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This abstract is a prologue to this paper. Prior to his health failing, Martin Gibbs began writing remembrances of his education and beginning a science career, particularly on the peaceful uses of nuclear radiation, at the U.S. Brookhaven National Laboratory (BNL), Camp Upton, NY. Two years before his death Martin provided one of us (Govindjee) a draft text narrating his science beginnings in anticipation of publication in Photosynthesis Research. Govindjee edited his draft and returned it to him. Later, when it became difficult for him to complete it, he phoned Govindjee and expressed the desire that Govindjee publish this story, provided he kept it close to his original. Certain parts of Martin's narrations have appeared without references (Gibbs 1999). The Gibbs family made a similar request since the narrations contained numerous early personal accounts. Clanton Black recently presented an elegant tribute on Martin Gibbs and his entire science career (Black 2008). Clanton was given the draft, which he and Govindjee then agreed to finish. This chronicle is their effort to place Gibbs's narrations about his education and his maturation scientifically, in context with the beginnings of biological chemistry work with carbon-14 at the BNL (see Gibbs 1999). Further, these events are placed in context with those times of newly discovered radioisotopes which became available as part of the intensive nuclear research of World War II (WW II). Carbon-14, discovered during WW II nuclear research in 1940, was extremely useful and quickly led to the rapid discovery of new carbon metabolism pathways and biochemical cycles, e.g., photosynthetic carbon assimilation, within a decade after WW II.

Current vision of the driving forces underlying the evolution of gas composition in the Earth’s atmosphere is presented. The main evolutionary factors are the decline of the natural emission of reduced elements from the Earth’s depths and the transfer of biota from chemolithotrophy to photosynthesis.

Results of comparative analysis of turnover times and the capacity of major global pools of organic carbon are presented; the place of photosynthetic carbon sequestration is defined; concept of its catalytic role in the regulation of the organic branch of the global carbon cycle is ground. Concept of reservoir-flux model of photosynthetic carbon sequestration and of the net photosynthetic production at the territory of Northern Eurasia is suggested.

Development of characteristics of the C4 syndrome was studied in cotyledons and leaves of NADP‐ME type C4 Salsola richteri, a desert shrub. This species has seeds in which the cotyledons contain chloroplasts, storage proteins, and lipid bodies but no starch. Following imbibition (day 0), tissue types are already apparent in the cotyledons, and the chloroplasts have extensive grana stacking, but Kranz type anatomy and C4 photosynthesis have not developed. At day 0, there is high Rubisco and low phosphoenolpyruvate carboxylase (PEPC) content, distributed throughout all tissue. After 15 d of development in the dark, the cotyledons were in a C3‐like default condition with three distinct layers of chlorenchyma (hypodermis, mesophyll, and bundle sheath [BS]); all contained Rubisco in their chloroplasts. Light was required for development of the C4 syndrome, including differentiation of chloroplasts in mesophyll and BS cells, development of thick BS cell walls, selective compartmentation of Rubisco in BS cells a...

Crassulacean acid metabolism (CAM) can be traced from Roman times through persons who noted a morning acid taste of some common house plants. From India in 1815, Benjamin-Heyne described a ‘daily acid taste cycle’ with some succulent garden plants. Recent work has shown that the nocturnally formed acid is decarboxylated during the day to become the CO2 for photosynthesis. Thus, CAM photosynthesis extends over a 24-hour day using several daily interlocking cycles. To understand CAM photosynthesis, several landmark discoveries were made at the following times: daily reciprocal acid and carbohydrate cycles were found during 1870 to 1887; their precise identification, as malic acid and starch, and accurate quantification occurred from 1940 to 1954; diffusive gas resistance methods were introduced in the early 1960s that led to understanding the powerful stomatal control of daily gas exchanges; C4 photosynthesis in two different types of cells was discovered from 1965 to ∼1974 and the resultant information was used to elucidate the day and night portions of CAM photosynthesis in one cell; and exceptionally high internal green tissue CO2 levels, 0.2 to 2.5%, upon the daytime decarboxylation of malic acid, were discovered in 1979. These discoveries then were combined with related information from C3 and C4 photosynthesis, carbon biochemistry, cellular anatomy, and ecological physiology. Therefore by ∼1980, CAM photosynthesis finally was rigorously outlined. In a nutshell, 24-hour CAM occurs by phosphoenol pyruvate (PEP) carboxylase fixing CO2(HCO3 −) over the night to form malic acid that is stored in plant cell vacuoles. While stomata are tightly closed the following day, malic acid is decarboxylated releasing CO2 for C3 photosynthesis via ribulose bisphosphate carboxylase oxygenase (Rubisco). The CO2 acceptor, PEP, is formed via glycolysis at night from starch or other stored carbohydrates and after decarboxylation the three carbons are restored each day. In mid to late afternoon the stomata can open and mostly C3 photosynthesis occurs until darkness. CAM photosynthesis can be both inducible and constitutive and is known in 33 families with an estimated 15 to 20 000 species. CAM plants express the most plastic and tenacious photosynthesis known in that they can switch photosynthesis pathways and they can live and conduct photosynthesis for years even in the virtual absence of external H2O and CO2, i.e., CAM tenaciously protects its photosynthesis from both H2O and CO2 stresses.

Morphological and physiological characteristics of leaves from plant species collected in steppe communities in the various climatic zones in Eurasia were compared. The changes in leaf structure correlated with the major climatic factors. The mean thickness of leaves increased with increasing mean temperature of July and decreasing mean precipitation, which corresponded to aridity increase. The increased leaf thickness correlated with an increase in the specific leaf weight. The content of chlorophylls ( a + b ) in leaves greatly var- ied with plant habitats, whereas the chlorophyll a/b ratio remained unchanged. The chlorophyll content in leaf tissues had a general tendency to decrease with increasing leaf thickness. The leaf chlorophyll content posi- tively correlated ( R 2 = 0.77) with the proportion of chlorenchyma in leaf tissues. It is concluded that steppe plants adapt to climate aridization at the structural level by increasing the proportion of protective heterotrophic components of the leaf without changing the functional activity of photosynthetic tissues.

The natural geographical occurrence, carbon assimilation, and structural and biochemical diversity of species with C4 photosynthesis in the vegetation of Mongolia was studied. The Mongolian flora was screened for C4 plants by using 13C/12C isotope fractionation, determining the early products of 14CO2 fixation, microscopy of leaf mesophyll cell anatomy, and from reported literature data. Eighty C4 species were found among eight families: Amaranthaceae, Chenopodiaceae, Euphorbiaceae, Molluginaceae, Poaceae, Polygonaceae, Portulacaceae and Zygophyllaceae. Most of the C4 species were in three families: Chenopodiceae (41 species), Poaceae (25 species) and Polygonaceae, genus Calligonum (6 species). Some new C4 species in Chenopodiaceae, Poaceae and Polygonaceae were detected. C4 Chenopodiaceae species make up 45% of the total chenopods and are very important ecologically in saline areas and in cold arid deserts. C4 grasses make up about 10% of the total Poaceae species and these species naturally concentrate in steppe zones. Naturalized grasses with Kranz anatomy,of genera such as Setaria, Echinochloa, Eragrostis, Panicum and Chloris, were found in almost all the botanical-geographical regions of Mongolia, where they commonly occur in annually disturbed areas and desert oases. We analyzed the relationships between the occurrence of C4 plants in 16 natural botanical-geographical regions of Mongolia and their major climatic influences. The proportion of C4 species increases with decreasing geographical latitude and along the north-to-south temperature gradient; however grasses and chenopods differ in their responses to climate. The abundance of Chenopodiaceae species was closely correlated with aridity, but the distribution of the C4 grasses was more dependent on temperature. Also, we found a unique distribution of different C4 Chenopodiaceae structural and biochemical subtypes along the aridity gradient. NADP-malic enzyme (NADP-ME) tree-like species with a salsoloid type of Kranz anatomy, such as Haloxylon ammodendron and Iljinia regelii, plus shrubby Salsola and Anabasis species, were the plants most resistant to ecological stress and conditions in highly arid Gobian deserts with less than 100 mm of annual precipitation. Most of the annual C4 chenopod species were halophytes, succulent, and occurred in saline and arid environments in steppe and desert regions. The relative abundance of C3 succulent chenopod species also increased along the aridity gradient. Native C4 grasses were mainly annual and perennial species from the Cynodonteae tribe with NAD-ME and PEP-carboxykinase (PEP-CK) photosynthetic types. They occurred across much of Mongolia, but were most common in steppe zones where they are often dominant in grazing ecosystems.

Most species of the genus Salsola (Chenopodiaceae) that have been examined exhibit C4 photosynthesis in leaves. Four Salsola species from Central Asia were investigated in this study to determine the structural and functional relationships in photosynthesis of cotyledons compared to leaves, using anatomical (Kranz versus non-Kranz anatomy, chloroplast ultrastructure) and biochemical (activities of photosynthetic enzymes of the C3 and C4 pathways, 14C labeling of primary photosynthesis products and 13C/12C carbon isotope fractionation) criteria. The species included S. paulsenii from section Salsola, S. richteri from section Coccosalsola, S. laricina from section Caroxylon, and S. gemmascens from section Malpigipila. The results show that all four species have a C4 type of photosynthesis in leaves with a Salsoloid type Kranz anatomy, whereas both C3 and C4 types of photosynthesis were found in cotyledons. S. paulsenii and S. richteri have NADP- (NADP-ME) C4 type biochemistry with Salsoloid Kranz anatomy in both leaves and cotyledons. In S. laricina, both cotyledons and leaves have NAD-malic enzyme (NAD-ME) C4 type photosynthesis; however, while the leaves have Salsoloid type Kranz anatomy, cotyledons have Atriplicoid type Kranz anatomy. In S. gemmascens, cotyledons exhibit C3 type photosynthesis, while leaves perform NAD-ME type photosynthesis. Since the four species studied belong to different Salsola sections, this suggests that differences in photosynthetic types of leaves and cotyledons may be used as a basis or studies of the origin and evolution of C4 photosynthesis in the family Chenopodiaceae.

The objective of this article is to compare the Charlson comorbidity index derived from medical record data (Chart Index) with the same index derived from billing data (ICD-9 Index) to determine how well each predicted inpatient and 30-day mortality, length of stay, and complications among Medicare beneficiaries hospitalized for carotid endarterectomy. Economic and time constraints have increased the need for risk adjusters derived from administrative data, yet few studies have compared these measures with those derived from chart review. Using logistic regression, the Chart Index was found to be a significant predictor of inpatient mortality, 30-day mortality, length of stay, and complications, after controlling for age, gender, and neurologic and medical risk factors (P values = 0.004, 0.056, 0.0001, and 0.042, respectively). The ICD-9 Index approached significance as a predictor of the outcomes (P values = 0.092, 0.100, 0.093, and 0.080, respectively). The Chart Index was shown to be superior to the ICD-9 Index within this patient sample.

We studied root and stem sucrose metabolism in trees excavated from a 9-year-old artificially regenerated loblolly pine (Pinus taeda L.) plantation. Sucrose synthase (SS) activities in stem and taproot vascular cambial tissues followed similar seasonal patterns until they peaked during September. After September, stem SS activity disappeared quickly, whereas taproots exhibited SS activity even in January. Pyrophosphate-dependent phosphofructokinase (PPi-PFK) activity tracked SS activity. The activities of ATP-dependent PFK and several other glycolytic enzymes (e.g., phosphoglucomutase and phosphoglucoisomerase) remained relatively constant in cambial tissues of stem, taproot, and all first-order lateral roots (FOLRs) throughout the year. However, during the growing season, individual FOLRs exhibited variable sucrose metabolic activities that were independent of root diameter or position on the taproot. The FOLRs with low or no SS activity also had low PPi-PFK activity. We propose that when intense competition for sucrose occurs among different organs of a tree, the variable activities of the sucrose metabolic enzymes in FOLRs ensure that enough sucrose is allocated to the stem and taproot for growth. For a tree's long-term survival and growth, second or higher-order roots can be sacrificed, whereas FOLRs, stem and taproot are essential.

About 95% of swamp tupelo (Nyssa sylvatica var. biflora (Walt.) Sarg.) and sweetgum (Liquidambar styraciflua L.) seedlings survived continuous root flooding for more than two years, whereas none of the swamp chestnut oak (Quercus michauxii Nutt.) and cherrybark oak (Q. falcata var. pagodifolia Ell.) seedlings survived one year of flooding. Death of oak seedlings occurred in phases associated with periods of major vegetative growth, e.g., after bud burst in spring, after summer stem elongation, and during the winter deciduous stage, suggesting that stored reserves and sources were inadequate to maintain the seedlings when vegetative sinks were forming. Additional evidence that flooding induced a source deficiency in oak was that leaves of flooded oak were 65 to 75% smaller than leaves of nonflooded oak. Flooded swamp tupelo seedlings had a normal leaf size and patchy stomatal opening compared with nonflooded seedlings. Flooding caused increases in alcohol dehydrogenase (ADH) specific activity in taproot cambial tissues and increases in starch concentrations of swamp tupelo seedlings that were reversed when seedlings were removed from flooding. Flooding had little effect on soluble sugar concentrations in swamp tupelo or sweetgum. In the long-term flood-dry-flood treatment, in which all species had survivors, upper canopy leaf photosynthetic rates were higher in all species during the dry period than in nonflooded controls, whereas their starch and soluble sugars concentrations were similar to those of nonflooded controls. Based on seedling survival and the sink-source relationships, the order of flood tolerance was: swamp tupelo > sweetgum > swamp chestnut oak > cherrybark oak.

The hypothesis we propose is that during photosynthesis the balance between potentially detrimental and beneficial photochemically induced events can be tipped beneficially toward increased photosynthesis and toward increased crop yield. To test this hypothesis a procedure has been devised with the rice plant, Oryza sativa, that has resulted in increasing both canopy photosynthesis and rice grain yield. Two elite rice varieties selected independently in the contrasting environments of either South China or Texas, each with distinct photosynthetic traits, were crossed to produce a hybrid with an increased canopy photosynthesis and grain yield that is regularly 20 to 22% higher than the mid-yields of the parents. The photosynthetic and mechanisms which may contribute to these beneficial results in the hybrid rice are: a reduction of the midday depression of photosynthesis; a rapid development of the canopy for photosynthetic light interception and an increased canopy photosynthesis; increased amounts of carotenoids for the xanthophyll cycle; an increased protection against free radicals induced by paraquat treatment; a 6 to 12 day shorter plant reproductive life cycle; and a 8 to 10 day increase in the longevity of the flag leaf over the parents. While the hybrid rice has successfully integrated these and likely other unknown characteristics to increase both crop photosynthesis and grain yield, we propose that understanding the underlying beneficial photosynthetic mechanisms supporting these crop plant traits is worthy of thorough investigation and application in crop production.

Onion (Allium cepa L.) plants were examined to determine the photosynthetic role of CO2 that accumulates within their leaf cavities. Leaf cavity CO2 concentrations ranged from 2250 μL L(-1) near the leaf base to below atmospheric (350 μL L(-1)) near the leaf tip at midday. There was a daily fluctuation in the leaf cavity CO2 concentrations with minimum values near midday and maximum values at night. Conductance to CO2 from the leaf cavity ranged from 24 to 202 μmol m(-2) s(-1) and was even lower for membranes of bulb scales. The capacity for onion leaves to recycle leaf cavity CO2 was poor, only 0.2 to 2.2% of leaf photosynthesis based either on measured CO2 concentrations and conductance values or as measured directly by (14)CO2 labeling experiments. The photosynthetic responses to CO2 and O2 were measured to determine whether onion leaves exhibited a typical C3-type response. A linear increase in CO2 uptake was observed in intact leaves up to 315 μL L(-1) of external CO2 and, at this external CO2 concentration, uptake was inhibited 35.4±0.9% by 210 mL L(-1) O2 compared to 20 mL L(-1) O2. Scanning electron micrographs of the leaf cavity wall revealed degenerated tissue covered by a membrane. Onion leaf cavity membranes apparently are highly impermeable to CO2 and greatly restrict the refixation of leaf cavity CO2 by photosynthetic tissue.

Hybrids have been made between species of Flaveria exhibiting varying levels of C4 photosynthesis. The degree of C4 photosynthesis expressed in four interspecific hybrids (Flaveria trinervia [C4] × F. linearis [C3-C4], F. brownii [C4-like] × F. linearis, and two three-species hybrids from F. trinervia × [F. brownii × F. linearis]) was estimated by inhibiting phosphoenolpyruvate carboxylase in vivo with 3,3-dichloro-2-dihydroxyphosphinoylmethyl-2-propenoate (DCDP). The inhibitor was fed to detached leaves at a concentration of 4 mm, and apparent photosynthesis was measured at atmospheric levels of CO2 and at 20 and 210 mL L−1 of O2. Photosynthesis at 210 mL L−1 of O2 was inhibited 32% by DCDP in F. linearis, by 60% in F. brownii, and by 87% in F. trinervia. Inhibition in the hybrids ranged from 38 to 52%. The inhibition of photosynthesis by 210 mL L−1 of O2 was increased when DCDP was used, except in the C4 species, F. trinervia, in which photosynthesis was insensitive to O2. Except for F. trinervia, control plants with less O2 sensitivity (more C4-like) exhibited a progressively greater change in O2 inhibition of photosynthesis when treated with DCDP. This increased O2 inhibition probably resulted from decreased CO2 concentrations in bundle sheath cells due to inhibition of phosphoenolpyruvate carboxylase. The inhibition of photosynthesis by DCDP is concluded to underestimate the degree of C4 photosynthesis in the interspecific hybrids because increased direct assimilation of atmospheric CO2 by ribulose bisphosphate carboxylase may compensate for inhibition of phosphoenolpyruvate carboxylase.

The degree of C4 photosynthesis was assessed in four hybrids among C4, C4-like, and C3-C4 species in the genus Flaveria using 14C labeling, CO2 exchange, 13C discrimination, and C4 enzyme activities. The hybrids incorporated from 57 to 88% of the 14C assimilated in a 10-s exposure into C4 acids compared with 26% for the C3-C4 species Flaveria linearis, 91% for the C4 species Flaveria trinervia, and 87% for the C4-like Flaveria brownii. Those plants with high percentages of 14C initially fixed into C4 acids also metabolized the C4 acids quickly, and the percentage of 14C in 3-phosphoglyceric acid plus sugar phosphates increased for at least a 30-s exposure to 12CO2. This indicated a high degree of coordination between the carbon accumulation and reduction phases of the C4 and C3 cycles. Synthesis and metabolism of C4 acids by the species and their hybrids were highly and linearly correlated with discrimination against 13C. The relationship of 13C discrimination or 14C metabolism to O2 inhibition of photosynthesis was curvilinear, changing more rapidly at C4-like values of 14C metabolism and 13C discrimination. Incorporation of initial 14C into C4 acids showed a biphasic increase with increased activities of phosphoenolpyruvate carboxylase and NADP-malic enzyme (steep at low activities), but turnover of C4 acids was linearly related to NADP-malic enzyme activity. Several other traits were closely related to the in vitro activity of NADP-malic enzyme but not phosphoenolpyruvate carboxylase. The data indicate that the hybrids have variable degrees of C4 photosynthesis but that the carbon accumulation and reduction portions of the C4 and C3 cycles are well coordinated.

Here it is reported that sucrose synthase can be readily measured in growing wild tomato fruits (Lycopersicon chmielewskii) when suitable methods are adopted during fruit extraction. The enzyme also was present in fruit pericarp tissues, in seeds, and in flowers. To check for novel characteristics, the wild tomato fruit sucrose synthase was purified, by (NH(4))(2)SO(4) fraction and chromatography with DE-32, Sephadex G-200, and PBA-60, to one major band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The following characteristics were obtained: native protein relative molecular weight 380,000; subunit relative molecular weight 89,000; K(m) values with: sucrose 53 millimolar, UDP 18.9 micromolar, UDP-glucose 88 micromolar, fructose 8.4 millimolar; pH optima between 6.2 to 7.3 for sucrose breakdown and 7 to 9 for synthesis; and temperature optima near 50 degrees C. The enzyme exhibited a high affinity and a preference for uridylates. The enzyme showed more sensitivity to divalent cations in the synthesis of sucrose than in its breakdown. Sink strength in tomato fruits also was investigated in regard to sucrose breakdown enzyme activities versus fruit weight gain. Sucrose synthase activity was consistently related to increases in fruit weight (sink strength) in both wild and commercial tomatoes. Acid and neutral invertases were not, because the published invertase activity values were too variable for quantitative analyses regarding the roles of invertases in tomato fruit development. In rapidly growing fruits of both wild and commercially developed tomato plants, the activity of sucrose synthase per growing fruit, i.e. sucrose synthase peak activity X fruit size, was linearly related to final fruit size; and the activity exceeded fruit growth and carbon import rates by at least 10-fold. In mature, nongrowing fruits, sucrose synthase activities approached nil values. Therefore, sucrose synthase can serve as an indicator of sink strength in growing tomato fruits.

An analog of phosphoenolpyruvate, 3,3-dichloro-2-dihydroxyphosphinoylmethyl-2-propenoate (DCDP), was used to inhibit phosphoenolpyruvate carboxylase and, therefore, assess the contribution of the C4 pathway to photosynthesis in detached leaves of several C3-C4 intermediate species. There was no effect of 4 millimolar DCDP on apparent photosynthesis or on inhibition of apparent photosynthesis by 210 milliliters per liter of O2 for the C3-C4 species Panicum milioides, Moricandia arvensis, and Neurachne minor or the C3 species Flaveria pringlei. However, when leaves of Flaveria linearis (C3-C4), Flaveria brownii (C4-like), and Flaveria trinervia (C4) were fed 4 millimolar DCDP, photosynthesis was reduced 32, 60, and 90%, respectively. Photosynthetic inhibition by 210 milliliter per liter of O2 was also significantly increased in 4 millimolar DCDP-fed leaves of F. linearis and F. brownii but not in F. trinervia when compared with control values. These results with DCDP clearly demarcate C3-C4 species into species including Panicum, Moricandia, and Neurachne whose reduced photorespiration occurs without any C4 photosynthetic involvement and species of Flaveria in which C4 photosynthesis contributes to CO2 assimilation.

A plasma membrane-enriched fraction was isolated from various tissues of developing lima bean seedlings, Phaseolus lunatus var Cangreen, to study β-1,3-glucan synthase activity changes. All tissues contained an active β-glucan synthase, including the cotyledons that will be senescent in mature lima bean plants. Young primary leaves exhibited a very active β-glucan synthase; but this activity dropped markedly, about fivefold, as the leaves gained weight and became photosynthetic. Some tissues, such as the hypocotyl and young stem, exhibited an increase in β-glucan synthase activity as the tissues were growing and a decrease as the growth rate slowed. Roots exhibited a high activity early in development that only decreased slightly, about 30%, as root growth increased. Surprisingly the senescent cotyledons contained an activity equivalent to some other tissues that was maintained over our measurement time of 21 days. Perhaps this callose synthesis activity is related to translocation processes as the cotyledons transfer their reserves to the growing seedling. We concluded that β-glucan synthase was not a good indicator of sink strength in these lima bean tissues. The plasma membrane fractions also were tested for other enzymes that might be present because an electron microscope study revealed a low contamination by other types of membranes. The membrane fractions had low but detectable activities of sucrose synthase, UDPglucose pyrophosphorylase, UDPase, alkaline invertase, and a general phosphatase; but these enzymes exhibited no consistent pattern(s) of activity change with plant development.

An unparalleled floral diversity is found in the continental deserts of Central Asia that stretch for thousands of miles from Iran and Afghanistan across Uzbekistan, Turkmenistan into Western China and Mongolia. Two major pressures subject Central Asian deserts to powerful forces that lead to desertification, namely, their extremely dynamic environments plus a host of human driven activities. Great natural contrasts exist in these continental environments, e.g., with mostly autumn-winter rains and almost absence of rainfall in summer along with quite high and low annual temperature fluctuations, and complicated desert, mountain, steppe and plain relief. Human activities demand lands, waters, plants, and other natural resources for activities such as domestic livestock grazing, fuels, cropping agriculture, irrigation, dams, reservoirs and canals, mining, drilling, roads, dwellings, and other human infrastructures. Such extreme natural environmental changes coupled with human activities often induce dynamic detrimental environments for the growth and seed reproduction of plants; indeed difficult environments for all biological life forms.

One of the main undesirable consequences of the process of desertification in the Central Asia countries is an amplification of salinity process resulting in a wide development of saline soils. The amplification of the salinity process under conditions of aridization of climate is caused by the high maintenance of salts both in the surface and in subsoil waters of dry lands of the Aral Sea Basin [1]. Besides that, the recent overuse of Amudarya, Zerafshan and Syrdarya river water has resulted in the waterlogging and secondary salinization (human caused) salt/affected lands on whole adjacent territories. Effects of these impacts include alteration or destruction of vegetation, frequent disappearance of many useful, endemic and relict species of desert plants, and consequently, establishment of annual plant communities dominated by weeds and exotic species. Up to 15,000 ha of pastures are annually affected by salinity and waterlogging that resulted in the reduction of population of more than 1,500 species of mammals, birds and plants in the whole of the Central Asia region [2, 3].

Crassulacean acid metabolism (CAM) can be traced from Roman times through persons who noted a morning acid taste of some common house plants. From India in 1815, Benjamin-Heyne described a 'daily acid taste cycle' with some succulent garden plants. Recent work has shown that the nocturnally formed acid is decarboxylated during the day to become the CO(2) for photosynthesis. Thus, CAM photosynthesis extends over a 24-hour day using several daily interlocking cycles. To understand CAM photosynthesis, several landmark discoveries were made at the following times: daily reciprocal acid and carbohydrate cycles were found during 1870 to 1887; their precise identification, as malic acid and starch, and accurate quantification occurred from 1940 to 1954; diffusive gas resistance methods were introduced in the early 1960s that led to understanding the powerful stomatal control of daily gas exchanges; C(4) photosynthesis in two different types of cells was discovered from 1965 to approximately 1974 and the resultant information was used to elucidate the day and night portions of CAM photosynthesis in one cell; and exceptionally high internal green tissue CO(2) levels, 0.2 to 2.5%, upon the daytime decarboxylation of malic acid, were discovered in 1979. These discoveries then were combined with related information from C(3) and C(4) photosynthesis, carbon biochemistry, cellular anatomy, and ecological physiology. Therefore by approximately 1980, CAM photosynthesis finally was rigorously outlined. In a nutshell, 24-hour CAM occurs by phosphoenol pyruvate (PEP) carboxylase fixing CO(2)(HCO(3) (-)) over the night to form malic acid that is stored in plant cell vacuoles. While stomata are tightly closed the following day, malic acid is decarboxylated releasing CO(2) for C(3) photosynthesis via ribulose bisphosphate carboxylase oxygenase (Rubisco). The CO(2) acceptor, PEP, is formed via glycolysis at night from starch or other stored carbohydrates and after decarboxylation the three carbons are restored each day. In mid to late afternoon the stomata can open and mostly C(3) photosynthesis occurs until darkness. CAM photo-synthesis can be both inducible and constitutive and is known in 33 families with an estimated 15 to 20 000 species. CAM plants express the most plastic and tenacious photosynthesis known in that they can switch photosynthesis pathways and they can live and conduct photosynthesis for years even in the virtual absence of external H(2)O and CO(2), i.e., CAM tenaciously protects its photosynthesis from both H(2)O and CO(2) stresses.

Diversity in photosynthetic pathways in the angiosperm family Chenopodiaceae is expressed in both biochemical and anatomical characters. To understand the evolution of photosynthetic diversity, we reconstructed the phylogeny of representative species of tribe Salsoleae of subfamily Salsoloideae, a group that exhibits in microcosm the patterns of photosynthetic variation present in the family as a whole, and examined the distribution of photosynthetic characters on the resulting phylogenetic tree. Phylogenetic relationships were inferred from parsimony analysis of nucleotide sequences of the internal transcribed spacer regions (ITS) of the 18S-26S nuclear ribosomal DNA of 34 species of Salsola and related genera (Halothamnus, Climacoptera, Girgensohnia, Halocharis, and Haloxylon) and representative outgroups from tribes Camphorosmeae (Camphorosma lessingii, Kochia prostrata, and K. scoparia) and Atripliceae (Atriplex spongiosa). A highly resolved strict consensus tree largely agrees with photosynthetic type and anatomy of leaves and cotyledons. The sequence data provide strong support for the origin and evolution of two main lineages of plants in tribe Salsoleae, with NAD-ME and NADP-ME C(4) photosynthesis, respectively. These groups have different C(4) photosynthetic types in leaves and different structural and photosynthetic characteristics in cotyledons. Phylogenetic relationships inferred from ITS sequences generally agree with classifications based on morphological data, but deviations from the existing taxonomy were also observed. The NAD-ME C(4) lineage contains species classified in sections Caroxylon, Malpigipila, Cardiandra, Belanthera, and Coccosalsola, and the NADP-ME lineage comprises species from sections Coccosalsola and Salsola. Reconstruction of photosynthetic characters on the ITS phylogeny indicates separate NAD-ME and NADP-ME lineages and suggests two reversions to C(3) photosynthesis. Reconstruction of geographic distributions suggests Salsoleae originated and diversified in central Asia and subsequently dispersed to Africa, Europe, and Mongolia. Inferred patterns and processes of photosynthetic evolution in Salsoleae should further our understanding of biochemical and anatomical evolution in Chenopodiaceae as a whole.

Studies on past changes in vegetation are a central key to understanding modern plant distribution, to reconstructing past climates, and to testing biome and climate models. This chapter is an initial attempt to reconstruct and to map spatial changes in the vegetation across Mongolia since ca 15,000 14C yr B.P. Our work is a logical continuation of extensive studies on the late Quaternary vegetation and environments of Mongolia done by Soviet and Mongolian scientists during recent decades (Giterman et al., 1968; Lavrenko & Rachkovskaya, 1976; Dinesman et al., 1989; Logatchov, 1989; Sevastyanov et al., 1994; etc.). Since the main publications only are published in Russian and poorly accessible for the English speaking scientific community, we first briefly will summarize previous studies, which reconstructed regional vegetation changes in Mongolia. These vegetation reconstructions are broadly correct, but some major discrepancies do appear. This summary demonstrates that Mongolian pollen records, rather than other sources of paleobotanical data, are the main information source for vegetation reconstructions and that these are based on relationships between modern pollen spectra and actual vegetation. Moreover, we will describe some potential problems that different types of sediments can cause in the interpretation of fossil pollen spectra.

An analysis of modern changes in plant communities reveals that the most important active factors today are climate and human-associated modifications. Indeed major detrimental effects are exerted by both climate cycles and human activities.

The dynamics of plant cover has long received much attention and is addressed in numerous publications. Methods for the investigation of vegetation dynamics were treated in detail in the monograph Field Geobotany (Aleksandrova, 1964). Today, in addition to these conventional methods, remote-sensing (Vostokova et al., 1988a, b) GIS and ecological databases are used extensively (Trofimova & Novikova, 1994).

Mongolia is at the center of the Asian continent and for a long time it has attracted attention from European scientists. Russian scientists and explorers also were keenly interested in this part of Central Asia. Their investigations were both pragmatic and scientific in character and were aimed at understanding this country which occupied the «crown» of Asia. Studies on the vegetation cover of Mongolia carried out by Russian scientists and explorers can be roughly subdivided into three periods: Brief route observations done alongside the main tasks of an expedition; Mainly floristic investigations aimed at collecting a comprehensive inventory of the region’s flora; Geobotanical investigations accompanied by studies on the distribution of plant communities and their mapping, as well as by studies on the physiological features of plants and their ecology.

Introduction to Studies on the Vegetation of Mongolia. Natural and Anthropogenic Factors and the Dynamics of Vegetation Distribution in Mongolia. 1.1. Introduction. 1.2. Natural Features of Mongolia. 1.3. Landscape-Ecological Regions. 1.4. Landscape and Ecological Factors of Vegetation Dynamics. 1.5. Conclusion. Late Quaternary Vegetation History of Mongolia. 2.1. Introduction. 2.2. An Overview of Previous Studies. 2.3. Data Used in this Study. 2.4. Regional Pollen Records from Individual Sites. 2.5. Holocene Changes in the Distribution of Tree and Shrub Taxa in Mongolia. 2.6. Spatial Reconstruction and Mapping of Mongolian Vegetation during the Last 15,000 Years. 2.7. General Discussion and Conclusions. Assessing Present-Day Plant Cover Dynamics. 3.1. Introduction. Modern Methods for Studying and Monitoring Plant Cover. 3.2. Mountain Plant Community Dynamics. 3.3. Plant Community Dynamics in Plains and Rocky Areas. 3.4. Dynamics of Water-Associated Vegetation. 3.5. Conclusions. Analysis of Present-Day Vegetation Dynamics. 4.1. Basic Changes in Vegetation. 4.2. Regressive Plant Community Successions. 4.3. Progressive Plant Community Regeneration. 4.4. Mapping Vegetation Dynamics. 4.5. Conclusions. Strategies for Nature Management and Vegetation Conservation. 5.1. Introduction. Methods for Vegetation Conservation. 5.2. Restoration and Conservation of Botanical Successions. 5.3. Systems for the Conservation of Botanical Diversity. 5.4. Conclusions. Summary Conclusions and Recommendations. References. Appendix 1. Appendix 2. Index.

The livestock-grazing based society of Mongolia is directly dependent upon the primary production of its vegetation. Vegetation on the vast fenceless steppes of Mongolia has sustained this society for many centuries. Evenso the vegetation of Mongolia is in a very strained ecological condition, hence work on plant cover dynamics is of central importance to help sustain and develop sound considered nature management programs.

Our analysis of modern plant cover dynamics has shown bi-directional successions in various plant communities with some ecosystems recovering and some being degraded currently in Mongolia. Across Mongolia the largest areas are occupied by plant communities that have been exposed to human-associated effects to varying extents and which are at different degradation stages. This vegetation degradation is a result of immediate and long-term human-associated modifications, the widespread effects of natural climatic cycles, water erosion processes, and strong wind movement of soils. Human effects of great importance now are: an expanded and intensive economic exploitation of natural resources; population growth caused by new enterprises to develop mineral resources; the growth of cities; and the widespread construction of new built-up areas. These are illustrated in the maps Ecosystems of Mongolia (1995) partially shown in Figure 5.1, which demonstrate some ecosystem disturbances with respect to vegetation degradation. Figure 5.1 shows some affects on plant cover with reference to grazing livestock breeding, to tree fellings, and to fires in forest steppes.

The Chenopodiaceae contains species with C3, C4 and possibly C3-C4 intermediate photosynthesis. This family has a second place in world flora in abundance of plants with C4 photosynthesis (about 350-400 species) and it displays a large diversity of biochemical mechanisms of CO2 fixation and Kranz-anatomy in mature leaves. C4 Chenopodiaceae species dominate in arid desert regions of Africa, Asia and Europe, and are adapted to extreme environment. Previous studies were concentrated on investigation of C4 photosynthesis in basic assimilative organs (leaves and assimilatory shoots) and demonstrated a large structural and biochemical diversity of C4 photosynthesis (1). At the same time, leaf-like organs of plants such as cotyledons were, studied poor, but give evidence of occurrence both C3 and C4 photosynthetic types in these organs (2–3). The purpose of this study was a comparative structural and biochemical investigation of photosynthetic types in leaves and leaf-like organs in Chenopodiaceae species differed in taxonomy, evolution position, structural and biochemical features of C4 photosynthesis.

Leaf anatomy was studied by light and electron microscopy and the leaf activities of RUBP carboxylase, PEP carboxylase, and malic enzyme were assayed in: Salsola australis and S. oreophila grown on the West Pamirs at 1800 m altitude; in S. australis grown on the East Pamirs at 3860 m; and in S. arbusculiformis grown in the Kisil-Kum desert in Middle Asia near 500 m. Carbon isotope fractionation ratio values also were measured on whole leaf tissue for 18 Salsola species field collected in these and other regions of the former USSR. S. australis leaves are cylindrical and in cross section exhibit a peripheral ring of mesophyll and then an inner ring of bundle sheath type cells; and its biochemical characteristics and deltaC values are typical of a C4 species of the NADP-malic enzyme malate-forming group. These traits were expressed independent of the plant growth altitude up to 4000 m. C4 type deltaC values were obtained in 14 of the Salsola species. Anatomical, structural, and biochemical features typical of the C4 syndrome were absent in S. oreophila and S. arbusculiformis. Four Salsola species, including these two, had C3-type deltaC values. Their cylindrical leaves in cross section exhibited two to three peripheral rings as layers of palisade parenchyma. Although their vascular bundles were surrounded by green bundle sheath cells, their organelle numbers were comparable to those in mesophyll cells. Neither bundle sheath cell wall thickenings nor dimorphic chloroplasts in two leaf cell types were observed. In S. oreophila, there was a high activity of RuBP carboxylase, but a low activity of C4 cycle enzymes. Interpretation of these data lends evidence to the hypothesis that a small group of C3 Salsola species, including S. oreophila, S. arbusculiformis, S. montana, and S. pachyphylla, arose as the result of a reversion of a C4 to a C3 type of photosynthetic CO2 fixation in the cooler climates of Middle Asia.

Each day a massive interlocked biochemical cycle occurs in the green tissues of crassulacean acid metabolism plants. The function of this interlocked cycle, in its simplest context, is to furnish most of the CO2 for CAM plant photosynthesis. In addition, this diel (24 h) cycle produces the primary identifying marks of a CAM tissue through two ancillary cycles. One cycle involves a nocturnal acidification and its loss the next day, while the second concerns the depletion of a carbohydrate reserve at night and its replenishment the next day. Formally Benjamin Heyne (1815) is credited with writing, nearly two centuries ago, about the “acid as sorrel” taste of a succulent green plant at dawn and the “bland taste” caused by acidity loss later in the day. In fact, the exact origins of these observations are lost in antiquity, but certainly are referred to in Roman and Biblical writings. The circumstantial cause of the acidity was postulated to be an organic acid about a century ago and the bland taste later was associated with starch; but these ideas were not plainly coupled together in theory nor quantitatively studied until the late 1940s. Then, with the discovery of major portions of intermediary metabolism and the advent of additional quantitative biochemical procedures, the nature of the daily reciprocal relation between the acid and the bland taste was recognized and measured quantitatively. The acid taste is caused principally by malic acid, while the bland taste is caused by deacidification plus the reciprocal synthesis of a bland tasting carbohydrate, e.g. a polysaccharide such as starch.

Sucrose synthase (SS) was the dominant enzyme of sucrose metabolism in both stem and root vascular cambial zone tissues of nursery-grown loblolly pine (Pinus taeda L.) seedlings. Acid invertase (AI) and neutral invertase (NT) activities were generally less than 10% of the SS activity in both tissues. In both cambial tissues, seasonal patterns of enzyme activity were observed for SS but not for AI or NI. The seasonal patterns of SS activity in stem and root cambia paralleled the periodic growth of stems and roots. Stems had high SS activity and growth during summer and early fall. Roots had substantial SS activity and growth during summer and fall, but SS activity and growth were even higher in winter. When seedlings were transplanted, about eight months elapsed before stem and root cambia resumed rates of growth and sucrose metabolism similar to those in control nontransplanted seedlings. Two months after transplanting, root SS was at its lowest, whereas AI activity in transplants was 50% higher than in control nontransplanted seedlings. In stems, SS activity decreased in response to transplanting, whereas AI and NI activities did not change appreciably. In loblolly pine tissues, SS was specific for uridylates, whereas the nucleotide triphosphate-dependent phosphofructokinase (NTP-PFK) had similar activity with either UTP or ATP. Except in winter, the NTP-PFK was less active than the pyrophosphate-dependent phosphofructokinase (PPi-PFK) during all seasons. The PPi-dependent PFK activity in nontransplanted seedlings followed similar seasonal and spatial patterns to those of SS activity. In actively growing tissues, such as stem cambial tissues in summer and root cambial tissues in winter, the measured total PFK to SS ratio ranged between 1.5/1 and 3/1. In contrast, in less actively growing tissues or transplanted seedlings, a greater decrease occurred in SS than in PFK activity, hence the ratio rose to as high as 12/1. It was concluded that: (1) SS was the dominant enzyme for sucrose metabolism in root and stem cambial tissues of loblolly pine seedlings; (2) both SS and PPi-PFK in the cambial tissues can be used as biochemical indicators of growth sink strength in stems and roots; and (3) both enzymes can be used as indicators of seedling stress caused by events such as transplanting and winter freezing.

Alkaline invertase from sprouting soybean (Glycine max) hypocotyls was purified to apparent electrophoretic homogeneity by consecutive use of DEAE-cellulose, green 19 dye, and Cibacron blue 3GA dye affinity chromatography. This protocol produced about a 100-fold purification with about a 11% yield. The purified protein had a specific activity of 48 μmol of glucose produced mg−1 protein min− (pH 7.0) and showed a single protein band in sodium dodecyl sulfate—polyacrylamide gel electrophoresis (PAGE) (58 kDa) and in native PAGE, as indicated by both protein and activity staining. The native enzyme molecular mass was about 240 kDa, suggesting a homotetrameric structure. The purified enzyme exhibited hyperbolic saturation kinetics with a Km (sucrose) near 10 m m and the enzyme did not utilize raffinose, maltose, lactose, or cellibose as a substrate. Impure alkaline invertase preparations, which contained acid invertase activity, on contrast, showed biphasic curves versus sucrose concentration. Combining equal activities of purified alkaline invertase with acid invertase resulted in a biphasic response, but there was a transition to hyperbolic saturation kinetics when the activity ratio, alkaline: acid invertase, was increased above unity. Alkaline invertase activity was inhibited by HgCl2, pridoxal phosphate, and Tris with respective Ki values near 2 μ m , 5 μ m , and 4 m m . Glycoprotein staining (periodic acid-Schiff method) was negative and alkaline invertase did not bind to two immobilized lectins, concanavalin A and wheat germ agglutinin; hence, the enzyme apparently is not a glycoprotein. The purified alkaline invertase, and a purified soybean acid invertase, was used to raise rabbit polyclonal antibodies. The alkaline invertase antibody preparation was specific for alkaline invertase and crossreacted with alkaline invertases from other plants. Neither purified soybean alkaline invertases nor the crude enzyme from several plants cross-reacted with the soybean acid invertase antibody.

Certain actively filling plant sucrose sinks such as a seed, a tuber, or a root can be identified by measuring the uridine diphosphate and pyrophosphate-dependent metabolism of sucrose. Sucrolysis in both active and quiescent sucrose sinks was tested and sucrose synthase was found to be the predominant sucrose breakdown activity. Sucrolysis via invertases was low and secondary in both types of sinks. Sucrose synthase activity dropped markedly, greater than fivefold, in quiescent sinks. The tests are consistent with the hypothesis that the sucrose filling activity, i.e. the sink strength, of these plant sinks can be measured by testing the uridine diphosphate and pyrophosphate-dependent breakdown of sucrose. Measuring the initial reactions of sucrolysis shows much promise for use in agriculture crop and tree improvement research as a biochemical test for sink strength.

The effects of temperature, O 2 , and CO 2 on titratable acid content and on CO 2 exchange were measured in detached pineapple ( Ananas comosus ) leaves during the daily 15-hour light period. Comparative measurements were made in air and in CO 2 -free air. Increasing the leaf temperature from 20 to 35 C decreased the total CO 2 uptake in air and slightly increased the total CO 2 released into CO 2 -free air. Between 25 and 35 C, the activation energy for daily acid loss was near 12 kcal mol −1 , but at lower temperatures the activation energy was much greater. Increasing O 2 or decreasing the CO 2 concentration decreased the total CO 2 fixation in air, whereas the total CO 2 released in CO 2 -free air was increased. The total acid content remained constant at 20 C, but it decreased progressively with increasing temperature both in air and in CO 2 -free air. The total acid content at 30 C remained constant in 2% O 2 irrespective of CO 2 concentration. The total acid content decreased in 21 and 50% O 2 as the CO 2 increased from 0 to 300, and 540 μl/l of CO 2 . The data indicate that photorespiration is present in pineapple. The lack of acid loss in 2% O 2 suggests that light deacidification is dependent upon respiration and that higher O 2 concentrations are required to saturate deacidification.

3-Mercaptopicolinic acid (3-MPA), an inhibitor of phosphoenolpyruvate carboxykinase, was employed to study the role of organic acid decarboxylation during C(4) photosynthesis. Treatment of detached Panicum maximum leaves with 5 mm 3-MPA inhibited photosynthesis 70 to 75%. Oxygen was found to have no effect on the degree of inhibition. The postillumination (14)CO(2) burst associated with P. maximum photosynthesis was almost abolished by 5 mm 3-MPA. The turnover rates of malate and aspartate during C(4) photosynthesis were severely reduced as well as the rates of formation of C(3) cycle intermediates in P. maximum leaves treated with 3-MPA. These results are interpreted as direct evidence for the fixation of CO(2), arising from the decarboxylation of oxaloacetate, by the C(3) cycle in bundle sheath cells of P. maximum leaves.

The participation of pyrophosphate-dependent phosphofructokinase (PPi-PFK) in plant glycolysis was examined using extracts from pea seeds (Pisum sativum L. cv Alaska). Glycolysis starting with fructose 6-phosphate was measured under aerobic conditions as the accumulation of pyruvate. Pyruvate accumulated in a medium containing PPi and adenosine diphosphate at about two-thirds of the rate in a medium containing adenosine diphosphate and adenosine triphosphate (ATP). The PPi-dependent pyruvate accumulation had the same reactant requirements and sensitivity to glycolysis inhibitors, sodium fluoride, and iodoacetamide, as the well-established ATP-dependent glycolysis. Added fructose 2,6-bisphosphate stimulated both the PPi-dependent pyruvate accumulation and PPi-PFK activity whereas this modulator had no effect on ATP-dependent glycolysis or ATP-PFK. Collectively these results demonstrate a PPi-dependent glycolytic pathway in plants which is responsive to fructose 2,6-bisphosphate.

A pyrophosphate-dependent phosphofructokinase (PPi-PFK) activity is detectable in extracts of a wide variety of primitive and advanced plants, the Charalean algae, and in the photosynthetic bacterium, Rhodospirillum rubrum. Angiosperms with extractable PPi-PFK activities 4- to 70-fold higher than the respective ATP-PFK activities tend to be succulent and to exhibit CAM. Even though PPi-PFK activity is not detected in crude extracts of some well known CAM plants, e.g. plants in the Crassulaceae, gel filtration of the extract and/or inclusion of the PPi-PFK activator, fructose 2,6-bisphosphate, in the assay reveals that a PPi-PFK activity is present in these species. Fructose 2,6-bisphosphate likewise activates PPi-PFK activities in extracts of C(3) and C(4) plants. C(3) and C(4) plant PPi-PFK activities are roughly equivalent to ATP-PFK activities in the same species. PPi-PFK activity is also detected in some bryophytes, lower vascular plants, ferns, and gymnosperms. The Charophytes, advanced algae presumed to be similar to species ancestral to vascular plants, exhibit at least 4-fold higher PPi-PFK than ATP-PFK activities. R. rubrum also exhibits a much higher PPi-PFK activity than ATP-PFK activity. These data indicate that PPi-PFK may serve as an alternate enzyme to ATP-PFK in glycolysis in a wide range of photosynthetic organisms.

The activity of adenosine 5′ triphosphate sulfurylase was determined in crabgrass mesophyll cells, bundle sheath strands, and whole leaf extracts. The enzyme was assayed by following molybdate-dependent pyrophosphate release from ATP, 35SO42− incorporation into adenosine 5′ phosphosulfate, and ATP synthesis dependent upon adenosine 5′ phosphosulfate and inorganic pyrophosphate. With all assays, greater than 90% of the activity was found in extracts from bundle sheath strands. The activities in whole leaf extracts were consistently intermediate between the activities of mesophyll and bundle sheath extracts and extract-mixing experiments gave no indication of enzyme activation or inhibition in vitro. Whole leaf activities were several hundred-fold less than concurrent measurements of ribulose 1,5-bisphosphate and phosphoenolpyruvate carboxylase activities, which is interpreted as being consistent with the relative amounts of elemental carbon and sulfur found in higher plants. A hypothesis is presented for the intercellular compartmentation of sulfur assimilation in relationship to NO3− and CO2 assimilation in leaves of C4 plants.

Neutral ethanol-soluble sugar pools serve as carbohydrate reserves for Crassulacean acid metabolism (CAM) in pineapple (Ananas comosus (L.) Merr.) leaves. Levels of neutral soluble sugars and glucans fluctuated reciprocally with concentrations of malic acid. Hexose loss from neutral soluble-sugar pools was sufficient to account for malic acid accumulation with about 95% of the required hexose accounted for by turnover of fructose and glucose pools. Hexose loss from starch or starch plus lower molecular weight glucan pools was insufficient to account for nocturnal accumulation of malic acid. The apparent maximum catalytic capacity of pyrophosphate:6-phosphofructokinase (PPi-PFK) at 15°C was about 16 times higher than the mean maximum rate of glycolysis that occurred to support malic acid accumulation in pineapple leaves at night and 12 times higher than the mean maximum rate of hexose turnover from all carbohydrate pools. The apparent maximum catalytic capacity of ATP-PFK at 15°C was about 70% of the activity required to account for the mean maximal rate of hexose turnover from all carbohydrate pools if turnover were completely via glycolysis, and marginally sufficient to account for mean maximal rates of acidification. Therefore, at low night temperatures conducive to CAM and under subsaturating substrate concentrations, PPi-PFK activity, but not ATP-PFK activity, would be sufficient to support the rate of glycolytic carbohydrate processing required for acid accumulation. These data for pineapple establish that there are at least two types of CAM plants with respect to the nature of the carbohydrate reserve utilized to support nighttime CO2 accumulation. The data further indicate that the glycolytic carbohydrate processing that supports acidification proceeds in different subcellular compartments in plants utilizing different carbohydrate reserves.

The succulent, cylindrical leaves of the C 4 dicot Portulaca grandiflora possess three distinct green cell types: bundle sheath cells (BSC) in radial arrangement around the vascular bundles; mesophyll cells (MC) in an outer layer adjacent to the BSC; and water storage cells (WSC) in the leaf center. Unlike typical Kranz leaf anatomy, the MC do not surround the bundle sheath tissue but occur only in the area between the bundle sheath and the epidermis. Intercellular localization of photosynthetic enzymes was characterized using protoplasts isolated enzymatically from all three green cell types. Like other C 4 plants, P. grandiflora has ribulose 1,5-bisphosphate carboxylase and the decarboxylating enzyme, NADP + -malic enzyme, in the BSC. Unlike other C 4 plants, however, phosphoenolpyruvate carboxylase, pyruvate, Pi dikinase, and NADP + -malate dehydrogenase of the C 4 pathway were present in all three green cell types, indicating that all are capable of fixing CO 2 via phosphoenolpyruvate carboxylase and regenerating phosphoenolpyruvate. Other enzymes were about equally distributed between MC and BSC similar to other C 4 plants. The enzyme profile of the WSC was similar to that of the MC but with reduced activity in most enzymes, except mitochondrion-associated enzymes. Intracellular localization of enzymes was studied in organelles partitioned by differential centrifugation using mechanically ruptured mesophyll and bundle sheath protoplasts. Phosphoenolpyruvate carboxylase was a cytosolic enzyme in both cells; whereas, ribulose 1,5-bisphosphate carboxylase and NADP + -malic enzyme were exclusively compartmentalized in the bundle sheath chloroplasts. NADP + -malate dehydrogenase, pyruvate, Pi dikinase, aspartate aminotransferase, 3-phosphoglycerate kinase, and NADP + -triose-P dehydrogenase were predominantly localized in the chloroplasts while alanine aminotransferase and NAD + -malate dehydrogenase were mainly present in the cytosol of both cell types. Based on enzyme localization, a scheme of C 4 photosynthesis in P. grandiflora is proposed. Well-watered plants of P. grandiflora exhibit a diurnal fluctuation of total titratable acidity, with an amplitude of 61 and 54 microequivalent per gram fresh weight for the leaves and stems, respectively. These changes were in parallel with changes in malic acid concentration in these tissues. Under severe drought conditions, diurnal changes in both titratable acidity and malic acid concentration in both leaves and stems were much reduced. However, another C 4 dicot Amaranthus graecizans (nonsucculent) did not show any diurnal acid fluctuation under the same conditions. These results confirm the suggestion made by Koch and Kennedy (Plant Physiol. 65: 193-197, 1980) that succulent C 4 dicots can exhibit an acid metabolism similar to Crassulacean acid metabolism plants in certain environments.

The activity of pyrophosphate: d-fructose-6-phosphate-1-phosphotransferase (EC 2.7.1.90, PPi-PFK) in cotyledons and sprouts of germinating pea seeds ( Pisum sativum cv Alaska or Green Arrow) increases rapidly during the first 2 to 3 days after imbibition and then declines to a lower activity. The reaction toward fructose 1,6-bisphosphate formation is activated greatly by fructose 2,6-bisphosphate (fru 2,6-P 2 ); however, the sensitivity of the enzyme9s activity to fru 2,6-P 2 activation changes during germination. The cotyledon enzyme was partially purified and exists in two forms apparently with different molecular weights. The large form shows little sensitivity to fru 2,6-P 2 , while the small form shows a high sensitivity to this effector ( K a = 15 nanomolar). Gel filtration experiments indicate that fru 2,6-P 2 is involved in converting the small form into the large form. We propose that the interconversion of two forms of the PPi-dependent PFK by fru 2,6-P 2 is one mechanism for regulating glycolysis during seed germination.