Nitrogen and irradiance levels affecting net photosynthesis and growth of young coffee plants (Coffea arabica L.)

Summary

Shoot growth attributes, leaf anatomical changes and net photosynthetic rates were determined in young coffee plants fertilized at high and low levels and subjected to shade or full sunlight. High nitrogen supply increased plant height irrespective of the light level imposed during growth, and promoted a larger leaf area in plants of the shade treatment. Specific leaf weight was 15% higher in plants grown in full sunlight than in shaded plants, at both nitrogen levels. The number of leaves developed on the orthotropic stem increased significantly under full irradiance and high nitrogen availability. Leaves were 11% thicker ih unshaded plants than in shaded ones, because of the increased size of the palisade and spongy parenchyma tissues. More thylakoids per granum and more grana per chloroplast were observed in shade-grown plants, mainly in those given high nitrogen treatment. Total nitrogen content expressed on a leaf-area basis was higher in sun plants supplemented with nitrogen, whereas chlorophyll a and b and protochlorophyll contents increased in shade-grown plants. Net photosynthetic rate in high nitrogen plants reached 7.19 µmol CO₂ m^?2 s^?1 in the full irradiance treatment, and 5.46 µmol CO₂ m^?2 s^?1 in shaded plants. Maximum net photosynthetic rates in the low nitrogen plants were 5.28 and 4.90 µmol CO₂ m^?2 s^?1 in sun and shade plants, respectively. Increased photosynthetic light saturation was observed in high irradiance plants (628 µmol m^?2 s^?1) relative to shade plants (359 µmol m^?2 s^?1) in the high nitrogen treatment. The same pattern was observed in low nitrogen plants. The apparent quantum yield of shade acclimated plants was 14% higher than in those grown in full sunlight. Our results indicate that coffee may be classified as a facultative shade species, exhibiting features of sun adapted plants coupled with shade acclimation attributes, this fairly high adaptive capacity to shade:sun transition being strongly influenced by the level of nitrogen nutrition given to the plants.     

The influence of light on the micropropagation of blackcurrant

The influence was investigated of irradiance on blackcurrant cv Baldwin shoot proliferation and subsequent rooting in vitro. Shoots were cultured under a range of irradiance levels between 0.9 and 28.4 Wm^-2 and the rate of proliferation expressed as shoot doubling times (t_d), was lowest at 0.9 Wm^-2 (t_d = 59.5 d) and rose to a maximum at 18.5 Wm^-2 (t_d =14.8 d). Rooting was influenced by the light level during the proliferation stage of culture as higher light levels increased the time of root emergence. The shoot dry weight at the end of the rooting period was positively correlated with the light level during proliferation and negatively correlated with the time of root emergence.     

Response of tomato plants to saline water as affected by carbon dioxide supplementation. II. Physiological responses

Summary

Photosynthesis of tomato plants (Lycopersicon esculentum (L.) Mill. cv. F144) was studied under conditions of CO₂ supplementation and salinity. The purpose of the study was to elucidate the mechanisms underlying the effects of salinity on the acclimation of tomato plants to CO₂ supplementation. Plants were grown under either low (355.mmol mol^–1) or elevated (1200.6.50 mmol mol^–1) CO₂ and were irrigated with low concentrations of mixed salts. The highest salinity level (E.C. 7 dS m–1) was that used to produce quality tomatoes in the Negev highlands, in Israel. During early development (three weeks after planting), the net photosynthetic rate of the leaves was much higher under elevated CO₂, and other than a slight decrease in quantum yield efficiency as measured by fluorescence (DF/F 9 ^m ), no signs of acclimation to high levels of CO₂ were apparent. Clear acclimation to high CO₂ concentration was evide t ten weeks after planting when the net photosynthetic rate, photosynthetic capacity, and carboxylation efficiency of leaves of non-salinized plants were strongly suppressed under elevated CO₂. This was accompanied by reductions in carboxylation efficiency, Rubisco activity and PSII quantum yield, and an increased accumulation of leaf soluble sugars. The reduction in photosynthetic capacity in the high CO₂ plants was less in plants grown at the highest salinity level. This was correlated with an increase in the PSII quantum yield parameters (F_v/F_m) and DF/F 9 m ) but not with Rubisco activity which was affected by the CO₂ treatments only. These results explain the effects of high CO₂ on yields in tomatoes grown at high levels of salt (Li et al., 1999).     

The role of calcium in regulating photosynthesis and related physiological indexes of cucumber seedlings under low light intensity and suboptimal temperature stress

The response of photosynthesis, antioxidant enzyme activity, and proline content to low light intensity and suboptimal temperature in Cucumis sativa L. seedlings pretreated with either distilled water, 10 mM CaCl₂, 1 mM LaCl₃, 3 mM ethyleneglycol-bis-(2-aminoethyl) tetraacetic acid (EGTA) or 0.05 mM chlorpromazine (CPZ) were investigated. The results showed that 10 mM CaCl₂ led to an increase in photosynthetic rate (Pn), carboxylation efficiency (CE), ribulose 1,5-biphosphate carboxylase (RuBPCase) activity, chlorophyll content, peroxidase (POD) and catalase (CAT) activity, and proline content of cucumber seedlings under low light intensity and suboptimal temperature, in comparison with the distilled water-pretreated seedlings. However, LaCl₃, EGTA and CPZ were in contrast to CaCl₂. These results suggest that CaCl₂ has beneficial effect on photosynthetic adaptation to low light and suboptimal temperature stress in cucumber seedlings. This might be related to the observed increase in RuBPCase activity, alleviation of lipid peroxidation and enhancement of osmoregulation, with these effects being inhibited by LaCl₃, EGTA and CPZ.     

Gas-exchange responses of rose plants to CO2 enrichment and light

Summary

This paper describes the response of gas exchange rates and water use efficiency of rose plants, by means of the characterization in situ and the analysis of the response of photosynthesis, transpiration and water use efficiency of whole plants to CO₂ enrichment under the irradiance conditions prevailing in greenhouses of southern France. Net CO₂ assimilation (A_n) and transpiration (E) of whole rose plants (Rosa hybrida, cv. Sonia) were measured during winter and spring periods. The response of A_n to light and CO₂ were fitted to a double hyperbola function (r² = 0.84). Maximum net assimilation rate (A_nmax), light and CO₂ utilization efficiencies (α₁, α_c) as well as light and CO₂ compensation points (Γ₁ , Γ_c) were calculated for the whole plant and compared with leaf and canopy data in the literature. The whole-plant characteristics generally had values intermediate between those related to leaf and canopy. Light saturation at sub-ambient air CO₂ concentration (C_a) was reached for relatively low PFFD values (300 µmol m^?2 s^?1), whereas at ambient and enriched C_a light saturation occurs for PPFD ≈ 1000 µmol m^?2 s^?1. Doubling C_a from 350 to 700 µmol mol^?1 increased A_nmax and α₁ by respectively 40% and 30%, while reducing Γ₁ by 27%. A threefold increase of C_a from 350 to 1050 µmol mol^?1 induced a reduction of 20% of E. Instantaneous transpirational water use efficiency, WUE (=A_n/E), is relatively insensitive to PPFD, although a slight decrease with PPFD is observed at high CO₂ concentration, but shows marked variations with C_a and leaf to air vapour pressure defiçit (D₁). Increase of C_a from 350 to 1000 µmol mol^?1 gave about 50% increase in WUE. Increase of D₁ from 0 to 2 kPa induced 30% decrease in WUE at ambient C_a and 50% decrease at 1000 µmol mol^?1.     

Photosynthetic responses of greenhouse tomato plants to high solution electrical conductivity and low soil water content

SUMMARY

Greenhouse tomato plants (Lycopersicon esculentum Mill. cv. Capello) were grown in a peal-moss based substrate and supplied with nutrient solutions of high (4.5 mS cm^-1) or low (2.3 mS cm^-1) electrical conductivity (EC) and under high (95 ± 5%) or low (55 ± 8% of capillary capacity) soil water content, to elucidate how EC and soil water status affect plant photosynthesis and related physiological processes. Two weeks after beginning the treatments, photosynthesis (Pn) was measured during changes of photo-synthetic photon flux (PPF) from 0 to 1200 u.mol m^-2 s^-1 using a gas exchange method. The rectangular hyperbolic model (Pn = P_max KI (1-KI)^-2 -r) provided a good fit for the photosynthetic light-response curve. High EC treatment changed the curve by increasing the initial slope (quantum yield) and decreasing photosynthetic capacity at high PPF. However, soil water deficit not only decreased the photosynthetic capacity, but also decreased quantum use efficiency. Depression of Pn was attributed to decreased stomatal (gs) and mesophyll (_gm) conductances, but g_s was depressed more than g_m. The ratio of _gm/(g_m + g_s), an indicator of water use efficiency and a measure of relative control of Pn by carboxylation and C02 supply, was higher for high-EC treated plants. Chlorophyll content was increased by high EC treatment, and was consistent with quantum yield. Leaf water potential was decreased by high EC and/or low soil water content and the decreases in leaf water potential ultimately accounted for the Pn depressions. The effects of high EC and soil water deficit were additive on photosynthesis and most related physiological processes.     

Moving lamps increase leaf photosynthetic capacity but not the growth of potted gerbera

To investigate the responses of leaf photosynthesis and plant growth to a moving lighting system, potted gerberas (Gerbera jamesonii H. Bolus ex J.D. Hook “Festival”) were grown under supplemental lighting in a greenhouse with either a stationary or a moving lighting system positioned above the benches. The stationary system consisted of a fixed high pressure sodium (HPS) lighting system, while the moving lighting system consisted of a moving HPS fixture attached to a cable system to move the light fixture back and forth over the crop. In both cases, the supplemental lighting was applied from 6:00 to 24:00 h with the same supplemental daily light integral (4.9 mol m⁻² day⁻¹). Moving lamps significantly increased leaf photosynthetic capacity as represented by light saturated net CO₂ exchange rate (NCER) (A_sat), light- and CO₂-saturated rate of NCER (A_max), maximum rate of Rubisco carboxylation (V_cmax), maximum rate of electron transport (J_max) and rate of triose phosphate utilization. However, in situ leaf NCER and stomatal conductance, leaf chlorophyll content index, leaf area, leaf thickness, fresh weight of plants were significantly lower under moving lighting than under stationary lighting. It is suggested that the reduced growth of plants under moving lighting might be due to (1) the overall lower light use efficiency of leaves under moving lighting than those under stationary lighting; (2) the slower response time of the photosynthetic system compared to the rate of change in light intensity under moving lighting.     

Nitric oxide alleviates adverse salt-induced effects by improving the photosynthetic performance and increasing the anti-oxidant capacity of eggplant (Solanum melongena L.)

Summary

Nitric oxide (NO) is an active molecule involved in many physiological functions in plants. To characterise the roles of NO in the tolerance of eggplant (Solanum melongena L.) to salt stress, the protective effects of exogenous sodium nitroprusside (SNP), a donor of NO, applied at different concentrations (0, 0.05, 0.1, or 0.2 mM), on plant biomass, photosynthesis, and anti-oxidant capacity were evaluated. The application of SNP alleviated the suppression of growth in eggplant under salt stress, as reflected by a higher accumulation of biomass. In parallel with growth, the application of SNP to salt-stressed plants resulted in enhanced photosynthetic parameters such as the net photosynthetic rate (P_n), stomatal conductance (g_s), transpiration rate (T_r), and intercellular CO₂ concentration (C_i), as well as an increased quantum efficiency of PSII (F_v/F_m), efficiency of excitation capture of open PSII centres (F_v’/F_m’), quantum yield of PSII ( _psii) and photochemical quenching coefficient (qP). Furthermore, exogenous SNP also reduced significantly the rate of production of O₂^{? –} radicals and the concentrations of malondialdehyde (MDA) and H₂O₂. It also increased the activities of superoxide dismutase (SOD), guaiacol peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) in eggplant leaves grown under salt stress. The results indicated that the protective effects of NO against salt stress in eggplant seedlings were most likely mediated through improvements in photosynthetic performance and the stimulation of anti-oxidant capacity.     

Tuber dry-matter accumulation of Zantedeschia in response to temperature and photosynthetic photon flux

Summary

Dry-matter accumulation and partitioning in plants of Zantedeschia ‘Best Gold’ were quantified under a range of temperature and photosynthetic photon flux (PPF) regimes using plant growth analysis. Initiation of tuber growth did not require an obligate environmental trigger. Under both PPF regimes, relative growth rate of the tuber (RGR_t) increased linearly with increasing temperature (13 to 28°C) up to a maximum at 28°C, with a base temperature of 3.2 ± 1.1°C. Optimum temperature for tuber growth was found to be PPF dependent, but maximum tuber dry mass was calculated as occurring under low PPF (348 µmol m^–2 s^–1) at 24.5 ± 0.1°. Mechanisms of acclimation under both PPF regimes suggested that tuber growth was principally source limited. Source limitation was expressed either in terms of: 1) enhanced inter-sink competition for assimilates, as occurred under the low PPF regime, where leaf area development was in direct competition with tuber growth (RGR_t) or, 2) efficiency of dry-matter accumulation by the leaf area present, as occurred under the high PPF regime, where large increases in RGR_t were correlated with increased net assimilation rate (NAR). Use of the daily increment of dry matter into tuber tissue (TMP) provided a more sensitive measure of short-term changes in partitioning than the conventionally used term, harvest index.     

白天短期不同温、光、CO_2对甜瓜幼苗叶片光合作用的影响

通过光照培养箱准确控制光温环境,对不同温度、光照强度和CO2浓度环境因子组合条件下的甜瓜苗期叶片净光合速率的连续测定,并通过单因素相关性分析温度、光照强度和CO2浓度对叶片光合作用的综合作用。结果表明:在光照强度600μmol·s-1·m-2一定的条件下,温度在12～30℃范围内,叶片净光合速率与温度呈正相关,且在30℃时达到最大值;温度在30～36℃范围内,净光合速率与温度呈负相关;固定CO2浓度为1000μL·L-1,光照强度在70～600μmol·s-1·m-2之间,净光合速率与光照强度呈正相关;在温度一定的条件下,CO2浓度在400～1600μL·L-1范围内,净光合速率与CO2浓度具有很好的正相关性。     

Light acclimation in rose (Rosa hybrida cv. Grand Gala) leaves after pruning: Effects on chlorophyll a fluorescence,nitrate reductase,ammonium and carbohydrates

Changes in light intensity have a particular effect on the photosynthetic apparatus. Most of the studies on light acclimation in higher plants have focused on the effects of fixed light intensity. Few works deal on sudden changes in light intensity due to pruning for long periods of time. Pruning the bent shoots in roses (cv. Grand Gala) can modify the light interception in internal leaves and change their photosynthetic reactions. Before pruning, internal leaves were acclimated to low light intensity and after pruning, internal and external leaves received the same light intensity. The aim of this work was to find out how the photosynthetic light reaction, measured by chlorophyll (Chl) a fluorescence in internal and external leaves of arched shoot could be modulated by light changes. Other parameters described as light dependent were also measured: nitrate reductase (NR) activity, NH₄⁺, sucrose and starch levels. Internal and external leaves in rose have shown a high plasticity, rapid and dynamical acclimation, in response to changes in incident sunlight produced by pruning, that can be explained by Chl a fluorescence parameters. The modified NR activity, NH₄⁺, sucrose and starch levels were difficult to associated with light intensity changes, and their modulation could be the response to long-time light acclimation.     

Light responses of photosynthesis and transpiration of two tomato cultivars under ambient and altered CO2 and O2

Young plants of two tomato (Lycopersicon esculentum L.) cultivars, ‘Sonatine’ and ‘F6-IVT’, were examined for whole plant photosynthesis and transpiration in a closed gas-exchange system under different light levels and a combination of high or low oxygen (21 or 1%) and high or low carbon dioxide concentrations (1850 or 550 mg m^?3). With saturating light, both cultivars showed approximately equivalent increases in photosynthesis in response to lowering the oxygen concentration, raising the carbon dioxide, or both. Under non-saturating light, ‘F6-IVT’ responded positively to lowered oxygen but CO₂ had little effect. In ‘Sonatine’, changes in O₂ as well as CO₂ gave photosynthetic enhancement under low light. Stomates responded primarily to CO₂ with little response to O₂. As a result of the stomatal behavior to light, plant water-use efficiency in the short term peaked at moderate light levels, was enhanced by low O₂, but was enhanced most by high CO₂, regardless of O₂ concentration.     

Mannitol-producing tobacco exposed to varying levels of water,light, temperature and paraquat

Summary

Transgenic mannitol-producing (+mtlD) and wild-type (–mtlD) tobacco plants were exposed to water deficit, varying light intensities, low temperatures, and paraquat applications to test whether mannitol was involved in protection against abiotic stresses. In the water deficit experiment, –mtlD and +mtlD plants were fully irrigated [100% evapotranspiration (ET)] or received 25% ET for 40 d. Water deficit reduced the relative water content (RWC) of both types of plant, starting on day 22, and the total stem length (TSL) of –mtlD 25% ET plants after 11 d, whereas the TSL of +mtlD 25% ET plants was reduced only after 34 d. After 30 d of water deficit, a higher percentage of mature foliage was retained by +mtlD 25% ET plants compared to –mtlD 25% ET plants. The mannitol-1-phosphate dehydrogenase activity of +mtlD plants was not affected by water deficit. The photosynthetic rates of +mtlD and –mtlD plants were measured at PPFD levels ranging from 0 to >2,000 μmol m^–2 s^–1. No differences in quantum yield, saturation and compensation points, or dark respiration were observed between the +mtlD and –mtlD plants. Exposing the leaves of +mtlD and –mtlD plants to 0°C for 24 h caused significant injury to cell membranes and was similar in both types of plant. The application of 0.2 mM paraquat onto expanding –mtlD leaves produced a higher percentage of necrotic leaf area (4.3%) compared to +mtlD leaves (0.48%). The amount of mannitol produced by +mtlD plants could not provide significant osmotic protection, or increases in photosynthesis, whereas it may provide a specific system to protect cells from free radical-induced damage.     

The responses of photosynthetic capacity,chlorophyll fluorescence and chlorophyll content of nectarine (Prunus persica var. Nectarina Maxim) to greenhouse and field grown conditions

Three nectarine (Prunus persica var. Nectarina Maxim.) cultivars grown under solar-heated greenhouse and open-field in northwest China, were tested to evaluate their photosynthetic and chlorophyll fluorescence response to both growth conditions, and whether nectarine plants acclimate to the solar-heated greenhouse growth condition. Comparisons of light-saturated photosynthetic capacity (Amax) and CO₂-saturated photosynthetic capacity (RuBPmax) indicated that each cultivar (Z, Zao-Hongzhu; H, Hua-Guang; Y, Yan-Guang) maintained similar rates of light-saturated and CO₂-saturated carbon assimilation when grown in both conditions. The curve of diurnal variation of net photosynthetic (P_N) rate showed double peaks in open-field but single when grown in greenhouse. Compared with open-field-grown plants, a significant increase of daily average P_N was found in Z but decreased in Y in greenhouse. The diurnal variation of F_v/F_m indicate that plants grown in greenhouse experience less photoinhibition than in open-field condition. A reduction in chlorophyll (chl) a/b ratio in leaves of greenhouse grown plants with significant increase in chlorophyll (chl) b content were obtained. The results suggest that some nectarine cultivars have the ability to acclimate to the solar-heated greenhouse growth condition.     

Interacting effects of temperature integration and light intensity on growth and development of single-stemmed cut rose plants

Energy conservation in horticulture can be achieved by allowing temperatures to fluctuate within predefined bandwidths instead of using rigid set points for heating and ventilation. In temperature integration, plants are supposed to compensate effects of temporarily deviations of the average temperature some time later by deviations in the opposite direction. However, little is still known on the effects of integration periods exceeding 1 day. In this study, effects of temperature integration on growth and development of single-stemmed cut rose plants were determined. Pruned rose shoots were placed in climate chambers in which light levels switched daily (2 days integration period) or weekly (14 days integration period) from high light intensity (300 μmol m⁻² s⁻¹) to low light (150 μmol m⁻² s⁻¹). Temperatures were kept continuously at 20 °C (control) or changed with the light intensity (phase, high temperature at high light intensity, low temperature at low light intensity) or changed opposite to the light intensity (counter phase). Bandwidths of temperature integration were 0, 6 or 10 °C. Under these conditions, buds grew out to harvestable shoots in approximately 45 days. At both integration periods, shoot length was significantly reduced with increasing bandwidths of temperature integration. Shoot dry weights were reduced when a bandwidth of 10 °C was applied. At both integration periods, rates of photosynthesis were primarily determined by light intensity. However, in the counter phase treatments, photosynthesis rate at high light and low temperature was reduced compared to the high light condition of the control. Under these conditions, starch content increased to approximately 10%, suggesting a feedback inhibition of the rate of photosynthesis. However, this did not (yet) affect plant growth or development.     

Effects of leaf aging and light duration on photosynthetic characteristics in a cucumber canopy

Photosynthetic characteristics, chlorophyll index and leaf area were examined in selected leaves of cucumber (Cucumis sativus L. cv. Euphorbia). In the first experiment, plants of cucumber were grown horizontally at a lighting period of 20 h day⁻¹. Photosynthetic measurements in horizontally growing cucumbers showed that there was no decline in photosynthetic capacity when cucumber leaves are developing under good light conditions. In a second experiment, plants were grown in a traditional high-wire cultivation system under 20 h day⁻¹ lighting period until they reached final height and then exposed to different lighting periods (20 and 24 h day⁻¹) for 3 weeks. In stands of cucumber plants photosynthetic measurements showed that the lower leaves have a significant reduction in photosynthetic capacity due to reduced light conditions. Three weeks exposure to 24 h day⁻¹ lighting period reduced leaf area by 20%. Plant grown under continuous light had also lower chlorophyll index compared to plants grown under 20 h day⁻¹ lighting period.     

Importance of the mitochondrial alternative oxidase (AOX) pathway in alleviating photoinhibition in cucumber leaves under chilling injury and subsequent recovery when leaves are subjected to high light intensity

The aim of this study was to assess the impact of the mitochondrial alternative oxidase (AOX) pathway on energy metabolism in chloroplast, and evaluate the importance of the AOX pathway in alleviating photoinhibition in cucumber (Cucumis sativus L.) leaves during chilling and the subsequent recovery period. Chilling (12°C) induced up-regultaion of the AOX pathway, which is important for chilled leaves to avoid overreduction of PSII and maintain photosynthetic electron transport. High light (200–300 µmol m^?2 s^?1) induced the decreases of maximal quantum yield of PSII photochemistry (Fv/Fm) and nonphotochemical quenching (NPQ), which was aggravated by 1 mM salicylhydroxamic acid (SHAM; AOX inhibitor), in cucumber leaves during chilling. However, Fv/Fm did not change and NPQ increased significantly in SHAM-treated leaves by chilling under low light. During recovery periods after chilling under low light, Fv/Fm, q_P, Φ_PSII, NPQ, and Fv’/Fm’ could return to normal degree in chilled leaves with or without SHAM. In contrast, high light induced more decrease of chlorophyll fluorescence parameters in chilled leaves during the recovery period, and SHAM treatment further aggravated the decrease. These results implied that up-regulation of AOX pathway in chilled leaves plays a critical role in protection against photoinhibition in leaves under excess light energy condition during chilling and the subsequent recovery period. However, thermal energy dissipation was more important to prevent photoinhibition in leaves exposed to chilling under low light.     

Effects of light intensity and quality on the obligate shade plant Aglaonema commutatum. I. Leaf size and leaf shape

The effect of different light intensities and light qualities were studied on Aglaonema commutatum plants grown in controlled environments. Three light intensities—2.7, 5.4 and 20.0 junolm-2s-1 provided by two light sources (fluorescent and blended-light lamps) were tested on two plant materials of different size. When plants completed their adaptation to low light intensities (2.7 and 5.4 umol m“2s_1) readaptation to high irradiances (20.0 (xmol m-2s_1) was studied. Ten to twelve months were required for a leaf initiated in each light treatment to become fully expanded. The adaptation of this species to low light was far slower than other sun- or shade-plants. Plants grown at 2.7 |xmol m-2s~‘ expanded smaller and thinner leaves, with lower length: width ratio. These responses were affected by the size of the primordia at the beginning of the light treatments. Light quality affected these too but the responses were weak and lacked a defined pattern. The readaptation to high light intensity of plants adapted to 2.7 or 5.4 (xmol m_2s_1 required 6-8 months, after that leaves showed the same sizes and shapes as controls in high irradiance.     

Effects of light,sucrose, and cytokinins on somatic embryogenesis in Lilium ledebourii (Baker) Bioss. via transverse thin cell-layer cultures of bulblet microscales

Summary

This is the first report describing the culture conditions necessary to induce somatic embryogenesis and plantlet regeneration from transverse thin cell-layers (tTCL) of the rare and endangered bulb species, Lilium ledebourii (Baker) Boiss. (Liliaceae). The tTCLs were transferred onto 1.0 Murashige and Skoog medium (MS) containing various sucrose concentrations [3.0, 4.5, or 6.0% (w/v)] and different combinations of two cytokinins [6-benzylaminopurine (BA) or thidiazuron (TDZ)] with 1.0 µM -naphthaleneacetic acid (NAA) in the dark, or exposed to light (40 µmol m^–2 s^–1). The aims of this work were to provide an improved propagation method torescue L. ledebourii, and to determine the effects of sucrose concentration, light, and different cytokinins on somatic embryogenesis. Embryogenic callus cultures were obtained only when the tTCLs were transferred onto 1.0 MS medium containing 1.0 µM NAA, various levels of BA (0.4, 1.1, or 2.2 µM), and sucrose [3.0, 4.5, or 6.0% (w/v)] after 3 months culture in the light or in darkness. Combinations of various concentrations of TDZ and NAA did not generate embryogenic calli. The highest rate of growth of embryogenic calli was achieved on 1.0 MS medium supplemented with 1.0µM NAA, 1.1 µM BA, and 4.5% (w/v) sucrose, in the light. Embryo-like structures were grown into plantlets after transfer onto 1.0 MS medium without any plant growth regulators and incubated in the light. Regenerated plants were successfully acclimatised to ex vitro conditions, with a survival rate of 90%.     

Sana Physiological responses of two grapevine (Vitis vinifera L.) cultivars to CycocelTM treatment during drought

The plant growth regulator Cycocel^TM [(2-chloroethyl)trimethylammonium chloride] can be used to produce drought tolerance in grapevine (Vitis vinifera L.) due to a reduction in the ratio between vegetative growth and fruit production. To evaluate the physiological responses of two grapevine cultivars to drought and Cycocel^TM treatment, a factorial experiment was conducted in a greenhouse. The factors included irrigation frequency (at 5-, 10-, or 15-day intervals corresponding to no, mild, or severe drought stress), Cycocel^TM concentration (0, 500, or 1000 mg l^–1), and cultivar (‘Rasheh’ or ‘Bidane-Sefid’). Stomatal conductance (g_s) the net rate of CO₂ assimilation (A_net), the rate of transpiration (T_r), and chlorophyll a and b concentrations decreased in plants exposed to mild or severe water-deficit stress, whereas carotenoid, proline, and total soluble sugar concentrations increased compared to plants with no drought stress. The relative water content (RWC) of leaves declined only under severe drought stress. A reduction in intercellular CO₂ concentrations (C_i) occurred under mild drought stress; however, under severe drought stress, C_i values increased. Under mild drought stress, the reduction in the net rate of photosynthesis was related to stomatal closure, whereas under severe drought stress, non-stomatal factors were dominant. Water-use efficiency (WUE) improved under mild drought stress relative to non-stressed plants, but under severe drought, it declined. Foliar applications of Cycocel^TM resulted in increased A_net, g_s, T_r, and WUE values, as well as proline and soluble sugar concentrations. ‘Rasheh’ was more tolerant to drought stress than was ‘Bidane-Sefid’. Foliar applications of Cycocel^TM, particularly at 1000 mg l^–1, mitigated the negative effects of drought stress by increasing A_net, WUE, RWC, compatible solute concentrations, such as proline, soluble sugar, and chlorophyll a and b concentrations.