Using saturation extract procedures, fifteen extractants were evaluated for their ability to remove B, Fe, Mn, and Zn from a peat and vermiculite (50:50% by volume) medium amended with three levels of micronutrients. A modified saturated media extract test procedure was developed in which 30 ml of .005M DTPA was added per 100 cc of sample to be extracted. The use of this method enhanced resolution of micronutrient cation test levels in 3 media while producing only minor changes in macronutrient, pH, or soluble salt test results when compared to DI water extractions.

Since the discovery of the plant growth-regulating properties of TRIA, a primary alcohol that is a natural constituent of plant waxes, and its second messenger L(+)-adenosine, the rapid response kinetics to these compounds have been enigmatic (Ries and Wert, 1988;Ries, 1991).TRIA increased the dry weight, free amino acids, reducing sugars, and soluble protein of rice (Oryza sativa L.) and maize (Zea mays L.) plants within 5 min (Ries, 1991). TRIA also elicited the appearance of L(+)-adenosine in the roots of plants whose shoots were sprayed with nanomolar concentrations within 1 min (Ries and Wert, 1988). This was the first evidence that L(+)-adenosine occurred in nature. Synthetic L(+)-adenosine increased the rate of growth of rice seedlings, as measured by total dry weight gain, by more than 50% within 24 h of foliar application of 0.01 to 100.0 kg L-' (3.7 X 10-" to 10-7 M), whereas D(-)-adenosine did not affect plant growth (Ries, 1991). 49site plant part, providing it was applied 1 min prior to TRIA application (Ries and Wert, 1988). TRIA applied to oat (Avena sativa L.) or tomato (Lycopersicon esculentum Mill.) shoots connected to rice roots by a 4-mm water column also resulted in the appearance of L(+)-adenosine (TRIM) in rice roots (Ries and Wert, 1988).In an attempt to determine other physiological responses to TRIA in addition to the elicitation of L(+)-adenosine, 20-to 25-d-old tomato seedlings were sprayed with water or TRIA, and after 1 min the plants were excised. Analysis of the diffusate from the excised shoots, as determined by HPLC and atomic absorption spectrophotometry, indicated large concentration differences in organic compounds and inorganic cations (unpublished data). The largest differences were in the cation concentration of the exudate from the stump of the excised tomato plant. Thus, the objective of this research was to use this observation to further elucidate the mode of action for the rapid responses of plants to TRIA and L(+)-adenosine.We present here evidence that foliar applications of both of these compounds at nanomolar concentrations cause rapid changes in soluble Ca2+, Mg2+, and K+ concentrations within xylem exudates from the stumps of excised stems and leaves. MATERIALS A N D METHODS Plant Crowth and TreatmentTomatoes (Lycopersicon esculentum Mill. cv Sunny), cucumbers (Cucumis sativa L. cv Flurry), and maize (Zea mays L.cv Pioneer 3780) were grown in a greenhouse with approximately 16 h of supplemental light (700 pmol s-' m-', metal halide) daily. Seeds were planted in 15-cm diameter clay pots containing a soil mix, and the plants were thinned to two or three per pot 8 to 10 d after emergence. Soluble fertilizer (20 N-8.6 P-16.6 K; 1.0 g L-' Peters 20-20-20, W.R. Grace and Co., Fogelsville, PA) was applied once or twice after planting and again prior to treatment. The pots were labeled, randomized for treatments within blocks, and isolated from each other on the greenhouse bench. They were not disturbed for several hours prior to initiation of the treatments.Experiment...

Cucumber plants were cultured in a greenhouse and subjected to either well-watered or water deficit conditions that reduced leaf water potential to-0.6 MPa. Leaf gas exchange measurements were conducted using an open gas exchange system. Carbon dioxide assimilation (A) attained saturation at a photon flux density (PFD) of 1000 μmol·m-2·s-1 (400-700 nm). There were no significant differences in A at ambient temperatures between 16 and 34C. Water use efficiency decreased rapidly with increasing vapor-pressure deficits to 2.5 kPa. Water stressed plants had lower stomata1 conductances and CO2 assimilation rates. The decrease in A was only partially due to stomata1 closure. The A vs. intercellular CO (Ci) relationship for stressed leaves revealed a change in the CO, compensation point, and that nonstomatal factors were contributing to the decrease in A in stressed plants. Thus, feedback inhibition of A may have occurred through photoassimilate accumulation. The concentrations of sucrose and raffinose were higher, and the concentration of stachyose was lower in leaves of stressed than of well-watered plants.

Seedlings of processing tomato `H 2653' (Lycopersicon esculentum Mill.) were cultured in 288-cell (< 6 cm3 volume) plug trays in a soilless growing medium. Pretransplant fertilization with nutrient solutions containing 10 or 20 mm N and 2 or 5 mm P for 10 days altered the total ammoniacal-N and P, and the soluble NO3-N and PO4-P concentrations in the shoot tissue at transplanting. Post-transplanting shoot and root growth were more rapid in late May plantings than in earlier plantings. The 20-mm N and 2-mm P pretransplant treatment caused the most rapid shoot growth following early season plantings in the field. Rapid seedling establishment after transplanting was generally not a good indicator of potential fruit yield. The 5-mm P pretransplant treatment produced higher marketable fruit yields in early plantings but not in later. Culture of seedlings under a low fertilization regime (5.4 mm N, 1.0 mm P, and 1.6 mm K) before pretransplant treatment produced as high or higher fruit yields than did seedlings from a higher regimen. Withholding fertilizer temporarily before transplanting resulted in a depletion in tissue N and P concentrations, slow post-transplanting shoot growth, and lower yields.

K+ content and concentration within the apoplast of mesophyll tissue of pea (Pisum sativum L., cv Argenteum) leaflets were determined using an elution procedure. Following removal of the epidermis, a 1 centimeter (inside diameter) glass cylinder was attached to the exposed mesophyll tissue and filled with 5 millimolar CaCI2 solution (10C). From time-course curves of cumulative K+ diffusion from the tissue, the amount of K+ of extracellular origin was estimated. Apoplastic K+ contents for leaves from plants cultured in nutrient solution containing 2 or 10 millimolar K+ were found to range from 1 to 4.5 micromoles per gram fresh weight, comprising less than 3% of the total K+ content within the lamina tissue. Assuming an apoplastic solution volume of 0.04 to 0.1 milliliters per gram fresh weight and a Donnan cation exchange capacity of 2.63 micromoles per gram fresh weight (experimentally determined), the K+ concentration within apoplastic solution was estimated at 2.4 to 11.8 millimolar. Net movement of Rb+ label from the extracellular compartment within mesophyll tissue into the symplast was demonstrated by pulse-chase experiments. It was concluded that the mesophyll apoplast in pea has a relatively low capacitance as an ion reservoir. Apoplastic K+ content was found to be highly sensitive to changes in xylem solution concentration.The apoplast within leaf tissue constitutes a potentially important pathway for K+ transport between vascular and mesophyll tissues (6,22,23) accumulate extracellulary within the vascular bundles, whereas lower concentrations would exist within the cell wall of mesophyll tissue more distant from the minor veins.The specific role(s) ofthe apoplast as related to K+ transport and accumulation within leaf lamina tissue cannot be fully elucidated without quantitative analysis of extracellular K+ content and concentration (20). Several indirect approaches have been reported for collection of apoplastic sap and estimation of ionic concentrations including analysis of xylem exudates, vacuum perfusion of leaf lamina discs (1), and pressure dehydration of leaves (14). X-ray microanalysis (7, 9, 12) and ion-sensitive microelectrodes have been used to measure directly extracellular ion concentrations ofepidermal guard cells (2) and the extensor and flexor cells within the pulvinus of legume leaves (26). The primary limitation of these procedures is the inability to estimate the ionic content within the apoplastic reservoir of the mesophyll.Apoplastic ion content is a function of the amount of ion bound to fixed, negatively charged sites within the cell wall, the Donnan free space, and that in solution within the cell wall. Although the cation exchange capacity of leaf cell walls has been investigated for a variety of plant species (19, 25), the 'functional' volume of apoplastic solution in situ is more difficult to estimate. The volume within a unit fresh weight of tissue in theory is influenced by the thickness of the cell walls and the mean size of mesophyll cells. In addition, the vo...