Duk Jun Yu

Stomatal and non-stomatal limitations to photosynthesis in field-grown grapevine cultivars

Diurnal changes of photosynthesis in the leaves of grapevine (Vitis vinifera × V. labrusca) cultivars Campbell Early and Kyoho grown in the field were compared with respect to gas exchanges and actual quantum yield of photosystem 2 (ΦPS2) in late May. Net photosynthetic rate (PN) of the two cultivars rapidly increased in the morning, saturated at photosynthetic photon flux density (PPFD) from 1200 to 1500 µmol m−2 s−1 between 10:00 and 12:00 and slowly decreased after midday. Maximum PN was 13.7 and 12.5 µmol m−2 s−1 in Campbell Early and Kyoho, respectively. The stomatal conductance (gs) and transpiration rate changed in parallel with PN, indicating that PN was greatly affected by gs. However, the decrease in PN after midday under saturating PPFD was also associated with the observed depression of ΦPS2 at high PPFD. The substantial increase in the leaf to air vapour pressure deficit after midday might also contribute to decline of gs and PN.

Limitation Factors for Photosynthesis in 'Bluecrop' Highbush Blueberry (Vaccinium corymbosum) Leaves in Response to Moderate Water Stress

The levels of stomatal, mesophyll and biochemical limitations in CO2 assimilation of ‘Bluecrop’ highbush blueberry leaves were compared at two different levels of leaf water potential. The leaf water potentials were −1.49 and −1.94 MPa in daily-irrigated (DI) and non-irrigated (NI) shrubs, respectively. The NI shrubs represented plants under moderate water stress. Mesophyll conductance (gm) and chloroplastic CO2 concentration (Cc) were estimated by combined measurements of gas exchange and chlorophyll fluorescence under various intercellular CO2 concentrations (Ci). Net CO2 assimilation rates (An) as a function of Cc were used for calculating maximum carboxylation efficiency (αcmax) at the real sites of CO2 assimilation. Maximum An (Anmax) from the light response curves at 400 μmol mol−1 air of ambient CO2 concentration (Ca) were lower in the leaves of NI shrubs than in those of DI ones. However, electron transport rates were higher in the leaves of NI shrubs than in those of DI ones. The decrease in CO2 assimilation following water stress may be caused by a decrease in gm rather than a decrease in stomatal conductance (gs) according to limitation analysis. Limitation rates by gs, calculated at 400 μmol mol−1 air of Ca in An-Ci curves, were not significantly different between the leaves of DI and NI shrubs. However, limitation rates by gm from An-Cc curves were significantly higher in the leaves of NI shrubs than in those of DI ones. Maximum carboxylation efficiency (αcmax) values calculated from the An-Cc curve, contrary to those calculated from the An-Ci curve, were higher in the leaves of NI shrubs than in those of DI ones. Consequently, mesophyll limitation than stomatal and biochemical limitations mainly down-regulated the photosynthesis in the leaves of ‘Bluecrop’ blueberry shrubs during moderate water stress.

Comparison of mid-Winter cold-hardiness and soluble sugars contents in the shoots of 21 highbush blueberry (Vaccinium corymbosum) cultivars

Summary Cold-hardiness and the soluble sugars contents of the shoots of 21 highbush blueberry (Vaccinium corymbosum) cultivars (‘Berkeley’, ‘Bluecrop’, ‘Bluegold’, ‘Bluehaven’, ‘Bluejay’, ‘Burlington’, ‘Chippewa’, ‘Collins’, ‘Dixi’, ‘Duke’, ‘Herbert’, ‘Jersey’, ‘Nelson’, ‘Northblue’, ‘Northland’, ‘Polaris’, ‘Rancocas’, ‘Sharpblue’, ‘Sierra’, ‘Spartan’, and ‘Sunrise’) were compared in mid-Winter. The level of cold-hardiness was determined by measuring electrolyte leakage at various freezing temperatures and was expressed as LT50, the temperature at which the incidence of injury reached 50%, and as Tmax, the temperature at which the rate of injury was maximal. The LT50 and Tmax values for the shoots of all 21 highbush blueberry cultivars ranged from –31.8º ± 0.09ºC to –41.1º ± 0.12ºC, and from –29.7º ± 0.06ºC to –36.9º ± 0.13ºC, respectively. Tmax values were significantly positively correlated with LT50 values (r = 0.98**, P ≤ 0.01). Based on their levels of cold-hardiness in terms of LT50 values, the 21 highbush blueberry cultivars were ranked in order as follows: ‘Jersey’ > ‘Northland’ > ‘Northblue’ > ‘Dixi’ > ‘Berkeley’ = ‘Sierra’ > ‘Chippewa’ > ‘Bluegold’ > ‘Burlington’ > ‘Bluejay’ > ‘Spartan’ > ‘Bluecrop’ = ‘Polaris’ > ‘Sunrise’ > ‘Duke’ > ‘Rancocas’ > ‘Herbert’ > ‘Sharpblue’ > ‘Collins’ > ‘Bluehaven’ > ‘Nelson’. Cold-hardiness, as estimated by LT50 and Tmax, was highly negatively correlated with total soluble sugars content (r = –0.78**, P ≤ 0.01 and r = –0.69**, P ≤ 0.01 for LT50 and Tmax, respectively). Among the soluble sugars detected, fructose and glucose concentrations, in particular, were significantly positively correlated with the levels of cold-hardiness in the shoots of all 21 highbush blueberry cultivars, but sucrose and raffinose concentrations were not correlated with cold-hardiness. Knowledge of intra-species differences in mid-Winter cold-hardiness in relation to soluble sugars contents will be useful during the breeding and cultivation of highbush blueberries.

Developmental Rate Equations for Predicting Blooming Date of `Yumyeong` (Prunus persica) Peach Trees

To predict the blooming date of `Yumyeong` peach trees, the models for flower bud developmental rate (DVR) were constructed. The DVRs were calculated from the demanded times at controlled air temperatures. The branches of `Yumyeong` peach trees were incubated at three different temperatures of 9.7, 15.2, and . The DVRs were also constructed with blooming dates and air temperatures in the field, collected from 1979 to 2008 at the experimental orchard of National Institute of Horticultural and Herbal Science, Suwon, Korea. All the DVRs increased linearly or exponentially with air temperature. The DVR equations evaluated under controlled air temperatures were y

Changes in anthocyanidin and anthocyanin pigments in highbush blueberry ( Vaccinium corymbosum cv. Bluecrop) fruits during ripening

We monitored accumulation in terms of different types of anthocyanidin, in association with fruit skin coloration, in ‘Bluecrop’ highbush blueberry (Vaccinium corymbosum L.) at three stages of ripening: pale green, ca. 30 days after full bloom (DAFB); reddish purple, ca. 40 DAFB; and dark purple, ca. 50 DAFB. Total anthocyanin contents increased during ripening, while fruit skin color steadily became darker and bluer, as reflected in decreasing L* (a color space coordinate describing lightness) and b* (describing blue-yellow coloration). Of the six anthocyanidins commonly found in fruits, pelargonidin was absent throughout the ripening process. Cyanidin was first detected at the pale green stage. Peonidin, delphinidin, petunidin, and malvidin were first detected after fruits had passed through the reddish purple stage. The contents of delphinidin and malvidin increased more rapidly than those of other anthocyanidins, and were closely correlated with changes in fruit skin color, demonstrating that the types and quantities of anthocyanidins, which in turn form anthocyanins, were major determinants of fruit skin coloration. Four anthocyanins were detected at the reddish purple stage, and 22 were identified at the dark purple stage. All anthocyanins detected were glycosylated with glucose, galactose, or arabinose.

Photosynthetic characteristics of highbush blueberry (Vaccinium corymbosum cv. Bluecrop) leaves in response to water stress and subsequent re-irrigation

SUMMARY Gas exchange and photosystem II (PSII) activities in the leaves of 2-year-old ‘Bluecrop’ highbush blueberry (Vaccinium corymbosum) were monitored during water stress and subsequent re-irrigation to investigate the effects of the intensity of water stress on changes in photosynthetic characteristics. The blueberry shrubs were not irrigated for 3 to 5 weeks, then re-irrigated daily up to 8 weeks. The decrease in soil water potential during water stress caused a progressive decrease in leaf water potential. Soil water potentials decreased to -0.26 MPa and -0.34 MPa at 3 and 5 weeks, respectively, following water stress, but recovered following subsequent re-irrigation, while the soil water potential in daily-irrigated shrubs was maintained at over -0.13 MPa throughout the experiment. Chlorophyll concentrations decreased with an increasing duration of water stress. Chlorophyll concentrations in leaves on shrubs subjected to water stress for 5 weeks did not recover following re-irrigation, unlike those subjected to water stress for 3 weeks. The leaves on shrubs subjected to water stress for 5 weeks maintained lower levels of chlorophyll during reirrigation. The net rate of CO2 assimilation (An) decreased significantly with an increasing duration of water stress. Reirrigation reversed the decrease in An in leaves on shrubs subjected to water stress for 3 weeks. Stomatal conductance (gs) exhibited a similar pattern to An. The actual quantum yield of photosystem II (ΦPSII) and the electron transport rate (ETR) also decreased significantly with an increasing duration of water stress, although the Fv/Fm ratio was not affected. ΦPPSII and ETR values in the leaves on shrubs subjected to water stress for 5 weeks did not recover after reirrigation, unlike those subjected to water stress for 3 weeks. Non-photochemical quenching increased with an increasing duration of water stress, but subsequent re-irrigation did not reverse the increase. These results indicate that the timing of re-irrigation of water-stressed ‘Bluecrop’ highbush blueberry is critical in order to maintain their photosynthetic capacity. Among the photosynthetic characteristics measured, ΦPSII and ETR could be used as sensitive indicators to assess the physiological status of leaves of ‘Bluecrop’ highbush blueberry growing under water stress conditions.

Estimation of carboxylation efficiency from net CO2 assimilation rate as a function of chloroplastic CO2 concentration in strawberry (Fragaria × ananassa cv. Maehyang) leaves

Carboxylation efficiency in fully expanded leaves of strawberry (Fragaria × ananassa cv. Maehyang) was estimated based on net CO2 assimilation rate (An) as a function of chloroplastic CO2 concentration (Cc). To estimate the mesophyll conductance (gm) and then construct An-Cc curves, An and electron transport rate as a function of intercellular CO2 concentration (Ci) were simultaneously determined at a range of 50 to 2,200 μmol CO2/mol air at a saturating photosynthetic photon flux (PPF), 1,200 μmol·m−2·s−1. Mitochondrial respiration rate (Rd) and CO2 compensation point in the absence of Rd required for calculating gm were found to be 0.15 μmol·m−2·s−1 and 44.1 μmol CO2/mol air, respectively, as determined from An-Ci curves below 200 μmol CO2/mol air at three different PPFs. Both stomatal conductance (gs) and gm decreased with increasing Ci. However, the gm responded more sensitively to various Ci than the gs. The gm was significantly lower than the gs at Ci beyond 600 μmol·mol−1 air examined. Maximum carboxylation efficiency (αcmax) derived from An-Cc curves was 0.28 μmol·m−2·s−1 and 2.2 times higher than that from An-Ci curve. Since the An-Ci curve was based on infinite gm, the αcmax derived from the An-Ci curve might be underestimated. Actually, gm was rather dynamic with changing Ci and thus a crucial component of the diffusional limitation of An. For estimating photosynthetic characteristics in strawberry leaves more accurately, An-Cc curve should be constructed in consideration of gm, especially for closed plant production systems.

Photosynthetic acclimatisation of leaves in response to a shade-to-sun transition following summer pruning in peach (Prunus persica cv. Changhoweonhwangdo) trees

Summary Photosynthetic characteristics and the capacity for adaptation were examined in those leaves near to fruit that changed from shade to a high-light environment (shade-to-sun leaves) following summer pruning in 7-year-old ‘Changhoweonhwangdo’ peach (Prunus persica L.) trees. The shoots of the trees were topped, with a thinning-out of fruit in early-June, then 50% of the vigorous shoots were thinned-out between late-July and early-August, at the end of the rainy season. Summer pruning increased the penetration of light, subsequently increasing air and leaf temperatures, and decreasing the relative humidity in the lower parts of the canopy. The new high-light environment created by summer pruning did not affect the structural characteristics or pigment concentrations in shade-to-sun leaves. However, shade-to-sun leaves had a higher total carotenoid:total chlorophyll ratio compared to sun leaves, whereas this ratio decreased continuously in shade leaves. Shade-to-sun leaves required a period of time to adapt photosynthetically to the new high-light environment. Shade leaves had a lower photosynthetic capacity than sun leaves. The apparent quantum yield (Φpsii) and electron transport rate (ETR) of photosystem II (PSII), stomatal conductance (gs), and net CO2 assimilation rate (An) were lower in shade leaves than in sun leaves at the higher photosynthetic photon flux density. Shade-to-sun leaves did not recover, in terms of An, within 1 week from photo-inhibition caused by a lower Φpsii and ETR, although gs was higher in shade-to-sun leaves than in shade leaves. Four weeks after summer pruning, however, shade-to-sun leaves recovered in terms of their Φpsii, ETR, and An, all of which were higher than in shade leaves. Consequently, summer pruning in ‘Changhoweonhwangdo’ peach trees affected the photosynthetic rate and capacity of shade-to-sun leaves through a change in pigment composition rather than through structural adaptation to an improved light environment within the canopy, thereby influencing the characteristics of tree growth and fruit quality.