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In the past decade, the potential of positioning LED lamps in between the canopy (intra-canopy) to enhance crop growth and yield has been explored in greenhouse cultivation. Changes in spatial heterogeneity of light absorption that come with the introduction of intra-canopy lighting have not been thoroughly explored. We calibrated and validated an existing functional structural plant model (FSPM), which combines plant morphology with a ray tracing model to estimate light absorption at leaflet level. This FSPM was used to visualize the light environment in a tomato crop illuminated with intra-canopy lighting, top lighting or a combination of both. Model validation of light absorption of individual leaves showed a good fit (R² = 0.93) between measured and modelled light absorption of the canopy. Canopy light distribution was then quantified and visualized in three voxel directions by means of average absorbed photosynthetic photon flux density (PPFD) and coefficient of variation (CV) within that voxel. Simulations showed that the variation coefficient within horizontal direction was higher for intracanopy lighting than top lighting (CV=48% versus CV= 43%), while the combination of intra-canopy lighting and top lighting yielded the lowest CV (37%). Combined intra-canopy and top lighting (50/50%) had in all directions a more uniform light absorption than intra-canopy or top lighting alone. The variation was minimal when the ratio of PPFD from intra-canopy to top lighting was about 1, and increased when this ratio increased or decreased. Intra-canopy lighting resulted in 8% higher total light absorption than top lighting, while combining 50% intra-canopy lighting with 50% top lighting, increased light absorption by 4%. Variation in light distribution was further reduced when the intra-canopy LEDs were distributed over strings at four instead of two heights. When positioning LED lamps to illuminate a canopy both total light absorption and light distribution have to be considered. [ABSTRACT FROM AUTHOR]

Organ temperature and variation therein plays a key role in plant functioning and its responses to e.g. climate change. There is a strong feedback between organ, especially leaf, temperature and the climate within the canopy (canopy climate), which in turn interacts with the climate outside the canopy (ambient climate). For greenhouses, the determinants of this interplay and how they drive differences between canopy and ambient climate are poorly understood. Yet, as many experiments on both regular greenhouse crops and field crops are done in greenhouses, this is crucial to know. Therefore, we designed an experiment to quantify the differences between ambient and canopy climate and leaf temperature. A path analysis was performed to quantify the interactions between components of the greenhouse canopy-climate system. We found that with high radiation the canopy climate can be up to 5°C cooler than the ambient climate, while for cloudy days this was only 2°C. Canopy relative humidity (RH) was up to 25% higher compared to ambient RH. We showed that radiation is very important for these climate differences, but that this effect could be partly counteracted by turning off supplementary light (i.e. due to its indirect effects e.g. changing light distribution). Leaf temperature was substantially different, both higher and lower, from the canopy air temperature. This difference was determined by leaf area index (LAI), temperature of the heating pipe and the use of supplementary light, which all strongly influence radiation, either shortwave or thermal radiation. The difference between leaf and ambient air temperature could be decreased by decreasing the LAI or increasing the temperature of the heating pipe. [ABSTRACT FROM AUTHOR]

Semi-closed greenhouses have been developed over the last decade to conserve energy. Energy consumption is reduced by collecting the excess solar energy in Summer, storing it in aquifers and re-using it in Winter to heat the greenhouse. Cooling systems placed in the lower part of the greenhouse, can cause vertical temperature gradients, which can be more than 5°C at high levels of solar radiation. Given the substantial effect that air temperature has on a number of plant physiological processes, we expected to observe effects on plant growth and fruit production. Tomato plants were grown in semi-closed greenhouses with or without a vertical temperature gradient. The gradient was most pronounced from June to September when, for 55% of the time, the temperature difference between the top and bottom of the canopy was > 2°C, and for 20% of the time the difference was > 5°C. Despite these large vertical temperature gradients, plant growth and fruit yields were mostly unaffected. Leaf and truss initiation rates did not differ between treatments, since air temperatures at the top of the canopy were comparable. The only observed response of plants to the vertical temperature gradient was a reduced rate of fruit development in the lower part of the canopy. This resulted in a longer time between anthesis and fruit harvest in the treatment with a vertical temperature gradient, and an increase in the average fruit weight in Summer. However, total fruit production over the whole season was not affected. These results are important when designing greenhouses, as well as heating and cooling systems for greenhouses. [ABSTRACT FROM AUTHOR]

The closed greenhouse is a recent innovation in the horticulture industry. Cooling by ventilation is replaced partly (in semi-closed greenhouses) or completely (in closed greenhouses) by mechanical cooling. Excess solar energy is collected and stored to be reused to heat the greenhouse. In temperate climates, this concept combines improved crop production with energy savings. This paper presents an overview of climate, crop growth and development, and crop yield in closed and semi-closed greenhouses. The technical principles of a closed greenhouse are described and the macroclimate and microclimate arising from this are studied. The consequences of the typical growth conditions found in closed greenhouses for crop physiology and crop yield are examined. Finally, the experiences of commercial growers are presented. In temperate climates, closed greenhouses can reduce the use of fossil fuel-derived energy by 25 - 35%, compared with open greenhouses. With high global radiation, the climate in closed greenhouses is characterised by high CO2 concentrations, high air humidity, improved temperature control, and a vertical temperature gradient. An annual increase in production of 10 - 20% is realistic, with reduced amounts of supplied CO2. The yield increase is primarily obtained through increased rates of photosynthesis due to the higher CO2 concentrations in closed greenhouses. To introduce this innovation into practice, knowledge transfer was a key factor for its implementation and the realisation of increased production levels. Future trends will require minimising the use of fossil fuels and increasing the level of control of the production process. Closed and semi-closed greenhouses fit seamlessly into this trend as they allow for a more controlled climate and higher levels of production, combined with savings in fossil fuel use. [ABSTRACT FROM AUTHOR]

Water stress in plants affects a number of physiological processes such as photosynthetic rate, stomatal conductance as well as the operating efficiency of photosystem II (PSII) and non-photochemical quenching (NPQ). Photochemical reflectance index (PRI) is reported to be sensitive to changes in xanthophyll cycle which occur during stress and could possibly be used to monitor changes in the parameters mentioned before. Therefore, the aim of this study was to evaluate the use of PRI as an early water stress indicator. Water stress treatment was imposed in a greenhouse tomato crop. CO2 assimilation, stomatal conductance, light-adapted and dark-adapted fluorescence as well as PRI and relative water content (RWCs%) of the rooting medium were repeatedly measured. The same measurements were also performed on well-irrigated plants that acted as a reference. The experiment was repeated in four consecutive weeks. Results showed a strong correlation between RWCs% and photosynthetic rate, stomatal conductance, NPQ and operating efficiency of PSII but not with PRI when the whole dataset was considered. Nevertheless, more detailed analysis revealed that PRI gave a good correlation when light levels were above 700 µmol m−2 s−1. Therefore, the use of PRI as a water stress indicator cannot be independent of the ambient light conditions. [ABSTRACT FROM AUTHOR]

In the Netherlands, sweet pepper (Capsicum annuum L.) plants are grown in heated greenhouses. Lowering the greenhouse temperature results in a substantial reduction in energy use. In order to grow crops under lowered temperatures, cultivars are required which are adapted to such conditions. In this study, we compared the variance in adaptation to low temperatures in six cultivated sweet pepper varieties to that in a collection of ten wild and cultivated Capsicum accessions. The adaptation to lowered temperatures was defined in terms of variation in the difference in relative growth rate (RGR) between plants grown under different temperature conditions. Our results illustrated that within the group of sweet peppers, the variation in low-temperature tolerance was limited, and that sweet pepper breeders should exploit the genetic variation in wild relative species in order to breed for this trait. RGR, however, is difficult and expensive to assess. Therefore, we also studied which morphological plant trait (e.g. leaf, stem, and total fresh- and dry mass, plant height, leaf area, or number of leaves) could be used to simplify the selection of RGR. The relationship between RGR and the various morphological plant traits was dependent on the amount of variation present for these traits in the experimental group of plants. As a result, the practical use of any of these traits as a measure for RGR was limited. However, relative leaf growth rate (RLGR) was shown to be a good alternative measure for RGR. [ABSTRACT FROM AUTHOR]

Levels of abortion of reproductive organs (i.e., buds, flowers, and young fruits) in sweet pepper plants (Capsicum annuum L.) are high, and cyclical fluctuations occur in fruit set. Stages susceptible to abortion are very young buds (< 2.5 mm), buds close to anthesis, and flowers and fruits up to 14 d after anthesis. An overview of factors and processes involved in flower and fruit abortion in sweet peppers is presented. More light, higher CO2 concentrations, and lower planting density, increase the availability of assimilates per plant, and decrease fruit abortion. The cyclical pattern in fruit set is caused by changes in demand for assimilates. High flower abortion occurs when fast growing fruit (at approx. 3 weeks after anthesis) are present, due to competition for assimilates. Fruit set increases when fast growing fruit are almost mature and have a low assimilate demand. Prior to abortion, auxin export from the reproductive organ diminishes, ethylene production increases, and lower levels of activity of sucrose-cleaving enzymes are found. Severe water stress and low nutrient supply also increase abortion levels. Low nightand high day-time temperatures hamper pollen development, causing low seed set, which can result in fruit abortion. Two theories have been used to explain abortion: unbalanced demand for and supply of assimilates, and hormonal dominance of developing fruit over young fruit. Attempts to prevent abortion or to diminish the cyclical pattern of fruit set have not yet been successful, but new suggestions are presented. [ABSTRACT FROM AUTHOR]

Differences in environmental conditions are known to influence plant growth and growth-related traits. The aim of this study was to identify the variation in relative growth rate (RGR), and its underlying physiological and morphological traits, in a group of ten wild and cultivated Capsicum accessions of four Capsicum species at two contrasting temperatures. Therefore, a growth analysis was performed at two temperature regimes (21.1°/18.7°C and 17.3°/14.7°C; day/night). Variation in RGR, growth-related traits and their mutual relationships were analysed at the start of branching. RGR at branching proved to be a reliable predictor for the development of dry mass pre-anthesis in Capsicum. The reduction in RGR and growth-related traits, in response to lowered temperatures, varied between these Capsicum accessions; some being better adapted to low temperatures than others. The variation in the reduction of RGR under lowered temperatures was due to changes in both net assimilation rate (NAR) and leaf area ratio (LAR). Dry mass allocation to the leaves (leaf mass fraction) was not influenced by temperature. Specific leaf area (SLA) was correlated with RGR under standard temperatures, but not under lowered temperatures. At both temperatures, NAR was the most important factor to explain variations in RGR between the different Capsicum accessions. From this study, and the work of others, it was concluded that NAR was the most important factor to explain variations in RGR in plants of the same genus or species, and even between closely-related plant species. [ABSTRACT FROM AUTHOR]

Abstract We studied the effects of phosphorus (P) and light on the physiological and morphological components of growth of young tomato plants (Lycopersicon esculentum Mill. cv. Capita). The importance of dry-mass partitioning and starch accumulation in explaining the effects of P limitation on growth was examined more closely. Plants were grown at a wide range of exponential P supply rates (between 70 and 320 mg g-1 d-1) and one free-access treatment (1 mm). Two light levels (70 and 300 µmol m-2 s-1) were applied. Growth response coefficients (GRCs) were calculated to address the importance of different growth parameters in explaining relative growth rate (RGR). At both light levels, net assimilation rate (NAR) was more important than leaf area ratio (LAR) in explaining the effects of P on growth as indicated by GRCs. At less severe P limitation, LAR became more important and NAR less important. Dry-mass partitioning to both roots and leaves played a minor role in determining the effects of P limitation on growth as indicated by low GRCs. The increase in starch at mild P limitation showed that the assimilate supply was not limiting. At severe P limitation, the rate of photosynthesis was decreased, as suggested by the decrease in starch accumulation. [ABSTRACT FROM AUTHOR]

The rates of dry weight increase and respiration of fruits were measured throughout fruit ontogeny at 20, 25 and 30°C in cucumber (Cucumis sativus L. cv. Corona). By maintaining one or five fruits per plant, which strongly affected fruit dry weight but not ontogeny, the effects of fruit size and ontogeny on respiration could be studied separately. The respiration rate per fruit followed a sigmoid curve during fruit ontogeny, while the specific respiration rate (respiration rate per unit dry weight) declined with time after anthesis. The specific respiration rate was almost linearly related to the relative growth rate. The specific respiratory costs for both growth and maintenance were highest in young fruits, but were not affected by fruit size. The average specific respiratory costs for growth and maintenance at 25°C were 3.3–3.9 mmol CO2 g-1 and 4.0 nmol CO2 g-1 s-1, respectively. An increase in temperature had no effect on the specific respiratory costs for growth, while the costs for maintenance increased with a Q10 of about 2. The costs for growth agreed reasonably well with theoretical estimates based on the chemical composition of the fruits but not with estimates based on only the carbon and ash content. The respiratory losses as a fraction of the total carbon requirement of a fruit changed during fruit ontogeny, but were independent of temperature and were similar for slow- and fast-growing fruits. The cumulative respiratory losses accounted for 13–15% of the total carbon requirement. [ABSTRACT FROM AUTHOR]

The photosynthetic contribution of a fruit to its carbon requirement throughout ontogeny and under different growing conditions was quantified in cucumber (Cucumis sativus L. cv. Corona). In addition, the effects of shading on fruit dry matter accumulation and the diurnal course of the elongation rate were studied. Fruit darkening had no photomorphogenic effect on fruit growth, while the cumulative photosynthetic contribution of a fruit to its own carbon requirement ranged from 1 to 5%. During the day there was always a net CO2 efflux. The photosynthetic rate per fruit, calculated as the difference between rates of CO2 exchange in light and dark, increased during fruit ontogeny, while the photosynthetic rate per unit fruit surface area declined. The latter was not dependent on fruit size. The photosynthetic activity per unit surface area of fruits was estimated to be about 20–30% as efficient as that of leaves. The rate of calculated photosynthesis was reduced by 60–65% when the photosynthetically active radiation incident on the fruit decreased from 200 to 50 µmol m-2 s-1. Temperature (20–30°C) had no pronounced effect on the rate of calculated fruit photosynthesis when fruits of the same developmental stage (temperature sum) were compared. However, the relative photosynthetic contribution of a fruit to its carbon requirement increased when temperature decreased. Moreover, this contribution increased when irradiance increased or fruit growth was reduced by competing fruits. During fruit ontogeny the daily photosynthetic contribution was highest (up to 15%) in young and old fruits, with a small growth rate. [ABSTRACT FROM AUTHOR]

The peripheral lymphocytes of 50 cases of human immunodeficiency virus (HIV) infection (13 of acquired immune deficiency syndrome (AIDS), 17 of AIDS related complex (ARC), and 20 healthy carriers) were studied immunoultrastructurally. The prevalence of "tubuloreticular structures" and "tubular confronting cisternae" increased with the progression of the disease. Numerous tubular confronting cisternae were noted in patients presenting with a high serum acid labile alpha-interferon values. The patients with depressed natural killer cell activity were characterised by circulating immature natural killer cells with abundant multivesicular bodies that were devoid of "parallel tubular arrays". With an immunogold staining technique the location of HIV antigen was detected ultrastructurally, both at the surface of "hand-mirror" natural killer cell lymphocytes and inside vacuolised cells, probably corresponding to infected T4 lymphocytes. These findings indicate the usefulness of electron microscopic techniques in evaluating the pathology and the pathogenetic outcome of AIDS. [ABSTRACT FROM PUBLISHER]

During an outbreak, 25 severely impaired patients (mean age 62) presented with severe infections due to Staphylococcus aureus resistant to oxadllin and aminoglycosides.All strains were isolated in pure culture and diagnostic procedures included transtracheal puncture and bone biopsy. Median MICs were: oxacillin 50 mg/l, gentamicin 12.5 mg/l, tetracycline 25 mg/l, vancomycin 0.195 mg/l, rifampicin 0.097 mg/l and minocycline 0/195 mg/l.All patients were treated with rifampicin (600 mg/day) and minocycline (200 mg or 400 mg/day) aministered together intravenously or orally bid. Mean duration of treatment was 22 days (range 5 to 119).Overall results were 19/25 infections cured and one improved. Five were failures due mostly to emergence of Staph. aureus resistant to rifampicin. No side effects were noted. These preliminary results suggest that rifampicin plus minocycline may be useful in the treatment of severe infections due to multi-resistant Staph. aureus. [ABSTRACT FROM PUBLISHER]

Trichosporon beigelii (Trichosporon cutaneum) was identified as the causative agent of chronic meningitis in a 15-year-old boy with acute lymphocytic leukaemia. After a neutropenic episode following cytostatic treatment and itraconazole therapy as prophylaxis, cerebrospinal fluid (CSF) samples yielded growth of Trichosporon beigelii. Treatment with amphotericin B, flucytosine and high doses of fluconazole was followed by clinical improvement, although CSF pleocytosis remained. The cross-reactivity between Cryptococcus neoformans and Trichosporon beigelii in a cryptococcal antigen latex test was used as a means of diagnosis in CSF and serum samples. [ABSTRACT FROM AUTHOR]

We performed a phase I-II trial of escalating doses of cisplatin (CDDP: 50–100 mg/m per course) plus carboplatin (CBDCA: 300–400 mg/m per course) as a potential way in which to maximize platinum doses without causing excessive toxic effects in patients with advanced ovarian cancer. Thirty-three patients with nonoptimally debulked disease of FIGO (International Federation of Gynecology and Obstetrics) stages IIc-IV [median age: 60 yr; median WHO (World Health Organization) performance status: 2; no prior chemotherapy] received a median of six courses of therapy. CBDCA was infused on day 1 and CDDP on day 2 with an aggressive 48-hour hydration regimen. Myelosuppression was dose-limiting: at the highest dose levels, WHO grade 4 neutropenia and thrombocytopenia led to dose reduction and/or treatment delay in 45% of the patients. Nonhematologic toxic effects included acute nausea and vomiting (97% of the patients), mild alopecia (45%), ototoxic effects (39%), neurotoxic effects (21%), and renal toxic effects (serum creatinine >1.5 mg/dL: 12.5%). The pathologic complete response rate was 22%. We conclude that CBDCA and CDDP can be given safely in combination at reasonably high doses (CBDCA at 300 mg/ m per course and CDDP at 100 mg/m per course) over a 6-month period, provided a close hematologic follow-up is conducted. Randomized clinical trials are needed to define whether this regimen is any better than standard combination chemotherapy. [J Natl Cancer Inst 82:703–707,1990] [ABSTRACT FROM PUBLISHER]