Leslie H. Fuchigami

Physiological and Environmental Requirements for Poplar (Populus deltoides) Bark Storage Protein Degradation.

In poplar (Populus deltoides Bartr. ex Marsh), a 32-kD bark storage protein (BSP) accumulates in the bark during autumn and winter and declines during spring shoot growth. We investigated the physiological and environmental factors necessary for the degradation of poplar BSP. Poplar plants were exposed to short-day (SD) photoperiods for either 28 or 49 d. Plants exposed to short days for 28 d formed a terminal bud but were not dormant, whereas exposure to short days for 49 d induced bud dormancy. BSP accumulated in bark of plants exposed to both SD treatments. The level of BSP declined rapidly when nondormant plants were returned to long days. BSP levels did not decline in dormant plants that were exposed to long-day (LD) conditions. If dormant plants were first treated with either low temperatures (0[deg]C for 28 d) or with 0.5 M H2CN2 to overcome dormancy and then returned to long days, the level of BSP declined. Removal of buds from non-dormant or dormant plants in which dormancy had been overcome inhibited the degradation of BSP in LD conditions. BSP mRNA levels rapidly declined in plants exposed to long days, irrespective of the dormancy status of the plants or the presence or absence of buds. These results indicate that the buds of poplars are somehow able to communicate with bark storage sites and regulate poplar BSP degradation. These results further support an association of BSP mRNA levels with photoperiod because short days stimulate BSP mRNA accumulation, whereas long days result in a decline of BSP mRNA abundance.

Urea uptake and nitrogen mobilization by apple leaves in relation to tree nitrogen status in autumn

Summary Bench-grafted Fuji/M.26 trees were fertigated with one of seven nitrogen concentrations (0, 2.5, 5, 7.5, 10, 15 or 20 mM), using a modified Hoagland’s solution from 30 June to 1 September. In mid-October, plants in each N treatment were randomly divided into three groups. One group was sampled destructively to determine background tree N status before foliar urea applications. The second was painted with a 3% 15N-enriched urea solution twice, at weekly intervals, on both sides of all leaves. The third group served as the control. All the fallen leaves from both the 15N-treated and the control trees were collected during leaf abscission. The trees were harvested at the end of natural leaf fall. Nitrogen fertigation during the growing season resulted in a wide range of tree N status, as indicated by leaf N (1.3–3.5.g m–2) in the autumn. The percentage of N partitioned into the foliage increased linearly with increasing leaf N content up to 2.2 g m–2, then reached a plateau of 50–55% with further rise in leaf N. 15N uptake and mobilization per unit leaf area and the percentage of 15N mobilized from the leaves decreased with increasing leaf N content. Of the 15N mobilized back to the tree, the percentage of 15N partitioned into the root system decreased with increasing tree N status. For the control trees, N mobilization per unit leaf area increased with increasing leaf N up to 3 g m–2, then levelled off with any further increase in N content. The percentage of N mobilization remained at approximately 60% until leaf N reached 3 g m–2, then declined with a further increase in leaf N content. Foliar 15N-urea applications reduced mobilization of endogenous leaf N regardless of tree N status. On a whole-tree basis, foliar 15N-urea applications increased the total amount of N across N fertigation treatments. We conclude that trees with low N status are more efficient in absorbing and mobilizing N from foliar urea than those with high N status. Likewise, more N derived from foliar urea is partitioned into the root systems of low N trees than of high N trees.

Foliar N application reduces soil NO 3 − -N leaching loss in apple orchards

A comparison of the effects of foliar and soil N application was made in field-grown mature fruiting Gala/M9 apple trees (Malus domestica Borkh) in 2001 and 2002 growing seasons under Pacific Northwest growing conditions in southern British Columbia, Canada. The trees, six years old at the start of the experiment, were treated: (1) with 5 g/l urea sprays supplied every two weeks (7 times) from mid May to mid August (total about 50 g N/tree/year), (2) with the same amount of N applied to the soil with the same timing and quantity as for the foliar treatment, and (3) with no N (control). Leaf color (as SPAD readings) and N concentrations (mg/g), and soil NH4+-N and NO3−-N were measured periodically throughout the two seasons. Leached NO3−-N was monitored monthly via an anion exchange probe from June to October in 2001 and from May to November in 2002. Shoot length was measured in October and N concentration of one-year-old wood and roots was determined in December of each growing s eason. Soil N application significantly increased shoot length relative to control or foliar N application. Leaf color, leaf N, and N concentration of one-year-old wood and roots were similarly increased relative to control by both soil and foliar N application. These treatments also increased fruit yield relative to control. There was no significant difference in yield and fruit quality between soil and foliar N applications. Soil N application increased soil NH4+-N and NO3−-N content in the root zone, and also increased the NO3− leaching loss below the root zone especially late in the growing season. Our results suggested that tree N status and yield and fruit quality could be maintained by multiple urea sprays during the growing season in apple orchards, and foliar N application will reduce the risk of soil NO3−-N leaching.

Effects of applied ABA on growth cessation, bud dormancy, cold acclimation, leaf senescence and N mobilization in apple nursery plants

Summary Commercial tree fruit nurseries can promote aggressive tree growth by adding greater amounts of N than is necessary. Although this practice may produce the largest stock possible, it often causes physiological problems such as delays in growth cessation, bud dormancy development, and cold acclimation, especially in late apple cultivars. In this study, abscisic acid (ABA) was applied to Fuji/M.26 apple (Malus domestica Borkh.) nursery plants that had been growing into the late season with a high N supply. We tested the hypothesis that exogenously applied ABA enhances growth cessation and that this is related to the improvement of bud dormancy development and cold acclimation. We also studied the effects on leaf senescence and mobilization of leaf N into perennial woody tissues. In September 1996, ABA at 1000.mg l-1 plus 0.1% Tween 80 was sprayed twice, at 7.d intervals. ABA treatment significantly enhanced shoot growth cessation and advanced the early stages of bud endodormancy development; these effects were closely related. Maximum growth cessation and bud dormancy were attained in mid-December similarly in both control and ABA treatments. In early November, stem cold hardiness measured by the electrolyte leakage method was significantly greater in the ABA-treated plants than in the controls, but was similar in late December. This indicated that cold acclimation was related to the depth of bud endodormancy development. N mobilization from the senescing leaves into perennial woody tissues was significantly enhanced by ABA treatment. Therefore, autumnal increases in total-N and soluble-protein concentrations were significantly higher in the ABA-treated plants (especially in the stem bark), but both control and ABA-treated plants reached similar maximum levels later when plants were completely defoliated.

Modeling bud development during the quiescent phase in red-osier dogwood (Cornus sericea L.)☆

Abstract Stages of bud development during the quiescent phase were numerically expressed by a degree growth stage (°GS) model. This phase extends from the end of rest (315°GS) to spring bud break (360°GS). This study determined temperature effects on bud development at different developmental stages during the quiescent phase. Results were used to develop a model for predicting daily bud development and spring bud break. At monthly intervals during the quiescent phase red-osier dogwood (Cornus sericea L.) plants were exposed in growth chambers to temperatures of 5–20°C and a 12-h photoperiod. Plants were placed in a greenhouse at 20/15°C day/night temperatures and a 16-h photoperiod, and bud development evaluated on the basis of time required for terminal vegetative buds to break. Bud development increased with increasing temperatures, from 5 to 20°C, and with increasing bud development from 315 to 360°GS. In two years of study a model was developed, which used bihourly temperatures and accumulating °GS to predict daily bud development and spring bud break within three days.

Abscisic Acid-Induced Cellular Alterations During the Induction of Freezing Tolerance in Bromegrass Cells

Summary Cellular alterations in bromegrass ( Bromus inermis Leyss cv Manchar) cell suspension cultures were characterized at different hardiness levels using fluorescence and transmission electron microscopy. After one day, when cells treated with abscisic acid (ABA) were 5 °C hardier than control cells, the hardier cells exhibited greater numbers of vacuoles and lipid bodies. However, no changes were observed in cell-wall thickness or cell size. Vacuole size in ABA-treated cells were equally distributed among three size classes, whereas control cells had a higher proportion of large vacuoles. Conversely, the lipid bodies in cells exposed to ABA treatment were consistently smaller than those in control cells. After 7 treatment days when hardiness had increased to -28 °C, the walls of ABA treated cells were significantly thicker than the control cells. The differences observed in lipid bodies after one day were accentuated in the hardier ABA treated cells after 7 days. The size of lipid bodies decreased and their numbers increased by a factor of ten. Osmiophilic granules and golgi apparati became more prevalent near the plasma membrane in the more frost tolerant cells. Cell-wall and protoplasm autofluorescence increased in response to ABA treatment and were quenched by methanol: chloroform extraction. These results show that ABA treatments at room temperature elicit ultrastructural changes associated with hardiness that are similar to those reported after low temperature acclimation.

Relationship between vegetative flushing and flowering of Macadamia integrifolia in Hawaii

Abstract Flowering patterns of the macadamia cultivars, ‘Kau’ (HAES 344), ‘Keaau’ (HAES 660), and ‘Kakea’ (HAES 508) were studied over three consecutive seasons at an orchard near Hilo, HI (elevation 27.4 m). These studies showed that all cultivars had broad flowering peaks with maximum anthesis occurring between January and April. The frequency of vegetative flushing was monitored during 1988, and raceme production by the flushes was observed during the subsequent flowering seasons (1988–1989, 1989–1990, 1990–1991, 1991–1992). Vegetative flushing occurred throughout the year for all cultivars but was more prominent during fall which coincided with the period of nut maturation. Sporadic flowering was observed within 1 year after vegetative flush emergence. For all cultivars, flowering of the 1988 flushes increased in 1989–1990, was most abundant in 1990–1991, and decreased in the 1991–1992 flowering season. Most racemes produced during 1989–1992 developed on flushes that were produced in the spring and fall of 1988.

Gibberellic acid causes earlier flowering and synchronizes fruit ripening of coffee.

The effect of 100 mgl−1 gibberellic acid (GA3) on flowering and fruit ripening synchrony, fruit set, fruit fresh weight, and vegetative growth were studied for different size classes of coffee (Coffea arabica L. cv. Guatemalan) flower buds. Flower buds that were > 4 mm, but not developed to the candle stage at the time of GA3 treatment, reached anthesis 20 days earlier than the controls, and their development was independent of precipitation, unlike the controls. Fruit from buds that were treated with GA3 at the candle stage showed earlier and more synchronous ripening than the control, although no differences in flowering were found during anthesis. Buds that were smaller than 4 mm at the time of treatment did not respond to GA3 applications. Treatment with GA3 did not affect fruit set, fresh weight of fruits, or vegetative shoot growth.

Spring growth of almond nursery trees depends upon nitrogen from both plant reserves and spring fertilizer application

Summary June-budded ‘Nonpareil’/‘Nemaguard’ almond (Prunus dulcis (Mill) D. A. Webb) trees were fertigated with one of five nitrogen (N) concentrations (0, 5, 10, 15, or 20 mM) from July to September. The trees were sprayed with either water or 3% urea in October, then harvested bareroot after natural leaf fall, and stored at 2°C. One set of trees was destructively sampled for total N content; the remaining trees were transplanted into N-free media in the spring after cold storage. After budbreak, these trees were supplied for 70.d with either N-free Hoagland’s solution or Hoagland’s solution containing 15N-NH4NO3. Nitrogen concentrations in both stem and root tissues were positively correlated with the N-fertigation concentration. Fall foliar urea applications increased levels of stem and root N regardless of the N-fertigation concentration. During the first 70 d of spring growth, the trees utilized nitrogen from both their reserves and spring fertilizer applications. The amount of N reserves used for growth of new shoots and leaves was proportional to the total amount of reserves. Trees with low N reserves relied primarily on the spring fertilizer as their source of nitrogen. We conclude, therefore, that both reserve N and spring-applied N fertilizers are important for enhancing the regrowth of bareroot almond nursery trees during establishment after transplanting. Nitrogen fertilization in the spring can especially improve the performance of trees with low N reserves.

Root damage affects nitrogen uptake and growth of young Fuji/M.26 apple trees

Summary Effects of root damage during the transplant process on growth and nitrogen (N) uptake were studied with one-year-old bench-grafted Malus domestica Borkh ‘Fuji’ on M.26 rootstock apple nursery plants. Plants were potted after grafting and grown outside for one season. At the end of the season uniform trees were selected and randomly divided into four groups. One group of plants were moved into a 2°C cold room with soil and container intact (IR Treatment). Plants in other groups were removed from pots and stored as bareroot in the same cold room for three months. In the spring, bareroot plants were either: (1) transplanted with about 10% of the root system damaged during transplant (TP Treatment and Control-CK); or (2) root pruned by 25% (by volume) prior to transplant (RP treatment). Five trees from each treatment received 1 g of 15NH415NO3 at 12, 41 and 76 d after repotting. Control (CK) trees received no N. Trees were harvested 10 d after each N application, and plant growth and total N and 15N content of different tissues were determined. Root pruning reduced plant total biomass and root biomass at the first two harvests, but the plants from the RP treatment had highest total plant biomass and root biomass at the third harvest. There was no significant difference in the new stem and leaf growth among IR, RP and CK treatments at harvests but the TP treatment reduced new shoot biomass. Plants with intact roots (IR) had the higher total N content while control plants (CK) had the lowest. Root pruning reduced 15N uptake rate at the first two harvests but promoted it at the third harvest. Our results suggest that plant growth and nutrient uptake was suppressed by root pruning/damage during transplanting only in the early season, and the negative effects on growth and N uptake were offset later in the season by compensative root regeneration.