Plant Amaranthus Research Articles

Light-dependent pH changes in leaves of C4 plants Comparison of the pH response to carbon dioxide and oxygen with that of C3 plants

Cytosolic and vacuolar pH changes caused by illumination or a changed composition of the gas phase were monitored in leaves of the NAD malic-enzyme-type C4 plant Amaranthus caudatus L. and the C3 plant Vicia faba L. by recording changes in the fluorescence of pH-indicating dyes which had been fed to the leaves. Light-dependent cytosolic alkalization and vacuolar acidification were maximal in the mesophyll cells under high-fluence-rate illumination and in the absence of CO2. Under the same conditions, measurements of light scattering and electrochromic absorption changes at 518 nm revealed maximum thylakoid energization. The results show an intimate relationship between the energization of the photosynthetic apparatus by light, an increase in cytosolic pH and a decrease in vacuolar pH. This was true for both the C4 and the C3 plant, although kinetics, extent and even direction of cytosolic pH changes differed considerably in these plants, reflecting the differences in photosynthetic carbon metabolism. Darkening produced rapid acidification in Vicia, but not in Amaranthus. Continued alkalization in Amaranthus is interpreted to be the result of the decarboxylation of a C4 intermediate and the release of liberated CO2. In the presence of CO2, energy consumption by carbon reduction decreased thylakoid energization, cytosolic alkalization and vacuolar acidification. Under low-fluence-rate illumination, thylakoid energization and light-dependent cytosolic and vacuolar pH changes were decreased in CO2-free air compared with thylakoid energization and pH changes in 1% oxygen/99% nitrogen not only in the C3 plant, but also in Amaranthus. Since oxygenation of ribulose bisphosphate initiates energy-consuming photorespiratory reactions in 21% oxygen, but not in 1% oxygen, this shows that photorespiratory reactions are active not only in the C3 but also in the C4 plant in the absence of external CO2. Photorespiratory conditions appeared to decrease energization not only in the chloroplasts, but also in the cytosol. This is indicated by decreased transfer of protons from the cytosol into the vacuole, a process which is energy-dependent.

Reflectance spectroscopy of fresh whole leaves for the estimation of chemical concentration

In an effort to further develop the methods needed to remotely sense the biochemical content of plant canopies, we report the results of an experiment to relate the concentrations of chlorophyll, protein, starch, sugar, amaranthin, and water in fresh whole leaves to their reflectance at wavelengths throughout the visible and near infrared. This is an analysis of laboratory data from a previously reported experiment (Curran et al., 1991) in which 163 freshly excised leaves of the plant Amaranthus tricolor were measured for reflectance and biochemical content. Stepwise regression was used to generate an equation for the estimation of chemical concentration from derivative reflectance in selected wavelengths. The reduction of instrument noise through Fourier filtering and a sample control procedure to minimize spectral overlap had little effect on the correlation between derivative reflectance in selected wavelengths and chemical concentration but did enable absorption features attributable to sugar and protein to be detected. However, the minimization of spectral overlap did increase the number of wavelengths attributable to known absorption features that were selected by stepwise procedures. Using only derivative reflectance in wavelengths that were attributable to absorption by the chemical of interest, the coefficients of determination (R 2) between estimated and measured concentrations of chlorophyll, amaranthin, starch, and water were 0.82 or above, with root-mean square errors that were 12.5% of the median or less.

ALLELOPATHIC CONTROL OF AMARANTHUS SPP. BY ALLIUM SPP.

The genus Amaranthus contains many species which are common weeds found on the Texas high plains. In a field experiment plant height and numbers of plants of Amaranthus varied when grown with different Allium genotypes: Allium fistulosum var. `Heshiko' and an interspecific F1 hybrid 81215 (Heshiko × A. cepa cv. `New Mexico Yellow Grano'). The genotypes that showed no allelopathic effect were A. cepa cv `New Mexico Yellow Grano', A. fistulosum var. `Ishikura', and their F1 hybrid 8273. On the basis of these observations experiments have been done to quantify the degree of suppression. A randomized complete block design was used under greenhouse conditions in order to measure growth characters of Amaranthus.

Control of photosynthesis by the carbohydrate level in leaves of the C4 plant Amaranthus edulis L.

Photosynthesis was studied in relation to the carbohydrate status in intact leaves of the C4 plant Amaranthus edulis. The rate of leaf net CO2 assimilation, stomatal conductance and intercellular partial pressure of CO2 remained constant or showed little decline towards the end of an 8-h period of illumination in ambient air (340 μbar CO2, 21% O2). When sucrose export from the leaf was inhibited by applying a 4-h cold-block treatment (1°C) to the petiole, the rate of photosynthesis rapidly decreased with time. After the removal of the cold block from the petiole, further reduction in photosynthetic rate occurred, and there was no recovery in the subsequent light period. Although stomatal conductance declined with time, intercellular CO2 partial pressure remained relatively constant, indicating that the inhibition of photosynthesis was not primarily caused by changes in stomatal aperture. Analysis of the leaf carbohydrate status showed a five- to sixfold increase in the soluble sugar fraction (mainly sucrose) in comparison with the untreated controls, whereas the starch content was the same. Leaf osmotic potential increased significantly with the accumulation of soluble sugars upon petiole chilling, and leaf water potential became slightly more negative. After 14 h recovery in the dark, photosynthesis returned to its initial maximum value within 1 h of illumination, and this was associated with a decline in leaf carbohydrate levels overnight. These data show that, in Amaranthus edulis, depression in photosynthesis when translocation is impaired is closely related to the accumulation of soluble sugars (sucrose) in source leaves, indicating feedback control of C4 photosynthesis. Possible mechanisms by which sucrose accumulation in the leaf may affect the rate of photosynthesis are discussed with regard to the leaf anatomy of C4 plants.

Biomass production and nitrate metabolism of Atriplex hortensis L. (C3 plant) and Amaranthus retroflexus L. (C4 plant) in cultures at different levels of nitrogen supply.

Pure and mixed cultures of the dicotyledons Atriplex hortensis L. (C3 plant) and Amaranthus retroflexus L. (C4 plant) were maintained under open air conditions in standard soil at low and high nitrogen supply levels.A comparison of shoot dry weight and shoot length in the various series shows that the growth of the aboveground parts of both species was severely reduced under low N conditions. In both pure and mixed cultures the differences resulting from low N vs. high N conditions was less pronounced with Atriplex (C3 plant) than with Amaranthus (C4 plant). The root dry weight of the two species was not reduced so much under low N conditions as was the shoot dry weight. The low N plants were found to contain a larger proportion of their biomass in the roots than did the high N plants. In general the root proportion of Atriplex was greater than that of Amaranthus. The contents of organic nitrogen and nitrate and the nitrate reductase activity (NRA) per g dry weight of both species decreased continually throughout the experiments. With the exception of young plants, the low N plants always had tower contents of organic nitrogen and nitrate and nitrate reductase activities than did the high N plants. The highest values of NRA were measured in the leaf laminae. The eaves also exhibited the highest concentrations of organic nitrogen. The highest nitrate concentrations, however, were observed in the shoot axis, and in most cases the lowest nitrate values were found in the laminae. At the end of ne growing season this pattern was found to have been reversed with Atriplex, but not with Amaranthus. Thus Atriplex was able to maintain a higher NRA in the laminae than Amaranthus under low N conditions.The transpiration per leaf area of the C4 plant Amaranthus during the course of a day was substantially lower than that of the C3 plant Atriplex. There were no significant differences in transpiration between the low N and high N series of Amaranthus. The low N plants of Atriplex, however, clearly showed in most cases higher transpiration rates than the corresponding high N plants. These different transpiration rates of the high N and the low N Atriplex plants were also reflected in a distinct 13C discrimination.The sum of these results points to the conclusion that the C3 plant Atriplex hortensis can maintain a better internal inorganic nitrogen supply than the C4 plant Amaranthus retroflexus under low N conditions and an ample water supply, due to the larger root proportion and the more pronounced and flexible transpiration of the C3 plant.

Acyl lipid synthesis by chloroplasts isolated from the chilling-sensitive plant Amaranthus lividus L

Mesophyll chloroplasts isolated from leaves of the chilling-sensitive C4 plant, Amaranthus lividus, exhibited high rates of light-dependent biosynthetic activities. Long-chain fatty acid synthesis from [1- 14C]acetate (up to 1.55 μmol of acetate incorporated/h per mg chlorophyll) and phosphatidylglycerol synthesis from phosphatidate were both strongly inhibited by the presence of Mg 2+ in incubation media. Phosphatidyl-glycerol synthesis in vitro was dependent upon exogenous. sn-glycerol 3-phosphate and CTP, and could account for up to 12%, whereas non-esterified fatty acids accounted for a minimum of 63% of incorporated acetate. Both phosphatidate and phosphatidylglycerol synthesised by A. lividus chloroplasts contained 84–88% saturated fatty acids and, therefore, were comprised of 68–76% disaturated molecular species. Non-esterified fatty acids, on the other hand, were comprised predominantly (75–80%) of oleate. In the absence of exogenous CTP, phosphatidate was hydrolysed to 1,2-diacylglycerol which was then converted to diacylgalactosylglycerol in the presence of UDPgalactose. A. lividus appears to synthesise highly saturated ‘prokaryotic’ glycerolipids because the chloroplast sn-glycerol-3-phosphate:acyl-acyl carrier protein acyltransferase does not discriminate between palmitoyl- and oleoyl-acyl carrier protein.

Characterization of Starch Granules from Waxy, Nonwaxy, and Hybrid Seeds ofAmaranthus hypochondriacusL.

Perisperm starch granules of the dicotyledonous plant Amaranthus hypochondriacus L. were prepared from two homozygous lines (WxWx and wxwx) and their hybrid (Wxwx). The hybrid line was obtained by natural hybridization. By Sephadex G-75 column chromatography of isoamylase-debranched starches, the amylose content of WxWx starch was 16.9%, that of Wxwx was 10.7, and wxwx was zero. SDS-polyacrylamide gel electrophoresis showed that starch granules from two genotypes (WxWx and Wxwx) contained a Wx protein (MW = 68,000) which was supposed to be a starch granule-bound starch synthase and was associated with amylose synthesis, as observed in nonwaxy maize. The intensities of the stained protein bands were apparently correlated with the number of the Wx alleles. The Wx protein was not detected in the wxwx starch. These findings suggest that the Wx allele produces the Wx protein and amylose in the perisperm of A. hypochondriacus, with incomplete dominance over the wx allele. The Wx allele did not affect the fine structure of amylopectin and had little if any effect on susceptibility to glucoamylase and pasting properties of starch granules from these genotypes.

Characterization of starch granules from waxy, nonwaxy, and hybrid seeds of Amaranthus hypochondriacus L.

Perisperm starch granules of the dicotyledonous plant Amaranthus hypochondriacus L. were prepared from two homozygous lines (WxWx and wxwx) and their hybrid (Wxwx). The hybrid line was obtained by natural hybridization. By Sephadex G-75 column chromatography of isoamylase-debranched starches, the amylose content of WxWx starch was 16.9%, that of Wxwx was 10.7, and wxwx was zero. SDS-polyacrylamide gel electrophoresis showed that starch granules from two genotypes (WxWx and Wxwx) contained a Wx protein (MW = 68,000) which was supposed to be a starch granule-bound starch synthase and was associated with amylose synthesis, as observed in nonwaxy maize. The intensities of the stained protein bands were apparently correlated with the number of the Wx alleles. The Wx protein was not detected in the wxwx starch. These findings suggest that the Wx allele produces the Wx protein and amylose in the perisperm of A. hypochondriacus, with incomplete dominance over the wx allele. The Wx allele did not affect the fine s...

The effect of low oxygen concentration on the acyl-lipid and fatty-acid composition of the C4 plant Amaranthus paniculatus L.

Acyl lipids and their constituent fatty acids were studied in leaves, chloroplasts and bundle-sheath strands of the C4 plant Amaranthus paniculatus L. grown under normal and 4%-oxygen-containing atmospheres. In all fractions the major lipids were found to be monogalactosyldiacylglycerol, digalactosyldiacylglycerol, sulphoquinovo-syldiacylglycerol and phosphatidylglycerol. Significant quantities of phosphatidylcholine and phosphatidylethanolamine were restricted to leaves and bundle-sheath strands. All lipids, except phosphatidylglycerol where 3-trans-hexadecenoic acid was also present, contained palmitic acid, stearic acid, oleic acid, linoleic acid and linolenic acid. On a chlorophyll basis and compared with whole leaves, the amounts of phosphatidylcholine and phosphatidylethanolamine in bundle-sheath strands were considerably reduced. Three weeks after the change from a normal to a 4% atmospheric O2 level, the galactolipid content, particularly in the bundlesheath strands, was enhanced. There were no significant differences in the degrees of saturationunsaturation of total acyl lipid for the plants grown in the low oxygen and normal atmospheres, although under 4% O2 the phosphatidylglycerol contained an increased proportion of 3-trans-hexadecenoic acid at the expense of palmitic acid.

Conversion of mature leaves into sinks on the dicotyledonous C4 plants Amaranthus caudatus and Gomphrena globosa

The effect of an artificially created sink leaf on translocation of 14C-labeled assimilates from a source leaf of the C4 plants Amaranthus caudatus L. and Gomphrena globosa L. was studied with autoradiography. Anatomical studies showed that the vasculature of two successive leaves within a given orthostichy is directly connected by stem bundles. Therefore, in an intact plant, much of the acropetally translocated 14C-labeled assimilates from a mature source leaf moved into the next younger leaf directly above. When such a young leaf on an otherwise illuminated plant was kept under sink conditions (dark, CO2-free air), its increased sink demand resulted in a clearly higher 14C-import, compared with a control. Even a mature leaf of Gomphrena subjected to the similar sink conditions developed sufficient sink demand to import a certain amount of basipetally transported 14C-labeled assimilates from a younger source leaf. In Amaranthus, there was no basipetal translocation from a younger source leaf and, consequently, no 14C-import into a mature leaf under sink conditions occurred. A complete conversion of a mature leaf into a sink was attained only with a pruned source–sink transport system of both plants under source and sink limitation. This conversion from the source to the sink status caused a change in the direction of assimilate flow within the petiolar and stem bundles. The data indicate that a mature leaf under sink conditions can be characterized as a sink with regard to assimilate translocation, although no growth or storage processes are involved in controlling this sink activity.

Biomass production of C3- and C4-plant species in pure and mixed culture with different water supply.

Pure and mixed cultures of the dicotyledons Atriplex hortensis L. (C3 plant) and Amaranthus retroflexus L (C4) on the one hand and of the grasses Avena sativa L (C3) and Panicum miliaceum L. (C4) on the other hand were maintained in a standard soil with different ground water tables. After 12 weeks the length, dry weight and nitrogen-content of the aboveground and belowground parts of the plants, and in addition the carbon-and ash-content and the δ13C value of the aboveground parts were determined. It turned out that the length and the dry weight of the shoots of the C3 species showed on increasing tendency with increased water supply, while the values of the C4 species were drastically diminished at the highest water level only. The roots showed in most cases an increased length and dry weight at drier conditions, more pronounced in the C4 than in the C3 species. The nitrogen content of the shoots was mostly higher in the shoots of the C3 plants and in the roots of the C4 plants; it changed in a non-regular manner with variations in water supply. Since the carbon content did not change markedly, the C/N ratio was variable. There was a slight tendency for a higher carbon content and mostly also for a higher C/N-ratio in the shoots of C4 plants. The δ13C values of both C3 as C4 plants were in general not at all influenced by the water supply; they were fixed genetically. The ash content of the analyzed species did not show a clear relationship to the type of photosynthetic CO2-fixation or to the water regime.The influence of light intensity was studied with mixed cultures of all four plant species, again with different water supply. There was a strong effect of light intensity on the competitive behaviour of the C3 and C4 plants under modified water conditions. The wild C3 plant Atriplex hortensis was most successful under conditions of relatively low light intensity and high water availability, while the cultivated 'artificial' species Avena sativa showed much less differences between full-light grown and shadow plants. The C4 plant Amaranthus retroflexus is most successful under competitive conditions at high water stress in full light. The C4 grass Panicum miliaceum showed maximum shoot growth in light, but was successful under competitive conditions especially also with good water supply. The light intensity had no effect on the δ13C values. - There was no indication that the soil-type as such has a distinct influence on the success of C3 or C4 plants in mixed cultures.

Oxygen Exchange in Leaves in the Light

Photosynthetic O(2) production and photorespiratory O(2) uptake were measured using isotopic techniques, in the C(3) species Hirschfeldia incana Lowe., Helianthus annuus L., and Phaseolus vulgaris L. At high CO(2) and normal O(2), O(2) production increased linearly with light intensity. At low O(2) or low CO(2), O(2) production was suppressed, indicating that increased concentrations of both O(2) and CO(2) can stimulate O(2) production. At the CO(2) compensation point, O(2) uptake equaled O(2) production over a wide range of O(2) concentrations. O(2) uptake increased with light intensity and O(2) concentration. At low light intensities, O(2) uptake was suppressed by increased CO(2) concentrations so that O(2) uptake at 1,000 microliters per liter CO(2) was 28 to 35% of the uptake at the CO(2) compensation point. At high light intensities, O(2) uptake was stimulated by low concentrations of CO(2) and suppressed by higher concentrations of CO(2). O(2) uptake at high light intensity and 1000 microliters per liter CO(2) was 75% or more of the rate of O(2) uptake at the compensation point. The response of O(2) uptake to light intensity extrapolated to zero in darkness, suggesting that O(2) uptake via dark respiration may be suppressed in the light. The response of O(2) uptake to O(2) concentration saturated at about 30% O(2) in high light and at a lower O(2) concentration in low light. O(2) uptake was also observed with the C(4) plant Amaranthus edulis; the rate of uptake at the CO(2) compensation point was 20% of that observed at the same light intensity with the C(3) species, and this rate was not influenced by the CO(2) concentration. The results are discussed and interpreted in terms of the ribulose-1,5-bisphosphate oxygenase reaction, the associated metabolism of the photorespiratory pathway, and direct photosynthetic reduction of O(2).

Lichtabhängige CO-Bildung grüner Pflanzen und ihre Bedeutung für den CO-Haushalt der Atmosphäre

Using a Siemens U 180 process gas chromatograph the CO content of the atmosphere has been recorded over several days at three sites of medium to low pollution by automobile traffic. At CO-concentrations observed in these measurements a plant of Nerium oleander L. did not reduce CO levels in an experimental gas atmosphere but consistently evolved an additional small amount of CO in the light. Light dependent CO net production was also observed with Vicia faba L. and with the C 4 plant Amaranthus paniculatua L. Increased O 2 concentration stimulated CO evolution in all of the three species; it highly reduced CO 2 net uptake in the C 3 species Nerium oleander L. and Viciafaba L., but as expected only slightly affected CO 2 uptake in the C 4 plant Amaranthus paniculatua L. CO evolution is much stimulated by increased temperature in all the three species. These results show that light dependent CO net evolution is closely correlated with photorespiration. A scheme of the possible reactions of CO metabolism in green leaves suggests that CO could be a by-product of photorespiration, where CO may be formed either after direct oxidative decarboxylation of glyoxylate or during formation of one molecule of serine from two molecules of glycine. The biological significance oflight dependent CO formation in leaves is not clear. The evolution of minimal amounts of CO (CO net evolution: CO 2 net uptake ≃ 25 × 10 −6 mole/mole in the three species investigated) may be just a, n unavoidable consequence of reaction equilibria during photorespiratory carbon flow.

Effect of Low Oxygen Partial Pressure during Growth on the Metabolism of Aspartic Acid and 3-Phosphoglyceric Acid in Leaves of the C4 Plant Amaranthus paniculatus

Differences in carbon metabolism between leaves of Amaranthus paniculatus plants grown for 40 days in atmospheres containing 4% or 21% oxygen are observed in kinetic 14 C 2 -feeding experiments on attached leaves during steady-state photosynthesis. Water-soluble leaf constituents were extracted from a defined area and the radioactivity and amount of certain metabolites measured. The basic difference was twice as much incorporation of 14 C-radioactivity into the pool of aspartic acid after 15 min of 14 CO 2 -fixation in 4% O 2 . This 14 C-accumulation in the pool of aspartic acid was observed even after 2 min. After growth at low oxygen partial pressure the amount of aspartic acid and glycerate-3-phosphate (3-PGA) increases twofold. As judged on the base of relative specific activities (per cent of the feeding gas specific activity in dpm μ g − 1 carbon) reached after 15 min of 14 CO 2 -feeding nearly the total pool of aspartic acid is actively metabolised at both oxygen concentrations, whereas the entire amount of 3-PGA seems to be subdivided in at least two compartments differing largely in the turnover rates. The possible modes of the pool size changes of the two important metabolites as well as an “in vivo” inhibition of phosphoenolpyruvate carboxylase activity are discussed.

Light-Enhanced Dark 14CO2 Fixation by Leaves in Relation to the C4 Dicarboxylic Acid Pathway of Photosynthesis

The technique of light-enhanced dark carbon dioxide fixation has been employed to critically examine the primary route of CO2 incorporation in leaves of two C4 plants (Setaria italica and Amaranthus paniculatus) in comparison with that of a C3 plant (Rumex vesicarius). Prior illumination of detached leaves enhanced their dark 14CO2 fixation five- to tenfold over that of unilluminated leaves. No variation was observed among C3 and C4 plants, in the conditions required for their light-enhanced dark fixation. Fifty to sixty percent of initially incorporated radioactivity by the leaves of R. vesicarius was in 3-phosphoglycerate. The leaves of S. italica and A. paniculatus fixed most of the radioactivity into the C4 acids malate and aspartate. Sugar phosphates, including 3-phosphoglycerate, were not labelled at all. Our data confirm that, in C4 plants, CO2 is initially fixed through phosphoenolpyruvate carboxylation and thus disprove earlier claims that ribulose bisphosphate can be the primary acceptor of CO2 in a C4 plant. The observations further suggested that aspartate formation during carbon fixation might be favoured by illumination.

NAD malic enzyme in leaves with C 4-pathway photosynthesis and its role in C 4 acid decarboxylation

Decarboxylating NAD-malate dehydrogenase (NAD-malic enzyme, NAD-ME, EC 1.1.1.39) has been investigated under a long-term drought during pre-anthesis, anthesis and seed-formation phases of ontogenesis of a NAD-ME type C4 plant Amaranthus cruentus L. using cytosol, chloroplast and mitochondrial fractions of mesophyll (M) and bundle sheath (BS) cells. We detected several molecular forms of NAD-ME with different subcellular localization patterns in the studied phases of amaranth ontogenesis. However, no enzyme activity was observed experimentally in chloroplasts of M and BS cells. In the pre-anthesis phase NAD-ME isoform with molecular weight of ∼115 kDa was found in cytosol of M and BS cells of control and drought-exposed plants. One of NAD-ME isoforms with molecular weight of 110 kDa was located in mitochondria of BS cells of control and drought-exposed plants, and a new isoform of ∼121 kDa was formed in mitochondria of BS cells under the influence of drought. After resuming watering this isoform (∼121 kDa) disappeared again. Approximately 90.6% and 9.4% of the total NAD-ME activity were localized in mitochondrial stroma and cytosol of BS cells, respectively, while in mesophyll cells 100% activity was found in cytosol fractions. The reaction catalyzed by NAD-ME follows Michaelis–Menten equation. NAD+, l-malate and Mn2+ activate this enzyme in mitochondria. Appearance of the ∼121 kDa isoform of NAD-ME in the mitochondrial fraction of BS cells under drought and its disappearance after resuming watering could be attributed to one of the protection functions of plants.

Light-induced changes in the content of some enzymes of the C 4-dicarboxylic acid pathway of photosynthesis and its effect on other characteristics of photosynthesis

Various effects of light and light-intensity on the content of several photosynthetic enzymes were examined. Included amongst the enzymes were, pyruvate, P i dikinase, phosphopyruvate carboxylase, adenylate kinase and alkaline pyrophosphatase, enzymes believed to have specific roles in the C 4-dicarboxylic acid pathway of photosynthesis. Maize and Amaranthus plants were grown at high or low light intensities for prolonged periods and their enzyme contents examined before and after transfer of high-light-grown plants to low light or vice versa. Ribulose 1,5-diphosphate carboxylase activity was unaffected by these treatments, but the contents of glyceraldehyde 3-phosphate dehydrogenase, adenylate kinase and pyrophosphatase were approximately 2 fold higher and pyruvate, P i dikinase and phosphopyruvate carboxylase between 5- and 10-fold higher in plants grown at the higher light intensities. During the 6 days following changes in the light regime the enzyme contents adapted almost completely to the new light conditions. These changes in enzyme activities were accompanied by changes in maximum photosynthesis rates and light-saturation characteristics of leaves. However studies with 14CO 2 provided no evidence for significant changes in the pathway of photosynthesis operative in these leaves. Other studies showed that the content of these and other photosynthetic enzymes were low in the leaves of maize plants germinated and grown in the dark but increased up to 15-fold, together with chlorophyll, following transfer of plants to the light for 35 hr. The possible regulatory significance of these findings are discussed.

Light and electron microscopy of virus inclusions in Amaranthus lividus cells.

Amaranthus plants infected with a virus of rod-shaped particles showed under the light microscope intracytoplasmic amorphous and crystalline inclusions.

DIURNAL FLUCTUATIONS IN THE MOISTURE CONTENT OF SOME HERBACEOUS PLANTS

1DIURNAI FLUCTUATIONS in the moisture content of the leaves of many plants have been reported by numerous workers including Lloyd (1913), Shreve (1914), Miller (1917), Metzger et al. (1925), and Hawkins (1927). Data from experiments reported by Kramer (1937) on changes in the moisture content of leaves confirm an observation of Miller that the maximum moisture content of the leaves of some herbaceous plants was reached during the middle of the night. It was also observed that the moisture content of the leaves of certain plants reached a peak early in the evening, declined towards 2 a.m. and then reached another peak towards sunrise. Although the data were not analyzed statistically, this trend was thought to be real. A review of the literature did not reveal any experiments performed to determine whether there are fluctuations in the moisture content of the plant as a whole. It was believed that simultaneous determinations of the moisture content of the roots, stems, and leaves of a group of plants over the course of a day might indicate whether the various plant organs maintain the same relative moisture content and react as a whole to the loss of water by transpiration, or whether internal factors might cause different reactions in the various organs of the plant. MET'IIODS.-Herbaceous species were used since it was felt that their large water content would allow the greatest possible daily fluctuation. Sunflower (Helianthus annuus L.) and amaranthus (Amaranthus spinosus L.) were the species employed. Experiments were performed during two summers, when a sufficient number of field grown plants of amaranthus and of sunflower were available to provide material for 6 groups of experiments. When the plants were approximately 7 weeks old and between 3 and 4 ft. in height, they were divided at random, by the use of Tippet's numbers, into thirteen groups of six plants each. Since moisture determinations were to be made every 2 hr. for 26 hr., each group represented the plants that were to be used foronedetermination. When it was believed that a clear day, which would approximate standard day conditions with a maximum temperature of 30350C., was at hand, the soil in which the plants were growing was thoroughly watered in the evening and the experiments started at 6 a.m. the following rnorning. Root, stem and leaf samples were taken every 2 hr. until 6 a.m. the following morning. The six plants, which constituted a sample, were