Search Results

You are looking at 51 - 60 of 919 items for :

  • "photosynthetic photon flux" x
  • Refine by Access: All x
Clear All
Free access

X. Cao and F.A. Hammerschlag

As part of a program to develop transgenic highbush blueberry (Vaccinium corymbosum L.) cultivars, studies were conducted to determine optimum conditions for high efficiency shoot regeneration from leaf explants of shoots propagated in vitro. The effects on shoot organogenesis of age of explant source, length of dark treatment, the addition of either thidiazuron (TDZ) at 1 or 5 μm, or zeatin riboside at 20 μm to the regeneration medium, and a photosynthetic photon flux (PPF) of either 18 ± 5 or 55 ± 5 μmol·m–2·s–1 were investigated. A maximum of 13.0, 13.0, 12.6, and 4.6 shoots regenerating per explant for cultivars Duke, Georgiagem, Sierra, and Jersey, respectively, occurred on regeneration medium with zeatin riboside and under a PPF of 55 ± 5 μmol·m–2·s–1. `Duke' regenerated equally well on medium with either zeatin riboside or 1 μm TDZ, whereas the number of shoots per explant for `Georgiagem' and `Sierra' was significantly higher on zeatin riboside. Regeneration of `Duke', `Jersey', and `Sierra' on zeatin riboside was significantly better under a PPF of 55 ± 5 μmol·m–2·s–1 than under 18 ± 5 μmol·m–2·s–1, but the higher PPF inhibited regeneration of `Duke' on 5 μm TDZ. There were no significant differences in percentage of regeneration or the number of shoots per explant from leaf explants derived from either 1-, 2-, or 3-week-old shoot cultures, or when either 1 week or 2 weeks of darkness preceded light treatments. Chemical names used: 1-phenyl-3-(1,2,3-thiadiazol-5-yl)urea (thidiazuron, TDZ); 9-(-β-ribofuranosyl)-6-(4-hydroxy-3-methyl-but-2-enylamino)purine (zeatin riboside).

Free access

Keith A. Funnell, Errol W. Hewett, Ian J. Warrington, and Julie A. Plummer

Dry matter accumulation and partitioning in plants of Zantedeschia Spreng. `Best Gold' aff. Z. pentlandii (Wats.) Wittm. (syn. Richardia pentlandii Wats.) were quantified under a range of temperature and photosynthetic photon flux (PPF) regimes using plant growth analysis. The relative rate of dry matter accumulation [relative growth rate (RGRM), g·g-1·d-1] was highly correlated with the partitioning of the daily increment of dry matter into leaf tissue [leaf matter partitioning (LMP), g·d-1 per g·d-1]. In contrast, a poor correlation existed between RGRM and net assimilation rate (NAR, g·m-2·d-1). Maximum values of RGRM increased linearly with increasing temperature (from 13 to 28 °C), with a base temperature of 2.1 ± 2.7 °C. The optimum temperature for growth was PPF dependent with maximum total plant dry mass occurring under high PPF (694 μmol·m-2·s-1) at 25 °C. However, as the plant responded to PPF by altering LMP, final total plant dry mass was actually greater under the low PPF regime (348 μmol·m-2·s-1) at temperatures <22 °C. The optimum temperature for dry matter accumulation was close to the average daily air temperature during the growing season for the natural habitat of the parent species. Similarly, the greater dry matter accumulation under the combination of either low PPF and cooler temperatures or high PPF and warmer temperatures was paralleled by the diversity of PPF habitats in the natural open grassland and forest margin the parent species occupies. It is therefore suggested that Zantedeschia `Best Gold' is well adapted to optimize growth under these environmental conditions.

Free access

David F. Graper and Will Healy

Abbreviations: DW, dry weight; FW, fresh weight; HPS, high pressure sodium; IR, infrared; PPF, photosynthetic photon flux; RGR, relative growth rate. 1 Currently Assistant Professor, Dept. of Horticulture, Forestry, Landscape and Parks, South Dakota

Free access

Stephen C. Myers

Abbreviations: DAH, days after harvest; DBH, days before harvest; PPFD, photosynthetic photon flux density; WSR. watersprout removal. 1 Associate Professor of Horticulture. A contribution of the Univ. of Georgia Agricultural Experiment Station

Free access

I.J. Warrington and R.A. Norton

Abbreviations: CE, controlled environment; PPF, photosynthetic photon flux. 1 Present address: Horticulturist, Washington State Univ. Research and Extension Unit, Mount Vernon, WA 98273. We gratefully acknowledge the assistance of Jill Stanley, the

Free access

Hiphil S. Clemente and Thomas E. Marler

Field-grown `Red Lady' papaya (Carica papaya L.) plants were used to measure foliar gas-exchange responses to rapid changes in irradiance levels to determine if papaya stomata are able to track simulated sun-to-cloud cover transitions. Natural sunlight and neutral shade cloth placed over the leaf were used to provide high photosynthetic photon flux (PPF) of about 2000 μmol·m-2·s-1 until leaves reached steady state within the cuvette, followed by three minutes with low PPF of about 325 μmol·m-2·s-1, and a return to PPF of about 2000 μmol·m-2·s-1. Net CO2 assimilation (A) declined from an initial 20 μmol·m-2·s-1 to about 9 μmol·m-2·s-1 within 20 seconds of initiating low PPF, and remained fairly stable for the duration of the three minutes of low PPF. Stomatal conductance (gs) declined within 60 seconds of initiating low PPF, from 385 to about 340 μmol·m-2·s-1 during the three minutes duration of low PPF. Following the return to high PPF, A rapidly increased to about 18 μmol·m-2·s-1, then gradually increased to the original value. After a lag of about 1 minute following the return to high PPF, gs began to increase and returned to the original value after three minutes. Container-grown `Tainung #1' papaya plants were used in a second study to determine the influence of mild drought stress on gas-exchange responses to rapid irradiance transitions. For drought-stressed plants, gs declined to a greater magnitude following the high-to-low PPF transition, and gs and A recovered more slowly following the transition from low-to-high PPF than for well-watered plants. Water use efficiency declined to a minimum immediately following the high-to-low PPF transition for both sets of plants, but recovered more rapidly for drought-stressed plants. These results indicate that papaya stomata are able to track rapid changes in irradiance, and mild drought stress enhances the tracking response.

Free access

Hector R. Valenzuela, Bruce Schaffer, and Stephen K. O'Hair

Abbreviations: A, net CO assimilation; DAP, days after planting; E, transpiration; g, stomatal conductance; PPF, photosynthetic photon flux; WUE, water-use efficiency. Florida Agricultural Experiment Stations Journal Series no. R-00590. We thank R

Free access

O. Ayari, M. Dorais, and A. Gosselin

Daily and seasonal variations of photosynthetic activity, chlorophyll a (Chl-a) fluorescence and foliar carbohydrate content were studied in situ on greenhouse tomato (Lycopersicon esculentum Mill. `Trust') plants grown under CO2 enrichment and supplemental lighting. The objective of this study was to assess the effect of seasonal variation of the photosynthetic photon flux (PPF) on photosynthetic efficiency of tomato plants and to determine the presence or absence of photosynthetic down-regulation under greenhouse growing conditions prevailing in northern latitudes. During winter, the fifth and the tenth leaves of tomato plants showed low, constant daily photosynthetic activity suggesting a source limitation under low PPF. In winter, the ratio of variable to maximum Chl-a fluorescence in dark adapted state (Fv/Fm) remained constant during the day indicating no photoinhibition occurred. In February, an increase in photosynthetic activity was followed by a decline during March, April, and May accompanied by an increase in sucrose and daily starch concentrations and constant but high hexose level. This accumulation was a long-term response to high PPF and CO2 enrichment which would be caused by a sink limitation. Thus, in spring we observed an in situ downregulation of photosynthesis. The ratio Fv/Fm decreased in spring compared to winter in response to increasing PPF. The daily decline of Fv/Fm was observed particularly as a midday depression followed by a recovery towards the end of the day. This indicated that tomato leaves were subject to a reversible inhibition in spring. Fv/Fm was lower in March than in April and May even though PPF was higher in April and May than in March. These results suggest that tomato plants develop an adaptive and protective strategy as PPF increases in spring.

Free access

David F. Graper and Will Healy

Abbreviation∼ CHO, carbohydrate; DW, dry weight PE, photoperiod extension; Pn, photosynthesis; PPF, photosynthetic photon flux; SLW, specific leaf weight. 1 Currently, Assistant Professor, Dept. of Horticulture, Forestry, Landscape, and Parks, South

Open access

Tomohiro Jishi, Ryo Matsuda, and Kazuhiro Fujiwara

, respectively ( Table 1 ). Fig. 1. Light irradiation treatments consisting of four relative spectral photosynthetic photon flux density change patterns—( A, E, I ) BR/BR; ( B, F, J ) R/BR; ( C, G, K ) B/BR; ( D, H, L ) B/R—over a 24-h cycle in combination