Distilled-deionized Water Research Articles

Effect of Selected Nitrogen-bases and Boron on the Ribonucleic Acid Content, Elongation, and Visible Deficiency Symptoms of Tomato Root Tips

In a previous paper Albert (2) reported the RNA content of root tips of intact tomato plants decreased and 'boron deficiency symptoms occurred concurrently when boron (B) was withheld from nutrient solutions in which the plants were growing. It was also observed that elongation of root tips stopped 6 to 12 hours and the RNA content of tips decreased 24 to 48 hours after B was withhheld. The DNA content of the tips did not change significantly during the experimental period. Using tomato plants in a similar experimental system, Yih and Clark (3) reported that root elongation ceased after 24 hours but that protein and carbohydrate con-tent of minus-B root tips (10 mm) did not decrease within 72 hours. A decreased RNA content, therefore, appears to be one of the earliest biochemical changes associated with the development of visible symptoms of B-deficiency after elongation in tomato root tips stops. Thus, if B is involved in some aspect of RNA metabolism, the feeding of appropriate metabolites or their analogues may reveal information about such a role. Compounds selected for investigation were adenine, cytosine, iguanine, thymine, uracil, orotic acid, barbituric acid, and 6-azauracil. Tomato plants (Lycopersicon esculentum Mill. var. Rutgers) were grown -from seeds (W. Atlee Burpee Company) planted in Perlite and watered with a Hyponex nutrient solution (Hydroponic Chemical Company, Inc.). When the seedlings had 2 small leaves (the largest about 1 cm long), they were transplanted to an aerated, modified Shive's nutrient solution contained in light-tight soft-glass gallon jars, one plant per jar (1). Deiorized-distilled water was used throughout. All plants received an adequate amount of B (0.1 mg/liter) throughout their growing period and nutrient solution's were changed every 7 to 10 days. The plants were approximately 15 cm in height (cotyledons to apex) with 6 to 8 leaves when they were used for experiments. Net root elongation was determined by placinlg India ink marks 10 mm from the tips and measuring subsequent elongation at the end of the experimental period (1). Prior to marking the tips, the roots and nutrient solution jar covers were thoroughly rinsed with deionized-distilled water. After marking the tips the plants were put into their respective treatmnent solutions which consisted of fresh nutrient solutions to which the appropriate compounds were added in the presence of B (0.1 mg/liter) or to solutions from whiich B was withheld. All plants were placed in the greenhouse for the experimental treatment period. The nitrogen4bases, adenine, cytosine, guanine. thymine, uracil, orotic acid, 'baebituric acid, and 6-azauracil (Mann Research Laboratories, Inc.) were dissolved at a concentration of 0.1 mm, except where noted otherwise, in the nutrient solutions with the aid of heat (60-80o) and, when necessary, by adjusting the solutions with concentrated H'Cl to a pH of 1 or 2. On cooling, the solutions were readjusted to a pH of 4.7 (?+ 0.1) with NaOH. The pH of regular nutrient solution was 4.7. At the end of the experimental period root elongation measurements were made and tips were harvested for nucleic acid analysis. The terminal 3 mm of the tips were excised (15 tips per plant), blotted, quickly weighed, and stored irn 2 ml of 80 % (v/v) ethanol at 20 until nucleic acid analvses were performed using a modified Schmidt-Thannhauser method (2). Typical results from experiments in which B and selected nitrogen-bases were added alone and in combination with each other, or withheld from nutrient solutions are given in table I. These data indicate that thymine, guanine and cytosine stimulated root elongation when B was withheld, while uracil, orotic acid, and adenine were less effective. Barbituric acid and 6-azauracil inhibited root elongation in both the presence and absence of B. Total RNA content of root tips decreased when B waswithheld from nutrient solutions. However, when B was withheld and thymine, guanine, or cytosine were present the RNA content of the root tips was only slightly less than the plus-B treatment. When uracil, orotic acid, or adenine was present in minus-B nutrient solutions root tips had an equal or slightly greater amount of RNA than did minus-B tips. Barbituric acid and 6-azauracil treatments resulted in a decreased RNA content of root tips for both plus and minus-B treated

Book Reviews

Inasmuch as the presence of endogenous gamma-aminobutyric acid (GABA) may affect benzodiazepine binding to tissue sections in autoradiographic studies, a protocol designed to check for this influence has been investigated. [3H]Flunitrazepam (1 nM) was used to label benzodiazepine receptors for autoradiographic localization. Bicuculline was added to the incubation medium of an additional set of tissue sections to antagonize any potential effect of endogenous GABA. Binding in these sections was compared to that occurring in another set in which excess GABA was added to "create" further GABA enhancement. Binding also was compared to adjacent sections which were treated similarly but also preincubated in distilled-deionized water to burst the cells by osmotic shock and eliminate endogenous GABA, thereby preventing any effect on benzodiazepine binding. The results indicated that endogenous GABA is indeed present in the slide-mounted tissue sections and is affecting benzodiazepine receptor binding differentially in various regions of the brain depending on the density of GABAergic innervation. Scatchard analysis of saturation data demonstrated that the alteration in benzodiazepine binding due to GABA was a result of a change in the affinity rather than number of receptors present. These experiments have been compared to the binding of the imidazodiazepine, [3H] Ro15-1788. We also show that the treatments affect endogenous GABA and not the receptors themselves. This suggests strongly that, when using a single nonsaturating concentration of radiolabeled benzodiazepine antagonist, autoradiographic studies to date may have been subject to erroneous interpretation due to the differential effects of endogenous GABA on benzodiazepine binding (increased affinity).(ABSTRACT TRUNCATED AT 250 WORDS)

Solubility of Oxygen in Water

IN a recent communication, Truesdale and Downing1 reported that the values for the solubility of oxygen in de-ionized distilled water, determined by the Winkler2 method, were significantly lower than the standard values commonly employed3. They gave a new empirical equation valid in the range 0–40° C, relating the solubility and the temperature.