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  • Author or Editor: Mark Ritenour x
  • Journal of the American Society for Horticultural Science x
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Heat treatments and exposure to elevated CO2 are known to reduce the incidence of chilling injury on grapefruit. In the current study, `Marsh' grapefruit (Citrus paradisi Macf.) were harvested on 17 Jan. or 22 Mar. 1996 and exposed to hot water (HW) dips (48 °C for 120 minutes) or exposed to controlled atmosphere (CA) of 10% or 16% CO2 during the first 3 weeks of an 8-week cold storage period (4.5 °C) to test their effects on the development of peel pitting (i.e., chilling injury) and proline and other compositional changes of the peel and juice. All HW and CA treatments from both harvests greatly reduced the development of peel pitting compared to the control. These treatments were also associated with lower average proline levels in the flavedo during storage. This suggests that HW and elevated CO2 may reduce chilling-induced peel pitting by facilitating proline metabolism in grapefruit flavedo tissue. HW and CA treatments resulted in higher peel total soluble and nonreducing sugar levels, but effects on peel reducing sugar and free amino acid concentrations were not consistent. In the juice, HW reduced titratable acidity (TA) concentrations while CA tended to increase both TA and ascorbic acid concentrations. Compared to the control, CA resulted in a slight decrease in total soluble solids during storage, while the effect of HW was inconsistent.

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Western immunoblot analyses showed that small heat shock proteins (smHSPs) are low or undetectable in the peel of `Fuji', `Jonagold', `Criterion', `Gala', and `Delicious' apples [(Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.] growing shaded within the tree canopy (shade apples), but are high in apples growing exposed to direct sunlight (sun apples). `Fuji', `Jonagold', and `Gala' sun apples sampled biweekly between 1 July and 21 Oct. 1997 were highest in content of smHSPs on 31 July, 13 Aug., and 10 Sept., corresponding to some of the warmest periods of the sampling period. The smHSPs started to disappear first in `Gala', the earliest maturing cultivar, and last in `Fuji', the latest maturing cultivar indicating that maturity might play a role in regulating smHSP accumulation. In sun apple fruit left on trees for 60 to 120 days beyond commercial maturity and exposed to field temperatures as low as -4 °C, a 71.7 ku (u = unified atomic mass unit) polypeptide was detected with a polyclonal antiwheat (Triticum aestivum L.) HSP70 in the peel and cortex of all five cultivars. While no smHSPs were detected in these apples, three smHSPs, as detected by antibodies against pea (Pisum sativum L.) cytosolic HSP18.1, could be induced in the same fruit 24 hours after heating to 45 °C for 4 hours. In `Fuji' shade apples heated at 40 °C, smHSP accumulation was detected after the second hour of a 4-hour heat treatment and continued to increase over the next 48 hours at 22 °C. Levels of HSP70 did not change in `Fuji' shade apples heated at 45 °C for 2, 4, or 6 hours, but smHSPs became detectable immediately after each of these heat treatments and further increased over the next 24 hours at 22 °C. Accumulation of smHSPs was maximal in the 4-hour heat treatment. After a 4-hour heat treatment at 45 °C, smHSPs increased during the next 48 hours at 22 °C and then declined by 72 hours. Using two-dimensional electrophoretic analysis, as many as 17 proteins ranging from 15 to 29 ku were found to accumulate in the peel 48 hours after a 4-hour heat treatment. Thus, apples can respond rapidly to high temperature stress, even at advanced stages of maturity, by synthesizing smHSPs, which likely play an important role in protecting cellular biochemical processes during these periods of stress.

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This study was undertaken to determine if endogenous IAA content and axillary bud development correlate with phenylalanine ammonia-lyase (PAL) induction and russet spotting (RS) susceptibility among RS susceptible and resistant cultivars of Iceberg lettuce (Lactuca sativa L.). Final levels of ethylene-induced PAL activity and RS development were highly correlated among cultivars, field conditions, and harvest dates. Harvested Iceberg lettuce midribs contained relatively low amounts of free IAA (maximum of 5.2 ng·g-1 fresh weight). There was poor correlation between free IAA content in lettuce leaf midribs and final RS development among all cultivars, growing conditions, and harvest dates. Axillary bud development, as measured by the number of visible buds per head, bud weight, or bud length, were not significantly correlated with final RS development or midrib IAA content. Cultivars with higher initial free IAA content lost much of their IAA after 8 days storage at 5C in air ± ethylene.

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