MARSOLAIS, A. A , , WILSON, D. P. M., TSUJITA, M. J . , and SENAKATNA, T. 1991. Somatic clnbryogenesis and artificial seed production in Zonal (Pelnrgoniutt~ X I~ortor~rrn) and Regal (Pelor-goniutn X dotne.sticurn) geranium. Can. J . Bot. 69: 1188-1193. Somatic embryos have been produced from petioles and hypocotyls of Zonal geranium and from petioles of Regal geranium. Somatic embryos of both species have been desiccated and subsequently germinated. Some important factors that influence the rate of somatic embryo production in geranium arc discussed. They include culture medium factors such as auxin and auxin dosage, carbohydrates, amino acids, pH, and basal medium composition. The donor plant genotype also appeared to have an effect on somatic embryogenesis and survival after desiccation.

A computer controlled semiclosed net CO2 exchange measurement system, employing an infrared gas analyzer and mass flow controllers to inject pure CO2 at preset rates, has been developed for measuring whole plant net CO2 exchange and net C gain in a controlled environment (i.e. CO2, light, and temperature). Data Many gas-exchange systems based on infrared gas analysis of CO2 have been designed to measure photosynthesis, photorespiration, and dark respiration of single plant leaves (2, 9, 15). However, measurement of leaf photosynthesis does not necessarily predict plant growth and crop productivity (3), since individual leaves are not representative of the photosynthetic behavior of the entire canopy. Furthermore, analysis of the metabolism of a single leaf does not take into account dark respiration of the entire plant and ignores both the problem of partitioning of photoassimilates and the evaluation of crop quality (5,14). A positive correlation between leaf photosynthetic rate and crop productivity requires considerable sampling (3,12) and is most easily obtained when studying a crop for which the vegetative portion of the plant (e.g. leaves or roots) is harvested for market (8,14,17). In spite of the problems in correlating photosynthesis with yield it is well known that over 95% of the dry matter of a plant is derived from photosynthesis and further that carbon (C) obtained from photosynthesis comprises approximately 40% of the plant dry weight under most growth conditions (1, 7). Even so, CO2 analysis itself is rarely used as a means of measuring growth rate.Growth rate is frequently defined as an increase in the physical size of the plants expressed simply as an absolute increase in dry weight with time (e.g. g gained * week-1) or as a relative increase I

Additional index words. Lilium longiflorum, photomorphogenesis, thermomorphogenesis, twilight Abstract. Potted bulbs of Lilium longiflorum Thunb. 'Ace' and 'Nellie White' and Lilium (Asiatic hybrid) 'Enchantment' were grown in a greenhouse under ambient photoperiod (APP), 8-h photoperiod by removing twilight from ambient by blackout cloth (8PP), or 8PP extended with 1 hour of low-intensity far-red radiation (9PP). Height of 'Ace', 'Nellie White', and 'Enchantment' increased by 24%, 18%, and 12%, respectively, under APP and by 118%, 100%, and 44%, respectively, under 9PP compared to 8PP. In a second experiment, the effects of reduced irradiance (0%, 25%, 50%, and 75% shade) were determined on the same cultivars grown under APP or 8PP. The effects of APP on height were similar in magnitude for 'Ace' and 'Nellie White' but were insignificant for 'Enchantment' compared to 8PP. Shading increased height linearly for all cultivars. The regression was greater under APP (2.8 mm/percent shade) than under 8PP (1.8 mm/ percent shade) for 'Ace' and 'Nellie White' combined. Plant height of 'Enchantment' was less affected by reduced irradiance. For all cultivars, APP or 9PP produced higher stem dry weight compared to 8PP. Shading decreased leaf and bulb dry weight of the Easter lily cultivars.

The influence of irradiance, CO2 concentration, and air temperature on leaf and whole-plant net C exchange rate (NCER) of Alstroemeria `Jacqueline' was studied. At ambient CO2, leaf net photosynthesis was maximum at irradiances above 600 μmol·m-2·s-1 photosynthetically active radiation (PAR), while whole-plant NCER required 1200 μmol·m-2·s-1 PAR to be saturated. Leaf and whole-plant NCERs were doubled under CO2 enrichment of 1500 to 2000 μl CO2/liter. Leaf and whole-plant NCERs declined as temperature increased from 20 to 35C. Whereas the optimum temperature range for leaf net photosynthesis was 17 to 23C, whole-plant NCER, even at high light and high CO2, declined above 12C. Dark respiration of leaves and whole plants increased with a Q10 of ≈2 at 15 to 35C. In an analysis of day effects, irradiance, CO2 concentration, and temperature contributed 58%, 23%, and 14%, respectively, to the total variation in NCER explained by a second-order polynomial model (R2 = 0.85). Interactions among the factors accounted for 4% of the variation in day C assimilation. The potential whole-plant growth rates during varying greenhouse day and night temperature regimes were predicted for short- and long-day scenarios. The data are discussed with the view of designing experiments to test the importance of C gain in supporting flowering and high yield during routine harvest of Alstroemeria plants under commercial greenhouse conditions.

The influence of irradiance, CO2, and temperature on whole-plant net CO2 exchange rate (NCER) of Rubus idaeus L. `Heritage' micropropagated raspberries was examined. Within the set of environmental conditions examined, irradiation was the most important factor, accounting for 58% of the whole-plant irradiance/CO2 concentration/temperature NCER model variation, followed by CO2 concentration (28%) and temperature (2.5%). Net photosynthesis (Pn) required irradiance levels >600 μmol·m-2·s-1 PPF for saturation, greatly increased under CO2 enrichment (up to 1500 μL·L-1), and was optimum at a whole-plant temperature of 20 °C. Temperature effects were partitioned in an experiment using varying air and root-zone temperatures (15, 20, 25, 30, and 35 °C) under saturated light and ambient CO2 levels (350 μL·L-1). Air and root-zone temperature influenced Pn, with maximum rates occurring at an air × root-zone temperature of 17/25 °C. The contribution of air and root-zone temperature to the NCER model varied, with air and root-zone temperature contributing 75% and 24%, respectively, to the total model variation (R2 = 0.96). Shoot dark respiration increased with air and root-zone temperature, and root respiration rates depended on air and root-zone temperature and shoot assimilation rate. Humidity also influenced Pn with a saturated vapor pressure deficit threshold >0.25 kPa resulting in a Pn decrease. Quantifying the physiological response of raspberries to these environmental parameters provides further support to recent findings that cool shoot/warm root conditions are optimum for raspberry plant growth.

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The effects of ethylene evolved from ethephon on leaf and whole plant photosynthesis in Xanthium strumarium L. were examined. Ethylene-induced epinasty reduced light interception by the leaves of ethephon treated plants by up to 60%. Gas exchange values of individual, attached leaves under identical assay conditions were not inhibited even after 36 hours of ethylene exposure, although treated leaves required a longer induction period to achieve steady state photosynthesis. The speed of translocation of recently fixed "C-assimilate movement was not seriously impaired following ethephon treatment; however, a greater proportion of the assimilate was partitioned downward toward the roots. Within 24 hours of ethephon treatment, the whole plant net carbon exchange rate expressed on a per plant basis or a leaf area basis had dropped by 35%. The apparent inhibition of net carbon exchange rate was reversed by physically repositioning the leaves with respect to the light source. Ethylene exposure also inhibited expansion of young leaves which was partially reversed when the leaves were repositioned. The data indicated that ethylene indirectly affected net C gain and plant growth through modification of light interception and altered sink demand without directly inhibiting leaf photosynthesis.The extent to which ethylene can affect photosynthetic CO2 fixation and potentially alter biomass accumulation and yield has been examined in several papers; however, the results have been inconsistent (10,(12)(13)(14)(15)(16)22). Studies ofwhole plant or attached whole leaf gas exchange have indicated that net carbon uptake is reduced in some but not all of the 30 species and cultivars surveyed (10, 12-16, 21, 22 stimulated ethylene release (5). Steady state laminar gas exchange in Zea mays L. and Pisum sativum L. was not inhibited by continuous exposure to ethylene gas (12) and the stomatal aperture of intact leaves was not affected by exposure to 10 ,L L' ethylene (1) even after a 24 h exposure (4).We recently reported (22) that continuous exposure to ethylene derived from ethephon had no effect on steady state photosynthesis and transpiration rates of Lycopersicon esculentum Mill. leaves. The partitioning of recently assimilated '4CO2 into sugar, amino acid, organic acid, and starch pools in the leaf was not altered by ethylene exposure, but during the 24 h following ethephon application there was an alteration in the partitioning of current photosynthate between root and shoot sinks, (e.g. developing flower clusters). Ethephon also caused a rapid epinastic response extending through the petioles and the leaves (22) suggesting that whole plant CO2 exchange (i.e. measured in a whole plant cuvette or a whole leafcuvette enclosing the petiole) could be significantly altered due to the reduction in total light interception (21).We have selected Xanthium strumarium L. as the experimental material for this study in order to avoid potentially anomalous conclusions arising from studies (21) on a single ethylene sensitive species s...