Low Photosynthetic Photon Flux Research Articles

(56) Transpiration and Photosynthesis of Grafted Watermelon Transplants as Affected by Environmental Factors during Graft Union Formation

Grafted transplants are widely used for watermelon culture in Korea mainly to reduce the yield and quality losses caused by soil-borne diseases. It is normal practice to cure the grafted transplants under high relative humidity (RH) and low photosynthetic photon flux (PPF) conditions for a few days after grafting to prevent the wilting of the transplants. Transpiration rate (TR) and net photosynthetic rate (NPR), however, could be suppressed under those environmental conditions. In the present study, TR and NPR of the grafted watermelon transplants were compared during graft union formation under 18 environmental conditions combining two air temperatures (20 and 28 °C), three RHs (60%, 80%, and 100%), and three PPF s (0, 100, and 200 μmol·m-2·s-1). Percentages of graft union formation and survival were also evaluated. TR and NPR dramatically decreased just after grafting but slowly recovered 2 to 3 days after grafting at 28 °C. The recovery was clearer at higher PPF and lower RH. On the other hand, the recovery of TR and NPR was not observed in 7 days after grafting at 20 °C. Differences in TR and NPR affected by RH were nonsignificant. Percentage of graft union formation was 98% when air temperature, RH, and PPF were 28 °C, 100%, and 100 μmol·m-2·s-1, respectively, which was the highest among all the treatments. Percentage of survival was over 90% when air temperature was 28 °C and RH was higher than 80% (when vapor pressure deficit was lower than 0.76 kPa). In addition, higher PPF enhanced TR and NPR and promoted rooting and subsequent growth of grafted transplants. Results suggest that the acclimation process for grafted watermelon transplants can be omitted by properly manipulating environmental factors during graft union formation.

Fruit load and branch ring-barking affect carbon allocation and photosynthesis of leaf and fruit of Coffea arabica in the field

Increasing fruit load (from no berries present to 25, 50 and 100% of the initial fruit load) significantly decreased branch growth on 5-year-old coffee (Coffea arabica L.) trees of the dwarf cultivar 'Costa Rica 95', during their third production cycle. Ring-barking the branches further reduced their growth. Berry dry mass at harvest was significantly reduced by increasing fruit load. Dry matter allocation to berries was four times that allocated to branch growth during the cycle. Branch dieback and berry drop were significantly higher at greater fruit loads. This illustrates the importance of berry sink strength and indicates that there is competition for carbohydrates between berries and shoots and also among berries. Leaf net photosynthesis (P(n)) increased with increasing fruit load. Furthermore, leaves of non-isolated branches bearing full fruit load achieved three times higher P(n) than leaves of isolated (ring-barked) branches without berries, indicating strong relief of leaf P(n) inhibition by carbohydrate demand from berries and other parts of the coffee tree when excess photoassimilates could be exported. Leaf P(n) was significantly higher in the morning than later during the day. This reduction in leaf P(n) is generally attributed to stomatal closure in response to high irradiance, temperature and vapor pressure deficit in the middle of the day; however, it could also be a feedback effect of reserves accumulating during the morning when climatic conditions for leaf P(n) were optimal, because increased leaf mass ratio was observed in leaves of ring-barked branches with low or no fruit loads. Rates of CO(2) emission by berries decreased and calculated photosynthetic rates of berries increased with increasing photosynthetic photon flux (PPF) especially at low PPFs (0 to 100 micromol m(-2) s(-1)). The photosynthetic contribution of berries at the bean-filling stage was estimated to be about 30% of their daily respiration costs and 12% of their total carbon requirements at PPF values commonly experienced in the field (200 to 500 micromol m(-2) s(-1)).

Low temperature stress modifies the photochemical efficiency of a tropical tree species Hevea brasiliensis: effects of varying concentration of CO<sub>2</sub> and photon flux density

Two clones of Hevea brasiliensis (RRII 105 and PB 235) were grown for one year in two distinct agroclimatic locations (warmer and colder, W and C) in peninsular India. We simultaneously measured gas exchange and chlorophyll (Chl) fluorescence on fully mature intact leaves at different photosynthetic photon flux densities (PPFDs) and ambient CO2 concentrations (Ca) and at constant ambient O2 concentration (21 %). Net photosynthetic rate (PN), apparent quantum yield for CO2 assimilation (Φc), in vivo carboxylation efficiency (CE), and photosystem 2 quantum yield (ΦPS2) were low in plants grown in C climate and these reductions were more predominant in RRII 105 than in PB 235 which was also reflected in their growth. We estimated in these clones the partitioning of photosynthetic electrons between CO2 reduction (JA) and processes other than CO2 reduction (J*) at low and high PPFDs and Ca. At high Ca (700 µmol mol-1) most of the photosynthetic electrons were used for CO2 assimilation and negligible amount went for other processes when PPFD was low (200-300 µmol m-2 s-1) both in the C and W climates. But at high PPFD (900-1 100 µmol m-2 s-1), J* was appreciably high even at a high Ca. Hence at normal ambient Ca and high irradiance, electrons can be generated in the photosynthetic apparatus far in excess of what can be safely utilised for photosynthetic CO2 reduction. However, at high Ca there was increased diversion of electrons to photosynthetic CO2 reduction which resulted in improved photosynthetic parameters even in plants grown in C climate.

Effects of in vitrorooting environments and irradiance on growth and photosynthesis of strawberry plantlets during acclimatization

Strawberry (Fragaria ananassaDuch. cv. Fengxiang) plantlets were cultured under two in vitroenvironments for rooting, and then acclimatized under two ex vitroirradiance conditions. At the end of rooting stage plant height, fresh weight and specific leaf area of T1-plants grown under high sucrose concentration (3 sucrose), low photosynthetic photon flux density (30 μ mol m−2 s−1) and normal CO2 concentration (350–400 μl l−1) were significantly higher than those of T2-plantlets grown under low sucrose concentration (0.5), high photosynthetic photon flux density (90 μ mol m−2 s−1) and elevated CO2 concentration (700–800 μl l−1). But T2-plantlets had higher net photosynthetic rate (Pn), effective photochemical quantum yield of PSII (ΦPSII), effective photosynthetic electron transport rate (ETR), photochemical quenching (qP) and ratio of chlorophyll fluorescence yield decrease (Rfd). After transfer, higher irradiance obviously promoted the growth of plantlets and was beneficial for the development of photosynthetic functions during acclimatization. T2-plantlets had higher fresh weight, leaf area, ΦPSII and ETR under higher ex vitroirradiance condition.

Potential Use of a 24-Hour Photoperiod (Continuous Light) with Alternating Air Temperature for Production of Tomato Plug Transplants in a Closed System

To evaluate the potential use of a 24-hour photoperiod for transplant production in a closed system, tomato (Lycopersicon esculentum Mill.) plug transplants were grown for 17 days either under a 24-hour photoperiod with a photosynthetic photon flux (PPF) of 200 μmol·m-2·s-1 or under a 16-hour photoperiod with a PPF of 300 μmol·m-2·s-1, resulting in the same daily integrated PPF (17.3 mol·m-2). Air temperatures were alternated between 28 °C during the first 16 hours and 16 °C for the subsequent 8 hours of each day. Fresh weight, dry weight and leaf area were 41%, 25%, and 64% greater, respectively, under the 24-hour photoperiod than under the 16-hour photoperiod. Physiological disorders (e.g., chlorosis and/or necrosis) were not observed under the 24-hour photoperiod, probably due to the alternating air temperature. Floral development of plants originating from both treatments did not differ significantly. Electric energy use efficiency of the closed system was 9% greater under the 24-hour photoperiod than under the 16-hour photoperiod. These results suggest that using a 24-hour photoperiod with relatively low PPF can reduce both initial and operational costs for transplant production in a closed system due to the reduction in the number of lamps.

Application of a novel disposable film culture system to photoautotrophic micropropagation of Eucalyptus uro-grandis (Urophylia x grandis)

To overcome various disadvantages of conventional culture vessls for plant micropropagation, we previously developed the photoautotrophic micropropagation technique, with special mention for the first practical film culture system, the ‘Miracle Pack’ (MP), which was made of fluorocarbon polymer film (Neoflo® PFA film) and supported by a polycarbonate frame. While the PFA film has superior thermal stability, high light transmittance and high gas permeability, making the MP system (MP-PFA) superior to conventional culture vessels for the micropropagation of various plant species, its high cost is a disadvantage. In this study, a possible alternative of lower-cost OTP® film made of TPX (4-methyl-1-pentane polymer) and CPP (a polypropylene), which possesses similar characteristics to PFA film, is evaluated to develop a novel disposable film culture vesel, termed ‘Vitron’, for culturing Eucalyptus (urophylla x grandis), plantlets. The three film culture systems, MP-PFA, MP-OTP (MP with OTP film), and Vitron, were placed under CO2 enrichment, low photosynthetic photon flux density (PPFD; 45 μmol m−2 s−1), and sugar-free medium, using phenol resin foam (Oasis®) as a substrate. In vitro and ex vitro growth and development of Eucalyptus shoots from the four-leaf stage to the rooting stage were compared for all three culture systems. The effects of the duration and concentration of CO2 enrichments on in vitro growth of Eucalyptus cultured in the Vitron film system were also examined. The best growth and quality of Eucalyptus plantlets was obtained for the Vitron vessel placed in 3000 ppm CO2 enrichment for 24 hours per day at low PPFD with sugar-free liquid medium and Oasis as substate. Results of this study suggest that the novel Vitron culture system is suitable for the photoautotrophic micropropagation of Eucalyptus.

Tall Fescue Photomorphogenesis as Influenced by Changes in the Spectral Composition and Light Intensity

The influence of deciduous foliage shade on turfgrass development has not been fully investigated. Previous research neglects changes in spectral distribution, e.g., red:far‐red light (R:FR) ratios common of foliage shade. Turfgrass plants may respond simultaneously but in different ways to changes in light intensity and spectral composition. A field study was conducted in 2001–2002 at the Ohio Turfgrass Research and Educational Facility, Columbus, OH. Two tall fescue (Festuca arundinacea Schreb.) cultivars of differing shade tolerance were established under low photosynthetic photon flux (PPF) in approximately 8% of full sunlight with high (>1) and low (<1) R:FR ratios to distinguish between developmental effects of R:FR ratio (spectral composition) and PPF (light intensity) on turfgrass photomorphogenesis. Few morphological differences in shade tolerance between the two cultivars were observed during the 2‐yr study. However, under low PPF, high R:FR ratios led to increased tillering, leaf blade width and thickness, and chlorophyll contents. Root mass declined under reduced PPF regardless of R:FR ratio. Results suggest that while turfgrass photomorphogenesis in shade is influenced by changes in PPF, many characters are further influenced by changes in the R:FR ratio.

EFFECTS OF GAP AND UNDERSTORY EVIRONMENTS ON THE REGENERATION OF QUERCUS ALIENA VAR. ACUTESERRATA AND FAGUS ENGLERIANA

Quercus aliena var. acuteserrata and Fagus engleriana are important species in the temperate and subtropical middle-elevation mountainous areas of China. In this study, we investigated the regeneration dynamics, diameter size class distributions, and the light response curve of these two species to better understand the effects of light availability on the regeneration of Q. aliena var. acuteserrata and F. engleriana. The results showed that both species had a high abundance of seedlings in the field, but the survival rate from seedling to sapling stage was nearly zero for Q. aliena var. acuteserrata and only 6%-8% for F. engleriana. In the mixed-forest that contained both species, the population of F. engleriana showed a stable pyramidal age structure, but the size structure of Q. aliena var. acuteserrata was dominated by a few cohorts of trees that were able to establish within a short time period. From the light saturation response curve of the two-year old cohort, Q. aliena var. acuteserrata seedlings in gaps had a higher maximum photosynthetic rate (4.61 #mu#mol·m~(-2)·s~(-1)) than F. engleriana (4.16 #mu#mol·m~(-2)·s~(-1)) and, for the seedlings under canopy, F. engleriana had higher maximum photosynthetic rate (3.89#mu#mol·m~(-2)·s~(-1)) than Q. aliena var. acuteserrata (3.68 #mu#mol·m~(-2)·s~(-1)). Moreover, seedlings of F. engleriana reached maximum photosynthetic rates with lower photosynthetic photon flux density than Q. aliena var. acuteserrata. The light induction curve indicated that both the response speed and the maximum photosynthetic rate of Q. aliena var. acuteserrata understorey seedlings were lower than that of F. engleriana, which demonstrated different competitive abilities and shade-tolerance characteristics of the two species. Resource allocation experiments showed that Q. aliena var. acuteserrata seedlings allocated more biomass to above-ground growth whereas F. engleriana seedlings allocated more biomass to under-ground growth. These results are consistent with the different light use strategies of the two species.

Light Intensity and Fertilizer Concentration: II. Optimal Fertilizer Solution Concentration for Species Differing in Light Requirement and Growth Rate

To evaluate the effects of increasing photosynthetic photon flux (PPF) on optimal fertilizer concentrations, we grew wax begonia (Begonia semperflorens-cultorum Hort.) and petunia (Petunia ×hybrida Hort. Vilm-Andr.) seedlings in a soilless growing medium without starter fertilizer under three PPF treatments (high, medium, and low corresponding to an average daily PPF of 23.2, 15.6, and 9.8 mol·m-2.d-1, respectively) and subirrigated with six fertilizer concentrations [electrical conductivity (EC) of 0.12, 0.65, 1.18, 1.71, 2.24, and 2.77 dS·m-1]. Compared to low PPF, shoot dry mass of wax begonia and petunia seedlings increased 2- and 3-fold, respectively, at high PPF. Fertilizer EC resulting in maximum shoot dry mass was the same (1.28 and 1.87 dS·m-1 for wax begonia and petunia, respectively) in the three PPF treatments. Shoot dry mass and leaf area of petunias decreased little at higher than optimal fertilizer EC in the three PPF treatments, while growth of begonia was inhibited at high fertilizer EC. The optimal fertilizer range, calculated as the lower and upper limits of fertilizer EC within which plant growth was not reduced by >10% as compared to the optimum EC was 0.65 to 1.71 dS·m-1 in wax begonia and 1.18 to >2.77 dS·m-1 for petunia. Compared to those grown at 1.18 dS·m-1, wax begonias grown at 1.71 dS·m-1 had similar dry mass, but were shorter in all three PPF treatments (average height reduction of 6.5%). In general, EC of the top layer of the growing medium was higher than that of the bottom layer of the growing medium, and this difference increased with increasing EC.

Membrane Filter와 Sucrose 농도가 도라지(Platycodon grandiflorum A. DC.) 기내 배양묘의 생장에 미치는 영향

The shoots of balloon flower (Platycodon grandiflorum A. DC.) in vitro germinated from seeds were cultured on MS basal medium containing 0.1 mg/L NAA under the various sucrose concentrations and with/without membrane filter (MF) on the lid of vessel. The growth responses were checked to obtain healthy plantlets. The and H concentration in vessel without MF were higher than those with MF. The concentration without MF was increased as days in culture went by whereas the H concentration was decreased. The plant growth with MF and high sucrose concentration was good. Fresh and dry weight of plantlets cultured in sucrose 4.5% with MF were higher than those in no sucrose without MF. Also the content of chlorophyll of plantlets cultured with MF was high and the content of sugar was shown a similar results and a remarkable difference between MF treatments, especially. Stomata cultured with MF was closer than that without MF and mesophyll of leaf were more developed with MF or in high sucrose concentration. When the plantlets were transplanted in the pot at 252, 75% relative humidity and low PPFD (photosynthetic photon flux density), the percentage of survival after 13 days without MF was 0% but it was 100% with MF regardless of sucrose concentrations.

Dynamics of non-structural carbohydrates in two Ficus species after transfer to deep shade

The present study aims at assessing the role of stored carbohydrates of F. benjamina L. and F. binnendijkii (Miq.) Miq., two tropical trees of horticultural significance, during acclimation to very low light intensities. Plants were grown at an average photosynthetic photon flux density (PPFD) of 90 μmol m −2 s −1, and then transferred to a low-light treatment, with a PPFD of 5 μmol m −2 s −1. Plants of both species showed negative growth rates for approximately 1 week, coinciding with a substantial decrease in the levels of total non-structural carbohydrates (TNC; starch and soluble sugars) in leaves and stems. TNC reached much lower levels in developing leaves than in fully grown leaves, and some of these developing leaves were shed in F. benjamina. In stems and leaves combined, TNC levels were 142 mg g −1 (plant) in F. benjamina and 160 mg g −1 (plant) in F. binnendijkii at the time of transfer to low light. Thirty days later, in fully acclimated plants, these levels had stabilised at 116 and 112 mg g −1. The relatively minor damage to the plants and short duration of a negative carbon balance, despite the low mean PPFD 5 μmol m −2 s −1, illustrate the capacity of both F. benjamina and F. binnendijkii to tolerate deep shade. Stored carbohydrates are important in plants that grow in environments like forest understories or indoor environments, where carbon balance can be negative for several days.

Transient release of oxygenated volatile organic compounds during light-dark transitions in Grey poplar leaves.

In this study, we investigated the prompt release of acetaldehyde and other oxygenated volatile organic compounds (VOCs) from leaves of Grey poplar [Populus x canescens (Aiton) Smith] following light-dark transitions. Mass scans utilizing the extremely fast and sensitive proton transfer reaction-mass spectrometry technique revealed the following temporal pattern after light-dark transitions: hexenal was emitted first, followed by acetaldehyde and other C(6)-VOCs. Under anoxic conditions, acetaldehyde was the only compound released after switching off the light. This clearly indicated that hexenal and other C(6)-VOCs were released from the lipoxygenase reaction taking place during light-dark transitions under aerobic conditions. Experiments with enzyme inhibitors that artificially increased cytosolic pyruvate demonstrated that the acetaldehyde burst after light-dark transition could not be explained by the recently suggested pyruvate overflow mechanism. The simulation of light fleck situations in the canopy by exposing leaves to alternating light-dark and dark-light transitions or fast changes from high to low photosynthetic photon flux density showed that this process is of minor importance for acetaldehyde emission into the Earth's atmosphere.

Effects of changes in the photosynthetic photon flux density on net gas exchange of Citrus limon and Nicotiana tabacum

The objective of this study was to evaluate the effects of changes in the photosynthetic photon flux density (PPFD) on net gas exchange of Citrus limon, a woody species, and Nicotiana tabacum, an herbaceous species. When PPFD was increased from 50 to 350 mumol.m-2.s-1 and returned to 50 mumol.m-2.s-1 after 60 min, the CO2 assimilation rate (A) increased and stabilized after 15 min in both species. Stomatal conductance (g s), however, continued to increase. After returning to low PPFD, A immediately diminished to a low value for both lemon and tobacco. Stomatal conductance of lemon diminished slowly over 60 min, whereas g s for tobacco took only 15 min to decrease. This difference in behavior is probably due to over-sensitivity of stomata of woody species, such as Citrus, when exposed to high light, retarding stomatal closure on return to low PPFD. Furthermore, when lemon, growing at a PPFD of 300 mumol.m-2.s-1, was submitted to a step increase of 600 mumol.m-2.s-1, there was an oscillatory behavior of A and g s requiring 150 min to stabilize. The causes of this behavior are discussed with respect to improved intrinsic water use efficiency by stomatal closure.

Optimizing Environmental Conditions for Mass Application of Mechano-dwarfing Stimuli to Arabidopsis

Obtaining uniform mechano-dwarfing of Arabidopsis thaliana (L.) Heynh. seedlings within dense plantings is problematic. Alternative forms of mechano-stimulation were applied to seedlings in effort to obtain uniform growth reduction compared with undisturbed controls in both greenhouse and controlled growth environments. Arabidopsis grown under low photosynthetic photon flux (PPF) artificial light grew upright with limited leaf expansion, which enhanced mechano-responsiveness compared to that of rosette-growing plants under filtered sunlight or high PPF artificial light. Hypocotyls of seedlings grown at PPFs > 60 micromoles m-2 s-1 elongated less and had 6% less sensitivity to mechanical stress than seedlings grown at PPFs < 60 micromoles m-2 s-1. Fluorescent lamps alone (F) or fluorescent plus incandescent (F+I) lamps were compared for seedling responses to mechanical stress. Under F lighting, hypocotyl elongation was reduced 25% to 40% by twice-daily brush or plate treatments, and brushed seedlings exhibited more growth reduction than did plate treatments. Seedlings grown under F+I lamps exhibited similar stress-induced growth reduction compared to seedlings grown under F only, but stressed F+I seedlings lodged to a greater extent due to excessive hypocotyl elongation. Temperature-response studies using standardized F-only lighting indicated increased hypocotyl elongation but decreased leaf expansion, and decreased mechano-responsivity to brushing over the temperature range from 20 to 28 degrees C. Daylength studies indicated similar degrees of mechano-inhibition of hypocotyl elongation over the daylength range of 12, 16, 20, and 24 hours, whereas fresh weight of stressed seedling shoots declined compared to controls. A combination of environmental growth parameters that give repeatable, visual mechanical dwarfing of Arabidopsis include low-PPF fluorescent lighting from 55 to 60 micromoles m-2 s-1, ambient temperatures from 22 to 25 degrees C, and twice-daily brush treatments.

Longevity and quality of cut ‘Master’ carnation and ‘Red Sandra’ rose flowers as affected by red light

Cut flowering stems (45 cm long) of carnation (cv. Master) and rose (cv. Red Sandra) were placed in test tubes containing distilled water with or without commercial preservative (20 ml l−1), under fluorescent tubes of 50 ± 10 μmol m−2 s−1 Photosynthetic photon flux (PPF). A mixed radiation from fluorescent tubes with red light provided by light emitting diodes (LEDs) and monochromic red light of low 50 or high 90 ± 10 μmol m−2 s−1 was also tested in the absence of preservative solution. Both red light with high PPF and the mixed radiation under low PPF extended the vase life of cut carnations, and flower freshness could be maintained for 10.9 days compared with a water/fluorescent light control. In cut rose, the treatment containing the preservative solution under fluorescent tubes alone and in red alone, regardless of light intensity, prolonged vase life for 4.6 and 4.2 days longer than the control, respectively. Treatment with red LEDs plus high PPF resulted in complete petal opening in carnation flowers.

Photosynthesis, Carbohydrate Metabolism, and Yield of Phytochrome‐B‐Overexpressing Potatoes under Different Light Regimes

Transgenic potatoes (Solanum tuberosum L.) overexpressing Arabidopsis thaliana (L.) Heynh. phytochrome B (phyB) have been reported to exhibit a substantially modified plant architecture, increased photosynthetic performance, reduced photoinhibition, delayed leaf senescence, and increased tuber yield. A greenhouse and a growth chamber experiment were conducted at Braunschweig, Germany, to elucidate the crop physiological basis for the yield differences between moderately phyB‐overexpressing transgenic (Dara‐5) and wild‐type potato plants. In the greenhouse experiment, Dara‐5 leaves showed a 23% greater leaf carbon exchange rate (CER) at light saturation, 32% greater leaf conductance, and 21% longer green leaf area duration (GLAD) than the wild‐type plants. The transgenic plants partitioned a considerably greater portion of their biomass to stems and roots, but tuber and total biomass yield did not significantly differ among genotypes. The leaves and stems of the transgenic plants had lower starch and soluble sugar concentrations but consistently higher N concentration than those of the nontransgenic plants. Light response curves showed increasing CER superiority of Dara‐5 leaves with increasing photosynthetic photon flux (PPF), suggesting higher productivity of the transgenic plants in high‐radiation environments. Therefore, the two genotypes were compared in growth chambers at low, medium, and high light levels of 300, 600, and 900 μmol m−2 s−1 PPF. Leaf CER of the transgenic plants reached 123, 115, and 120% of the wild‐type plants at low, medium, and high PPF, but only at low PPF did the transgenic plants produce significantly greater (+8%) tuber yield than the nontransgenic plants. It is supposed that enhanced C loss from respiration is responsible for the lack of consistent transgenic yield superiority.

Seedling growth of understorey species of a Southeast Brazilian tropical forest

Thirteen understorey species of a mesophyllous tropical forest were studied under two different photosynthetic photon flux densities (PPFD). Seedlings were grown in the glasshouse under 51% and 2.6% solar PPFD. Growth of the seedlings was evaluated by 1-) total height; 2-) leaf number; 3-) leaf dry mass;4-) stem dry mass; 5-) root dry mass; 6-) stem length/mass; 7-)shoot/root mass; 8-) percent allocation to leaf, stem and roots. For most of the parameters recorded, low PPFD drastically reduced growth. It seemed that the strategy of these understorey species was a reduction of growth under low PPFD saving energy for survival.

Effects of Irradiance on Photosynthesis and Activity of Protease Inhibitors in Amaranthus hypochondriacus

Amaranthus hypochondriacus plants were grown under three photosynthetic photon flux densities (PPFD). Mature plants grown at full sunlight (38.8 mol m−2 d−1) had higher maximum net photosynthetic rate (PN) and significantly higher leaf trypsin inhibitor activity than plants that developed under lower PPFD (19.4 and 12.8 mol m−2 d−1). In contrast, seeds collected from plants fully exposed to sunlight showed the lowest activity of trypsin inhibitor, higher rate of germination and susceptibility to infection by Aspergillus niger.

VENTILATION AND LIGHT INTENSITY DURING IN VITRO CULTURE AFFECT RELATIVE GROWTH RATE AND PHOTOSYNTHATE PARTITIONING OF CALADIUM PLANTLETS AFTER TRANSPLANTING TO EX VITRO

Caladium bicolor 'Candidum' plantlets were cultured on medium containing 2% sucrose and 0.8% agar in vitro under different conditions of ventilation and photosynthetic photon flux density (PPFD) and then transplanted to an ex vitro environment. During in vitro culture, the plantlets were fed with 13 CO 2 . Dry weight of plantlets cultured in the high-ventilated vessel was no greater than that cultured in a low-ventilated vessel, however, after transplanting, the relative growth rate of the plantlets cultured in the high-ventilated vessel was greater than that cultured in a low-ventilated vessel. Culturing in the low-ventilated vessel increased partitioning of 13 C to a stem during in vitro culture and in the long term after transplanting. Culturing under low PPFD did not affect the distribution ratio of 13C in plant parts, but after acclimatization, the 13C atom % excess in the whole plant cultured under low PPFD was lower than that cultured under high PPFD, indicating that the photosynthates obtained under low PPFD conditions were less re-translocated to new tissues and organs. The results indicate that the ventilation condition and light intensity during in vitro culture affect the translocation of photosynthates not only during the culture but also in the long term after transplanting to ex vitro.

Photosynthetic photon flux density influences grass responses to extended photoperiod

While plant sensitivity to extended photoperiod has been well documented, virtually no attention has been given to the possibility that low-level photosynthetic photon flux density (PPFD) during the extended photoperiod has an influence on the expression of the photoperiodic response. This study was undertaken with four grasses (Pensacola bahiagrass, Paspalum notatum Flugge, Tifton 85 bermudagrass, Cynodon dactylon L., Florakirk bermudagrass, Florona stargrass, Cynodon nlemfuensis Vanderyst var. nlemfuensis) grown under field conditions to examine their photoperiodic responses under a PPFD gradient. Individual lamps were positioned above each experimental plot to impose a PPFD gradient (from 0.1 to 30 μmol m −2 s −1) during the extended photoperiod treatment. The experiment was undertaken during two seasons of short daylengths and plant responses were measured as mass accumulation and height. There was a linear increase in both measured variables with increasing PPFD up to a level where the plant responses were light saturated. Saturating PPFD was generally consistent between mass accumulation and height within a species, but there were substantial differences among grasses. Grasses with the greatest relative increase in mass accumulation under saturating PPFD for the extended photoperiod also were found to require the greatest PPFD for saturation. Overall, these results provided original observations on the quantitative response of plants to PPFD showing that there was a linear increase in response at very low PPFD and a saturating PPFD that varied among the grasses.