和大气温度呈不显著正相关,与大气相对湿度和大气CO2浓度呈不显著负相关.早花品种‘太平的小鼓’和‘铜雀春深’具有较高的LSP以及较低的LCP和表观量子效率(AQY),对光照强度的适应范围较大,可栽培在光照较强的环境中;品种‘早粉盘’和‘檀香狮子’具有较高的LCP、AQY和LSP,对强光的利用能力较强;晚花品种‘关东新侠’、‘绿牡丹’和‘星光灿烂’具有较高的LCP和AQY以及较低的LSP,具有一定的耐阴能力,可种植在光照较弱的环境中.     

Long-distance CO(2) signalling in plants.

Stomatal numbers are tightly controlled by environmental signals including light intensity and atmospheric CO(2) partial pressure. This requires control of epidermal cell development during the early phase of leaf growth and involves changes in both the density of cells on the leaf surface and the proportion of cells that adopt a stomatal fate. This paper reviews the current understanding of how stomata develop and describes recent advances that have given insights into the regulatory mechanisms involved using mutant Arabidopsis plants that implicates a role for long-chain fatty acids in cell-to-cell communication. Evidence is presented which indicates that long-distance signalling from mature to newly developing leaves forms part of the mechanism by which stomatal development responds to environmental cues. Analysis of mutant plants suggests that the plant hormones abscisic acid, ethylene and jasmonates are implicated in the long-distance signalling pathway and that the action may be mediated by reactive oxygen species.     

胡杨不同叶形光合特性、水分利用效率及其对加富CO2的响应

 胡杨（Populus euphratica Oliv.）叶形多变化,大致归纳为杨树叶（卵圆形叶）和柳树叶（披针形叶）两大类。在内蒙古额济纳旗胡杨林自然保护区,选择成年树同时具有卵圆形叶和披针形叶的标准株,将枝条拉至同一高度,通过活体测定,比较了其光合特征、水分利用效率及对CO2加富的响应。结果表明：在目前大气CO2浓度下,当光强为1 000 μmol·m－2·s－1时,卵圆形叶（成年树主要叶片）（A）和披针形叶（成年树下部萌条叶片）(B)的净光合速率（Pn）分别为16.40 μmol CO2·m－2·s－1和9.38 μmol CO2·m－2·s－1;水分利用效率（WUE）分别为1.52 mmol CO2·mol－1 H2O和1.18 mmol CO2·mol－1 H2O;A的光饱和点和补偿点分别为1 600 μmol·m－2·s－1和79 μmol·m－2·s－1,B的相对应值则为1 500 μmol·m m－2·s－1和168 μmol·m－2·s－1。当CO2浓度加富到450 μmol·mol－1时,A的光饱和点升高了150 μmol·m－2·s－1,光补偿点降低了36 μmol·m－2·s－1;而B的光饱和点降低了272 μmol·m－2·s－1,光补偿点则升高了32 μmol·m－2·s－1。这表明,柳树叶的光合效率较低,以维持生长为主;随着树体长大,柳树叶难以维系其生长,出现杨树叶,杨树叶更能耐大气干旱,光合效率高,通过积累光合产物,使胡杨在极端逆境下得以生存并能达到较高的生长量,这就是胡杨从幼苗到成年树叶形变化的原因。随着CO2加富,两种叶片表现出截然相反的响应,柳树叶的光合时间缩短,光能利用率减小;而杨树叶的光合时间延长,光能利用率提高。如果地下水位下降,近地层空气变干燥,或随着大气CO2浓度升高,气候变暖,柳树叶可能会逐渐减少以至消失。     

Chloroplast Movement in the Shade Plant Tradescantia albiflora Helps Protect Photosystem II against Light Stress

The role of high-light-induced chloroplast movement in the photoprotection of the facultative shade plant Tradescantia albiflora was investigated by comparison with pea (Pisum sativum L.) leaves, both grown in 50 [mu]mol photons m-2 s-1. Photoinactivation of photosystem II (PSII) in vivo was induced in 1.1% CO2 by varying either duration (0-2 h) of illumination (fixed at 1800 [mu]mol m-2 s-1) or irradiance (0-3000 [mu]mol m-2 s-1) at a fixed duration (1 h) after infiltration of leaves with water or lincomycin (an inhibitor of chloroplast-encoded protein synthesis). At all photon exposures, PSII of T. albiflora leaves showed a greater resistance to light stress than pea leaves, although both utilization of absorbed light by photosynthesis and psbA gene product synthesis were smaller than for pea leaves. This greater tolerance was not due to differences in PSII antenna size or the index of susceptibility of PSII to light stress, because these two parameters were comparable in both plants. However, the transmittance increase mediated by chloroplast movement was greater in T. albiflora than pea, resulting in a 10% decrease of absorbed light at high light. We suggest that the greater tolerance of PSII against light stress in T. albiflora may be partly ascribed to its light-induced chloroplast rearrangement.     

Study on Leaf Anatomy and Photosynthesis of Cymbidium sinense

The leaf surface of Cymbidium sinense(Andr.) Willd was covered with cuticle and wax. The stomata were distributed in the dorsum of the leaf, the density being 100–130 mm-2 There was a stomatal cover on each stoma. The mesophyll was not differentiated into spongy tissue and palisade tissue. No chloroplast was observed in the vascular bundle sheath cells. The chloroplast in the mesophyll cells had well developed grana, with lightly stacked thylakoids and osmiophilic granules. The highest quantum yield of functional leaf was 0.082. The light compensation point of photosynthesis was about 5 μE·m-2·s-1, the light saturation point was about 200 μE·m-2·s-1. The photosynthetic ra,e of Cymbidium sinense was very low, generally 2.0–2.6 μmol CO2· m-2·s-1. The optimum temperature of photosynthesis of one-year-old leaf was 25℃. The photosynthe,ic rate of the three-year-old leaf declined with temperature rise. The ratio of chlorophyll a/b was about 2.7. The CO2 compensation point of photosynthesis was 105–220 ppm. All these data show that Cymbidium sinense belongs to the typical shade plants with low photosynthetic rate and high CO2 compensation point that explains that the growth of Cymbidium sinense is slow in nature.     

Effect of local irradiance on CO(2) transfer conductance of mesophyll in walnut

The acclimation responses of walnut leaf photosynthesis to the irradiance microclimate were investigated by characterizing the photosynthetic properties of the leaves sampled on young trees (Juglans nigraxregia) grown in simulated sun and shade environments, and within a mature walnut tree crown (Juglans regia) in the field. In the young trees, the CO(2) compensation point in the absence of mitochondrial respiration (Gamma*), which probes the CO(2) versus O(2) specificity of Rubisco, was not significantly different in sun and shade leaves. The maximal net assimilation rates and stomatal and mesophyll conductances to CO(2) transfer were markedly lower in shade than in sun leaves. Dark respiration rates were also lower in shade leaves. However, the percentage inhibition of respiration by light during photosynthesis was similar in both sun and shade leaves. The extent of the changes in photosynthetic capacity and mesophyll conductance between sun and shade leaves under simulated conditions was similar to that observed between sun and shade leaves collected within the mature tree crown. Moreover, mesophyll conductance was strongly correlated with maximal net assimilation and the relationships were not significantly different between the two experiments, despite marked differences in leaf anatomy. These results suggest that photosynthetic capacity is a valuable parameter for modelling within-canopies variations of mesophyll conductance due to leaf acclimation to light.     

Leaf area and photosynthesis of newly emerged trifoliolate leaves are regulated by mature leaves in soybean

Leaf anatomy and the stomatal development of developing leaves of plants have been shown to be regulated by the same light environment as that of mature leaves, but no report has yet been written on whether such a long-distance signal from mature leaves regulates the total leaf area of newly emerged leaves. To explore this question, we created an investigation in which we collected data on the leaf area, leaf mass per area (LMA), leaf anatomy, cell size, cell number, gas exchange and soluble sugar content of leaves from three soybean varieties grown under full sunlight (NS), shaded mature leaves (MS) or whole plants grown in shade (WS). Our results show that MS or WS cause a marked decline both in leaf area and LMA in newly developing leaves. Leaf anatomy also showed characteristics of shade leaves with decreased leaf thickness, palisade tissue thickness, sponge tissue thickness, cell size and cell numbers. In addition, in the MS and WS treatments, newly developed leaves exhibited lower net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (E), but higher carbon dioxide (CO ₂ ) concentration in the intercellular space (Ci) than plants grown in full sunlight. Moreover, soluble sugar content was significantly decreased in newly developed leaves in MS and WS treatments. These results clearly indicate that (1) leaf area, leaf anatomical structure, and photosynthetic function of newly developing leaves are regulated by a systemic irradiance signal from mature leaves; (2) decreased cell size and cell number are the major cause of smaller and thinner leaves in shade; and (3) sugars could possibly act as candidate signal substances to regulate leaf area systemically.     

北方粳稻光合速率、气孔导度对光强和CO2浓度的响应

 以东北地区主栽的粳稻（Oryza sativa var. japonica）品种为对象,用美国LI-cor公司生产的Li 6400光合作用测定仪控制光强、CO2浓度和温度等环境条件,阐述了光合作用和气孔导度对光和CO2浓度的响应特征及其耦合关系。结果表明,光合速率随光强或CO2浓度的提高而增大,均遵循米氏响应;在不同CO2浓度下,表观量子效率随CO2浓度的提高而增大,但CO2浓度达到800 μmol•mol－1以上时,表观量子效率有所减小;在不同光强下,表观羧化效率也随光的增强而增大,但光强达到1 600 μmol•m-2•s-1以上时,表观羧化效率也有所减小;在光强和CO2浓度协同作用下,光合速率的响应遵循双底物的米氏方程,在光强和CO2浓度均趋于饱和时,北方粳稻（品种：辽粳294）剑叶的潜在最大光合速率为71.737 8 μmol•m-2•s-1,表观量子效率为0.056 0 μmolCO2•μmol-1 photons,表观羧化效率为0.103 1 μmol•m-2•s-1/μmol•mol－1。气孔导度也随光的增强而增大,对光强的响应规律也可以用Michaelis-Menten曲线模拟,而叶面CO2浓度的提高会使气孔导度减小,气孔导度（Gs）对叶面CO2浓度（Cs）的响应可以用Gs=Gmax,c/(1+Cs/Cs0)的双曲线方程模拟。在光强(PFD)和CO2浓度协同作用下,气孔导度可以用式Gs=Gmax(PFD/PFDc)/［(1+PFD/PFDc)(1+Cs/Cs0)］+Gct估算,当CO2浓度趋于0而光强趋于饱和时,北方粳稻的潜在最大气孔导度（Gmax）为0.670 9 mol•m-2•s-1。在光强和CO2浓度协同作用下,Ball-Berry模型及其修正形式依然能很好地表达气孔导度-光合速率的耦合关系,并且用叶面饱和水汽压差（Ds）修正耦合关系中的相对湿度可以提高模拟精度。     

Evidence that carbon dioxide enrichment alleviates ureide-induced decline of nodule nitrogenase activity

The hypothesis that elevated [CO(2)] alleviates ureide inhibition of N(2)-fixation was tested. Short-term responses of the acetylene reduction assay (ARA), ureide accumulation and total non-structural carbohydrate (TNC) levels were measured following addition of ureide to the nutrient solution of hydroponically grown soybean. The plants were exposed to ambient (360 micromol mol(-1)) or elevated (700 micromol mol(-1)) [CO(2)]. Addition of 5 and 10 mM ureide to the nutrient solution inhibited N(2)-fixation activity under both ambient and elevated [CO(2)] conditions. However, the percentage inhibition following ureide treatment was significantly greater under ambient [CO(2)] as compared with that under elevated [CO(2)]. Under ambient [CO(2)] conditions, ARA was less than that under elevated [CO(2)] 1 d after ureide treatment. Under ambient [CO(2)], the application of ureide resulted in a significant accumulation of ureide in all plant tissues, with the highest concentration increases in the leaves. However, application of exogenous ureide to plants subjected to elevated [CO(2)] did not result in increased ureide concentration in any tissues. TNC concentrations were consistently higher under elevated [CO(2)] compared with those under ambient [CO(2)]. For both [CO(2)] treatments, the application of ureide induced a significant decrease of TNC concentrations in the leaves and nodules. For both leaves and nodules, a negative correlation was observed between TNC and ureide levels. Results indicate that product(s) of ureide catabolism rather than tissue ureide concentration itself are critical in the regulation of N(2)-fixation.     

Salinity tolerance of 'Valencia' orange trees on rootstocks with contrasting salt tolerance is not improved by moderate shade

The effects of shading in combination with salinity treatments were studied in citrus trees on two rootstocks with contrasting salt tolerance to determine if shading could reduce the negative effects of salinity stress. Well-nourished 2-year-old 'Valencia' orange trees grafted on Cleopatra mandarin (Cleo, relatively salt tolerant) or Carrizo citrange (Carr, relatively salt sensitive), were grown either under a 50% shade cloth or left unshaded in full sunlight. Half the trees received no salinity treatment and half were salinized with 50 mM Cl- during two 9 week salinity periods in the spring and autumn interrupted by an 11 week rainy period. The shade treatment reduced midday leaf temperature and leaf-to-air vapour pressure deficit regardless of salinity treatments. In non-salinized trees, shade increased midday CO2 assimilation rate (A(CO2)) and stomatal conductance, but had no effect on leaf transpiration (E(lf)). Shade also increased leaf chlorophyll and photosynthetic water use efficiency (A(CO2)/E(lf)) in leaves on both rootstocks and increased total plant dry weight in Cleo. The salinity treatment reduced leaf growth and leaf gas exchange parameters. Shade decreased Cl- concentrations in leaves of salinized Carr trees, but had no effect on leaf or root Cl- of trees on Cleo. There were no significant differences in leaf gas exchange parameters of shaded and unshaded salinized plants but the growth reduction from salinity stress was actually greater for shaded than for unshaded trees. Shaded trees on both rootstocks had higher leaf Na+ than unshaded trees after the first salinity period, and this shade-induced elevated leaf Na+ persisted after the second salinity period in trees on Carr. Thus, shading did not alleviate the negative effects of salinity on growth and Na+ accumulation.     

Manipulation of light and CO2 environments of the primary leaves of bean (Phaseolus vulgaris L.) affects photosynthesis in both the primary and the first trifoliate leaves: involvement of systemic regulation.

Possible involvement of systemic regulation of the photosynthetic properties of young leaves by the local environments and/or photosynthate production of the mature leaves were examined using Phaseolus vulgaris plants. When primary leaves (PLs) were treated with air containing 150 microL CO2 L(-1) with the other plant parts in ambient air at a photosynthetic photon flux density (PPFD) of 300 micromol photon m(-2) s(-1), decreases in the photosynthetic rate measured at 360 microL CO2 L(-1) and a PPFD of 300 micromol photon m(-2) s(-1) (A360) were markedly retarded in both PLs and the first trifoliate leaves (TLs) as compared to plants treated with 400 microL CO2 L(-1). Conversely, when PLs were treated with 1000 microL CO2 L(-1), decreases in A360 were accelerated in both PLs and TLs. Shading of PLs accelerated the decrease in PL A360, and delayed the decrease in TLs. In the CO2 treatments, changes in A360 in TLs were mainly attributed to the changes in ribulose bisphosphate (RuBP) carboxylation rate, while the shading of PLs caused increases in both the RuBP carboxylation and regeneration rates in TLs. The ribulose 1.5-bisphosphate carboxylase/oxygenase (Rubisco) activity on chlorophyll basis, an indicator of sun/shade acclimation, differed both among PLs and among TLs in accordance with the redox state of photosystem II (PSII) in PLs. Although carbohydrate contents of TLs were not affected by any manipulation of PLs, changes in the photosynthetic capacities of TLs acted to compensate for changes in PL photosynthesis. These results clearly indicate that the CO2 and shade treatments of PLs not only affect photosynthetic properties of the PLs themselves, but also systemically affected the photosynthetic properties of TLs. Possible roles of the redox state and photosynthate concentration in PLs in regulation of photosynthesis in PLs and TLs are discussed.     

Structure and Photosynthetic Characteristics of Awns of Wheat and Barley

The surface and the cross section of awns of wheat and barley were examined by scanning electron microscopy,ultrastructure of cells were observed under a transmisson electron microscope and the photosynthetic rates were measured with an oxygen, electrode and infra-red CO2 analyser. The main results were as follows :The cross section of wheat awn appeared to be acutely trianglular whereas that of barley awn was obtusely triangular. There were rows of stomota on either side of epidermis in both wheat and barley awns. Under the stomatic band there were green tissues. The green cells in the awn were differentiated from the parenchyma cells . The mature green cells possessed papillae which were rich in chloroplasts and mitochondria. The tamella system in chloroplasts was well developed and contained many starch grains. There were three vascular bundles in each awn. The sheath cells near the green tissues contained chloroplasts. The photosynthate in the green cells might pass through the sheath cells and companion cells to sieve elements. The highest photosynthetic rate of the awn was seen at the flowering stage ,reaching about 20 μmol CO2·m-2·s-1. The light compensation point was 70—80 μE·m-2· s-1. The light saturation point was about 1500 μE·m-2·s-1. The CO2 compensation point was 50—60 ppm and the CO2 saturation point was about 900ppm . The photosynthetic rate and stomatal conductance were easily effected by CO2 concentration, light intensity and the duration of illumination . There was a positive correlation between the photosynthetic rate and the chloro-phyll content in the awns. The CO2-releasing rate in photorespiration of awn was about 4–5 μmol CO2·m-2·s-1.