Culture method and photosynthetic photon flux affect photosynthesis,growth and survival of Limonium ‘Misty Blue’ in vitro

Microcuttings (shoots each with two leaves) of Limonium ‘Misty Blue’ were cultivated in vitro for 28 days under photoautotrophic (sucrose-free culture medium; CO₂ and photosynthetic photon flux (PPF) enriched conditions), photomixotrophic (medium with 30 g l⁻¹ sucrose; CO₂ and PPF enriched conditions) and heterotrophic (medium with 30 g l⁻¹ sucrose; CO₂ non-enriched conditions) methods. Several growth variables were measured during and at the end of cultivation: shoot fresh and dry weight, percentage of shoot dry matter, root fresh weight, number of leaves, leaf area, chlorophyll and sugar content of leaves, stomatal density and size, net photosynthetic rate (NPR) and percent survival of plantlets ex vitro. Plantlets grown in photoautotrophic and photomixotrophic methods had more leaves, high chlorophyll and sugar contents, high NPR, and showed high percent survival. However, these plantlets possessed less number of stomata per square millimeter. In contrast, the plantlets grown by the heterotrophic method showed decreased values of these growth variables except for the number of stomata per square millimeter. These results indicate that CO₂ enrichment for plantlets in vitro at a relatively high PPF would promote photosynthesis and hence growth of chlorophyllous explants/plantlets in vitro. The resulting plantlets were acclimatized better and sooner on ex vitro transplantation.     

Morpho-physiological disorders in in vitro culture of plants

The special conditions during in vitro culture results in the formation of plantlets of abnormal morphology, anatomy and physiology. Tissue culture conditions that promote rapid growth and multiplication of shoots often results in the formation of structurally and physiologically abnormal plants. They are often characterized by poor photosynthetic efficiency, malfunctioning of stomata and a marked decrease in epicuticular wax. Qualitatively also, the waxes present on the surface of the leaves of in vitro cultured plants may vary. The conditions under which most laboratories done tissue culture is high relative humidity and low light, no supplemental CO₂, high sucrose and nutrient containing medium may contribute to a phenotype that cannot survive the environmental conditions when directly placed in a greenhouse or field. Understanding these abnormalities is a prerequisite to develop efficient transplantation protocols. The present review summaries the major abnormalities in in vitro culture of plants and also highlight the current and developing methods that are satisfactory for acclimatization of in vitro cultured plantlets.     

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.     

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).     

温度和光照对‘红地球’葡萄试管苗光合特性的影响

 以‘红地球’葡萄(Vitis vinifera L. ‘Red Globe’) 试管苗为试材, 采用密闭系统落差法研究了在不同温度和光照强度下培养28 d的试管苗的光合特性。结果表明: 培养温度在20～30 ℃之间, 试管苗的暗呼吸速率(Rd ) 随温度的升高而升高, 但净光合速率( Pn ) 以25 ℃最高, 30 ℃次之, 20 ℃最低;而CO₂补偿点以25 ℃最低, 20 ℃次之, 30 ℃最高; 光照强度在40～200μmol·m ^-2 ·s^-1之间, 葡萄试管苗的P_n随光照强度( PAR) 的升高而升高, CO₂补偿点随PAR的升高而降低。在光照条件下, 容器内CO₂浓度迅速降低, 并接近CO₂补偿点, CO₂供应不足是影响试管苗同化能力的主要原因。在室内培养阶段,采用弱光、昼夜变温和改善培养容器的通气性有利于提高试管苗的光合能力; 在移栽驯化过程中, 逐步提高光照强度和延长光照时间有利于试管苗同化产物的积累和培养壮苗。     

An effective in-vitro acclimatization using uniconazole treatments and ex-vitro adaptation of Phalaenopsis orchid

The in-vitro acclimatization of Phalaenopsis plantlets under photoautotrophic conditions, with 0 (control), 3.43, 6.86 and 13.72 μM uniconazole (UCZ) treatments for 30 days was investigated before the plantlets were transferred to ex-vitro environments for 14 days. The physiological and growth characters of in-vitro acclimatized, and ex-vitro adapted plantlets were measured. Chlorophyll a (Chl_a), chlorophyll b (Chl_b), total chlorophyll (TC) and total carotenoid (C_x+c) content in plantlets treated with 6.86 μM UCZ were maintained at higher levels than those in plantlets of the control, by 1.82, 1.85, 1.83 and 1.93 times, respectively, leading to enrichment of the pigments in ex-vitro conditions. The maximum quantum yield of PSII (F_v/F_m), photon yield of PSII (Φ_PSII), photochemical quenching (qP) and non-photochemical quenching (NPQ) in UCZ treated plantlets and in ex-vitro adaptation were not significantly different. Proline was accumulated in the control plantlets in both in-vitro acclimatization and ex-vitro conditions, while proline in those plantlets with UCZ treatments was maintained at a low level, which was defined by unstressed conditions. Net photosynthetic rate (P_n) in 6.86 μM UNZ treated plantlets peaked at a higher level than that of the control plantlets, both in-vitro and ex-vitro, by 3.27 and 2.93 times, respectively. In addition, proline content and P_n were inversely related in both in-vitro acclimatization and ex-vitro adaptation. The P_n in UCZ acclimatized plantlets was negatively correlated with plant dry-weight. In-vitro photoautotrophic Phalaenopsis plantlets were successfully acclimatized using a 6.86 μM UCZ treatment which caused them to adapt quickly to ex-vitro environments.     

In vitro multiplication of statice plantlets using sugar-free media

Clumps of statice (Limonium latifolium) plantlets grown photomixotrophically were used as explants and cultured for 25 days on a sugar-free modified Murashige and Skoog (MS) medium in Magenta-type vessels with the number of air exchanges of the vessel (NAE) being 3.8 h⁻¹, at a photosynthetic photon flux (PPF) of 100 μmol m⁻² s⁻¹ and a CO₂ concentration of 1500 μmol mol⁻¹ in the culture room. A factorial experiment was conducted with three levels of 6-benzylaminopurine (BA) concentration, namely 0, 0.25 and 0.5 mg L⁻¹, and two types of supporting material, agar and Florialite (a porous material). The control treatment was a photomixotrophic culture using a sugar- and BA (0.25 mg L⁻¹) containing agar medium in the vessel with NAE of 0.2 h⁻¹, at a PPF of 50 μmol m⁻² s⁻¹ and a CO₂ concentration of 400 μmol mol⁻¹ in the culture room. Leaf area, chlorophyll concentration and net photosynthetic rate were greater in the sugar-free medium treatment with a BA concentration of 0.25 mg L⁻¹ and Florialite than those in the control treatment. The number of shoots and dry weight per clump in the sugar-free medium treatment were comparable to those in the control treatment. Among the sugar-free medium treatments, the number of shoots increased with increasing BA concentration, however, the leaf area, dry weight, chlorophyll concentration and net photosynthetic rate decreased with increasing BA concentration. The use of Florialite significantly enhanced the growth and root induction as well as net photosynthetic rate, compared with the treatments that use agar. These results indicated that sugar-free medium micropropagation could be commercially applied to the multiplication of statice plantlets.     

Influence of ventilation and sucrose on growth and leaf anatomy of micropropagated potato plantlets

Potato single nodes were cultured in vessels containing MS medium supplemented with 10, 20 and 30 g/l of sucrose. Vessels were closed with a clear polypropylene lid with or without 10 mm microporous polypropylene membrane. Sucrose concentration significantly increased plantlet height, shoot fresh weight and chlorophyll a content. Plantlets grown in ventilated vessels were significantly shorter, had lower shoot fresh weight and higher shoot dry weight than those in non-ventilated vessels. The highest leaf chlorophyll a content (21.83 mg/g fresh weight) was found in plantlets grown in ventilated vessels using MS medium with 20 g/l of sucrose, whereas those grown on medium with 10 g/l of sucrose had the highest chlorophyll b content (24.00 mg/g fresh weight). Total chlorophyll content was significantly higher when plantlets were grown in ventilated vessels containing medium with 10 or 30 g/l sucrose than in non-ventilated vessels. There was no significant difference in total chlorophyll content among plantlets grown in ventilated vessels with different concentrations of sucrose. Stomatal density was significantly lower when plants were grown under ventilated conditions. Leaf replica examination showed that stomata under non-ventilated condition were spherical with wide openings whereas, those in ventilated vessels were elliptical with narrow openings. Plantlets grown in non-ventilated vessels had thinner leaves and failed to build up a distinct defined upper epidermis, palisade parenchyma layer and spongy cells. On the other hand, leaves under ventilated conditions showed comparatively well organized layers with small intercellular space. The vascular system of leaves under the ventilated conditions demonstrated very well developed xylem unlike leaves under non-ventilated conditions. Thus, ventilated vessels with the 20 g/l of sucrose under ambient CO₂ in the growth room could successfully promote photomixotrophic culture and produce healthy plantlets.     

Acclimatisation to mannitol-induced water deficit in miniature rose (Rosa hybrida) plantlets cultivated in vitro under autotrophic conditions

Summary

Miniature rose plantlets at the flower development stage were grown photo-autotrophically on MS medium and subsequently exposed to water deficits of –0.23, –0.32, –0.40, or –0.67 MPa osmotic potential ( _s) for 14 d. The _s in the culture medium was raised by increasing the concentration of mannitol, which caused abnormal floral development in terms of the flowering percentage and the number of flowers per plantlet, as well as delayed flowering. In vitro flowering and the number of flowers per plantlet declined significantly when miniature rose plantlets were exposed to water deficit stress at –0.40 MPa or –0.67 MPa. Reductions in growth, pigment degradation, chlorophyll a fluorescence, and net photosynthetic rate (Pn) were greatest in plantlets exposed to a water deficit stress of –0.67 MPa. This was particularly evident in the case of Pn, with a decline of 73.7% compared to non-stressed control plantlets. In contrast, proline levels increased in plantlets under water deficit stress, as proline performs a key role as an osmoprotectant under such conditions. The flowering stage in miniature rose plantlets is particularly susceptible to water deficit stress, which suppresses the development of reproductive organs. Knowledge of the responses to water deficit stress at the reproductive stage may be applied to identify effective indices for the selection of genotypes with increased tolerance to water deficit in miniature rose breeding programmes.     

Responses of leaf photosynthesis and plant growth to altered source–sink balance in a Japanese and a Dutch tomato cultivar

We investigated the effects of altered source/sink ratio by leaf or fruit pruning on leaf photosynthetic characteristics and whole-plant growth of ‘Momotaro York’, a Japanese cultivar, and ‘Dundee’, a Dutch cultivar and verified a hypothesis for sink-limitation of plant growth proposed by Tanaka and Fujita (1974). Plants were grown hydroponically with a high-wire system in a greenhouse for 11 weeks. Light-saturated photosynthesis of young, fully expanded leaves measured at atmospheric CO₂ partial pressure of 37 Pa and at an intercellular CO₂ partial pressure of 20 Pa was not influenced by alteration of source/sink ratio for either cultivar. Although soluble sugars were accumulated in leaves under high source/sink conditions, the amount of ribulose-1,5-bisphosphate carboxylase/oxygenase, a rate-limiting factor for CO₂-limited photosynthesis, was not affected by the altered source–sink balance. Net assimilation rate of a whole plant increased with decreasing source/sink ratio, but this can be accounted for by the changes in light interception per unit leaf area, without taking the source–sink relationship into consideration. It was concluded that the altered source/sink ratio did not change leaf photosynthetic capacity and the sink-limitation hypothesis cannot be applied to either cultivar under the conditions of the present study.     

Root restriction-induced limitation to photosynthesis in tomato (Lycopersicon esculentum Mill.) leaves

Root restriction often depresses photosynthetic capacity and the mechanism for this reduction, however, remains unclear. To identify the mechanism by which root restriction affects the photosynthetic characteristics, tomato (Lycopersicon esculentum Mill.) seedlings were subjected to root restriction stress with or without supplemental aeration to the nutrient solution. With the development of the root restriction stress, CO₂ assimilation rate was decreased only in confined plants without supplemental aeration. There were also significant decreases in leaf water potential, stomatal conductance (g_s), intercellular CO₂ concentration (C_i), and increases in the stomatal limitation (l) and the xylem sap ABA concentration. Meanwhile, the maximum carboxylation rate of Rubisco (V_cmax) and the capacity for ribulose-1,5-bisphosphate regeneration (J_max) also decreased, followed by substantial reductions in the quantum yield of PSII electron transport (Φ_PSII). Additionally, root restriction resulted in accumulation of carbohydrates in various plant tissues irrespective of aeration conditions. It is likely that root restriction-induced depression of photosynthesis was mimicked by water stress.     

Effect of elevated CO2 on vegetative and reproductive growth characteristics of the CAM plants Hylocereus undatus and Selenicereus megalanthus

This study examined the vegetative and reproductive growth responses of the crassulacean acid metabolism (CAM) vine-cactus fruit crop species Hylocereus undatus and Selenicereus megalanthus to CO₂ enrichment (1000 μmol mol⁻¹ vs. control of 380 μmol mol⁻¹). H. undatus plants enriched with CO₂ demonstrated 52%, 22%, 18%, and 175% increases, relative to plants measured in ambient CO₂, in total daily net CO₂ uptake, shoot elongation, shoot dry mass, and number of reproductive buds, respectively. The responses of S. megalanthus plants exposed to elevated CO₂ were greater than those of H. undatus under the same conditions. Compared to plant responses in ambient CO₂, under conditions of CO₂ enrichment, S. megalanthus showed 129%, 73%, 68%, and 233% increases in total daily net CO₂ uptake, shoot elongation, shoot dry mass, and number of reproductive buds, respectively. Moreover, for H. undatus, there was no significant change in fruit fresh mass although it showed a slight (7%) upward trend. On the other hand, fruit fresh mass of S. megalanthus significantly increased by 63% in response to elevated CO₂. These results indicate the high potential of CAM plants to respond to CO₂ enrichment. It is thus apparent that S. megalanthus grown under CO₂ enrichment may benefit from elevated CO₂ to a greater extent than H. undatus grown under sub-optimal growth conditions.     

Alleviation of salt-induced adverse effects in eggplant (Solanum melongena L.) by glycinebetaine and sugarbeet extracts

Two eggplant cultivars, Dilnasheen and Bemisal, were selected to assess whether pure GB and sugarbeet extract could effectively ameliorate the harmful effects of salt stress on eggplant (Solanum melongena L.), under saline conditions. Salt stress markedly suppressed the growth, yield, photosynthetic capacity, internal CO₂ level, transpiration, and stomatal conductance in both cultivars. Potassium (K⁺) and Ca²⁺ contents and K⁺/Na⁺ ratios of both root and leaf were also reduced, while GB and proline in leaves, and Na⁺ and Cl⁻ contents in roots and leaves were significantly enhanced. Exogenously applied glycinebetaine and sugarbeet extracts significantly counteracted the salt-induced adverse effects on growth, yield, various gas exchange characteristics, GB and leaf K⁺, Ca⁺, Cl⁻ and Na⁺. However, GB and sugarbeet extract showed differential effects on photosynthetic rate, stomatal conductance and transpiration, internal CO₂ level, C_i/C_a ratio, leaf K⁺, Ca²⁺, and Cl⁻ contents, and K⁺/Na⁺ ratio. Sugarbeet extract proved better than the GB in improving growth, photosynthetic rate, transpiration, stomatal conductance, yield and GB accumulation. Since, sugarbeet extract contains a substantial amount of GB along with a variety of other important nutrients so it was found as effective as pure GB in improving growth and some key physiological processes in eggplant under salt stress. Thus, it can be used as an alternative cheaper source of GB for its use as an ameliorative agent for protecting plants against the hazardous effects of salt stress.     

Recovery of haploid and diploid plantlets from anther culture of Citrus clementina Hort,ex Tan. and Citrus reticulata Blanco

Summary

Research on androgenesis in two clementine cultivars (Nules and S.R.A. 63) and two mandarin cultivars (Avana and Tardivo di Ciaculli) was carried out with the aim of obtaining haploids. The anthers, collected at the uninucleated stage were cultured first on 11 media, differing either in the basic medium, the growth regulators, the carbon source and concentration, or the presence of activated charcoal. Calli, shoots, embryos and then plantlets were obtained. Significant differences were observed between the different cultural conditions and genotypes. Cytological observations on calli and plantlets from ‘Nules’ anthers revealed the haploid chromosome number, while mandarin calli and plantlets, and S.R.A. 63 calli had the diploid chromosome number. Electrophoretic analyses on calli and leaf tissues showed that ‘Nules’ had a homozygous genotype and confirmed that these tissues had developed from microspores.     

Growth characteristic and sink strength of fruit at different CO2 concentrations in a Japanese and a Dutch tomato cultivar

The aim of the present study was to elucidate how fruit growth was limited by the source and sink capacities in a Japanese (‘Momotaro York’) and a Dutch (‘Dundee’) tomato cultivar. The two cultivars were grown hydroponically with a high-wire system in greenhouses for 25 weeks, and the growth characteristics and sink strength of fruit were determined. Fruits were pruned to four (4F) or one (1F) per truss. The latter were used to determine potential fruit growth, an indicator of fruit sink strength. Growth was also determined under normal (LC) and enriched (HC, 700 μmol mol⁻¹) CO₂ concentrations to examine the effect of source enhancement on fruit production. In both cultivars under normal CO₂, the growth rate of fruit pruned to 4F per truss was lower than that in 1F, indicating that maximum potential fruit growth was not achieved. Under HC conditions, fruit growth rate of ‘Dundee’ achieved in 4F trusses was lower than that in 1F. In ‘Momotaro York’ in HC, fruit growth in 4F trusses was close to potential. This implies that fruit growth was source-limited irrespective of CO₂ concentrations in ‘Dundee’ cultivar while fruit growth in ‘Momotaro York’ under normal and enriched CO₂ conditions was limited by source and sink strengths, respectively. Adjustments of cultural practices including increasing fruit number per truss and/or genetic approaches to enhancing fruit sink strength by breeding may improve fruit yields of Japanese cultivars under high source/sink conditions.     

Response of tomato plants to saline water as affected by carbon dioxide supplementation. I. Growth,yield and fruit quality

Summary

Tomato plants (Lycopersicon esculentum (L.) Mill. cv. F144) were irrigated with low concentrations of mixed salts; the highest level (E.C. 7 dS m^–1) simulated conditions used to produce quality tomatoes in the Negev highlands. CO₂ enrichment (to 1200.mmol mol^–1, given during the daytime) increased plant growth at the early stage of development. However, later growth enhancement was maintained only when combined with salt stress. In the absence of CO₂ supplementation, overall growth decreased with salt (7 dS m^–1) to 58% and fresh biomass yields to 53% of the controls. However, under elevated CO₂ concentrations total plant dry biomass was not reduced by salt stress. CO₂ enrichment of plants grown with 7 dS m^–1 salt increased total fresh fruit yields by 48% and maintained fruit quality in terms of total soluble salts, glucose and acidity. Fruit ripening was about 10.d earlier under CO₂ enrichment, regardless of salinity treatment. It is suggested that a combined utilization of brackish water and CO₂ supplementation may enable the production of high-quality fruits without incurring all the inevitable loss in yields associated with salt treatment.     

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.     

Effect of light,temperature and CO2 on the growth of Campanula isophylla stock plants and on the subsequent growth and development of their cuttings

Stock plants of Campanula isophylla Moretti were subjected to different temperature and light conditions and to various CO₂ regimes. The number and the fresh and dry weight of the cuttings produced were recorded. The after-effect of stock-plant treatment on root formation and growth of cuttings was studied.Increasing light intensity and CO₂ supply strongly promoted cutting production and increased both fresh and dry weight of the cuttings. These factors also markedly influenced root formation and root growth of the cuttings. Stock plant conditions also strongly influenced the growth and lateral shoot formation of the rooted cuttings. It is concluded that cuttings from stock plants grown under favourable light (10 Klx) and CO₂ conditions (900 v.p.m.) contain factors beneficial for root formation, growth and shoot formation. The results are discussed in relation to the carbohydrate content of the cuttings.     

Ventilation of culture vessels. II. Increased water movement rather than reduced concentrations of ethylene and CO2 is responsible for improved growth and development of Delphinium in vitro

Summary

Delphinium plantlets were cultured during Stage III in vessels modified to give different gas exchange rates. Modifications were achieved by the fitting of a covered aperture, or by the sealing of the lids. The concentrations of CO₂ and ethylene were measured in conjunction with measurements of relative humidity, water loss, the uptake of mineral nutrients and growth. Both CO₂ and ethylene concentrations were low in intact vessels, and significantly higher in vessels sealed with parafilm. Water loss was similar in intact and in sealed vessels, indicating that the vessel lid acted as a good barrier to water but allowed high rates of gas exchange. Plant growth rate was not affected by the level of ventilation of the vessels although leaf area was greater in vessels having lower gas exchange rates. After one week of culture, tissue concentrations of calcium and magnesium were highest in the vessels having the highest gas exchange rates. Relative humidity within the culture vessels was not affected by the level of ventilation. Improved stomatal performance, growth and survival of Delphinium from ventilated vessels appears to be due to an increased flow of water, and not to amelioration of the gaseous environment.