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F. Liu and H. Stützel

This study was designed to quantify the responses of leaf expansion, stomatal conductance, and transpiration of four genotypes of vegetable amaranth [Amaranthus tricolor L. (Hin Choi), A. tricolor L. (Co. 2), A. blitum L. (WS80-192), and A. cruentus L. (RRC 1027)] to soil drying. Two greenhouse experiments were conducted during 1999 and 2000. Soil water status was expressed as the fraction of transpirable soil water (FTSW). Leaf expansion rates, stomatal conductances, and transpiration rates of the stressed plants were determined relative to those of nonstressed plants, and expressed as relative leaf expansion (RLE), relative stomatal conductance (RSC), and relative transpiration (RT), respectively. The rate of soil water extraction differed among genotypes, with RRC 1027 depleting soil water fastest and Hin Choi slowest. Whereas in 1999 all genotypes were equally efficient in soil water use, RRC 1027 extracted a greater volume of transpirable soil water than the other genotypes in 2000. The responses of RLE, RSC, and RT to FTSW were well described by linear-plateau models which allowed calculation of soil-water thresholds for leaf expansion (CL), stomatal conductance (CS), and transpiration (CT). Values for CL were higher than for CS and CT. CL was similar for the four genotypes in each year, whereas, CS and CT differed among genotypes. CS and CT was lowest for Hin Choi and highest for WS80-192. Differences of CL, CS, and CT between the two experiments might have been due to the different soils used in the experiments and the different evaporative demands during the drought cycles. Under drought stress, the reduction of transpiration of vegetable amaranth was due mainly to reduction of stomatal conductance, not to reduction of leaf expansion. The relative reduction of dry weight caused by drought stress was positively correlated with CS or CT across the four genotypes. Variation in CS and CT among amaranth genotypes revealed different responses to drought stress, which could make them suitable for different drought situations.

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Desmond G. Mortley, P.A. Loretan, C.K. Bonsi, and W.A. Hill

Growth chamber studies were conducted to evaluate the effect of four diurnal temperatures (24/18C, 26/20C, 28/22C, and 30/24C) on yield, leaf expansion and unfolding, and vine length of sweetpotatoes [Ipomoea batatas (L.) Lam]. Four vine cuttings (15 cm in length) of `TI-155' and `Georgia Jet' were grown for 120 days using a modified half-Hoagland nutrient solution with a 1:2.4 N:K ratio. Irradiance at canopy level averaged 600 μmol·m–2·s–1 at an 18/6 photoperiod, and RH of 70%. Storage root number/plant for both cultivars decreased with increased temperature. Storage root fresh and dry weights for both cultivars increased with temperatures up to 28/22C and declined at 30/24C. Foliage fresh and dry weights were not influenced by temperature for either cultivar. Leaf expansion rate and vine length were highest at 26/20C and lowest at 24/18C for both cultivars. Leaf unfolding rate was not affected by temperature foe either cultivar, but was more influenced by time of measurements.

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Youping Sun, Sarah A. White, David Mann, and Jeffrey Adelberg

collection. Times to shoot emergence (≈2 to 5 cm long bud emergence from bulb) and leaf expansion (a minimum of three fully expanded leaves) were recorded for plants in both bulb size treatments in the growth room (shoot emergence n = 5; leaf expansion n = 5

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Katrine Heinsvig Kjaer and Carl-Otto Ottosen

and physiology. During the first 21 d, leaf expansion of the second unfolded leaf was similar in all three treatments ( Fig. 2A ). However, during the last 7 d, these leaves expanded faster in the LD treatment, and after 27 d, the leaves were

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Susanna Marchi, Luca Sebastiani, Riccardo Gucci, and Roberto Tognetti

Net photosynthesis, dark respiration, chlorophyll and carbohydrate content, and leaf and shoot growth of deciduous peach [Prunus persica (L.) Batsch] saplings, grown in greenhouse conditions, were measured to assess changes in carbon balance during leaf development. The 6th, 12th, and 16th leaf node were measured from the first flush at the base through expansion to maturity (the first node being the oldest). Shoot and leaves expanded following a sigmoid pattern in all nodes. The shape of the logistic curve did not vary between the 6th and the 16th leaf node, while the 12th leaf node showed a steeper response, suggesting that the latter reached 50% expansion relatively earlier. Photosynthesis varied with leaf development as young leaves had low CO2 assimilation rates that were reflected in their chlorophyll concentration. Net daily CO2 assimilation was negative in young expanding leaves. The sink-source transition, defined to be the time when the increase in daily carbohydrate exchange rate exceeded the daily increase in leaf carbohydrate content, occurred before full leaf expansion. The transition from import to export was attained 11-12 days after budbreak (corresponding to 41% to 45% of full leaf expansion) for the 6th leaf, about 7-9 days after (38% to 52% of full expansion) for the 12th leaf and after 9-10 days (32% to 38% of full expansion) for the 16th leaf. Below 30% to 50% of full expansion leaves might not respond to assimilate requirements from sinks, being sinks themselves.

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Carleton B. Wood, Timothy J. Smalley, Mark Rieger, and David E. Radcliffe

Container-grown Viburnum plicatum Thunb. var. tomentosum (Thunb.) Miq. `Mariesii' were planted in unamended planting holes, tilled plots, and tilled plots amended with aged pine bark. A 36-day drought was initiated 108 days after planting. Amending induced N deficiencies, reduced shoot growth, and increased root growth. Plants harvested from tilled and planting-hole plots at drought initiation had 63% and 68% more dry weight, respectively, than plants from amended plots. Between 8 and 19 days after drought (DAD) initiation, plants from tilled plots maintained higher relative leaf water content (RLWC) than plants from planting holes. Plants in amended plots maintained higher RLWC than both other treatments between 7 and 33 DAD. Amended and tilled treatments had higher relative leaf expansion rates (RLERs) than the planting-hole treatment 8, 11, 13, and 15 DAD. As the drought lengthened, plants in amended plots maintained higher RLERs than plants in tilled plots. While plants in pine bark-amended plots were more drought tolerant than those in tilled plots, it is unclear if increased drought tolerance was caused by the improved rooting environment or N deficiency.

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G.R. Panta and D.S. NeSmith

Eight muskmelon (Cucumis melo reticulatus L.) cultivars were selected to test whether a model could be developed to estimate leaf area across cultivars. Regression analyses of leaf area vs. leaf width and length revealed several models that could be used for estimating the area of individual muskmelon leaves. A linear model using leaf width squared was the best overall, yielding the equation A = 3.3 + 0.63 (W2), where A is area of an individual leaf lamina (square centimeter) and W is leaf width (centimeter) at the widest point perpendicular to the leaf midrib. Forcing the intercept through the origin did not significantly alter prediction capability and resulted in a simple model of the form A = 0.64 (W2) that was applicable to all eight cultivars.

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Ralf Uptmoor, Mildred Osei-Kwarteng, Susanne Gürtler, and Hartmut Stützel

environmental conditions, the two-phase linear function describing LA development under optimum growth conditions was combined with a plateau function, which estimates the effects of drought on leaf expansion rates (LER). The plateau function is a special form

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Thomas E. Marler

of wind-exposed plants was approximately half of that for protected plants by Week 3 ( Fig. 1C ). Leaf area, leaf expansion rate, and root extension rate were not influenced by cultivar, wind, or their interaction ( Table 1 ). Table 1. Single leaf

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Nobuyuki Fukuoka, Takamoto Suzuki, Keisuke Minamide, and Tatsuro Hamada

exhibited an identical pattern with lower CGA content observed in the shaded leaves ( Fig. 2B ). Although there was an abrupt increase in the content of anthocyanin in the early stage of leaf expansion, the content decreased rapidly as the leaves matured