The effects of water stress and GA, on breaking dormancy of flower buds of coffee (Coffea arabica L.) were investigated. In the first experiment, water was withheld until the trees reached leaf water potentials (WP) of -1.20, - 1.75, -2.65, or -3.50 MPa. Water potential, ethylene production, and ion leakage of flower buds and leaf disks were examined from release from water stress until anthesis. Trees that had experienced leaf WP of less than - 2.65 MPa, and flower bud WP of about - 4.0 MPa flowered within 9 days after irrigation. In flower buds where dormancy had been broken with water stress, ethylene production was low compared to dormant buds and flowers at anthesis. In the second experiment, O, 50, 100, or 200 mg GA3/liter was painted on branches of nonstressed trees. In experiment three, water was withheld until plants reached leaf WP of -0.6, -1.3, - 2.1, or - 3.0 MPa, then two branches per tree were painted with O, 50, and 100 mg GA3/liter. Gibberellic acid partially compensated for insufficient water stress to initiate flower opening. Ethylene evolution of flower buds was affected by water stress but not by GA3 treatment. Severe water stress treatments and GA, treatment (200 mg·liter-1) increased ethylene evolution of leaf disks. Ion leakage of flower buds and leaf disks was increased by severe water stress. Ion leakage of flower buds was highest at anthesis. After water stress, dormant and nondormant flower buds at the 4-mm stage could be distinguished based on their ethylene evolution. Chemical name used: gibberellic acid (GA3).
Ursula K. Schuch, Leslie H. Fuchigami, and Mike A. Nagao
Heat-shock induced chilling tolerance in excised discs of tomato fruit pericarp tissue significantly alter the kinetics of chilling-induced ion leakage from the discs into an aqueous isotonic mannitol solution. Pericarp discs were excised from mature-green tomato fruit, trimmed of locular material to 5-mm thickness, held overnight (ca. 16 h) at 20 °C and then subjected to various heat-shock (45 °C) treatments before being chilled at 2.5 °C for up to 30 days. Two discs were immersed in 20 mL of 0.3 m mannitol in a 50-mL plastic centrifuge tube and the conductivity of the aqueous solution periodically measured. The tube was capped and frozen at -20 °C. Total conductivity was measured once the tube had warmed to 20 °C with shaking. The percent ion leakage was calculated as the percent of total, and subjected to an analysis to partition rates of leakage into symplastic and apoplastic components. The symplastic component was not affected by the heat-shock treatment, while the apoplastic component showed reductions consistent with reduced chilling-induced damage to the cellular membrane. The protective heat-shock treatments also significantly increased the tissues resistance to fungal infection.
Frans J.M. Bonnier, Joost Keurentjes, and Jaap M. van Tuyl
The viability of `Avignon' and `Esther' (Asiatic hybrids), `Star Gazer' (Oriental hybrid), and `Snow Queen' lily bulb scales (L. longiflorum Thunb.) was determined after storage at –2C for 0.5, 1.5, and 2.5 years. Ion leakage, the percentage of scales that formed bulblets, and the number and weight of these bulblets were determined on scales from the inner, middle, and outer part of bulbs. During storage, the outer scales of all cultivars and the inner and middle scales of `Snow Queen' showed increased ion leakage accompanied by a decreased ability to form scale bulblets during storage. Concurrently, the percentage of scales forming bulblets declined, and more and smaller scale bulblets were formed per regenerative scale. Thus, ion leakage is a useful criterion to measure viability of lily scales.
Babita Thapa, Rajeev Arora, Allen D. Knapp, and E. Charles Brummer
et al., 1993 ). A key function of cold acclimation is to stabilize membranes against freezing-induced cellular dehydration ( Thomashow, 1999 ). Ion leakage (IL) resulting from decreased membrane integrity of freeze-damaged tissues can be easily
Navjot Kaur and Jiwan P. Palta
We investigated the use of lysophosphatidylethanolamine (LPE) for prolonging vase life of snapdragon (Antirrhinum majus L.). Freshly cut snapdragon spikes were set into a LPE solution at 25 mg·L-1 for 24 h and then transferred to deionized water. The vase life was enhanced by LPE. The flowers on spikes treated with LPE showed symptoms of wilting or browning 4 or 6 days later than those on the spikes given deionized water in inbred or `Potomac White', respectively. All the spikes were of marketable quality for 5 to 7 days after harvest when treated with LPE, whereas in the control only about half of the flowers were of marketable quality at 2 days after harvest. LPE treatment also delayed fresh mass loss, lowered endogenous ethylene production, and reduced ion leakage. These results suggest that LPE has commercial potential in enhancing vase life of snapdragons.
Maalekuu Kissinger, Sharon Tuvia-Alkalai, Yavin Shalom, Elazar Fallik, Yonatan Elkind, Matthew A. Jenks, and Mark S. Goodwin
Fruit of pepper (Capsicum annuum L.) is hollow by nature, which limits its water reservoir capacity, and as such, small amounts of water loss result in loss of freshness and firmness, which reduce fruit quality, shelf life, and market value. In order to understand the basis for water loss from fruit, 10 pepper accessions with wide variation in water loss rate were used to study physiological and biochemical factors associated with postharvest water loss in ripe pepper fruit during storage. Postharvest water loss rate in ripe pepper fruit stored at 20 °C, and 85% relative humidity, was found to be associated with cell membrane ion leakage, lipoxygenase activity, and total cuticular wax amount. Total cuticular wax amounts were highest in the high-water-loss pepper fruit, and lowest in the low-water-loss fruit. However, total cuticle amount (isolated enzymatically and quantified gravimetrically), total cutin monomer amount, and the amount of individual cutin monomer and wax constituents (determined using gas chromatography mass spectrometry) indicated no direct association with postharvest water loss rates. Fruit fresh weight, pericarp weight, pericarp surface area, pericarp thickness, initial water content, and dry matter were highly associated with each other, but less so with water loss rate. Fruit of accessions displaying high fruit water loss rate matured and ripened earlier than fruit of accessions displaying low-water-loss rate. Cell membrane ion leakage and lipoxygenase activity were higher after storage than immediately after harvest. Pepper fruit total cuticle wax amount, lipoxygenase activity, and cell membrane ion leakage were directly related to postharvest water loss rate in pepper fruit during storage.
Mikal E. Saltveit
appear during prolonged chilling or during warming after chilling ( Saltveit and Morris, 1990 ). The severity of CI can be quantified by visual inspection of quality parameters, by measuring the rate of ion leakage from excised tissue into an isotonic
Rajeev Arora, Michael E. Wisniewski, and Donald J. Makus
Frost damage to `Jersey Giant' asparagus (Asparagus officinalis L.) spears was evaluated in noncovered and black plastic-covered field plots following a spring frost episode. In the noncovered plots, 78% of spears were killed as compared to only 17% under the plastic rowcovers. Laboratory studies using natural frost simulations indicated that the spears of both treatments were frost hardy to -2.8C. Air temperature data in the field plots during the frost episode indicated that spears in noncovered plots were at lower temperatures (-4.0 to -4.8C vs. -2.8C) ≈4 to 5 hours longer than spears under rowcovers. The large difference in the spear-kill may be due to the difference in the combined effect of the degree and duration of freezing to which the spears had been exposed.
Roberto M. Cabrera and Mikal E. Saltveit Jr.
Symptoms of chilling injury were reduced by intermittently warming cucumber fruit (Cucumis sativus L. cv. Poinsett 76) from 2.5 to 12.5C for 18 hr every 3 days. Fruit continuously held at 2.5C for 13 days developed severe pitting and decay after 6 days at 20C, while fruit continuously held at 12.5C or intermittently warmed showed no pitting or decay during subsequent holding at 20C. The increased rate of C2H4 production during the first warming period, from 12 nl·(kg·hr)-1 at 2.5C to 201 nl·(kg·hr)-1 at 12.5C, was significantly greater than that during the second or third warming periods, i.e., 53 to 98 and 53 to 55 nl C2H4/(kg·hr), respectively. Respiration increased 3-fold during the initial warming period, but only 2-fold during subsequent warming periods. Leakage of cellular ions from excised disks of mesocarp tissue was around 6% and 10% of the total ion content of the tissue for control and intermittently warmed fruit, respectively, but increased to 17% for fruit that were continuously held at 2.5C for 10 days. After 320 hr (three cycles) of chilling and warming, chilled fruit showed significantIy lower ethylene-forming enzyme activity than the control or intermittently warmed fruit. Fruit held at 12.5C contained 0.09 to 0.34 nmol·g-1 of ACC. ACC levels were 6.23 nmol·g-1 in fruit exposed to 2.5C for 320 hr. In contrast, intermittently warmed fruit only showed 30% and 27% increases in ACC content during the first and second warming periods, respectively. Periodic warming appears to allow chilled fruit to acclimate to subsequent periods of chilling. Chemical names used: 1-aminocyclopropane-1-carboxylic acid (ACC).
Zienab F.R. Ahmed and Jiwan P. Palta
development of soft edible fruits ( Prasanna et al., 2007 ; Tapre and Jain, 2012 ). Some of the primary changes during this ripening process include an increase in membrane permeability (ion leakage), loss of fruit pulp firmness, decrease in starch, increase