Comparison of photosynthetic activity of <Emphasis Type="Italic">Orychophragmus violaceus</Emphasis> and oil-seed rape

Orychophragmus violaceus, Brassica campestris cv. Chuanyou No.8, and Brassica juncea cv. Luzhousileng diurnal changes of net photosynthetic rate (P _N) and activities of carbonic anhydrase (CA) of leaves were studied. One uni-modal curve occurred at the diurnal changes of P _N in O. violaceus, but bimodal curves were found in B. campestris and B. juncea. Thus photosynthetic midday depression was not found in O. violaceus but in both Brassica species. Midday depression of P _N in O. violaceus was not related to high temperature or low humidity at midday but to the activity of CA.     

Effect of 28-homobrassinolide treatment on nickel toxicity in <Emphasis Type="Italic">Brassica juncea</Emphasis>

Plants of Brassica juncea L. cv. T-59 were supplied with 50 or 100 μM nickel (Ni₅₀, Ni₁₀₀) at 10 d after sowing (DAS), and sprayed with 28-homobrassinolide (HBR) at 20 DAS. The plants treated with Ni alone exhibited reduced growth, net photosynthetic rate, content of chlorophyll, and the activities of nitrate reductase (E.C.1.6.6.1) and carbonic anhydrase (E.C. 4.2.1.1) at observed 40 DAS, whereas, the contents of peroxidase (PER), catalase (CAT), and proline were increased. However, the spray of HBR partially neutralized the toxic effect of Ni on most of the parameters. Moreover, the treatment of HBR in association with either of the Ni concentration boosted the contents of PER and CAT in leaves and that of proline both in leaves and roots.     

Responses of Vigna radiata to Foliar Application of 28-Homobrassinolide and Kinetin

Effects of 28-homobrassinolide (HBR) and kinetin (KIN) on photosynthesis, nitrogen metabolism, and the seed yield were studied. The leaves of 25-d-old plants of Vigna radiata (L.) Wilczek were sprayed with 0.01, 1.0 or 100 M aqueous solution of KIN, or 0.0001, 0.01 or 1.0 M that of HBR. KIN and especially HBR increased the activities of nitrate reductase and carbonic anhydrase, chlorophyll and total protein contents and net photosynthetic rate in the leaves, and pod number and seed yield, at harvest.     

Photoautotrophic culture conditions and photosynthetic photon flux influence growth of <Emphasis Type="Italic">Lilium</Emphasis> bulblets <Emphasis Type="Italic">in vitro</Emphasis>

Summary Lilium Asiatic hybrid ‘Mona’ bulblets were cultured in vitro for 100 d under photoautotrophic (CO₂-enriched conditions and without sucrose in the medium) and heterotrophic (non-enriched CO₂ conditions and sucrose-supplemented medium) methods and under various levels of photosynthetic photon flux (PPF). Bulblet growth and net photosynthetic rate (NPR) were analyzed. CO₂₋ and PPF-enriched conditions enhanced the overall growth of bulblets, scale leaves, and roots. Heterotrophic conditions enhanced bulblet growth but higher PPF levels were inhibitory to the development of scale leaves. These results indicate the CO₂₋ and PPF-enriched conditions (photoautotrophic conditions) are beneficial for the production of high-quality bulblets of Asiatic hybrid lilies in vitro     

Effects of irradiance on photosynthetic characteristics and growth of <Emphasis Type="Italic">Mosla chinensis</Emphasis> and <Emphasis Type="Italic">M. scabra</Emphasis>

Photosynthetic and growth characteristics of Mosla chinensis and M. scabra were compared at three irradiances similar to shaded forest understory, forest edge, and open land. At 25 % full ambient irradiance, M. chinensis and M. scabra had similar photosynthetic characteristics, but saturation irradiance, compensation irradiance, and apparent quantum yield of M. chinensis were higher than those of M. scabra at full ambient irradiance and 70 % full ambient irradiance. At the same irradiance treatment, specific leaf area and leaf area ratio of M. chinensis were lower than those of M. scabra. Photon-saturated photosynthetic rate and water use efficiency of M. chinensis, however, were not significantly higher than those of M. scabra, and the leaf area and total biomass were lower than those of M. scabra. As a sun-acclimated plant, the not enough high photosynthetic capacity and lower biomass accumulation may cause that M. chinensis has weak capability to extend its population and hence be concomitant in the community.     

Comparative photosynthesis characteristics of <Emphasis Type="Italic">Calycanthus chinensis</Emphasis> and <Emphasis Type="Italic">Chimonanthus praecox</Emphasis>

Calycanthus chinensis is an endangered plant of the national second-grade protection of China restricted in a small area in Zhejiang Province. We studied parameters of photosynthesis, chlorophyll (Chl) contents, and Chl fluorescence (minimum fluorescence, F₀, maximum fluorescence, F_m, variable fluorescence, F_v, and F_v/F_m) of C. chinensis and Chimonanthus praecox. C. chinensis had lower compensation irradiance but higher saturation irradiance than C. praecox. Hence C. chinensis has more advantage in obtaining and utilizing photon energy and higher Chl content, and is more adaptive to higher temperature and propitious to thermal dissipation than C. praecox. In addition, C. chinensis produces abundant, well-preserved seed with a higher germination rate and a wider adaptability to temperature than C. praecox. Thus C. chinensis is prone to survival and viability, and gets rid of the endangered plant species of the national second-grade protection of China.     

Photosynthetic characteristics of <Emphasis Type="Italic">Hordeum,Triticum, Rumex</Emphasis>, and <Emphasis Type="Italic">Trifolium</Emphasis> species at contrasting altitudes

Photosynthetic characteristics were compared between plants of low altitude (LA) grown at LA (Palampur; 1 300 m) and at high altitude, HA (Kibber; 4 200 m), and plants naturally occurring at different altitudes (Palampur, 1 300 m; Palchan, 2 250 m; and Marhi, 3 250 m). Net photosynthetic rate (P _N) was not significantly different between altitudes. However, the slopes of the curve relating P _N to intercellular CO₂ concentration (C _i) were higher in plants at Palchan, Marhi, and Kibber compared to those at Palampur, indicating that plants had higher efficiency of carbon uptake (the initial slope of P _N/C _i curve is an indication) at HA. They had also higher stomatal conductance (g _s), transpiration rate, and lower water use efficiency at HA. g _s was insensitive to photosynthetic photon flux density (PPFD) for plants naturally occurring at Palampur, Palchan, and Marhi, whereas plants from LA grown at Palampur and Kibber responded linearly to increasing PPFD. Insensitivity of g _s to PPFD could be one of the adaptive features allowing wider altitudinal distribution of the plants.This research is supported by the Department of Biotechnology (DBT), Government of India vide grant number BT/PR/502/AGR/08/39/966-VI.     

Responses of the resurrection plant <Emphasis Type="Italic">Haberlea rhodopensis</Emphasis> to high irradiance

The effect of high irradiance (HI) during desiccation and subsequent rehydration of the homoiochlorophyllous desiccation-tolerant shade plant Haberlea rhodopensis was investigated. Plants were irradiated with a high quantum fluence rate (HI; 350 μmol m⁻² s⁻¹ compared to ca. 30 μmol m⁻² s⁻¹ at the natural rock habitat below trees) and subjected either to fast desiccation (tufts dehydrated with naturally occurring thin soil layers) or slow desiccation (tufts planted in pots in peat-soil dehydrated by withholding irrigation). Leaf water content was 5 % of the control after 4 d of fast and 19 d of slow desiccation. Haberlea was very sensitive to HI under all conditions. After 19 d at HI, even in well-watered plants there was a strong reduction of rates of net photosynthesis and transpiration, contents of chlorophyll (Chl) and carotenoids, as well as photosystem 2 activity (detected by the Chl fluorescence ratio R_Fd). Simultaneously, the blue/red and green/red fluorescence ratios increased considerably suggesting increased synthesis of polyphenolic compounds. Desiccation of plants in HI induced irreversible changes in the photosynthetic apparatus and leaves did not recover after rehydration regardless of fast or slow desiccation. Only young leaves survived desiccation.     

Drought tolerance in the Mediterranean species <Emphasis Type="Italic">Quercus coccifera,Quercus ilex,Pinus halepensis</Emphasis>, and <Emphasis Type="Italic">Juniperus phoenicea</Emphasis>

We investigated the strategies of four co-occurring evergreen woody species Quercus ilex, Quercus coccifera, Pinus halepensis, and Juniperus phoenicea to cope with Mediterranean field conditions. For that purpose, stem water potential, gas exchange, chlorophyll (Chl) fluorescence, and Chl and carotenoid (Car) contents were examined. We recognized two stress periods along the year, winter with low precipitation and low temperatures that led to chronic photoinhibition, and summer, when drought coincided with high radiation, leading to an increase of dynamic photoinhibition and a decrease of pigment content. Summer photoprotection was related to non-photochemical energy dissipation, electron flow to alternative sinks other than photosynthesis, decrease of Chl content, and proportional increase of Car content. Water potential of trees with deep vertical roots (Q. coccifera, Q. ilex, and P. halepensis) mainly depended on precipitation, whereas water potential of trees with shallow roots (J. phoenicea) depended not only on precipitation but also on ambient temperature.     

Ca<Superscript>2+</Superscript> reduces the effect of hypoxia in mosses <Emphasis Type="Italic">Mnium undulatum</Emphasis> and <Emphasis Type="Italic">Polytrichum commune</Emphasis>

Gametophores of mosses Mnium undulatum and Polytrichum commune were submerged in distilled water or in calcium chloride solution (0.9 mM Ca²⁺) to induce hypoxia. The net photosynthetic (P_N) and dark respiration rate (R_D) were measured in the air containing 300–400 μmol(CO₂)·mol⁻¹(air) and 0.21 mol(O₂)·mol⁻¹(air). P_N of M. undulatum gametophores decreased to 58 % of the control after 1-h submersion in water, whereas to 80 % of the control in P. commune gametophores. A smaller decrease in P_N was observed when the gametophores were immersed in CaCl₂ solution. In hypoxia, R_D in the tested mosses species was a little higher than in the control.     

Physiological comparisons of true leaves and phyllodes in <Emphasis Type="Italic">Acacia mangium</Emphasis> seedlings

We found differences between true leaves (TL) and phyllodes (Ph) during ontogeny of Acacia mangium plants as reflected in chlorophyll (Chl) and carotenoid contents, gas exchange, Chl fluorescence, and growth. The production of TL enhanced the relative growth rate of the A. mangium seedlings, allowing the plants to accumulate enough dry biomass for later growth, while the production of thicker Ph in the later growth stage of A. mangium could help plants to cope with higher irradiance in their natural growth conditions.     

<Emphasis Type="Italic">In vitro</Emphasis> direct organogenesis and regeneration of <Emphasis Type="Italic">Medicago sativa</Emphasis>

A rapid and efficient plant regeneration protocol for a wide range of alfalfa genotypes was developed via direct organogenesis. Through a successive excision of the newly developed apical and axillary shoots, a lot of adventitious buds were directly induced from the cotyledonary nodes when hypocotyl of explants were vertically inserted into modified Murashige and Skoog (MS) medium supplemented with 0.025 mg dm⁻³ thidiazuron (TDZ) and 3 mg dm⁻³ AgNO₃. When the lower part of shoots excised from explants were immersed into the liquid medium with 1.0 mg dm⁻³ α-naphthaleneacetic acid (NAA) for 2 min, and then transferred to hormone free half-strength MS medium, over 83.3 % of the shoots developed roots, and all plantlets could acclimatize and establish in soil. The protocol has been successfully applied to eight genotypes, with regeneration frequencies ranging from 63.8 to 82.5 %.     

Photosynthetic characteristics of an endangered species <Emphasis Type="Italic">Camellia nitidissima</Emphasis> and its widespread congener <Emphasis Type="Italic">Camellia sinensis</Emphasis>

Saturation (SI) and compensation (CI) irradiances [μmol(photon) m⁻² s⁻¹] were 383.00±18.40 and 12.95±0.42 for wild C. nitidissima (in mid-July) and 691.00±47.39 and 21.91±1.28 for wild C. sinensis, respectively. C. nitidissima is a shade tolerant species, whereas C. sinensis has a wide ecological range of adaptability to irradiance. Both wild and cultivated C. nitidissima demonstrated low maximum net photosynthetic rate, maximum carboxylation rate, maximum electron transfer rate, and SI, which indicated low photosynthesis ability of leaves that were unable to adapt to strong irradiance environment. Both C. nitidissima and C. sinensis demonstrated strong photosynthetic adaptabilty in new environments. Hence proper shading may raise photosynthetic efficiency of cultivated C. nitidissima and promote its growth.     

The impact of <Emphasis Type="Italic">trans</Emphasis>-zeatin <Emphasis Type="Italic">O</Emphasis>-glucosyltransferase gene over-expression in tobacco on pigment content and gas exchange

The responses of tobacco plants over-expressing trans-zeatin O-glucosyltransferase gene under constitutive or senescence-inducible promoter (35S:ZOG1 and SAG12:ZOG1) and of wild type (WT) plants to water stress and subsequent rehydration were compared. In plants sufficiently supplied with water, both transgenics have higher net photosynthetic rate (P_N) in upper and middle leaves and higher stomatal conductance (g_s) in middle leaves than WT. Water use efficiency (WUE = P_N/E) was higher in both transgenics than in WT. During prolonged water stress, both P_N and E declined to a similar extent in both transgenics and WT plants. However, 7 d after rehydration P_N in SAG:ZOG (upper and middle leaves) and 35S:ZOG (upper leaves) was higher than that in WT plants. Increased content of endogenous CKs in 35S:ZOG plants did not prevent their response to ABA application and the results obtained did not support concept of CK antagonism of ABA-induced stomatal closure. The chlorophyll (Chl) a+b content was mostly higher in both transgenics than in WT. During water stress and subsequent rehydration it remained unchanged in upper leaves, decreased slightly in middle leaves only of WT, while rapidly in lower leaves. Total degradation of Chl, carotenoids and xanthophyll cycle pigments (XCP) was found under severe water stress in lower leaves. Carotenoid and XCP contents in middle and upper leaves mostly increased during development of water stress and decreased after rehydration. While β-carotene content was mostly higher in WT, neoxanthin content was higher in transgenics especially in 35S:ZOG under severe stress and after rehydration. The higher content of XCP and degree of their deepoxidation were usually found in upper and middle leaves than in lower leaves with exception of SAG:ZOG plants during mild water stress.     

Responses of dominant desert species <Emphasis Type="Italic">Artemisia ordosica</Emphasis> and <Emphasis Type="Italic">Salix psammophila</Emphasis> to water stress

Morphology, biomass accumulation and allocation, gas exchange, and chlorophyll fluorescence were compared for one-year-old seedlings of Salix psammophila and Artemisia ordosica, two dominant desert species, in response to two water supplies (equivalent to 315.0 mm for present precipitation in growing season and to 157.5 mm for future decreasing precipitation) during 105 d. For both species, photochemical efficiency of photosystem 2 (F_v/F_m), net photosynthetic rate, transpiration rate, stomatal conductance, biomass accumulation in different organs, tree height, number of leaves, and leaf area were reduced in response to the decrease in water supply. For both species, instantaneous water use efficiency was not affected by the water deficit. However, diurnal patterns of gas exchange and biomass allocation were affected in different ways for the two species, with notably a decrease in specific leaf area and an increase in root : shoot ratio for S. psammophila only. Overall, S. psammophila was more responsive to the decreasing precipitation than A. ordosica.     

Crassulacean acid metabolism in the epiphytic fern <Emphasis Type="Italic">Patycerium bifurcatum</Emphasis>

The epiphytic fern Platycerium bifurcatum grows in different habitats characterized by drought and high irradiance stress. The plant shows diurnal malate oscillations, indicative for CAM expression only in cover leaves, but not in sporotrophophyll. In P. bifurcatum cover leaves exposed to high irradiance and desiccation, the decrease in both CO₂ assimilation (P _N) and stomatal conductance (g _s) was accompanied with occurrence of diurnal malate oscillations. Exogenously applied abscisic acid (ABA) induced the decrease in P _N and g _s, but no clear change in malate oscillations. The measurements of the maximum quantum efficiency of photosystem 2 (F_v/F_m) under high irradiance showed distinct photoinhibition, but no clear changes in F_v/F_m due to desiccation and ABA-treatment were found.     

Chloroplast ultrastructure,photosynthetic apparatus activities and production of steviol glycosides in <Emphasis Type="Italic">Stevia rebaudiana in vivo</Emphasis> and <Emphasis Type="Italic">in vitro</Emphasis>

The accumulation of steviol glycosides (SGs) in cells of Stevia rebaudiana Bertoni both in vivo and in vitro was related to the extent of the development of the membrane system of chloroplasts and the content of photosynthetic pigments. Chloroplasts of the in vitro plants, unlike those of the intact plants, had poorly developed membrane system. The callus cells grown in the light contained proplastids of almost round shape and their thylakoid system was represented by short thylakoids sometimes forming a little number of grana consisting of 2–3 thylakoids. In cells of the etiolated in vitro regenerants and the callus culture grown in the dark, only proplastids practically lacking the membrane system were observed. All the chloroplasts having developed thylakoids and forming at least a little number of grana were equipped with photochemically active reaction centers of photosystems 1 and 2. Leaves of in vivo plants accumulated greater amount of the pigments than leaves of the in vitro plants. In both the callus culture grown in the light and the etiolated in vitro regenerants, the content of the pigments was one order of magnitude lower than that in leaves of the intact plants. The callus tissue grown in the dark contained merely trace amounts of the pigments. Leaves of the intact and the in vitro plants did not exhibit any significant differences in photosynthetic O₂ evolution rate. However, photosynthetic O₂ evolution rate in the callus cells was much lower than that in the differentiated plant cells. The in vitro cell cultures containing merely proplastids did not practically produce SGs. However, after transferring these cultures in the light, both the formation of chloroplasts and the production of SGs in them were detected.     

Cryopreservation of <Emphasis Type="Italic">Robinia</Emphasis><Emphasis Type="Italic">pseudoacacia</Emphasis>

Cryopreservation of Robinia pseudoacacia explants by vitrification achieved 78% survival following the stepwise preculture of shoot tips in (0.3 + 0.5 + 0.7 M) sucrose with a 80 min incubation in PVS2; compared to 87% survival after desiccation of explants to 30% water content, following 3 days alginate bead (with glycerol and sucrose treatments) preculture in 0.7 M sucrose.     

Effects of reduced irradiance on leaf morphology,photosynthetic capacity,and fruit yield in olive (<Emphasis Type="Italic">Olea europaea</Emphasis> L.)

One-year-old olive trees (cv. Koroneiki) were grown in plastic containers of 50 000 cm³ under full daylight and 30, 60, and 90 % shade for two years. The effects of shade on leaf morphology and anatomy, including stomatal density and chloroplast structure, net photosynthetic rate (P _N), stomatal conductance (g _s), and fruit yield were studied. Shade reduced leaf thickness due to the presence of only 1–2 palisade layers and reduced the length of palisade cells and spongy parenchyma. The number of thylakoids in grana as well as in stroma increased as shade increased, while the number of plastoglobuli decreased in proportion to the reduced photosynthetically active radiation (PAR). The higher the level of shade, the lower the stomatal and trichome density, leaf mass per area (ALM), g _s, and P _N. Shade of 30, 60, and 90 % reduced stomatal density by 7, 16, and 27 %, respectively, while the corresponding reduction in P _N was 21, 35, and 67 %. In contrast, chlorophyll a+b per fresh mass, and leaf width, length, and particularly area increased under the same shade levels (by 16, 33, and 81 % in leaf area). P _N reduction was due both to a decrease in PAR and to the morphological changes in leaves. The effect of shade was more severe on fruit yield per tree (32, 67, and 84 %) than on P _N indicating an effect on bud differentiation and fruit set. The olive tree adapts well to shade compared with other fruit trees by a small reduction in stomatal and trichome density, palisade parenchyma, and a significant increase in leaf area.