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Qi Chai, Fang Jin, Emily Merewitz and Bingru Huang

ions, carbohydrates, and organic acids), and changes in cellular/tissue elasticity [i.e., bulk elastic modulus (ɛ)] ( Touchette, 2006 ). Osmotic adjustment and high cell wall elasticity can modify the relationship between turgor pressure and cell volume

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Martin Brüggenwirth and Moritz Knoche

cell walls. Tissue cylinders (8 mm diameter) were punched using a biopsy punch (Kai Europe, Solingen, Germany) and cut to discs of 2.5 mm height using parallel razor blades. The discs comprised cuticle, epidermis and hypodermis, and the outer mesocarp

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Jaroslav Ďurkovič, Ingrid Čaňová, Lucia Javoříková, Monika Kardošová, Rastislav Lagaňa, Tibor Priwitzer, Roman Longauer and Jana Krajňáková

this new AFM technique to the point that it enables high-resolution imaging of algae ( Pletikapić et al., 2012 ) and woody plant cell walls ( Ďurkovič et al., 2012 , 2013 ; Ren et al., 2015 ), as well as fibrillar protein aggregates and native

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Martin Brüggenwirth and Moritz Knoche

investigated here must be accounted for within these two tissues. Mechanically relevant properties of soft tissues include the amount of applied stress, the properties of cell walls, and of the middle lamellae. Also involved are cell turgor, the permeability of

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E.V. Wann

Tissue firmness of ripe tomatoes is controlled by cell wall integrity of the fruit tissue and by the enzymatic softening that normally occurs during ripening. This study was conducted to determine the physical characteristics of cells and tissues of mature green (MG) and ripe fruit that might account for differences in firmness between `Rutgers' (normal), `Flora-Dade' (Firm), and two mutant lines called high-pigment (T4065 hp) and dark-green (T4099 dg), both of which possess extra firm fruit. Fruit samples were tested for resistance to a force applied to whole fruit and to sections of the pericarp tissue and by stress-relaxation analysis. Determinations were also made of cell density and cell wall content within the pericarp tissue. Fruit of mutant lines had firmer tissue than either `Rutgers' or `Flora-Dade' at MG or ripe. Whole fruit compression measurements showed that T4099 dg was firmer than T4065 hp or `Rutgers' at MG and firmer than `Flora-Dade' and `Rutgers' when ripe. Whole fruit of `Flora-Dade' were significantly firmer than `Rutgers' at MG and ripe. Firmness measured by compressive strength also showed that mutant lines had firmer pericarp tissue than the wild types at both MG and ripe stages. Stress-relaxation analysis showed that MG fruit of T4099 dg had greater tissue elasticity than `Rutgers' or `Flora-Dade'. Ripe fruit of both mutant lines had more tissue elasticity than wild types. There were no apparent differences among the genotypes due to tissue relaxation. From these analyses, tissue elasticity appears to be a significant parameter in determining tissue firmness in the tomato genotypes used in this study. Firmness and textural quality of ripe tomatoes appeared to be dependent on elasticity of the pericarp tissue and on the level of enzymatic softening during ripening.

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Milton E. Tignor Jr. and Russell L. Weiser

Alaska peas (Pisum sativum `Alaska') germinated in a dark growth chamber were treated ABA dissolved in a small amount of acetone before diluting in distilled water with 0.1% spreader. A blank solution was identically prepared without ABA. Both solutions were applied via paintbrush to the epicotyls of the peas every twelve hours for seven days following emergence. The blank solution was applied to two controls, chronological and physiological. A methanol bath was used to induce freezing and chilling stresses. ABA significantly improved cold tolerance (electrolyte leakage) in the pea seedlings for both freezing and chilling stress as compared to the physiological and chronological controls. Visual observation of the pea stems suggested a difference in stem flexibility among ABA treated peas and the controls. Pea stem elasticity and plasticity were measured along with plant dry weight, cell wall weight/gram fresh weight, and the quantity of cell wall sugars and amino acids.

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Graham J.J. Clarkson, Steve D. Rothwell and Gail Taylor

Baby salad leaves of salad roquette, arugula in the U.S. (Eruca vesicaria ssp. sativa) had an increased postharvest shelf life of 2 to 6 days, while lollo rosso lettuce (Lactuca sativa L. `Ravita') and red chard [Beta vulgaris L. var. flavescens (Lam.) Lam] baby salad leaves had increased shelf life of 1 to 2 days when harvested at the end of the day compared with leaves harvested at the start of the day. We have shown that improved shelf life of salad roquette and lollo rosso following end-of-day harvest was correlated with altered biophysical characteristics of the cell walls, with increased cell wall extensibility (percent plasticity and elasticity) measured at end of day. Leaf turgor pressure (P, MPa) was also highest in salad roquette and red chard at the end of day. Improved shelf life following `end of day' harvest was also associated with the accumulation of leaf sucrose in salad roquette but not lollo rosso and red chard following daily photosynthesis. Diurnal alterations of leaf starch concentration were detected in lollo rosso and red chard but not in salad roquette. The degree of leaf shelf life extension in salad roquette and red chard was further associated with the peak rates of leaf photosynthetic activity. These data suggest that, depending on species, significant improvements to postharvest shelf life could be achieved through the rescheduling of time of day for harvest and also provide relevant information on the selection of traits for future genetic improvement.

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Robert Augé

The determination of tissue water potential components is important for understanding plant growth and response to the environment. Pressure-volume (PV) analysis is often considered to give the most accurate estimate of symplastic osmotic potential. Additional information about tissue water relations can also be computed from PV curves estimates of bulk cell wall elasticity, symplastic water volume, and turgor potential at various states of tissue water content. The generation of PV curves is a time-consuming procedure, however, and involves considerable computation. This presentation describes a computer spreadsheet template for traditional evaluation of a PV curve through linear regression of the zero turgor segment. The template allows real-time plotting of the inverse ψ/ water loss relating, provides estimates of most commonly calculated PV characteristics and permits instant graphic visualizations of changes in water potential components and elasticity with changes in water potential, total tissue water and symplastic water content. The advantages of spreadsheet analysis of PV curves are simplicity, consistency, thoroughness and speed. A fleeting acquaintance with spreadsheet software and a thorough understanding of pressure-volume theory on the part of the user is assumed.

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W.D. Lane, M. Meheriuk and D.-L. McKenzie

Fruit were studied to determine if anatomical and physiological features explain the difference in susceptibility to rain-induced cracking of the sweet cherry (Prunus avium L.) cultivars Sue (resistant), Lapins (moderately resistant), and Van (susceptible). Water uptake as a percentage of fruit weight at cracking tended to be high in `Sue', medium in `Lapins', and low in `Van' and was related to the percentage of cherries remaining sound after 4 hours of immersion, suggesting that this trait is a factor in determining resistance. Mesocarp cells of `Sue' were more rectangular in section than those of the other cultivars. Skin elasticity and thickness of the cuticle did not explain resistance of `Sue' to cracking. Magnesium, copper, and phosphorus mineral contents were not related to cracking susceptibility, but the content of calcium, which influences cell wall integrity, in the epidermis of `Sue' was lower than in `Van'. Calcium content was not different in the hypodermal cells of the two cultivars. None of the anatomical features examined in this study explain the resistance to fruit cracking of `Sue'.

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Eckhard Grimm and Moritz Knoche

, swelling of the cell walls was quantified by determining cell wall thickness using image analysis (Cell-P, Olympus Europa). The osmolarity of incubation media and of juice extracted from the same fruit as that used in the plasmolysis and cell wall swelling