Patrick J. Breen

UDP-glucose: Flavonoid O-glucosyltransferase from strawberry fruit

Abstract An enzyme catalysing the glucosylation of quercetin at the 7-hydroxyl group using uridine diphosphate- d -glucose (UDPGlc) as the glucosyl donor was partially purified ca 100-fold from ripening strawberry ( Fragaria ananassa Duch. cv Tillikum) fruit. The apparent K m values for UDPGlc and quercetin were 0.14 and 0.04 mM, respectively. The optimum pH of this glucosylation reaction was 7.5. Enzymatic activity was slightly stimulated by Ca 2+ and Mg 2+ , but was completely inhibited by Cu 2+ and p -chloromercuribenzenesulphonic acid (PCMBS). A M r of ca 55 000 was determined by gel filtration. The substrate specificity was broad. Flavonoids glucosylated included flavonols, flavonones and a flavone, but the highest activity was observed with the isoflavone, biochanin A.

Growth of strawberry fruit and sugar uptake of fruit discs at different inflorescence positions

Abstract The growth of fruit from greenhouse-grown ‘Brighton’ strawberry plants ( Fragaria × ananassa Duch.) was analyzed from anthesis to ripening, Absolute growth rates neared a maximum at the onset of ripening when the rates for primary, secondary, tertiary and quaternary fruit were 106, 53, 22 and 3 mg dry weight day −1 , respectively. Length, diameter, fresh weight and dry weight were greatest in primary fruit throughout development, and were progressively smaller in fruit at lower rankings. At 15 days after anthesis, fresh weight of secondary, tertiary and quaternary fruit were, respectively, 55, 13 and 3% of primary fruit weight. The amount and rate of fruit expansion, estimated from achene separation, was highest in primary fruit, the maximum rate being over twice that of secondary fruit. Relative growth rate was also highest in primary fruit from anthesis to red-ripe. To relate fruit growth to rates of sucrose uptake, discs of fruit cortex tissue were incubated in 10 mM 14 C-sucrose solutions. The rate of sucrose uptake by tissue discs from primary fruit was greater than uptake by secondary or tertiary fruit tissue and similar to the rate of dry matter accumulation in intact fruit. In primary fruit, sucrose uptake reflected dry matter accumulation at increasing ages, the rate of both activities decreasing 60% from 9 to 17 days after anthesis. Results suggest that sucrose uptake may relate to rates of strawberry fruit growth.

Partitioning of 14C-assimilate in Easter Lily as affected by growth stage and flower removal

Abstract Three weeks before anthesis, flower buds of Easter Lily plants received 47 and 12% of 14C translocated from Leaf 5 (upper) and 25 (middle), respectively, whereas the bulb received 5 and 52%, respectively. Flower bud removal increased the fraction in the bulb to 52% (Leaf 5) and 63% (Leaf 25). At anthesis, the flowers received 78% (Leaf 5) and 65% (Leaf 25) of translocated 14C-assimilate, nearly all of which was in the second flower which was still expanding. Less than 5% of the 14C from either leaf moved to the bulb in intact flowering plants, but upon flower removal, the bulb received 26 and 59% of the labelled assimilate from Leaf 5 and 25, respectively. Five weeks after anthesis, nearly 85% of the 14C-assimilate from either leaf was in the bulb. The fraction of 14C moving into the daughter bulb increased from less than 10%, 3 weeks before, to over 50%, 5 weeks after anthesis. Regardless of treatment, sink activity of the daughter scales was 2- to 12-fold higher than that of the mother scales. Although much of the current assimilate from the upper half of the intact lily shoot moves to flowers before anthesis, flower-bud removal is an effective way to increase carbon supply to the bulb.

Influences of water status and temperature on leaf elongation in strawberry

Abstract Irrigated (IR) and non-irrigated (NIR) strawberries (Fragaria × ananassa Duch. cultivar ‘Olympus’) were compared in terms of water potential (ψ), solute potential (ψs), turgor potential (ψp), and leaf elongation rate (LER), during diurnal cycles in 1978 and 1979. LER was maximal during a 5-hour period beginning 1 hour before sunset. Low leaf temperature (below 16–18°C) apparently limited LER during the remainder of the night, and low ψp or water supply to leaves was probably the limiting factor in the afternoon in both IR and NIR plants. In 1978, leaflet length was measured daily from 13 to 27 days after the start of differential irrigation. The mean LER during the first week was 52% higher, and the area of the center leaflets averaged 85% greater, for IR than NIR plants on Day 27. In 1979, after 62 days of irrigation treatments, the total leaf area of IR plants was 205% greater, which was the combined effect of greater leaf size and number. Osmotic adjustment, an adaptive response to water deficit, increased ψp at a given ψ in NIR field-grown strawberries, but did not prevent a reduction in LER, which was often only one-third that of irrigated plants during a diurnal cycle. The average LER was determined during 3 days in growth chambers at 10, 15, 22 or 28°C, and was maximal at 28°C. After 2 weeks in the 28°C-chamber, the LER of new leaves declined, however, suggesting that 28°C was supra-optimal for strawberry.

Stomatal behavior and leaf water status of strawberry in different growth environments

Abstract Leaves of irrigated (IR) and non-irrigated (NIR) strawberries ( Fragaria × ananassa Duch, cultivar ‘Olympus’) were compared in terms of water potential (ψ), turgor potential ( ψ p ), and leaf conductance ( K 1 ) during diurnal cycles in growth chamber, glass-house, and 2 field studies (1977 and 1979). Irrigation was withheld for 3–5 days before measurements were made in the greenhouse and growth chamber, and for 21 days (1977) and 36 days (1979) in the field. In the field, minimum mid-day leaf ψ was usually near −15 bars in both IR and NIR plants. On clear days, such as the 1977 date, ψ and ψ p were not greatly affected by irrigation, except that ψ in IR plants dropped more slowly in early morning and recovered faster near sunset. On the 1979 date, mid-day ψ was higher in IR than NIR plants due to lower solar radiation, but ψ p was very similar in the 2 treatments during most of the day. K 1 rates in NIR plants were half those in IR plants throughout the day, and diurnal patterns of K 1 were similar in 1977 and 1979 despite the differences in water status of IR plants. While stomata clearly responded to soil moisture deficit, the relationship between K 1 and leaf ψ or ψ p depended on the growth environment and irrigation history, as well as other influences on stomata. In contrast to the behavior of field-grown plants, ψ and ψ p of NIR glasshouse plants dropped well below those of IR plants as soil dried, probably due to small pot volume. Also, K 1 at a given ψ was lower in the growth chamber than in the field, perhaps due to a direct effect of low light on stomata. A threshold ψ at which strawberry K 1 drops sharply (indicating stomatal closure) was not observed. The existence of such thresholds in other crops is questionable if their occurrence was inferred from leaf resistance ( R 1 ) rather than K 1 data.

Photosynthesis of meadowfoam leaves at various photon fluxes and CO2 concentrations

Abstract Meadowfoam (Limnanthes alba Hartweg ex Benth.) is a new oilseed crop. Information regarding the effects of photosynthetic photon flux (PPF) and carbon dioxide concentration [CO2] on net photosynthesis is important for understanding the potential capacity and the limitations of this crop to assimilate CO2. Such information is useful for further improvement of meadowfoam seed and oil yield, as well as for growing this plant in controlled environments. The steady-state CO2 exchange rates (CER; leaf area basis) of Mermaid meadowfoam (L. alba subsp. alba) leaves were measured in a semi-closed compensating system at various PPF and [CO2]. Measurements were made on rosette leaves of controlled environment-grown plants during vegetative growth, early stem elongation and early flowering. At all stages of development, CER responded hyperbolically to PPF and reached near saturation at a PPF of about 900 μmol m−2 s−1 when [CO2] was 340 μl l−1. At saturating PPF, leaf CER was 18 μmol m−2 s−1 during the vegetative stage, 15 μmol m−2 s−1 at early stem elongation and 8 μmol m−2 s−1 at early flowering. The apparent quantum yield (mole CER per mole PPF at leaf surface) determined at low PPF when the response curve was linear was the same during vegetative and early stem elongation. The 99% confidence intervals for the apparent quantum yield of these plants were 0.038 and 0.046. The 99% confidence intervals for light compensation point during these stages were 63 and 79 μmol m−2 s−1. During both vegetative and early stem elongation stages, the CER increased sharply as [CO2] increased (PPF=1200 μmol m−2 s−1) and reached a plateau near 650 μl l−1 CO2. At this saturating [CO2], the CER was 45 μmol m−2 s−1 during the vegetative stage and 33 μmol m−2 s−1 during early stem elongation. The [CO2] compensation point measured transiently on four plants during vegetative stage was 74±5 μl l−1. The photosynthetic rate and efficiency of L. alba were similar to those for cool-season C3 grasses.