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Vegetative and fruit responses of ‘Montmorency’ sour cherries to Alar were evaluated from 1966 to 1968. Mature trees were treated with from 1000 to 8000 ppm of Alar at 2 weeks after full bloom. Alar significantly increased fruit color and decreased the force required to separate the fruit from its pedicel early in the harvest season. These differences were sufficient to advance the start of commercial harvesting one week. Fruit firmness was significantly increased in both handpicked and mechanically harvested fruit. Alar treated fruit showed a significant ability to resist softening when mechanically harvested. Fruit color and firmness enhancement was evident in both canned and frozen processed fruit. Alar altered the fruit growth curve and contributed to a more uniform size. Fruit acidity and respiration were significantly reduced. Alar reduced terminal growth, by reducing internode length, but increased flower bud initiation.

Nitrate reductase was found in leaves of apricot Prunus armeniaca, sour cherry P. cerasus, sweet cherry P. avium, and plum P. domestica, but not in peach P. persica, from Grasmanis and Nicholas (8) extracted an active nitrate reductase from apple roots, but they were unable to determine its physiological electron donor. Then Klepper and Hageman (11), employing insoluble PVPW in the extraction medium, obtained a typical NADH-dependent nitrate reductase from apple roots. Adding excess nitrate ions to the root medium of apple seedlings, they also found nitrate ions and both nitrite and nitrate reductases in the leaves; the enzyme was readily induced by immersing excised leaves in 0.1 M KNO3. Trace amounts of nitrate and nitrate reductase were found in leaves of mature apple trees receiving low annual amounts of nitrogen.The situation in other plant species which normally reduce nitrate in their roots appears to be similar to that found in apple trees. Wallace and Pate (19) found that in the field pea all nitrate was metabolized in the roots and only reduced nitrogen was found in exuded sap, provided the supply of nitrate to the roots was normal. However, when plants were supplied with nitrate levels higher than 10 mg/ml, nitrate was transported to the shoot and nitrate reductase was induced. The present study was undertaken to determine if nitrate reductase would be induced in leaves of Prunus species when supplied with nitrate ions.Recent commercial attempts to supply part of the nitrogen requirement of stone fruit trees as nitrate foliar sprays (3) has raised questions regarding nitrate metabolism by the leaves of Prunus species. In deciduous fruit trees, the site of nitrate reduction classically is regarded to be the fine roots (14). Early evidence (5, 18) indicated that in apple trees reduction of nitrate and synthesis of amino acids took place mainly in the roots; however, nitrate ions were translocated, unreduced, to the buds during bud burst or to the leaves when excess nitrate was applied to the roots. The literature does not exclude reduction in the leaf in special circumstances. Eckerson (5) reported nitrate reductase activity in apple tree roots, buds, and leaves. However, as Beevers and Hageman (2) have pointed out, nonenzymatic conversion of nitrate to nitrite may have been responsible, because even boiled plant extracts effected the conversion.More recently Bollard (4) failed to find nitrate in tracheal sap extracted from one-year-old shoots of mature stone and pome fruit trees. The absence of nitrate in apple and peach scion tissues has been confirmed in mature trees (17).

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The poor response of Prunus spp. to foliar nitrate sprays under field conditions (Leece and Kenworthy 1971) is not caused by an inability of Prunusleaves to metabolize nitrate ions (Leece, Dilley, and Kenworthy 1972). This is analogous to the response ofPrunus spp. to urea sprays (Dilley and Walker 1961a). Dilley and Walker (1961b) demonstrated that pretreatment of peach leaf disks by immersion in acetone to dissolve lipid components of the cuticle increased subsequent urea absorption. Bukovac (1965) found that lightly brushing the upper and lower surfaces of peach leaves with a camel-hair brush enhanced uptake of 3-chlorophenoxy-a-propionic acid by 22 and 34% respectively. Brushing was assumed to have partially removed or rearranged the epicuticular waxes.This paper reports that the uptake of nitrate ions by apricot leaf disks, via the astomatous cuticle, was enhanced by partial removal or disruption of the epicuticular waxes. Materials and MethodsFully expanded, mid-shoot leaves were obtained from 5-year-old apricot trees (Prunus armeniaca L. cv. Curtis) growing at East Lansing during the summer of 1970. The leaves were transferred to the laboratory in polyethylene bags at 0-4°C.Nitrate ion uptake by apricot leaves was assayed by measuring the induction of nitrate reductase in excised leaf disks, following cuticular penetration. Apricot leaf disks were prepared for the uptake studies using the technique of Sargent and Blackman (1962) as modified by Greene and Bukovac (1971). Glass cylinders (height 10 mm; external diameter 24 mm; internal diameter 21 mm) were attached to the upper, astomatous surface of leaf disks (diameter 25 mm) using RTV Illiquid silicone rubber (General Electric Company, Waterford, New York) hardened with Harter T I catalyst (Wacher Chemie GMBH Company, Munich, Germany)_ The disks were placed in 9-cm Petri dishes lined with moist filter paper, and 1·0 ml ofO'4M KCl (control) or 0·4M KNOa (enzyme induction solution) was pipetted into each cylinder. Both solutions contained 0·1 % (v/v) X 77 surfactant (alkylarylpolyoxyethylene glycols, free fatty acids, and isopropanolChevron Chemical Company, Ortho Division, San Francisco, California). The dishes were incubated in a water-bath at 25°C for 15 hr and at a light intensity (from fluorescent tubes) of 8600 lux at leaf level. Following incubation, the glass cylinders were peeled off the disks, the disks were rinsed with distilled water, blotted dry, then assayed for nitrate reductase as previously reported (Leece, Dilley, and Kenworthy 1972).Where required, disruption and partial removal of epicuticular waxes was achieved either by brushing (10 strokes in one direction with a camel-hair brush), or with 80% (v/v) aqueous acetone (leaf wiped with acetone-treated tissue paper then dried immediately with untreated paper). Chloroform proved unsuitable for wax removal as it produced leaf senescence within 3 hr.