Pairs of homozygous near-isogenic glycinebetaine-containing (Betl/Betl) and -deficient (betlhetl) F, lines of Zea mays L. (maize) were tested for differences in salt (1 50 mM NaCl or 127.25 mM NaCl plus 22.5 mM CaCI,) tolerance. The Betl/Betl lines exhibited less shoot growth inhibition (as measured by dry matter accumulation, leaf area expansion rate and/or, plant height extension rate) under salinized conditions in comparison to their nearisogenic betl/betl sister lines. These growth differences were associated with maintenance of a significantly higher leaf relative water content, a higher rate of carbon assimilation, and a greater turgor in Betl/Betl lines than in b e t l h e t l lines under salinized conditions. These results strongly suggest that a single gene conferring glycinebetaine accumulation (and/or a tightly linked locus) plays a key role in osmotic adjustment in maize. Yancey (1994) has recently discussed the roles of betaines and their sulfonio analogs as compatible solutes and in cell volume regulation. These solutes are excluded from the hydration sphere of proteins and tend to stabilize the tertiary structure of proteins (Yancey, 1994). They also prevent or reverse the disruption of the tertiary structure caused by noncompatible (perturbing) solutes such as urea (Bateman et al., 1992). It is probable that these compounds have similar functions in higher plants (Wyn Jones and Storey, 1981;Grumet and Hanson, 1986;Robinson and Jones, 1986; Rhodes and Hanson, 1993), but rigorous genetic experiments with higher plant mutants defective in betaine synthesis are needed to verify this point.Genetic tests for the role of glycinebetaine in osmotic stress resistance in Zea mays L. (maize) are now possible because of the development of a series of near-isogenic F, pairs of glycinebetaine-containing and glycinebetaine-deficient lines (Yang et al., 1995). Here we report the growth, water relations, gas-exchange characteristics, and solute compositions of these glycinebetaine-containing and gly-

A series of near-isogenic glycinebetaine-containing and -deficient F, pairs of Zea mays 1. (maize) lines were developed. The pairs of lines differ for alternative alleles of a single locus; the wild-type allele conferring glycinebetaine accumulation is designated Betl and the mutant (recessive) allele is designated betl. The nearisogenic lines were used to investigate whether glycinebetaine deficiency affects the pool size of the glycinebetaine precursor, choline, using a new method for glycinebetaine and choline determination: stable isotope dilution plasma desorption mass spectrometry. Glycinebetaine deficiency in maize was associated with a significant expansion of the free choline pool, but the difference in choline pool size was not equal to the difference in glycinebetaine pool size, suggesting that choline must down-regulate its own synthesis. Consistent with this, glycinebetaine deficiency was also associated with the accumulation of the choline precursor, serine. A randomly amplified polymorphic DNA marker was identified that detects the betl allele. In 62 F, families tested the 10-mer primer 5'-GTCCTCGTAG produced a 1.2-kb polymerase chain reaction product only when DNA from Betl/betl or betl/betl lines was used as template. AI1 26 homozygous Betl/Betl F, families tested were null for this marker.It is now well established that betaines and their sulfonio analogs can play important roles in osmotic adjustment and/or osmoprotection in bacteria (Csonka and Hanson, 1991), cyanobacteria (Borowitzka, 1986), marine algae (Blunden and Gordon, 1986), and mammals (Garcia-Perez and Burg, 1991) (see Yancey [1994] for a recent review of the role of betaines and their sulfonio analogs as compatible solutes). It is probable that these compounds have similar functions in higher plants (Robinson and Jones, 1986;Rhodes and Hanson, 1993). Toward the goal of genetically testing the role of glycinebetaine in osmotic stress resistance in maize (Zea mays L.), we have developed a series of near-

tion, many organisms synthesize solutes that either help retain water within cells or protect cellular components Glycinebetaine (GB) accumulation has been suggested to be an from injury caused by dehydration. One such solute, glyadaptive response to several abiotic environmental stresses. Genetic cinebetaine (GB) has been shown to act in both capacitand metabolic studies of GB accumulation in maize (Zea mays L.) indicate that recessive alleles of a single locus are responsible for the

Maize (Zea mays L.) is a betaine-accumulating species, but certain maize genotypes lack betaine almost completely; a single recessive gene has been implicated as the cause of this deficiency (D Rhodes, PJ Rich [1988] Plant Physiol 88: 102-108). This study was undertaken to determine whether betaine deficiency in diverse maize germplasm is conditioned by the same genetic locus, and to define the biochemical lesion(s) involved. Complementation tests indicated that all 13 deficient genotypes tested shared a common locus. One maize population (P77) was found to be segregating for betaine deficiency, and true breeding individuals were used to produce related lines with and without betaine. Leaf tissue of both betaine-positive and betaine-deficient lines readily converted supplied betaine aldehyde to betaine, but only the betaine-containing line was able to oxidize supplied choline to betaine. This locates the lesion in betaine-deficient

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Yellow pitaya, Selenicereus megalanthus (Schum. ex. Vaupel) Moran, is a potential new fruit in Taiwan. It sprouts mostly in winter and flowers in late spring and fall. In this study, an average of 60% shoots within canopies flowered. Shoots sprouted in the current winter flowered in fall and produced winter fruits, and shoots sprouted earlier than the current winter flowered in late spring and produced summer fruits. Floral buds on most shoots appeared at the distal end. The weight, pulp percentage, and total soluble solids of winter fruits were significantly higher than those of summer fruits. The number of black seeds was positively correlated with pulp weight (R2 = 0.87). The total soluble solids in the core region of winter fruits reached 22.7 °Brix, higher than that in other regions. Future efforts to improve yellow pitaya production in Taiwan include increasing winter fruit production by enhancing growth of the current year's new shoots through proper canopy management and increasing the size of summer fruit by artificial pollination, fruit thinning, and other means.

Glycinebetaine (GB) accumulation has been suggested to be an adaptive response to several abiotic environmental stresses. Genetic and metabolic studies of GB accumulation in maize (Zea mays L.) indicate that recessive alleles of a single locus are responsible for the phenotype of GB nonaccumulation. The present study was undertaken to determine whether a similar genetically determined range of GB levels exists in the related C4 species Sorghum bicolor (L.) Moench. In a preliminary analysis of 240 sorghum genotypes, sampled at the postflowering stage, total quaternary ammonium compound (QAC) levels in the betaine fraction of the flag leaves were found to range from as low as 0.1 μmol g−1 FW to as much as 33 μmol g−1 FW. Stable isotope dilution desorption chemical ionization mass spectrometry of six genotypes with high QAC levels and five genotypes with low QAC levels confirmed that this variation could be attributed almost exclusively to genetic variability for GB level. GB‐nonaccumulating sorghum genotypes were confirmed to be GB‐non‐accumulating in a second year of field‐testing, and in greenhouse studies under salinized and non‐salinized conditions. GB levels increased with seedling age and/or salinization in GB‐accumulating genotypes. Also, GB levels were highest in the youngest leaves of GB‐accumulating sorghum genotypes. This work shows that GB is the major QAC in sorghum, that genetic differences in GB accumulation exist in sorghum as they do in maize, and that the level of GB in GB‐accumulating lines is developmentally and environmentally regulated. A list of GB levels of publicly available lines of sorghum is also provided.

A rapid and sensitive method for the identification of quaternary ammonium and tertiary sulfonium compounds is described. The method utilizes plasma desorption mass spectrometry (PDMS) in which a "' Cf ionizing source produces fission fragments which interact with the sample to yield ions which are then analyzed by a time-of-flight mass spectrometer. The method was applied to analyses of authentic standards and to the identification of quaternary ammonium and tertiary sulfonium compounds in higher plant leaf extracts purifed by ion-exchange chromatography. Plant species from 14 different families were tested, including species which are known glycinebetaine, /?-alaninebetaine, prolinebetaine or /?-dimethylsulfoniopropionate accumulators. PDMS results confirmed and extended the known taxonomic distributions of these compounds. Glycinebetaine was found in one species Krameriu parvifolia from a family (Krameriaceae) not previously known to accumulate this compound. Pipecolatebetaine was identified in Achillea jilipendulina (Asteraceae). The Occurrence of prolinebetaine and hydroxyprolinebetaine(s) was confirmed in three species (Lumium maculatum, Stachys byzantina and Phlom's fruticosa) of the tribe Lamieae of the subfamily Lamioideae in the family Lamiaceae, but not in a fourth member of this tribe (Physostegia virginiana). The last species accumulated only trigonelline. The PDMS method was also used to identify trigonelline-deficient Zea mays lines.