from that of Trillium. The influence of temperature is a very real possibility and is presently under investigation. In conclusion it may be said that for diploid plants a relationship does exist between the minimum mitotic cycle time, the interphase nuclear volume, and the DNA content per cell. Moreover, the relationship is such that if any one of the three cell variables is known, an estimate can be made of the remaining two. Summary.-Experiments were performed to determine the relationship between interphase nuclear volume and DNA content per cell and the minimum mitotic cycle time in several diploid plant species. All measurements were made on meristem cells contained in the terminal 2 mm of the root. The results indicated that linear relationships exist between the interphase nuclear volume and the minimum mitotic cycle time, and between the DNA content per cell and the minimum cycle time. Linearity, however, does not exist if extrapolation is carried out to include the lower forms of life, such as bacteria and viruses. The relationships are to some extent independent of chromosome number and the amount of DNA per chromosome. The data presented enable the estimation of any two of the above three variables, if the third variable is known. The authors wish to thank Miss Huei-Kuen Ying and Mrs. Anne F. Rogers for their technical assistance, and Mrs. Rhoda C. Sparrow and Mrs J. Van't Hof for aid in preparing the manuscript. * Research carried out at Brookhaven National Laboratory under the auspices of the U.S. Atomic Energy Commission.

The large majority of proteins of alkaliphilic Bacillus pseudofirmus OF4 grown at pH 7.5 and 10.5, as studied by two-dimensional gel electrophoresis analyses, did not exhibit significant pH-dependent variation. A new surface layer protein (SlpA) was identified in these studies. Although the prominence of some apparent breakdown products of SlpA in gels from pH 10.5-grown cells led to discovery of the alkaliphile S-layer, the largest and major SlpA forms were present in large amounts in gels from pH 7.5-grown cells as well. slpA RNA abundance was, moreover, unchanged by growth pH. SlpA was similar in size to homologues from nonalkaliphiles but contained fewer Arg and Lys residues. An slpA mutant strain (RG21) lacked an exterior S-layer that was identified in the wild type by electron microscopy. Electrophoretic analysis of whole-cell extracts further indicated the absence of a 90-kDa band in the mutant. This band was prominent in wild-type extracts from both pH 7.5-and 10.5-grown cells. The wild type grew with a shorter lag phase than RG21 at either pH 10.5 or 11 and under either Na ؉ -replete or suboptimal Na ؉ concentrations. The extent of the adaptation deficit increased with pH elevation and suboptimal Na ؉ . By contrast, the mutant grew with a shorter lag and faster growth rate than the wild type at pH 7.5 under Na ؉ -replete and suboptimal Na ؉ conditions, respectively. Logarithmically growing cells of the two strains exhibited no significant differences in growth rate, cytoplasmic pH regulation, starch utilization, motility, Na ؉ -dependent transport of ␣-aminoisobutyric acid, or H ؉ -dependent synthesis of ATP. However, the capacity for Na ؉ -dependent pH homeostasis was diminished in RG21 upon a sudden upward shift of external pH from 8.5 to 10.5. The energy cost of retaining the SlpA layer at near-neutral pH is apparently adverse, but the constitutive presence of SlpA enhances the capacity of the extremophile to adjust to high pH.Bacillus species have been a major component of the extremely alkaliphilic bacterial flora isolated both from highly selective environments such as alkaline lakes and from ostensibly unselective environments such as conventional soils (21,24,26). While many studies have focused on useful products of alkaliphilic bacilli (21), others have focused on the basis for alkaliphily itself (19,26,28). Among the questions that immediately arise are how can those membranous and protein structures that are exposed to the alkaline medium function, and how can cells growing above pH 10 maintain a cytoplasmic pH that is well below the external pH? With respect to the first question, recent structural studies of extracellular enzymes from extreme alkaliphiles and numerous deduced protein sequences of alkaliphile proteins have begun to indicate properties that may correlate with the ability to function at extremely high pH (26). The adaptations, moreover, appear to depend upon whether a high net charge is important to the function of the molecule or molecular segment. When that is the case, the...

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Stimulated lower labial (LLGF) and parotid salivary volumes and IgG, IgA, and IgM concentrations were measured in 264 subjects whose ages ranged from 17 to 76 years. A significant (p < 0.001) age-related decline in LLGF output was observed for subjects over this age range. Sixty-three percent of the subjects in the 18-20-year-old group (n = 46) secreted at least 10 microL of labial saliva in a 7-10-minute period, while approximately 70% of the subjects in the two oldest groups (61-70 and 71-76 years old) secreted less than 1 microL of LLGF during this time period (n = 64). No significant gender-based differences occurred in the volumes of labial saliva secreted. Stimulated parotid salivary flow showed no age-related trend in these subjects. Lower labial gland salivary IgA concentrations in an older population (mean age +/- SD = 55.6 yr +/- 1.3) were significantly lower (p < 0.025) than IgA concentrations in a younger population (20.7 yr +/- 0.8), when IgA was expressed as microgram/mL LLGF collected. Immunoglobulin A concentrations in parotid saliva and IgG and IgM concentrations in labial and parotid saliva were not significantly different when the two age populations were compared. These data suggest that the physiological and immunological potential of labial gland saliva may decrease with age.

The atp operon of alkaliphilic Bacillus pseudofirmus OF4, as in most prokaryotes, contains the eight structural genes for the F-ATPase (ATP synthase), which are preceded by an atpI gene that encodes a membrane protein of unknown function. A tenth gene, atpZ, has been found in this operon, which is upstream of and overlapping with atpI. Most Bacillus species, and some other bacteria, possess atpZ homologues. AtpZ is predicted to be a membrane protein with a hairpin topology, and was detected by Western analyses. Deletion of atpZ, atpI, or atpZI from B. pseudofirmus OF4 led to a requirement for a greatly increased concentration of Mg 2؉ for growth at pH 7.5. Either atpZ, atpI, or atpZI complemented the similar phenotype of a triple mutant of Salmonella typhimurium (MM281), which is deficient in Mg 2؉ uptake. atpZ and atpI, separately and together, increased the Mg 2؉ -sensitive 45 Ca 2؉ uptake by vesicles of an Escherichia coli mutant that is defective in Ca 2؉ and Na ؉ efflux. We hypothesize that AtpZ and AtpI, as homooligomers, and perhaps as heterooligomers, are Mg 2؉ transporter, Ca 2؉ transporter, or channel proteins. Such proteins could provide Mg 2؉ , which is required by ATP synthase, and also support charge compensation, when the enzyme is functioning in the hydrolytic direction; e.g., during cytoplasmic pH regulation. P rokaryotic atp operons encode the cell membrane F-type ATPase (ATP synthase) that couples the energy of an electrochemical H ϩ gradient (or sometimes Na ϩ ), to the synthesis of ATP, from ADP and P i . In the reverse reaction, the ATPase hydrolyzes ATP concomitant with H ϩ (or Na ϩ ) efflux, thereby contributing to cytoplasmic pH regulation and͞or generation of a transmembrane electrochemical gradient under fermentative conditions (1-4). Most atp operons, like that of Escherichia coli, contain the eight structural genes for the ATPase, atpBEFHAGDC, which are preceded by atpI (5). The Escherichia coli atpI is expressed, and its product associates with the membrane, as predicted from its deduced sequence (6-9). Whereas there is no demonstrated effect of AtpI on expression or assembly of the ATPase, an atpI deletion strain of E. coli has been reported to have a reduced growth yield (7). There is no function established for this "mysterious ninth gene" (10) that accounts for such an effect. We report here the finding of another gene, encoding a membrane protein, that is upstream of the atpI gene, and within the atp operon of alkaliphilic Bacillus pseudofirmus OF4. This gene, designated atpZ, was discovered during attempts to introduce site-directed changes in alkaliphilespecific motifs of the membrane-embedded F-ATPase subunits of B. pseudofirmus OF4 (11). A cassette introduced just upstream of the putative atp promoter abolished atp expression. This finding led us to reexamine the location of the atp operon promoter, to the inclusion of atpZ in the extended operon, and then to an exploration of the effects of deleting atpI as well as atpZ. The results suggest a cation translocation function ...