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Jiwan P. Palta

In recent years evidence has been presented that implicates the role of free (cytosolic) Ca2+ as a major metabolic and developmental controller in plants. Calcium concentrations in the cytoplasm are kept very low under normal conditions (10-6 to 10-8 M). Small changes in the absolute amount of calcium can create a 10- to 100-fold change in the Ca2+ concentration without upsetting the ionic balance of the ceil. This feature makes Ca2+ an excellent candidate as a second messenger. Thus, a stress induced change in the cytosolic Ca2+ could bring a cellular/plant response to stress. This response is thought to be mediated through activation of Ca2+ and/or Ca2+-calmodulin-dependent protein kinases which in turn mediate the activity of various enzymes via phosphorylation. Recent evidences from the impact of salinity, low temperature, high temperature, and biotic stresses support such a role of calcium. Data on the association between stress-induced injury and perturbation of membrane/cytosolic calcium are available. In addition, evidences for the role of calcium in acclimation to stress have been reported. These studies suggest that manipulation of cellular Ca2+ may be one of the approaches we have on hand to bridge the gap between science and technology.

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Jiwan P. Palta* and Gerard Simon

Freezing stress resistance is composed of several components namely tolerance, avoidance and acclimation ability. These three components of freezing stress are heritable traits. We have demonstrated that progress in the improvement of freezing stress resistance can be made by individually selecting for various components of this resistance and then recombining them to get the desired plan. Freeze-thaw injury in carrots is manifested as damage to the foliage, cracks on the roots (especially on the crown), and crown root rot. We found that foliage damage following freeze-thaw stress was related to the tolerance of the foliage to ice formation. The formation of cracks in the crown and root tissue was related to formation of ice itself. The carrot breeding lines we tested varied considerably for the crown position in relation to soil surface. The carrot crowns and roots below the soil surface will be better in avoiding ice in the tissue, thus avoiding cracks. The freeze-thaw injury observed on the foliage in the field was highly correlated to the freeze-thaw tolerance of leaf tissue (measured as ion leakage from the leaf tissue) determined by controlled freeze-thaw test in the laboratory. Based on this work we developed a breeding strategy to improve frost hardiness in carrots by combining the characteristics that avoid ice in the crown and root tissues (e.g., crown position underground) with the characteristics that reduce foliage and root injury by ice (freezing tolerance of foliage). By using this strategy we were able to successfully obtain the desired plant. Two hardy carrot hybrids (Eskimo, Artico) were released by Vilmorin and their hardy characteristics have been confirmed under field conditions.

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Senay Ozgen and Jiwan P. Palta

Tuberization in potato is known to be under complex biochemical control involving hormones. A number of studies have provided evidence for a critical role of GA in tuberization. There is also evidence that GA in plants can be modulated by a Ca/calmodulin pathway. The purpose of the present study was to determine the influence of supplemental Ca fertilization on tuber size and tuber number. Plantlets of Solanum tuberosum `Russet Burbank' raised in tissue culture were planted in 20-L pots filled with sandy loam field soil with the pH of 6.9 and exchangeable soil Ca level of 350 ppm. All treatments received the same total amount of N (equivalent to the rate of 280 kg·ha-1). Four treatments were evaluated: nonsplit N (from ammonium nitrate), split N (from ammonium nitrate), split N+Ca (from calcium nitrate), split N+Ca (50% N from urea, 50% N from ammonium nitrate and Ca from calcium chloride). The total Ca was applied at the rate equivalent to 168 kg·ha-1 on a split schedule (equally split at four, six, eight and ten weeks after planting). Four months after planting tubers were harvested and evaluated. As expected tuber tissue Ca was increased by Ca application from 144 to 245 μg·g-1. In general, the two Ca treatments had significantly lower tuber number per plant as compared to the nonsplit and split N treatments. A plot of mean tuber Ca and tuber number for individual plants showed a significant negative relationship. Both Ca treatments produced tubers with higher mean tuber weight compared to nonsplit N. This increase in tuber size with Ca application was not apparent when compared with split N treatment. These results show that Ca application to soil can decrease tuber number suggesting that soil Ca may influence tuberization in potato.

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Mustafa Ozgen and Jiwan P. Palta

Ethephon [2-(chloroethyl) phoshonic acid] is used widely to maximize the yield of ripe tomato fruit. However, ethephon causes rapid and extensive defoliation, overripening, and promotes sunscald damage to the fruit. Recent studies from our laboratory have provided evidence that lysophoshatidylethanolamine (LPE) can reduce leaf senescence. We investigated the potential use of LPE to reduce damaging effect of ethephon on tomato foliage. Three-month-old tomato plants (variety Mountain Spring) grown in greenhouse conditions were sprayed with 200 ppm LPE (with 3% ethanol) at 6 and 24 h before ethephon treatment. After 8 days, plants treated with ethephon alone showed about 80% foliar damage while plant treated with LPE before ethephon treatment showed about 25% foliar damage. In a parallel study, LPE together with ethephon was found to maintain three to four times greater chlorophyll content in the leaves compared to ethephon alone. Treatments of LPE did not reduce the fruit ripening response by ethephon. Both sources of LPE were effective in preventing damaging effects of ethephon on the foliage. These results suggest that LPE treatments 6 and 24 h before ethephon application can prevent damaging effects of ethephon on foliage while allowing the acceleration of fruit ripening.

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Sookhee Park and Jiwan P. Palta

High temperature effects potato production by reducing overall growth and partitioning of photosynthate to tubers. Recent studies from our laboratory demonstrated that these effects can be reduced by increasing rhizospheric calcium. This present study was conducted to determine if this mitigation of heat stress effect on potato is due to modulation of heat shock protein by calcium during stress. An inert medium and nutrient delivery system capable of maintaining precise rhizospheric calcium levels were used. Biomass was measured and protein samples were collected from potato leaves. Using electroblotting, heat shock proteins were detected by antibodies to Hsp21 and Hsp70 (obtained from Dr. Elizabeth Vierling). Injury by prolonged heat stress was mitigated at calcium concentration >5 ppm. The calcium concentration of leaf and stem tissues were twice as high in 25 ppm calcium-treated plant compared to 1 ppm calcium-treated plants. Total foliage fresh weight was 33% higher and dry weight 20% higher in plants supplied with 25 ppm of calcium than supplied with 1 ppm of calcium. HSP21 was expressed only at high temperature and at greater concentrations in 25 ppm calcium treatment. HSP70 was expressed in both control, 20 °C/15 °C (day/night) and heat-stressed tissue, 35 °C/25 °C (day/night) under various calcium treatments (1 to 25 ppm). Also, there were some differences in HSPs expression patterns between young and mature leaves. Young tissue responded immediately to the heat stress and started to express HSP21 within 1 day. Mature tissue started to express HSP21 after 2 days. HSP21 of young tissue disappeared sooner than mature tissue when heat stress-treated plants were returned to normal conditions. These results support our earlier studies indicating that an increase in rhizospheric calcium mitigate heat stress effects on the potato plant. Furthermore these results suggest that this mitigation may be due to modulation of HSP21by rhizospheric calcium during heat stress.

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Navjot Kaur and Jiwan P. Palta

Freshly cut snapdragon (Antirrhinum majus L) spikes or carnation (Dianthus caryophyllus L cv. White Sim) stems were put in LPE (10 ppm for carnation, 25 ppm for snapdragon) solution for 24 hours and then transferred to deionized water. Parallel controls were kept continuously in deionized water. Snapdragon spikes were harvested when they had one-third of the florets opened which is a standard commercial practice. The carnations used in the experiment were harvested at three different stages of flower development starting from open brush bud stage (Stage IV) to fully opened (Stage VII, petals 45(to the stem) flower. LPE treatment delayed senescence in snapdragon by four days. Furthermore, it enhanced the opening of floral buds and opened all the florets on every spike. LPE treatment also significantly delayed loss in fresh weight of spikes associated with senescence, lowered the endogenous ethylene production and reduced ion leakage from florets. LPE had a similar effect on fresh weight and ion leakage from carnations if it was applied at an early stage of flower opening. Older carnations (Stage VII) were found unresponsive to LPE. In conclusion, LPE has the potential in enhancing the vase life of snapdragons and carnations. Carnations must be harvested at the open brush bud stage for effective LPE application. Our results suggest that LPE is prolonging vase life of cut flowers by reducing ethylene production and maintaining membrane integrity.

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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.

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Zienab F.R. Ahmed and Jiwan P. Palta

Banana is one of the most consumed tropical fruits around the world. It is marketed nearly all year-around and has a relatively short shelf life. Fruits are harvested mature green and treated with ethylene to stimulate ripening before distribution and sale. The fruits generally ripen within 4–5 days after ethylene treatment and sold primarily at yellow stage of ripening. After turning yellow the fruit becomes unsuitable for marketing in 1–3 days. Thus 1–2 days of improvement in the fruit shelf life could enhance the market value of banana. Previous studies conducted in our laboratory have demonstrated that both pre- and postharvest application of lysophosphatidylethanolamine (LPE) can retard aging and improve shelf life of various fruits. The objective of this study was to investigate the possibility of improving shelf life of banana fruit by a postharvest dip in LPE. For this purpose, whole fruits obtained from the market at ripeness stage of 2.5 (about 75% green) were dipped in solution of 500 ppm LPE for 30 minutes and observed for a period of five days at room temperature. Each treatment was applied to 50 uniform fruits. From each hand bought, an equal number of fruits were separated for LPE and control treatments to reduce the variability. Five days after dip treatment, the fruit treated with LPE were firmer and thicker as compared with the control. Starch breakdown was also delayed in the LPE-treated fruits. LPE treatment slowed the development of brown spots on the peel tissue. Both peel and pulp tissue of LPE-treated fruits had lower ion leakage compared with the control. Fruit peel slices treated with LPE for 3 hours also showed a decrease in ion leakage and respiration rate at 24 hours after treatment. Results of the present study indicate that a postharvest dip treatment with LPE may improve shelf life of banana fruit by 1–2 days. These results suggest that LPE may improve shelf life by maintaining membrane integrity, reducing respiration, and slowing the breakdown of starch and cell walls during ripening and senescence of banana fruit tissue.