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Juan M. Quintana, Helen C. Harrison, James Nienhuis, and Jiwan P. Palta

Flow rate, Ca content, and Ca concentration of sieve sap were measured at four developmental stages (flowering and 1, 2, and 3 weeks after flowering) in six commercial snap bean cultivars to better understand physiological factors associated with genetic differences for pod Ca concentration. Sampling began 5 weeks after greenhouse planting and consisted of 1) decapitation of the plant at the first node; 2) covering the stem with preweighed dry cotton; and 3) removing the cotton, reweighing it, and saving it for Ca determination. Flow rate was defined as the difference in cotton weight (expressed as milliliter) per 12 hours. Ca determinations were made using an atomic absorption spectrophotometer. Calcium content was defined as milligram of Ca per total volume of sieve sap after 12 hours. Concentration of Ca was the quotient of Ca content by flow rate (expressed as milligrams Ca per milliliter sap). A positive correlation between flow rate and total Ca content of sieve sap (R 2 = 0.83), flow rate and Ca concentration of sieve sap (R 2 = 0.36), and Ca content and Ca concentration (R 2 = 0.80) were found. Maturity appeared to be an important factor affecting flow rate and Ca influx in snap bean plants. Significant differences between genotypes for Ca content and flow rate were observed. High Ca genotypes reflected a high flow rate regardless developmental stage.

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Bjorn H. Karlsson, Jiwan P. Palta, Laurie S. Weiss, James F. Harbage, and John B. Bamber

Cold-induced changes in gene expression have been demonstrated in a number of species that vary in freezing tolerance and acclimation capacity. Relative freezing tolerance was measured based on ion leakage for both nonacclimated and acclimated S. commersonii and S. cardiophyllum parents, F1 and backcross progeny segregating for cold tolerance and acclimation capacity. Western blot analyses showed increase in a dehydrin band (47 kD)(antisera courtesy of T. Close) following cold acclimation of cold tolerant S. commersonii, and a slight increase in cold sensitive S. cardiophyllum. Expression of 47 kD cosegregated with non acclimated freezing tolerance but not with acclimated freezing tolerance. Our results show that (i) expression of dehydrins is a heritable trait in the Solanum diploid population, (ii) there is no direct relationship between relative freezing tolerance and the presence or absence of dehydrm protein following cold acclimation and (iii) based on assays measuring the residual activity of the lactate dehydrogenase (LDH) enzyme following freezing, the cryoprotective influence of `boiling stable' proteins was species dependent and is related to the freezing tolerance of the species. Supported by USDA/NRI grant 91-3700-6636 to J.P.P. and J.B.B..

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Juan M. Quintana, Helen C. Harrison, Jiwan P. Palta, and James Nienhuis

To understand physiological factors associated with genetic differences for pod Ca concentration between snap bean genotypes, flow rate and Ca uptake of sieve sap were measured, as well as pod Ca concentration. Measurements for flow rate and Ca uptake were done at three developmental stages (fl owering and 1 and 3 weeks after) in two commercial snap bean cultivars (Hystyle and Labrador) grown aeroponically. Pods were collected 2 weeks after flowering only. Flow rate and Ca uptake sampling began 4 weeks after transplanting and consisted of: 1) decapitation of the plant at the first node; 2) covering the stem with pre-weighed dry cotton; and 3) removing the cotton, reweighing it, and saving it for Ca determination. Flow rate was defined as the difference in cotton weight (expressed as ml) per 17 hr divided by foliage mass. Ca uptake was defined as mg of Ca per total volume of sieve sap after 17 hr divided by foliage mass. Ca determinations were made using an atomic absorption spectrophotometer. A positive correlation between flow rate and total Ca uptake of sieve sap (R 2 = 0.90), flow rate and pod Ca concentration (R 2 = 0.47), and Ca uptake and pod Ca concentration (R 2 = 0.42) were found. Hystyle reflected 1.5 times more flow rate and pod Ca concentration than Labrador. Significant differences between genotypes for pod Ca concentration, Ca uptake, and flow rate were observed. Results were consistent across developmental stages.

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Matthew D. Kleinhenz, R. Vaughan James, Walter R. Stevenson, and Jiwan P. Palta

Plots set up on a commercial seed farm were supplemented with 0 or 168 Ca/ha supplied from liquid calcium nitrate at 3 and 6 weeks after hilling (84 kg Ca/ha per application). Paired measurements of tuber medullary tissue Ca concentration and decay severity after inoculation with Erwinia carotovora pv. atroseptica (Eca.) were taken on identical tubers from these separate plots of `Atlantic', `Superior', `Red Norland', and `Russet Burbank'. Fresh-cut seed pieces sprayed with a suspension of Eca. (108 cfu/ml) were planted in separate 1-liter containers filled with field soil maintained under two soil moisture regimes: 1) air-dry days 1–5, saturation days 6–10, field moisture capacity (FMC) days 11–18, or 2) FMC days 1–18. Containers were placed at 22C constant air temperature at the Univ. of Wisconsin–Madison Biotron. Decay severity (percent volume seed piece decay) and decay incidence (percent tubers with any decay) were rated after 18 days. Eight seed pieces per treatment were evaluated. The mean tuber Ca concentration was higher in plots receiving calcium compared to nonsupplemented plots. Mean medullary Ca concentration varied among cultivars as `Russet Burbank' > `Atlantic' > `Superior' > `Red Norland'. The influence of cultivar on decay showed an incidence and severity pattern `Atlantic' = `Russet Burbank' > `Superior' = `Red Norland'. Decay incidence and severity were greatest in seed pieces kept in temporarily saturated soil compared with those in soil maintained at FMC. Decay incidence and severity were ≈6% lower in tubers produced on Ca-supplemented soil. A scatter plot of decay severity × Ca concentration for seed pieces held at FMC suggests that a threshold of Ca concentration exists above which little or no decay occurs.