Search Results

Chlorophyll fluorescence measurements are providing insights into Photosystem II (PSII) quantum efficiency and hence are able to provide a good estimation of carbon assimilation under field conditions. A F₂ generation of sibcross seedlings from a cross of `Goldspur' × `Redspur' were selected to identify genetic variations and the relationships among fluorescence parameters, carbon assimilation, and carbon partitioning in apple leaves. Mature leaves from extension shoots were analyzed for chlorophyll fluorescence with a CF-1000 chlorophyll fluorescence measurement system, photosynthetic rate with a LI-6200 portable photosynthesis system, and carbohydrates with a Shimadzu HPLC. Significant variations in leaf chlorophyll fluorescence parameters and photosynthetic rates were found. The ratio of Fv: Fm, an estimation of photochemical efficiency of PSII, decreased from ≈0.90 in June to ≈0.75 in September while the photosynthetic rates decreased from ≈8.5 in June to ≈4.5 μmol·m^–2·s^–l in September. The relationships between fluorescence parameters, photosynthesis, and carbohydrate partitioning were analyzed and the ratio of sorbitol to sucrose in relation to the efficiency of PSII and NADPH production will be discussed.

One-year-old `Gala' apple trees which experienced either water stress (WS) or no stress (CK) were exposed to a 60-min pulse of ¹⁴CO₂. The distributions of newly-fixed ¹⁴C-photosynthates and total individual carbohydrates (both labelled and non-labelled) were monitored every 2 or 4 h for a 24-h period. During the 24-h period, half the WS and CK plants received 24-h continuous light and the other half received a 12-h photoperiod (8:00 am to 8:00 PM). WS stimulated the ¹⁴C partitioning into sucrose (suc) during the first 2-4 h period while the partitioning into glucose (glu) and fructose (fru) was inhibited in mature leaves. WS significantly inhibited the partitioning of ¹⁴C into starch. At the end of the 24-h period, a greater partitioning of ¹⁴C into sorbitol (sor) was observed under WS in leaves, stems and roots. WS lowered starch levels in all plant parts and the dark cycle further stimulated starch breakdown. Starch breakdown during the dark cycle resulted in the accumulation of glu and suc but not sor whereas in light sor accumulated with higher sorbitol/starch ratios. Light and energy requirements for sor synthesis and metabolism will be discussed.

Previous results showed that active sorbitol accumulation occurs under water stress. We tested the hypotheses that sorbitol accumulation is due to reduced sorbitol export from leaves or from increased synthesis of glucose to sorbitol. To test the hypotheses, 230 μl ¹⁴C-sucrose was introduced through the stems to detached `Jonathan' apple shoots which had either water stress or no stress. Following uptake of ¹⁴C-sucrose, 0% or 10% PEG was applied to shoots for 24 hours. The results showed that 73% of ¹⁴C-sucrose in non-stressed leaves was broken down within 1 hour and 44% was recovered in sorbitol. PEG initially stimulated the breakdown of ¹⁴C-sucrose to glucose and fructose, but further conversion to sorbitol was reduced. However, the percentage of ¹⁴C-sorbitol in mature leaves increased gradually in 10% PEG until it exceeded that of control at 24 hours. In contrast to mature leaves, young leaves and stems showed significantly less sorbitol under 10% PEG 24 hours after treatment. These results supported the hypothesis that sorbitol accumulation under water stress was due to the reduced sorbitol transport.

Greenhouse grown 2-year-old potted `Jonathan' apple trees (Malus domestica Borkh.) were subjected to various levels of water stress in February. Midday leaf water potential (ψ_W), leaf osmotic potential (ψ_S), soluble sugars, and starch contents of mature leaves were measured throughout the development of water stress to determine whether active osmotic adjustment could be detected and whether carbohydrates were involved. Active adjustments of 0.6 MPa were observed 3 and 5 days, respectively, after water stress was initiated. Leaf turgor potential (ψ_P) could not be maintained through the osmotic adjustment when ψ_W dropped below -1.6 MPa. Sorbitol, glucose, and fructose concentrations increased while sucrose and starch levels decreased significantly as water stress developed, strongly suggesting that sugar alcohol and monosaccharide are the most important osmotica for adjustment. Sorbitol was a primary carbohydrate in the cell sap and accounted for > 50% of total osmotic adjustment. The partitioning of newly fixed W-labeled photosynthates in mature leaves was not affected by water stress immediately after the 30-min ¹⁴CO₂ treatment. All the W-labeled carbohydrates decreased in the labeled leaves very rapidly after ¹⁴CO₂ labeling. The decrease in ¹⁴C-sorbitol was greater than the decrease in other carbohydrates under both well-watered and stressed conditions. After 24 hours of water stress, however, the percentage of ¹⁴C-sorbitol increased while the percentages of sucrose, starch, glucose, and fructose decreased significantly with increasing levels of stress. The ratio of ¹⁴C-sorbitol in leaves with ψ_W = -3.5 MPa to leaves with ψ_W = -0.5 MPa was significantly higher than that of ¹⁴C-sucrose, ¹⁴C-glucose, W-fructose, or ¹⁴C-starch.

Four phases of development from emergence to anthesis of the opium poppy (Papaver somniferum L.) are recognized based on transfer studies using 9- and 16-hour photoperiods: a photoperiod-insensitive juvenile phase (JP), a photoperiod-sensitive inductive phase (PSP), a photoperiod-sensitive postinductive phase (PSPP), and a photoperiod-insensitive postinductive phase (PIPP). The objective of this experiment was to determine how the durations of the photoperiod-sensitive phases changed when the plants were exposed to different photoperiods. Plants were grown in lamplit growth chambers with a 12-hour thermoperiod of 25 °C day/20 °C night. They were transferred from a noninductive 9-h to an inductive 12-, 14-, or 16-hour photoperiod or vice versa at 1- to 4-day intervals to determine the durations of the four phases. The average number of days to flower by plants grown continuously in a 16-hour photoperiod was 32 days. Days to flower were delayed by 10 days in the 14-hour photoperiod and by 36 days in the 12-hour photoperiod. The durations of the four phases were not equally affected by photoperiod. The first three phases were photoperiod-dependent, the photoperiod effect being nonlinear. The durations of JP, PSP, and PSPP were 3, 5, and 17 days in the 16-hour; 4, 8, and 23 days in the 14-hour; and 7, 14, and 40 days in the 12-hour photoperiod, respectively. The final phase was not sensitive to photoperiod (i.e., PIPP lasted 7 days regardless of photoperiod). Based on these results, we conclude that the so-called juvenile phase cannot be regarded as photoperiod-insensitive. To model the development of opium poppy under field conditions, a knowledge of daylength as early as seedling emergence may be necessary. The number of inductive cycles needed for floral induction and the rate of floral development largely depend on the photoperiod experienced.

Estimating yields of illicit narcotic crops requires knowledge of how climate, soil, and geography affect these crops. One method for estimating yields is to create databases from which to develop simulation models. This experiment is part of one of those databases, designed to determine if flowering time can be affected in young poppy seedlings by manipulating photoperiod (PP) and temperature. Plants were grown in chambers under a 12-, 13-, 14-, or 24-h PP and a 12-h thermoperiod of 25/20C. Plants at 10 or 20 days after emergence were transferred to separate chambers and treated for 48 h with either a) 10C and a 12-h PP or b) a 24-h PP and a 12-h thermoperiod of 25/20C. Days to flowering (DTF) decreased with increased PP, especially between 12 and 13 h. The 48-h PP interruption decreased DTF for PPs <24 h for both seedling ages, the effect being more pronounced for 10 d and for the 12-h PP. The 48-h 10C interruption had no effect on DTF. The poppy capsule, from which the gum is harvested, was a larger proportion of the shoot biomass under PPs >14 h, but capsule biomass was a positive linear function of DTF. DTF depends on PP and biomass at flowering depends on DTF.

It has been suggested that shoot demand for nitrogen controls nitrate uptake in plant roots. In turfgrasses, shoots are partly removed by regular mowing, which may severely alter nitrate uptake ability. However, reported groundwater nitrate concentrations under intensively managed turf are well below the USEPA maximum contaminant limit of 10 mg·L^-1 nitrate-N in potable water. We hypothesize that the turfgrass root can also exert significant control over its nitrate uptake ability. The present study was to test this hypothesis by comparing nitrate uptake rates of excised roots and intact, whole plants of six Kentucky bluegrass (Poa pratensis L.) cultivars. Three replications or cultures of each cultivar were grown in sand for 15 months. For whole-plant nitrate uptake, the roots were placed in a flask filled with 200 mL of a nutrient solution containing 0.125 mm nitrate. Nitrate depletion was monitored at 20-minute intervals over an 8-hour period under ≈600 μmol·m^-2·s^-1 photosynthetic photon flux density. After the whole-plant experiment, the plants were placed in an N-free nutrient solution for 15 hours, and the roots were then excised. The excised roots were placed in a beaker containing 60 mL of the 0.125-mm nitrate nutrient solution and nitrate depletion was monitored at 20-minute intervals over a 6-hour period. Whole-plant nitrate uptake rate differed significantly (P ≤ 0.05) among cultivars and was twice that of excised roots. Excised root nitrate uptake rate exhibited no cultivar difference but was positively and significantly (P ≤ 0.05) correlated with whole-plant nitrate uptake rate. Our results indicate that turfgrass roots exert substantial control over nitrate uptake.

The U.S. State Dept. annually publishes estimates of narcotic drug crop production worldwide. The areas under cultivation are well known but yields per unit land area are not. Determining opium gum yield from illicitly grown poppy Papaver somniferum L. is difficult and dangerous. Removing plants from the field and harvesting gum in a safe place would allow us to measure gum yield from one short field visit. To interpret these results in terms of total gum yield from the field, one must know how the measured gum is affected by gum collecting method, capsule age, and phenotype. Opium poppy seeds from three phenotypes (purple, white, and red-white flowers) were grown in a greenhouse and plants were either cut at the soil level or left intact for opium gum harvest at 7, 12, and 22 days after flowering (DAF). Capsule firmness was measured to estimate gum yield and capsule age, and the relationship between total gum yield and yield from the first lancing was examined. The average gum yield (8.4 mg·g^–1 dry weight capsule) for the purple-flowered phenotypes was 17% and 25% lower than for the white- and red/white-flowered phenotypes, respectively. Capsule firmness of the three phenotypes varied from ≈800 to 2300 N·m^–1 as the capsule aged. Gum yield and capsule firmness increased with capsule age but the timing of those changes differed among phenotypes. No significant correlations were found between capsule firmness and gum yield or between capsule firmness and age. Therefore, capsule firmness cannot be used to predict gum yield or capsule age. Gum yield from the first lancing was linearly correlated with total gum yield (r² = 0.82). Since this relationship changes with growing condition, it is insufficient to predict total gum yield. Gum yield from cut plants was significantly lower than from intact plants for all three phenotypes at 22 DAF and for white-flowered phenotypes at 12 DAF. No difference in gum yield was observed between cut and intact plants at 7 or 12 DAF for purple and red/white-flowered phenotypes. The relationship between gum yield from cut and intact plants was too variable to predict gum yield from intact plants by measuring gum yield from cut plants.