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Lailiang Cheng and Leslie H. Fuchigami

Based on the curvilinear relationship between carboxylation efficiency and leaf N in apple leaves, we hypothesized that deactivation of Rubisco accounts for the lack of response of photosynthesis to increasing leaf N under high N supply. A wide range of leaf N content (from 1.0 to 5.0 g·m–2) was achieved by fertigating bench-grafted Fuji/M26 apple trees for 6 weeks with different N concentrations using a modified Hoagland solution. Analysis of photosynthesis in response to intercellular CO2 under both 21% and 2% O2 indicated that photosynthesis at ambient CO2 was mainly determined by the activity of Rubisco. Measurements of Rubisco activity revealed that initial Rubisco activity increased with leaf N up to 3.0 g·m–2, then leveled off with further rise in leaf N, whereas total Rubisco activity increased linearly with increasing leaf N throughout the leaf N range. As a result, Rubisco activation state decreased with increasing leaf N. Photosynthesis at ambient CO2 and carboxylation efficiency were both linearly correlated with initial Rubisco activity, but showed curvilinear relationships with total Rubisco activity and leaf N. As leaf N increased, photosynthetic nitrogen use efficiency declined with decreasing Rubisco activation state.

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Lailiang Cheng and Leslie H. Fuchigami

Ribulose bisphosphate carboxylase/oxygenase (Rubisco) initiates the photosynthetic carbon metabolism;therefore, its activity has been measured in many physiological studies. However, information on in vitro Rubisco activity from leaves of deciduous fruit crops is very limited and the reported activities are suspiciously low. We measured Rubisco activity in crude extracts of leaves of apple, pear, peach, cherry, and grape by using a photometric method in which RuBP carboxylation was enzymically coupled to NADH oxidation. Replacing polyvinylpyrrolidone with polyvinylpolypyrrolidone in the extraction solution significantly increased extractable Rubisco activity. Depending on species, freezing leaf discs in liquid nitrogen followed by storage at –80°C for only 24 hr reduced both initial and total Rubisco activity to 5% to 50% of that obtained from fresh leaves. Initial Rubisco activity from fresh leaf tissues of all species was well correlated with maximum Rubisco activity (Vcmax) estimated from gas exchange; an exception was pear, where initial Rubisco activity was higher than Vcmax. In most cases, initial Rubisco activity was approximately two to three times higher than net photosynthesis.

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Pinghai Ding* and Leslie H. Fuchigami

Differential exothermal characteristics in relations to bud water content and dormant periods were dynamically investigated within the buds of apple, pear, peach, plum, Grape, persimmon, and black walnut from late autumn to early spring. Differential thermal analysis (DTA) indicated that bud cold hardiness and two exotherms, the high temperature exotherm (HTE) and low temperature exotherm (LTE), were different among species and dormant periods. According to whether buds have deep supercooling during the dormant winter period the species tested can be divided into two groups. The first group, without supercooling, includes the buds of apple and pear, in which LTE was undetectable. The second group, with supercooling, includes the buds of peach, plum, grape, persimmon, and black walnut, in which LTE was detectable. The second group can be further divided into peach and plum subgroup, and grape, persimmon, and black walnut subgroup. Both HTE and LTE can be detected in the buds of peach and plum subgroup, in which bud cold hardiness can be further divided into three different stages; whereas in the buds of grape, persimmon and black walnut subgroup only LTE can be detected, in which bud cold hardiness can be further divided into five stages according to the detection dynamics of HTE and LTE. Bud differential exothermal characteristics and deep supercooling dynamics are closely related to bud water content and cold hardiness stages. No detection of LTE in the buds of apple and pear and no detection of HTE in the buds of grape, persimmon and black walnut were both closely associated with bud water content.

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Pinghai Ding* and Leslie H. Fuchigami

Sunburn can be caused either by heat stress or by UV-B radiation. Under natural conditions fruit sunburn is usually caused by the combination of both heat stress and UV-B radiation. To evaluate the use of reflectance spectroscopy in early detection of fruit sunburn, 5-year-old `Fuji' apple bearing trees growing in pot-in-pot system at the Lewis-Brown Horticulture Farm of Oregon State Univ. were used in the experiment. Fruit sunburn was monitored either under natural conditions or treated with UV-B, heat or both under controlled conditions after detached from the tree. Under natural conditions, the sun-exposed side of Fuji fruit has much higher anthocyanins than the shaded side. The increase in anthocyanins at the sun-exposed side is to protect the fruit from sunburn. When the temperature higher than 40 °C the sunburn symptom initiated first by change the color of the sun-exposed side from red to tan, then to yellow patches, and finally turn to brown and dark brown patches. The peel pigments analysis results indicated that anthocyanins decreased earlier than chlorophyll in the symptom development. The results of detached fruit exposure to 30,000μW/cm2 UV-B lights or to 40 °C at control conditions for 2, 4, 6, 8, 10, and 12 hours indicated that high intensity UV-B lights or high temperature alone can cause sunburn respectively. The UV-B and temperature combination treatment enhanced the sunburn processes. The apples with sunburn caused under natural conditions or under UV-B and temperature controlled conditions were scanned by using reflectance spectroscopy of FOSS NIR system at different stage of the sunburn. The results indicted that Fuji apple sunburn can be efficiently detected at the early stage of sunburn in both natural and controlled conditions.

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Lailiang Cheng and Leslie H. Fuchigami

Reserve N and carbohydrate levels of bench-grafted Fuji/M26 plants were altered by fertigation with seven N concentrations from 30 June to 1 Sept. in combination with or without 3% foliar urea application in mid-October. The plants were harvested after natural leaf fall and stored at 2 °C. One set of plants were destructively sampled in January for reserve N and carbohydrates analysis, and the remaining plants were transplanted into a N-free medium in the spring and supplied with or without 5 mM 15N-ammonium nitrate in a Hoagland solution for 60 days after budbreak. Plants fertigated with higher N concentrations had higher reserve N content and lower carbohydrate concentrations. Foliar urea application increased whole plant N content and decreased reserve carbohydrate concentration at each given N concentration used in fertigation. Regardless of N supply in the spring, total new shoot and leaf growth of plants fertigated with N was closely related to the amount of reserve N but not reserve carbohydrates. Plants treated with foliar urea had more new shoot and leaf growth than the fertigated controls. By pooling all the data concerning reserve N used for growth regardless of the spring N supply, a linear relationship was found between the amount of reserve N used for new shoot and leaf growth and the total amount of N. We conclude that the growth of apple nursery plants in the spring is mainly determined by reserve N, not reserve carbohydrates. The amount of reserve N used for new shoot and leaf growth in the spring is dependent on the total amount of reserve and is not affected by the current N supply.

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Leslie H. Fuchigami and Michael Wisniewski

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Sunghee Guak and Leslie H. Fuchigami

Spring-grafted potted `Fuji'/M26 apple (Malus domestica Borkh.) trees were fertigated with Plantex (20N–10P–20K) weekly until 28 Aug., and sprayed with 1000 ppm abscisic Acid (ABA) two times at 5-day intervals in early September. Nitrogen concentrations of leaves, bark, wood, and root tissues were analyzed using near-infrared reflectance (NIR) spectroscopy at 20to 30-day intervals beginning in August. In general, during leaf senescence, the content of leaf nitrogen decreased and stem nitrogen increased. ABA enhanced leaf senescence and the mobilization of nitrogen from the leaves to the stem tissues. ABA significantly enhanced terminal bud set, endodormancy induction, and cold acclimation. Eventually, the controls attained the similar degree of nitrogen concentration in the stem, terminal bud set, endodormancy, and hardiness.

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Liping Zhen and Leslie H. Fuchigami

Hydrogen cyanamide (CY) induced earlier, more uniform, and a higher percentage of budbreak in poplar (Populus alba × P. gradidentata, N C 5339). c y was phytotoxic at 0.5 M or higher concentration. Percent budbreak increased and percent dieback decreased when plants were treated with a mixture of CY and Cys. No difference was found in percent budbreak or dieback between plants treated with CY alone and a mixture of CY and Ser. Mixing CY with Cys concentrations in vitro reduced the percentage of the cyano group, and mixing of Cys with CY concentrations decreased the percentage of the SH group remaining in the mixture. Mixing CY with Ser concentrations in vitro had no effect on CY level. These studies suggest that the SH group reacts with CY directly and the improvement of budbreak and toxicity caused by mixing CY and Cys may be due to the reduction of CY concentration.

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Sanliang Gu and Leslie H. Fuchigami

“Legend' roses were grown in various potting mixtures of processed fiber (PF, a by-product of anaerobically digested dairy waste), peat moss, pumice, or bark to test the applicability of PF as a substitute of peat moss and bark. A commercial mix (peat moss and bark, 1 to 1 by volume) was used as the control. Plant appearance, growth of leaves, shoots, and flowers were the same in straight PF, commercial mix, and PF mixtures of 50% or less pumice. Plants grown in mixtures of peat moss, pumice, and bark were inferior to those in PF. This study demonstrated that PF media was better than peat moss and bark for rose production.

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Lailiang Cheng, Sunghee Guak and Leslie H. Fuchigami

Fertigation of young Fuji/M26 apple trees (Malus domestica Borkh.) with different nitrogen concentrations by using a modified Hoagland solution for 6 weeks resulted in a wide range of leaf nitrogen content in recently expanded leaves (from 0.9 to 4.4 g·m–2). Net photosynthesis at ambient CO2, carboxylation efficiency, and CO2-saturated photosynthesis of recently expanded leaves were closely related to leaf N content expressed on both leaf area and dry weight basis. They all increased almost linearly with increase in leaf N content when leaf N < 2.4 g·m–2, leveled off when leaf N increased further. The relationship between stomatal conductance and leaf N content was similar to that of net photosynthesis with leaf N content, but leaf intercellular CO2 concentration tended to decrease with increase in leaf N content, indicating non-stomatal limitation in leaves with low N content. Photosynthetic nitrogen use efficiency was high when leaf N < 2.4 g·m–2, but decreased with further increase in leaf N content. Due to the correlation between leaf nitrogen and phosphorus content, photosynthesis was also associated with leaf P content, but to a lesser extent.