亚热带季雨林植物罗伞气体交换对光质的反应

亚热带季雨林林下阴生植物罗伞(Ardisia quinquegona)叶片的气体交换速率(PN.μmol.m~(-2),s~(-1))随光强(PFD,μmol,m~(-2),s~(-1))增高而增大。在光强低于80μmol,m~(-2),s~(-1),PN=29.21PFD×10~(-3)+0.36。在光强150μmol,m~(-2),s~(-1)对出现气体交换的光饱和现象。在低光强下,气孔传导率(G,m mol,m~(-2),s~(-1)与光强(m mol,m~(-2),s~(-1)的关系为G=265.6 PFD+4.6。在低光强下。开阔地的阳生灌木桃金娘(Rhodmyrtus tomentosa)的气体交换速率和气孔传导率与光强关系曲线的直线部分斜率皆较罗伞的低,在红光上,罗伞叶片气体交换速率(μmol,m~(-2),s~(-1)与光强(μmol,m~(-2),s~(-1)的关系为PN=32.4 PFD×10~(-3)-0.04。气孔传导率(m mol,m~(-2),s~(-1)与光强(m mol,m~(-2),s~(-1)的关系为G=339.08 PFD+7.37。同时气体交换速率的饱和红光光强亦较白光的高。在蓝光光强低时,气体交换速率(μmol,m~(-2),s~(-1))与光强(μmol,m~(-2),s~(-1))的关系为PN=13.54 PFD×10~(-3)—0.17,而气孔传导率(m mol,m~(-2),s~(-1))与光强(mμmol,m~(-2),s~(-1))的关系为G=80.5 PFD+4.35。在低的蓝光下,体交换速率和气孔传导率与光强关系曲线的直线部分斜率显著较在白光和红光下的低。罗伞叶片气体交换对红光的反应敏感。     

Study of the senescence process in primary leaves of sunflower (Helianthus annuus L.) plants under two different light intensities

Different parameters that vary during leaf development may be affected by light intensity. To study the influence of different light intensities on primary leaf senescence, sunflower (Helianthus annuus L.) plants were grown for 50 days under two photon flux density (PFD) conditions, namely high irradiance (HI) at 350 μmol(photon) m^?2 s^?1 and low irradiance (LI) at 125 μmol(photon) m^?2 s^?1. Plants grown under HI exhibited greater specific leaf mass referred to dry mass, leaf area and soluble protein at the beginning of the leaf development. This might have resulted from the increased CO₂ fixation rate observed in HI plants, during early development of primary leaves. Chlorophyll a and b contents in HI plants were lower than in LI plants in young leaves. By contrast, the carotenoid content was significantly higher in HI plants. Glucose concentration increased with the leaf age in both treatments (HI and LI), while the starch content decreased sharply in HI plants, but only slightly in LI plants. Glucose contents were higher in HI plants than in LI plants; the differences were statistically significant (p<0.05) mainly at the beginning of the leaf senescence. On the other hand, starch contents were higher in HI plants than in LI plants, throughout the whole leaf development period. Nitrate reductase (NR) activity decreased with leaf ageing in both treatments. However, the NR activation state was higher during early leaf development and decreased more markedly in senescent leaves in plants grown under HI. GS activity also decreased during sunflower leaf ageing under both PFD conditions, but HI plants showed higher GS activities than LI plants. Aminating and deaminating activities of glutamate dehydrogenase (GDH) peaked at 50 days (senescent leaves). GDH deaminating activity increased 5-fold during the leaf development in HI plants, but only 2-fold in LI plants. The plants grown under HI exhibited considerable oxidative stress in vivo during the leaf senescence, as revealed by the substantial H₂O₂ accumulation and the sharply decrease in the antioxidant enzymes, catalase and ascorbate peroxidase, in comparison with LI plants. Probably, systemic signals triggered by a high PFD caused early senescence and diminished oxidative protection in primary leaves of sunflower plants as a result.     

苋菜的光合特性

宽菜Amaranthus cruentus cv.生长在调控的温室条件。在光强0至800μmol.m~(-2)S~(-1),光合速率(PN,μmol.CO_2m~(-2)、s~(-1))随光强(PFD,μmol、m~(-2)、s~(-1))增高而增大,其关系为PN=56.82 PFD×10~(-3)—2.13。光补偿点为60μmol.m~(-2)、s~(-1)。叶片在1400 μmol.m~(-2)、s~(-1)达到光合光饱和点。在叶温35℃,叶片/空气水蒸汽压陡度20 m Pa、Pa~(-1)和外界CO_2浓度340μ1、1~(-1),光饱和光合速率为51.63±4.90μ mol.CO_2、m~(-2)、S~(-1)。在光强0至600μmol.m~(-2)、s~(-1),气孔传道率随光强增高而增大。光强高于600μmol.m~(-2)、s~(-1),气孔传道率变化较小。细胞间CO_2浓度为120μ1.1~(-1)由于细胞间CO_2浓度在光合速率——CO_2关系曲线的转折点,可能表明光合作用不受气孔限制。结果表明,苋菜适于高光强环境生长,在干旱条件下具有高的光合速率。     

Photosynthesis but not CAM responded flexibly to changes in irradiance in Plectranthus marrubioides (Lamiaceae)

Well-watered plants of Plectranthus marrubioides Benth., a crassulacean acid metabolism (CAM) species naturally inhabiting sun exposed succulent places, were grown at photosynthetically active photon flux densities (PPFD) of either 150 (LL) or 300 (HL) μmol m-2 s-1 in a controlled environment. Photosynthesis of LL plants was saturated by irradiance of ca. 500 μmol m-2 s-1 while in HL plants saturation was not reached up to 1200 μmol m-2 s-1 and photosynthetic capacity was nearly 50 % higher than in the LL plants. However, maximum photon yield was 55 % lower and compensation irradiance was 25 % higher in LL plants. The former also had larger, more succulent leaves, i.e., they were morphologically more sun adapted. On the other hand, nocturnal accumulation of malic and citric acid, nighttime CO2 gain, and the low relative carbon recycling were independent of the prevailing PPFD. Furthermore, photosynthetic performance was flexibly and reversibly adjusted in HL plants after transfer to 600 or 150 μmol m-2 s-1 while nocturnal CO2 uptake was not influenced. Photosynthesis showed a high acclimation potential to high PPFD and patterns of gas exchange became more C3-like the higher the irradiance was, without a direct effect on CAM in P. marrubioides.     

Contribution of the adaxial and abaxial surfaces of olive leaves to photosynthesis

Leaves of olive cultivars Frantoio and Maurino were irradiated with different irradiances from above, from below, or simultaneously from both directions to determine the contribution of the abaxial and adaxial leaf surfaces to photosynthesis. In both cultivars, irradiation of both sides of the leaf caused increases in net photosynthetic rate (P _N) and apparent quantum yield compared to irradiating only one surface with the equal photosynthetic photon flux density (PPFD), but the PPFD needed to saturate P _N decreased. At high and medium PPFD the P _N determined at irradiating both leaf surfaces was less than the sum obtained at irradiation of only the upper or the lower surface with the same PPFD. At PPFD higher than 1000 μmol m-2 s-1 in cv. Frantoio and 1200 μmol m-2 s-1 in cv. Maurino, P _N did not vary. At low PPFD (<200 μmol m-2 s-1), P _N at irradiating the adaxial and abaxial leaf surfaces simultaneously was about the sum of the values obtained by irradiating the upper and lower surfaces separately. Consequently the compensation irradiance was reduced from about 50 μmol m-2 s-1 to about 30 μmol m-2 s-1 when irradiating both leaf surfaces. The natural leaf orientation of the olive cultivar influenced the utilization of radiant energy by the abaxial surface. This revised version was published online in September 2006 with corrections to the Cover Date.     

Leaf anatomy during leaf development of photoautotrophically <Emphasis Type="Italic">in vitro</Emphasis>-grown tobacco plants as affected by growth irradiance

Tobacco (Nicotiana tabacum L.) plants were cultured in vitro photoautotrophically at three levels of irradiance (PAR 400–700 nm): low (LI, 60 μmol m⁻² s⁻¹), middle (MI, 180 μmol m⁻² s⁻¹) and high (HI, 270 μmol m⁻² s⁻¹). Anatomy of the fourth leaf from bottom was followed during leaf development. In HI and MI plants, leaf area expansion started earlier as compared to LI plants, and both HI and MI plants developed some adaptations of sun species: leaves were thicker with higher proportion of palisade parenchyma to spongy parenchyma tissue. Furthermore, in HI and MI plants palisade and spongy parenchyma cells were larger and relative abundance of chloroplasts in parenchyma cells measured as chloroplasts cross-sectional area in the cell was lower than in LI plants. During leaf growth, chloroplasts crosssectional area in both palisade and spongy parenchyma cells in all treatments considerably decreased and finally it occupied only about 5 to 8 % of the cell cross-sectional area. Thus, leaf anatomy of photoautotrophically in vitro cultured plants showed a similar response to growth irradiance as in vivo grown plants, however, the formation of chloroplasts and therefore of photosynthetic apparatus was strongly impaired.     

Decline in photosynthesis as related to alterations in chloroplast ultrastructure of a cotton leaf during ontogeny

Field studies were conducted to investigate ontogenic changes in leaf photosynthesis and chloroplast ultrastructure of a single cotton (Gossypium hirsutum L.) leaf subtending the fruit. A 20-d old leaf was the most physiologically active with net photosynthetic rate (PN) of 16.5 mol m-2 s-1 and nitrogen (N) concentration of 168 mmol m-2. These values declined with leaf age and a close relationship existed between them. Concurrent with declines in PN, ultrastructural alterations occurred in the chloroplast: the 20-d old leaf had increased grana number and thylakoids per granum and a few plastoglobuli. Afterwards, the grana number and thylakoids per granum declined with leaf age indicating disintegrated grana and stroma lamellae. Concomitant with disintegrated membrane system was the presence of numerous large plastoglobuli. The PN was closely related to grana number and thylakoids per granum suggesting that the decline in PN with leaf age was associated with ultrastructural changes in the chloroplast.     

A role for leaf epidermis in the control of leaf size and the rate and extent of mesophyll cell division

Little is known about the control of leaf size in plants, yet there must be mechanisms by which organ size is measured. Because the control of leaf size extends beyond the action of individual genes or cells, an understanding of the role of leaf cell layers in the determination of leaf size is warranted. Following the construction of graft chimeras composed of small- and large-leaf genotypes of Nicotiana, bilateral leaf blade asymmetry was observed on leaves possessing either a genetically larger or smaller epidermis on one side of the midrib. Although cell size was unaffected by the genotype of the epidermis, the rate and extent of cell division in leaf epidermis altered the rate and extent of cell division in mesophyll and affected leaf size. The data presented neither prove nor disprove whether the mesophyll impacts epidermal cell division but provide the first unequivocal evidence that the extent of cell division in the leaf epidermis alters the extent of cell division in the mesophyll and is a factor regulating blade expansion and ultimate leaf size.     

Effects of reduced irradiance on hydraulic architecture and water relations of two olive clones with different growth potentials

The hydraulic architecture and water relations of two olive genotypes, ‘Leccino Dwarf’ (LD) and ‘Leccino Minerva’ (LM) growing at two irradiance levels i.e. full sunlight irradiance (HI) and 50% sunlight irradiance (LI) were studied. The two clones showed similar plant hydraulic conductances (K_plant) and similar conductance of roots and leaves (K_root and K_leaf) when growing at equal irradiance levels. However, both K_plant and K_root were significantly lower in LI plants than in HI ones. On the contrary, K_leaf was unaffected by the light regime. One-year-old twigs of LI plants produced longer xylem conduits but lower average diameter of conduits and less conduits per unit xylem cross-sectional area compared to HI plants. As a consequence total conductive cross-sectional area of twigs was computed to be about 16% smaller in LI individuals than in HI ones.The LM genotype resulted potentially more vulnerable to cavitation than the LD one, although shading did not influence this variable. Shading influenced root biomass negatively with stronger reduction in LM genotype than in LD one. Although transpiration rates were substantially lower in shaded than in HI plants minimum diurnal leaf water potential was about ?1.2 MPa for both clones regardless the irradiance regime. Our conclusion is that the hydraulic efficiency of both olive clones was adjusted to meet the evaporative demand imposed by the irradiance regime with consequently similar equal hydraulic sufficiency.     

Analysis of Qualitative Contribution of Assimilatory and Non-Assimilatory De-Excitation Processes to Adaptation of Photosynthetic Apparatus of Barley Plants to High Irradiance

The adaptation of barley (Hordeum vulgare L. cv. Akcent) plants to low (LI, 50 µmol m^–2 s^–1) and high (HI, 1000 µmol m^–2 s^–1) growth irradiances was studied using the simultaneous measurements of the photosynthetic oxygen evolution and chlorophyll a (Chl a) fluorescence at room temperature. If measured under ambient CO₂ concentration, neither increase of the oxygen evolution rate (P) nor enhancement of non-radiative dissipation of the absorbed excitation energy within photosystem 2 (PS2) (determined as non-photochemical quenching of Chl a fluorescence, NPQ) were observed for HI plants compared with LI plants. Nevertheless, the HI plants exhibited a significantly higher proportion of Q_A in oxidised state (estimated from photochemical quenching of Chl a fluorescence, q_P), by 49–102 % at irradiances above 200 µmol m^–2 s^–1 and an about 1.5 fold increase of irradiance-saturated PS2 electron transport rate (ETR) as compared to LI plants. At high CO₂ concentration the degree of P stimulation was approximately three times higher for HI than for LI plants, and the irradiance-saturated P values at irradiances of 2 440 and 2 900 µmol m^–2 s^–1 were by 130 and 150 % higher for HI plants than for LI plants. We suggest that non-assimilatory electron transport dominates in the adaptation of the photosynthetic apparatus of barley grown at high irradiances under ambient CO₂ rather than an increased NPQ or an enhancement of irradiance-saturated photosynthesis.     

Short-term effect of elevated CO2 concentration and high irradiance on the antioxidant enzymes in bean plants

The effect of short-term exposure to elevated CO₂ concentration and high irradiance on the activity of superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidases (GPX) and catalase (CAT), and on the extent of the lipid peroxidation was studied in bean (Phaseolus vulgaris L.) plants. Plants were exposed for 4 d (8 h a day) to irradiance of 100 (LI) or 1000 (HI) μmol m⁻² s⁻¹ at ambient (CA, 350 μmol mol⁻¹) or elevated (CE, 1300 μmol mol⁻¹) CO₂ concentration. Four-day exposure to CE increased the leaf dry mass in HI plants and RuBPC activity and chlorophyll content in LI plants. Total soluble protein content, leaf dry matter and RuBPC activity were higher in HI than in LI plants, although the HI and CE increased the contents of malonyldialdehyde and H₂O₂. Under CA, exposure to HI increased the activity of APX and decreased the total SOD activity. Under CE, HI treatment also activated APX and led to reduction of both, SOD and GPX, enzymes activities. CE considerably reduced the CAT activity at both irradiances, possibly due to suppressed rate of photorespiration under CE conditions.     

Changes in net photosynthetic rate and chlorophyll fluorescence in potato leaves induced by water stress

Net rates of photosynthesis (PN) saturated by irradiance of >500 mol m-2 s-1 (PAR) significantly decreased in water-stressed potato (Solanum tuberosum L. cv. Kufri Sindhuri) plants. The quantum yield of photochemical energy conversion (Fv/Fm), relative electron transport rate (ETR), and photochemical quenching (Qp) exhibited a parallel decline at high irradiance. A slight decrease in relative water content (RWC) was accompanied by a drastic decline in leaf water potential (w) from -0.2 to -1.0 MPa. Dehydrated leaves showed an increase in the amount of total soluble sugars per unit leaf area which inhibited the photosynthesis in a feedback manner. After rewatering, PN and Fv/Fm were restored to the values of control plants within 24 h, and the restoration was accompanied by a proportionate lowering of content of total soluble sugars in the leaves.     

Effects of CO2 and photosynthetic photon flux on yield, gas exchange and growth rate of Lactuca sativa L. 'Waldmann's Green.'

Enrichment of CO2 to 46 mmol m-3 (1000 mm3 dm-3) at a moderate photosynthetic photon flux (PPF) of 450 micromoles m-2 s-1 stimulated fresh and dry weight gain of lettuce leaves 39% to 75% relative to plants at 16 mmol m-3 CO2 (350 mm3 dm-3). Relative growth rate (RGR) was stimulated only during the first several days of exponential growth. Elevating CO2 above 46 mmol m-3 at moderate PPF had no further benefit. However, high PPF of 880-900 micromoles m-2 s-1 gave further, substantial increases in growth, RGR, net assimilation rate (NAR) and photosynthetic rate (Pn), but a decrease in leaf area ratio (LAR), at 46 or 69 mmol m-3 (1000 or 1500 mm3 dm-3) CO2, the differences being greater at the higher CO2 level. Enrichment of CO2 to a supraoptimal level of 92 mmol m-3 (2000 mm3 dm-3) at high PPF increased leaf area and LAR, decreased specific leaf weight, NAR and Pn and had no effect on leaf, stem and root dry weight or RGR relative to plants grown at 69 mmol m-3 CO2 after 8 d of treatment. The results of the study indicate that leaf lettuce growth is most responsive to a combination of high PPF and CO2 enrichment to 69 mmol m-3 for several days at the onset of exponential growth, after which optimizing resources might be conserved.     

Enhanced photochemical light utilization and decreased chilling-induced photoinhibition of photosystem II in cotton overexpressing genes encoding chloroplast-targeted antioxidant enzymes

The aim of this study was to determine whether increases in stromal superoxide dismutase (SOD; EC 1.15.1.1), ascorbate peroxidase (APX; EC 1.11.1.11) and glutathione reductase (GR; EC 1.6.4.2) via transformation could reduce photosystem (PS) II photoinhibition at low temperature for cotton (Gossypium hirsutum L.) plants and to determine by what mechanism this protection may be realized. During 3-h exposures of lincomycin-treated leaf discs to 10 degrees C and a photon flux density of 500 &mgr;mol m-2 s-1, all transgenic plants exhibited significantly greater PSII activity and O2 evolution than did wild-type plants. Also, the rate constant of PSII photoinactivation was significantly lower for all transgenic plants than for wild-type plants. No significant differences existed between genotypes in non-photochemical quenching of chlorophyll a fluorescence and the regulated component of the thermal dissipation of excitation energy. The relationship between changes in variable to maximum chlorophyll fluorescence (Fv/Fm) and the time-dependent averaged excessive light exposure was similar for all genotypes. This observation excluded the possibility that differences in PSII photodamage were due to improvements in the direct protection of PSII from active oxygen by antioxidant enzyme overproduction. Similar decreases in Fv/Fm during the stress treatment for all genotypes when leaves were pre-treated with 3-(3',4'-dichlorophenyl)-1,1-dimethylurea (DCMU) suggested that the effect of overproduction involved events downstream of PSII in the electron transfer pathway. Since all transgenic plants exhibited a significantly higher photochemical quenching of chlorophyll fluorescence during the chilling treatment, we concluded that, under the conditions used in this study, the enhancement of the protection of PSII from photodamage by increasing the stromal antioxidant enzyme activity in cotton leaves was due to the maintenance of a higher rate of electron transport and, consequently, a lower reduction state of QA.     

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。     

Photosynthesis but not CAM responded flexibly to changes in irradiance in Plectranthus marrubioides (Lamiaceae)

Well-watered plants of Plectranthus marrubioides Benth., a crassulacean acid metabolism (CAM) species naturally inhabiting sun exposed succulent places, were grown at photosynthetically active photon flux densities (PPFD) of either 150 (LL) or 300 (HL) μmol m-2 s-1 in a controlled environment. Photosynthesis of LL plants was saturated by irradiance of ca. 500 μmol m-2 s-1 while in HL plants saturation was not reached up to 1200 μmol m-2 s-1 and photosynthetic capacity was nearly 50 % higher than in the LL plants. However, maximum photon yield was 55 % lower and compensation irradiance was 25 % higher in LL plants. The former also had larger, more succulent leaves, i.e., they were morphologically more sun adapted. On the other hand, nocturnal accumulation of malic and citric acid, nighttime CO2 gain, and the low relative carbon recycling were independent of the prevailing PPFD. Furthermore, photosynthetic performance was flexibly and reversibly adjusted in HL plants after transfer to 600 or 150 μmol m-2 s-1 while nocturnal CO2 uptake was not influenced. Photosynthesis showed a high acclimation potential to high PPFD and patterns of gas exchange became more C3-like the higher the irradiance was, without a direct effect on CAM in P. marrubioides. This revised version was published online in June 2006 with corrections to the Cover Date.     

Carbon,Nitrogen, and Nutrient Interactions in Beta vulgaris L. as Influenced by Nitrogen Source,NO3- versus NH4+

Sugar beets (Beta vulgaris L. cv F58-554H1) were grown hydroponically in a 16-h light, 8-h dark period (photosynthetic photon flux density of 0.5 mmol m-2 s-1) for 4 weeks from sowing in half-strength Hoagland nutrient solution containing 7.5 mM nitrate. Half of the plants were then transferred to 7.5 mM ammonium N; the rest remained in solution with 7.5 mM nitrate N. Upon transfer from nitrate to ammonium, the total N concentration decreased sharply in the fibrous roots and petiole/midribs and increased substantially in the leaf blades. This was because of the decreased nitrate concentrations in fibrous roots and petioles and a concomitant increase in amino acid/amide-N and protein N in leaf blades. Sugar beets acclimated to ammonium partly by a 2.5-fold increase in glutamine synthase activity in fibrous roots and a 1.7-fold increase in leaf blades. Rapid ammonium assimilation into glutamine consumed carbon skeletons, leading to a depletion of foliar starch, sucrose, and maltose. Ammonium treatment stimulated activities of some glycolytic/Krebs cycle enzymes, e.g. pyruvate dehydrogenase. Nitrate-fed leaf blades contained substantially larger concentrations of osmolytes (i.e. nitrate, cations, and sucrose), which may have contributed to the faster rates of leaf expansion in nitrate-fed compared to ammonium-fed plants.     

Photosystem II Excitation Pressure and Photosynthetic Carbon Metabolism in Chlorella vulgaris

Chlorella vulgaris grown at 5[deg]C/150 [mu]mol m-2 s-1 mimics cells grown under high irradiance (27[deg]C/2200 [mu]mol m-2 s-1). This has been rationalized through the suggestion that both populations of cells were exposed to comparable photosystem II (PSII) excitation pressures measured as the chlorophyll a fluorescence quenching parameter, 1 - qP (D.P. Maxwell, S. Falk, N.P.A. Huner [1995] Plant Physiol 107: 687-694). To assess the possible role(s) of feed-back mechanisms on PSII excitation pressure, stromal and cytosolic carbon metabolism were examined. Sucrose phosphate synthase and fructose-1,6-bisphosphatase activities as well as the ratios of fructose-1,6-bisphosphate/fructose-6-phosphate and sucrose/starch indicated that cells grown at 27[deg]C/2200 [mu]mol m-2 s-1 appeared to exhibit a restriction in starch metabolism. In contrast, cells grown at 5[deg]C/150 [mu]mol m-2 s-1 appeared to exhibit a restriction in the sucrose metabolism based on decreased cytosolic fructose-1,6- bisphosphatase and sucrose phosphate synthase activities as well as a low sucrose/starch ratio. These metabolic restrictions may feed-back on photosynthetic electron transport and, thus, contribute to the observed PSII excitation pressure. We conclude that, although PSII excitation pressure may reflect redox regulation of photosynthetic acclimation to light and temperature in C. vulgaris, it cannot be considered the primary redox signal. Alternative metabolic sensing/signaling mechanisms are discussed.     

Relationship between Photosynthetic Activity and Chlorophyll Content in an Isolated Quercus Ilex L. Tree during the Year

The relationship between chlorophyll (Chl) content and net photosynthetic rate (PN) in an isolated Quercus ilex tree, growing inside Villa Pamphili Park in Rome, was explored. The highest PN was in March, May, and September (10.1 mol m-2 s-1, maximum rate). PN decreased by 65 % (with respect to the yearly maximum) when leaf temperature reached 34 °C, and by 50 % when leaf temperature was 9 °C. The highest Chl contents were in April, October [1.47 g kg-1 (d.m.), maximum value], and December. The lowest Chl content was found in July (0.78 g kg-1). The decrease of PN in July was in close connection with the decrease of Chl content. On the contrary, the high Chl content during winter did not correspond with PN of this season. Discordances between Chl content and PN over the year influenced the regression analysis, which although positive did not show very high correlation coefficients (r = 0.7). The high Chl (a+b) content during most of the year indicated that the photosynthetic apparatus remained basically intact also during stress periods.     

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.