constitute the main sink for photoassimilates during the fruit growth period. Removing or retaining fruit has often been used in studies of plant source-sink relationships ( Syvertsen et al., 2003 ; Vaast et al., 2005 ). Reduced photosynthetic rates under
Jieshan Cheng, Peige Fan, Zhenchang Liang, Yanqiu Wang, Ning Niu, Weidong Li, and Shaohua Li
Lili Zhou, Maria Eloisa Q. Reyes, and Robert E. Paull
total photosynthetic capacity of papaya plants. Papaya has a characteristic C 3 anatomy ( Campostrini and Glenn, 2007 ; Marler et al., 1994 ). The net photosynthetic carbon assimilation rate at 2000 μmol·m −2 ·s −1 PAR ranges from 25 to 35 μmol·m −2
David M. Hunter and John T.A. Proctor
Paclobutrazol applied as a soil drench at 0, 1, 10, 100, or 1000 μg a.i./g soil reduced photosynthetic CO2 uptake rate of leaves formed before paclobutrazol treatment within 3 to 5 days of treatment and the reductions were maintained for 15 days after treatment. The percentage of recently assimilated 14C exported from the source leaf was reduced only at the highest paclobutrazol dose, and there was little effect of treatment on the partitioning of exported 14C between the various sinks. In response to increasing doses of paclobutrazol, particularly at the higher doses, an increasing proportion of recent photoassimilates was maintained in a soluble form in all plant components. Reduced demand for photoassimilates as a result of the inhibition of vegetative growth may have contributed to a reduction in photosynthetic CO2 uptake rate, but this reduction in photosynthesis rate could not be attributed to a feedback inhibition caused by a buildup of starch in the leaves. Paclobutrazol had only a minor effect, if any, on photosynthetic electron transport. Chemical name used: β-[(4-chlorophenyl) methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).
Toshio Shibuya, Yoshiaki Kitaya, Toyoki Kozai, and Masaichi Nakahara
Net photosynthetic and evapotranspiration rates of tomato (LAI = 2.3) and lettuce (LAI = 6.6) plug sheets were estimated based on measurements of the weight of plug sheets and vertical profiles of CO2 concentration above the plug sheets. The measurements were continued in situ for several days in a greenhouse when plugs were at transplant stage. The maximum net photosynthetic rates of tomato and lettuce plug sheets were 0.8 and 2.0 mg CO2/m2 per sec on a plug sheet area basis, respectively. The maximum evapotranspiration rates of those sheets were 100 mg·m–2·s–1. Net photosynthetic and evapotranspiration rates of tomato and lettuce plug sheets increased linearly with an increase in solar radiation flux, with a correlation coefficient of 0.9.
Chieri Kubota and Toyoki Kozai
Growth and net photosynthetic rate of potato (Solanum tuberosum L.) `Benimaru' plantlet in vitro were studied under a conventional photomixotrophic condition [with 20 g sucrose/liter in the medium and under 70 μmol·m-2·s-1 photosynthetic photon flux (PPF)] with minimal ventilation (MV) and under photoautotrophic conditions (without sugar in the medium and under 190 μmol·m-2·s-l PPF) with enhanced natural ventilation using an air diffusive filter (DV) or with forced ventilation (FV). Fresh weight of the plantlets cultured in the FV and DV treatments was 2.4 times that of the plantlets cultured in the MV treatment. Net photosynthetic rate and dry weight per plantlet were the highest in FV followed by DV. For photoautotrophic micropropagation, FV was superior to DV.
Chieri Kubota, Natsuko Kakizaki, Toyoki Kozai, Koichi Kasahara, and Jun Nemoto
Nodal explants of tomato (Lycopersicon esculentum Mill.) were cultured in vitro to evaluate the effects of sugar concentration, photosynthetic photon flux (PPF), CO2 concentration, ventilation rate of the vessel, and leaf removal on growth and photosynthesis. After 20 days of culture, the dry weights of plantlets derived from explants with leaves and cultured photoautotrophically (without sugar in the medium) under high PPF, high CO2 concentration, and high ventilation rate were more than twice as great as those of plantlets derived conventionally from explants without leaves and cultured photomixotrophically (with sugar in the medium) under low PPF, low CO2 concentration, and low ventilation rate (107 and 45 mg per plantlet, respectively). Under photomixotrophic micropropagation conditions, the dry weights of plantlets from explants with leaves increased more than did those of plantlets from explants without leaves. High PPF, high CO2 concentration, and high ventilation rate increased net photosynthetic rate and promoted growth of the plantlets under photomixotrophic micropropagation conditions. Photomixotrophic conditions produced the greatest dry weight and the longest shoots, but photoautotrophic conditions produced the highest net photosynthetic rate. The number of leaves did not differ significantly between photoautotrophically and photomixotrophically cultured plantlets. Thus, photoautotrophic micropropagation is applicable to the production of high quality tomato transplants.
Cheryl R. Hampson, Anita N. Azarenko, and John R. Potter
In hazelnut (Corylus avellana L.), vigorous vegetative growth and traditional orchard practices that include little or no pruning combine to produce a dense, shady canopy. A study designed to quantify the effect of shade on reproduction and photosynthetic rate in this shade-tolerant species was undertaken to assess whether some degree of pruning might improve productivity. Shade cloth was used to exclude 30%, 47%, 63%, 73%, or 92% of ambient sunlight from whole `Ennis' and `Barcelona' trees from mid-May until harvest. Photosynthetic light response curves were obtained for leaves that had developed in full sunlight, deep inside the canopy of unshaded trees, or in 92% shade. Light-saturated net photosynthetic rates were 12.0, 6.1, and 9.3 μmol·m-2·s-1 of CO2 and dark respiration rates were 2.0, 1.1, and 0.7 μmol·m-2·s-1 of CO2, respectively, for the three light regimes. Light-saturated photosynthetic rates of leaves from 30% or 63% shade differed little from the control (0% shade). Area per leaf increased by 49% and chlorophyll concentration (dry weight basis) by 157% as shading increased from 0% to 92%. Shading to 92% reduced specific leaf weight (68%), stomatal density (30%), light compensation point (69%), and dark respiration rate (63%) compared to controls. Female inflorescence density declined by about one-third and male inflorescence density by 64% to 74% in the most heavily shaded trees of both cultivars compared to controls. Shade was more detrimental to yield than flowering: yield per tree dropped by >80%, from 2.9 to 3.4 kg in full sun to 0.6 to 0.9 kg in 92% shade. Shade reduced yield primarily by decreasing nut number and secondarily by decreasing nut size. The incidence of several kernel defects increased as shade increased. Therefore, hazelnut leaves showed considerable capacity to adapt structurally and functionally to shade, but improving light penetration into the canopy would probably increase orchard productivity.
Adriane Cannon*, Dennis Deyton, Carl Sams, and William Klingeman
Two experiments were conducted in a greenhouse to evaluate soy-bean oil (SO) formulations for effects on powdery mildew (PM) and photosynthesis of dogwood trees. In the first experiment, one-year-old potted trees were sprayed with different formulations of 2% SO one day before exposure to PM. The formulations were emulsified with: teric/termul, lauriciden, lecithin, lecithin/MD 1, lecithin/MD 2, or Latron B-1956. A commercial formulation of Golden Natur'l was also used. The trees were arranged in a completely randomized design with six replications and eight treatments. In the second experiment, trees were sprayed 4 days after initial exposure to PM with the same treatments and arranged in a similar experimental design. The severity of PM infection was rated using the scale: 1 = 0%, 2 = 1% to 3%, 3 = 4% to 6%, 4 = 7% to 12%, 5 = 13% to 25%, 6 = 26% to 50%, 7 = 51% to 87%, and 8 = 88% to 100% of leaves visually displaying PM. The net photosynthetic (Pn) rates were measured using an infrared gas analyzer. In the first experiment, trees sprayed pre-inoculation with Golden Natur'l, lecithin, lecithin/MD 1, or Latron B-1956 formulation had less PM than control trees at 19 and 24 days after spraying (DAS). Pn of leaves sprayed with lecithin or Latron B-1956 formulations had 68% and 40% lower Pn rates, respectively, of the control leaves at one DAS. However, by 11 DAS, none of the SO formulations significantly affected Pn rates. Leaves of plants (expt. 2) sprayed with teric/termul, lauriciden, lecithin, and lecithin/MD 2 formulations had less PM than control trees at 28 DAS. All formulations reduced Pn rates at 6 DAS, with only Golden Natur'l treated leaves recovering to rates similar to control leaves by 15 DAS.
Jeffrey Adelberg, Kazuhiro Fujiwara, Chalermpol Kirdmanee, and Toyoki Kozai
Growth and net photosynthetic rates of shoots of a triploid melon clone, `(L-14 × B) × L-14', were observed over 21 days following transfer from a multiplication MS medium containing 3% sucrose and 10 μM BA to a shoot development medium containing 1 μM BA at varying levels of sucrose in the medium (0%, 1%, and 3%), and light (50, 100, and 150 PPF) and CO2 (500, 1000, and 1500 ppm) in the headspace. Largest numbers of shoot buds were observed in media with 3% sucrose. Increased light and CO2 had a positive interactive effect. Fresh and dry weights were greatest at highest levels of sucrose, light, and CO2. Although there was less growth in the absence of sucrose, fresh or dry weight of shoot buds grown without sucrose in the media still doubled over the 21 days of culture. Net photosynthetic rates of buds were negative 4 days after initiation of culture and approximately zero after 20 days of treatment. When transferring buds to fresh, sugar-free media, net photosynthetic rates became highly positive. Buds that had been cultured in the absence of sucrose and at highest light levels had the highest net photosynthesis rates upon transfer to fresh, sugar-free media.
How-Chiun Wu and Chun-Chih Lin
in photosynthesis ( Kubota et al., 2001 ; Xiao and Kozai, 2006 ), whereas increases in chlorophyll content are also reported. Findings by Xiao et al. (2005) showed that the net photosynthetic rate and chlorophyll concentration of Gerbera jamesonii