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`Lovell' peach seeds were stratified for 0 to 12 weeks at 4°C under moist conditions. Differential Scanning Calorimetry (DSC) was used to study the respiratory capacity for the cytochrome (CP) and alternative (AP) pathway of the embryos during this period. Azide and SHAM titration curves were obtained by measuring the heat of metabolism produced by the excised embryos after vacuum infiltration with appropriate combinations of the two inhibitors.
Uninhibited total respiratory activity increased steadily with the stratification treatment. AP capacity of the embryos was higher than CP capacity for the first 4 weeks of stratification. Between 4 and 6 weeks, CP capacity increased markedly and after 6 weeks was at least 40% higher than AP capacity. This rise on CP capacity coincided with the point at which an increase in seedling vigor and germinative capacity was observed and is in agreement with previous studies suggesting a change in respiratory efficiency as being responsible for the increase in seedling vigor.
Some cultivars of prune (i.e. `Brooks') consistently set good crops while others (i.e. `Italian') are erratic bearers. Fall-applied ethephon increases fruit set. Ovule longevity has been hypothesized to be an important factor in fruit retention. The effects of the cultivar and fall ethephon application on ovule longevity were determined.
Ethephon (0 and 500 mg·l-1) was applied to `Italian' and `Brooks' prune trees at the 50% leaf drop stage. The following spring, flower buds were emasculated and covered to prevent pollination. Ten flowers were sampled every two days from anthesis until 20 days after anthesis (DAA). Flowers were fixed in FAP and ovule longevity determined using fluorescence microscopy. Ovule longevity was longer in `Brooks' than `Italian'. At 20 DAA, all of the `Brooks' flowers still had viable ovules. Only 40% of the `Italian' flowers had viable ovules. The `Italian' flowers excised from ethephon-treated trees had at least one non-senescent ovule at 17 DAA. Ethephon prolonged ovule longevity in `Italian' prune flowers. No effect of ethephon was observed on the ovule longevity of the `Brooks' prune.
Some cultivars of prune (i.e. `Brooks') consistently set good crops while others (i.e. `Italian') are erratic bearers. Fall-applied ethephon increases fruit set. Ovule longevity has been hypothesized to be an important factor in fruit retention. The effects of the cultivar and fall ethephon application on ovule longevity were determined.
Ethephon (0 and 500 mg·l-1) was applied to `Italian' and `Brooks' prune trees at the 50% leaf drop stage. The following spring, flower buds were emasculated and covered to prevent pollination. Ten flowers were sampled every two days from anthesis until 20 days after anthesis (DAA). Flowers were fixed in FAP and ovule longevity determined using fluorescence microscopy. Ovule longevity was longer in `Brooks' than `Italian'. At 20 DAA, all of the `Brooks' flowers still had viable ovules. Only 40% of the `Italian' flowers had viable ovules. The `Italian' flowers excised from ethephon-treated trees had at least one non-senescent ovule at 17 DAA. Ethephon prolonged ovule longevity in `Italian' prune flowers. No effect of ethephon was observed on the ovule longevity of the `Brooks' prune.
Four ratio-based efficiency expressions (yield/trunk cross-sectional area, yield/canopy area, yield/pruning weight, CO2 assimilation/leaf area) were evaluated. These expressions depend on the size of the denominator if the function describing the relationship between the denominator and the numerator has a non-zero intercept. When this occurs, it is difficult to determine if statistically different efficiency expressions reflect physiological differences or are caused by comparing expressions with different sized denominators. When denominators and numerators of efficiency expressions are plotted, the edge of the data cloud can often be statistically identified. The function describing the edge of the data cloud defines the maximum possible value (MPV) obtainable for a given value of the denominator. The percentage of MPV (%MPV) is an alternate efficiency expression that is not influenced by differing trunk cross-sectional area, canopy area, pruning weight, or leaf area. The difference between MPV and observed performance can be used to define improvement potential (IP). These alternate assessments can supplement traditional efficiency expressions. It is also possible to determine if statistical differences in traditional efficiency expressions are caused by differences in potential, differences in a plant or leaf's ability to achieve its potential, or differences in the size of the efficiency expression denominators.
It is not appropriate to compare ratio-based expressions for different cultivars or treatments if a plot of the denominator versus the numerator of a ratio-based expression has a nonzero y-intercept and the values for either the denominators or numerators differ with cultivars or treatments. Whenever nonzero y-intercepts are encountered, the value for a ratio-based expression will be dependent on both the denominator and numerator. The “ratio problem” is demonstrated with shoot N concentration in blueberries (Vaccinium corymbosum L.) and amino acid accumulation in almonds [Prunis dulcis (Mill.) D.A. Webb]. Data were collected from the first and second growth flush of blueberry shoots on plants that were at two in-row spacings and two rates of N fertilizer. Free amino acid:total amino acid ratios were measured in dormant almond trees fertilized at different rates with and without foliar N supplements. Functions describing the relationship between dry weight and total N content in blueberry tissues have positive y-intercepts for both N fertilizer application rates. Functions describing the relationship between total amino acids and free amino acids in almond trees have a negative y-intercept. Differences attributable to fertilization rate in blueberries probably were the result of differences in N uptake and N utilization, but the effects of spacing and growth flush are indirect and can be accounted for by differences in dry weight. Likewise, effects of fertilization rate and foliar N supplement in almonds are indirect and can be accounted for by differences in the total amino acids in dormant trees. With regression one can determine if the relationship between the denominator and numerator differs for the groups or treatments being studied. When an analysis of covariance is used to account for differences in the denominators of ratio-based expressions, results are consistent with the regression analysis. When a conclusion is based on statistical differences of a ratio-based expression, it is the researcher's responsibility to determine whether these effects are direct or indirect.
Net photosynthetic rates often are dependent on leaf size when expressed on a leaf-area basis (CO2 assimilation as μmol·m−2·s−1). Therefore, distinguishing between leaf-size-related and other causes of differences in net photosynthetic rate cannot be determined when data are presented on a leaf-area basis. From a theoretical perspective, CO2 assimilation expressed on a leaf-area basis (μmol·m−2·s−1) will be independent of leaf area only when total net CO2 assimilation (leaf CO2 assimilation as μmol·s−1) is linearly related to leaf area and the function describing this relationship has a nonzero y intercept. This situation was not encountered in the data sets we evaluated; therefore, ratio-based estimates of CO2 assimilation were often misleading. When CO2 assimilation data are expressed on a per-leaf-area basis (the standard procedure in the photosynthesis literature), it is difficult to determine how photosynthetic efficiency changes as leaves or plants mature and difficult to compare the efficiency of treatments or cultivars when leaf size or total plant leaf area varies.