64 Martinez-Trinidad et al.: Temporal and Spatial Glucose and Starch Partitioning the allocation of carbohydrates to storage tissues could arise from varied requirements of different organs, different needs during growth, or maintenance respiration required among different spe- cies (Dean 2001; Barbaroux et al. 2003). Variation in starch con- centrations could indicate different rates of production, demand, or shifts in allocation (Ludovici et al. 2002). In trees, the continu- ous pathways of transport and storage of previous-year assimilates are essential for subsequent growth processes, so the coordination and interrelations of morphogenic and photosynthetic processes are very important (Kaipiainen and Sofronova 2003). Carbohy- drates can also be used under stress conditions as a precursor for secondary compounds used to resist biotic or abiotic stress (Webb 1981; Renaud and Mauffette 1991). Understanding carbohydrate partitioning in live oaks can help in understanding the transloca- tion of the main carbohydrate, glucose and starch in semi-ever- green species as well as the relationships between phenological stages and movement and utilization of available energy resources. The objective of this research was to study the non- structural carbohydrate content, glucose and starch, in tree roots, trunks, twigs, and leaves of large, field-grown live oaks as well as to determine the impacts of seasonal in- fluences on carbohydrate concentrations and utilization. MATERIAL AND METHODS Plant Material Five, field-grown live oaks, about 10 cm (4 in) trunk di- ameter measured 30 cm (12 in) above ground, were ran- domly selected from within a nursery at Monaville, TX (29º57’1.59”N, 96º3’28.73”W). Trees selected in the 2005- year were planted in 1999 at 5 m (16.4 ft) spacing, and grown under similar conditions. The soil was a deep, moderately well drained, slowly permeable Lake Charles clay, and trees were annually fertilized (20-20-20, water soluble tree fertilizer). Tissue samples from roots, trunk, and canopy were collected from opposing sides of the tree (across and between rows of trees) corresponding to the four cardinal points. Root samples consisted of 4 mm (0.16 in) diameter increment cores from the buttress (woody) roots [2 cm (0.79 in) from the base of the trunk]. Tissues from the trunk, cores 4 mm diameter, were collected using an increment hammer (Haglof© ; Langsele, Sweden) at 1.3 m (4.3 ft) height from the ground. Increment cores were approximately 100 mm (3.94 in) in length. Canopy samples consisted of five 5 cm (2 in) long twigs with leaves, which were randomly collected from the lower two-thirds of the canopy (Mclaughlin et al. 1980). Samples from the different parts of the trees were collected within two hours in July 2005, September 2005, January 2006, and March 2006. Samples were stored on blue ice (Rubbermaid® , Fairlawn, OH) immediately after collection in the field, transported to the lab with- in two hours, and oven-dried at 80 ºC (176 ºF) until weights stabi- lized (approximately 48 hours). After drying, samples were ground and stored in plastic bottles at -20 ºC (-4 ºF) until the carbohy- drate concentrations were analyzed (Kolb and McCormick 1991). Carbohydrate Analysis Glucose and starch concentrations were determined for each sam- ple using Sigma® pernatant from the extract or glucose standards was mixed with 5 ml (0.17 fl oz) of anthrone reagent (Jaenicke and Thiong’o 1999). Absorbance of samples and standards were read at 625 nm within 30 minutes using a spectrophotometer (Spectronic 20, Baush & Lomb, Rochester, NY). Glucose concentrations were calculated through standard linear regressions and expressed as mg per g of dry weight. Starch content was determined by enzymatic conver- sion of starch to glucose. In the remaining pellet after glucose ex- tractions, amyloglucosidase, an enzyme responsible for the con- version of starch to glucose, was used. Standards were prepared using potato starch, and the samples were read at 540 nm within 30 minutes. Starch content was calculated through standard linear regressions and expressed as mg of glucose per g of dry weight. (Haissig and Dickson 1979; Renaud and Mauffette 1991). Data Analysis An analysis of variance was conducted on data including in the model cardinal orientation, type of tissue, and time of year. Results from samples collected from opposite side of the tree (North-South, and West-East) were pooled in order to compare differences among and between rows in the nurs- ery. The data was analyzed with the procedure General Linear Model (GLM) using the Statistical Package for the Social Sci- ences (SPSS, v. 13) for Windows (SPSS, Chicago, IL). Com- parisons among tissues and within orientations were per- formed using Fisher’s Least Significant Differences (LSD) to determine differences in carbohydrate concentration in trees. RESULTS AND DISCUSSION Statistical analysis revealed no main or interactive effect (P > 0.5) of cardinal orientation. When data from opposing orienta- tions (N-S and E-W) were pooled, no differences were found (data not shown). These results indicate that future research in- volving tissue sampling for carbohydrates may not be impacted by cardinal direction when sampling similar tissues at similar heights. However, carbohydrate reserve concentrations varied from base to the top in the trunk of sessile oak (Quercus pe- trea L.) and beech (Fagus sylvatica L.) (Babaroux et al. 2003). Differences in glucose concentrations among tissues varied (P < 0.001) across seasons (Figure 1). Glucose content was higher in leaves than in other tissues tested through the year, except in September when there were no significant differences in glucose GAGO-20 reagents (Sigma, St. Louis, MO). Glu- cose was extracted from tissues using methanol:chloroform:water (MCW, 12:5:3, v/v/v) solution, and 0.5 mL (0.02 fl oz) of the su- ©2009 International Society of Arboriculture Figure 1. Glucose concentrations (mg/g dry weight) measured in live oak samples collected at four different dates. Bars represent the SE of the mean.
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