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The difference between night and day temperature (DIF = day - night temperature) has been shown to affect plant height. A positive DIF (+DIF), cooler night than day temperature, increases stem elongation while a negative DIF (- DIF), warmer night than day temperature, decreases stem elongation. The physiological mechanism underlying the growth response to DIF is not understood, however, and the effects of day/night temperature differentials on root permeability to water and root elongation rate have not been studied. The objective of this study was to describe how +DIF and -DIF temperature regimes affect leaf water relations, root water flux (Jv ), root hydraulic conductivity (Lp ), and root elongation rates of `Boaldi' chrysanthemum [Dendranthema ×grandiflora Kitam. `Boaldi' (syn. Chrysanthemum ×morifolium Ramat.)] plants over time. Leaf turgor pressure (ψp) was 0.1 to 0.2 MPa higher in plants grown in a +6 °C DIF environment throughout both the light and dark periods, relative to those in a -6 °C DIF environment. Jv differed markedly in roots of plants grown in +DIF vs. -DIF environments. Rhythmic diurnal patterns of Jv were observed in all DIF treatments, but the relative timing of flux minima and maxima differed among treatments. Plants grown in positive DIF regimes exhibited maximum root flux at the beginning of the light period, while those in negative DIF environments had maximum root flux during the first few hours of the dark period. Plants grown in +DIF had significantly higher Lp than -DIF plants. Plants grown in +DIF and -DIF environments showed differences in the diurnal rhythm of root elongation. During the dark period, +DIF plants exhibited minimal root elongation rates, while -DIF plants exhibited maximal rates. During the light period, the converse was observed. In -DIF temperature regimes, periods of rapid root elongation coincided with periods of high Jv . Results of this study suggest that negative DIF environments lead to leaf turgor reductions and markedly alter diurnal patterns of root elongation. These changes may, in turn, act to reduce stem elongation.

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Tap roots of two coarse rooted species, Nyssa sylvatica and Quercus acutissima, were subjected to six treatment materials which were cut to fit or placed on the bottom of a 7.61 container. Each treatment material (paint only, Styrofoam plug tray, 3M floor buffer mat, peat fiber sheet, stone and weed barrier fabric) was either painted with Spin Out™ of impregnated with Spin Out™ WP. Treatments that allowed the tap root to penetrate the material, i.e. weed barrier fabric, stone and 3M floor buffing mat, were more effective in controlling tap root elongation. The weed barrier fabric significantly reduced tap root length of Quercus acutissima and Nyssa sylvatica by 80% and 67% respectively compared to controls and by 65% and 53% respectively compared to the paint only treatment. In some cases the 3M and stone treatments were more effective than the weed barrier fabric but were impractical because of weight or expense.

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physiological processes, such as cell wall and membrane synthesis and function, nucleic acid and carbohydrate metabolism, root elongation, pollen germination, and pollen tube growth ( Camacho-Cristóbal et al., 2008 ; Goldbach et al., 1991 ; Goldbach and Wimmer

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Two studies were conducted to determine how greenhouse irrigation systems alter root elongation, root morphology, shoot growth, and water status of `TAM-Mild Jalapeño-1' pepper (Capsicum annuum L.) seedlings. Transplants were grown in containerized trays for 48 days in a greenhouse. Irrigation systems were 1) flotation (FI), 2) 28 days FI plus 14 days overhead (OI; FI + OI), 3) alternate OI and FI (OI–FI), and 4) OI. FI and OI–FI transplants maintained a uniform lateral root length increase between 20 and 41 days after seeding (DAS). In FI + OI and OI transplants, lateral root elongation tended to plateau at ≈31 DAS; however, by increasing the number and length (33%) of basal roots, OI transplants had a total root growth compensation during the remaining growth period. At 41 DAS, OI transplants had a higher shoot: root ratio (S: R = 5) and maintained a higher shoot water potential (Ψstem = –0.58) than FI transplants (S: R = 3; Ψstem= –0.69 MPa, respectively). In the second study, OI transplants maintained higher Ψstem than FI transplants. The latter had a lower stomatal conductance and photosynthesis rate than OI and FI + OI transplants. FI may be used to lower the S: R ratio and promote hardiness in jalapeño transplants.

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Rapid and timely production of kiwi (Actinidia deliciosa) seedlings is often hampered by poor and erratic seed germination. This investigation was conducted to assess the effect of gibberellic acid, cold stratification (5° C), and their combinations on seed germination and subsequent radicle elongation. Germination counts and radicle elongation measurements were made two weeks after incubation at 25.4° C under continuous light and approximately 100% RH. GA treatments broke dormancy and increased germination and radicle elongation with increasing concentration up to 2500 ppm. At 5000 ppm, germination and radicle elongation were reduced. Cold stratification (1 and 2 week durations) alone did not affect germination nor break dormancy. Combined cold stratification and GA treatments significantly enhanced seed germination and radicle elongation with the best response at the highest GA concentration (5000 ppm) and longest stratification (2 weeks), regardless of whether the seeds were stratified prior to or after GA treatments.

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.H. Kim et al., 2004 ). For example, studies have been conducted to compare the growth of cucumbers ( Cucumis sativus L.) reared under red or blue light-emitting diodes (LEDs). The findings showed that, compared with irradiation under white light, root

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To root tissue-cultured apple cultivars, shoots from proliferating cultures were first transferred to root induction medium with IBA for 1 week in the dark. Shoots were later transferred to the same medium without IBA and incubated under light for elongation of the roots. Rooted shoots were then transferred to Jiffy-7s supplemented with biological plant protectant and fertilizer, and incubated in plastic humidity trays. After 2 to 3 weeks, plants were transferred to pots and covered with plastic bags to facilitate acclimation. This technique has resulted in 70% to 100% of shoots selected in vitro producing vigorously growing, healthy plants in the greenhouse. Chemical name used: indolebutyric acid (IBA).

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al., 2006 ). In addition, solution culture could remove border cells and mucilages that possibly protect root tips from Al toxicity ( Miyasaka and Hawes, 2001 ). Relative root growth, which is a measure of root elongation inhibition, can be used as an

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greater drought sensitivity are the first to lose roots when water becomes limited. In contrast, drought-resistant cultivars, particularly ‘Penn A-4’, had the ability to maintain root elongation and production even when drought was imposed. These results

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plants. Left unanswered, however, is the question of how carbohydrates in seed (both pre-existing and those accumulating during germination) affect germination and root elongation under salt stress. We assessed germination and carbohydrate status of seeds

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