Xantha Mutants Research Articles

MUTAGENICITY OF SOME COMMON PESTICIDES IN BARLEY

The perusual of literature reveals the desirability to screen the mutagenicity of pesticides. The present report deals with the cytological aberrations and chlorophyll mutations induced by Thiodan, Folithion, Lebaycid and Kitazin, employing barley as the test material. The chromosomal aberrations were examined both at mitotic and meiotic level. The root tip cells from pesticide treated barley grains revealed various abnormalities at metaphase including fragmentation, unequal chromosome, chromosomes with displaced satellite and increased number of chromosome. The laggards, bridges, tripolarity, tetrapolarity and micronuclei were seen at later stages. A positive correlation between dose and aberration was noticed. The meiotic analysis of PMC's from plants raised from pesticide treated barley grains, revealed quadrivalents and univalents at metaphase-I. Anaphase-I was atypical in having unequal distribution, laggards, bridges — single or double. The persistent bridges at telophase and micronuclei were not unfrequent. The pollen fertility was reduced. — M2 analysis at the seedling stage revealed albina, xantha and tigrina mutants. The tigrina's were more frequent. Lebaycid was the most effective while Thiodan was the most efficient.

Polypeptide composition of thylakoids from viridis and xantha mutants in barley

The chloroplast membrane proteins from four recessive nuclear gene mutants of barley were studied with sodium dodecyl sulfate gel electrophoresis. The protein patterns of two mutants,xantha-b 12 andviridis-zd 69, consist of a summation of the polypeptides present in the chloroplast and etioplast membranes of the wild type. The pattern ofviridis-c 12, a mutant deficient in photosystem II activity was lacking two bands, one of which is considered to be a component of the reaction center of photosystem II. The pattern ofviridis-k 23 lacked three chloroplast specific bands, two of which are components of chlorophyll-protein complex II. The results are discussed in relation to previously established functional and structural characteristics of the mutant plastids.

The Growth and Photosynthetic Activity of Artificial Chlorophyll Mutants in Rice Plant

In artificial chlorophyll mutants (albina, xantha, viridis, striata and tigrina) of rice and their parent, a cultivar, Norin-8 (0ryza.sativa L.), several growth and photosynthetic parameters were measured and compared with each other. The following results were obtained: (1) Albina (CM-33, CM-35 and CM-53) and xantha (CM-123 and CM-213) mutants possessed no chlorophylls except for CM-123, one of xantha mutants with a small amount of chlorophyll. These mutnats including CM--123 were lethal after the fourth leaf stage. Viridis (MGS-359, MGS-859 and CMV-44) and tigrina (M-501) mutants were survival, but their dry weights and ear weights were less than their parent, normal rice plant (Norin-8). The other strains, M-516 (striata) and M-511 (viridis), showed almost normal growth patterns. (2) The chlorophyll contents of three viridis strains (MGS-359, MGS-859 and CMV-44) were about half or below of the normal type, especially deficient in chlorophyll b. The ratio of chlorophyll a to b in these viridis types was 9-20 as compared with about 3 in the normal. Also, they showed the higher levels of carotenoid than the normal plants. (3) 0n a chlorophyll basis, three viridis strains have about 1.7 to 3.0 times higher net photosynthetic rate than leaves of the normal rice. The photosynthetic rate on a leaf area basis was the same or slightly low for mutant and normal leaves. Also, the Hill reaction activities on a chlorophyll basis in the Chloroplast suspensions from mutant leaves were about 2 times of normal. The high net photosynthetic rate seems to be directly related to the lower chlorophyll contents of the mutant leaves. (4) The leaf blade in three viridis strains had a reduced thickness compared with normal plants and their spectral absorbance was below that of the normal leaves throughout the visible spectrum, especially in near 550, 600, and 650 nm

Distribution Patterns of Allagochrome, Chlorogenic Acid, and Capacity for Secondary Synthesis of Allagochrome

Allagochrome is a blue-green, water-soluble pigment found in alkaline extracts of many plant species. Unique properties of allagochrome are its color changes in response to oxidation and reduction (blue-green to yellow) and to changes in pH (blue-green to red). Some plant materials exhibit the phenomenon of secondary synthesis (i.e., increased yields of allagochrome when chlorogenic acid is added during extraction). To determine whether allagochrome (A), chlorogenic acid (C), and capacity for secondary synthesis (S) always occur together or can be found independently, over 200 plant species were assayed for these factors. Because each factor can be either positive or negative, there are in all eight possible descriptive categories with respect to these components The assay data show that every category is represented among the species tested. The two most numerous categories are A+ C+ S+ and A- C- S-. Mutants can differ from their wild types with respect to these factors. Wild-type Helianthus annuus leaves are A+ C+ S+, while xantha mutant leaves are A- C+ S+ and albina leaves are A- C- S-. Also, other parts of a plant can differ from leaves in their assay values; wild-type sunflower stems and roots are A- C- S+. Because these factors are descriptive characteristics for both species and larger plant taxa, they are potentially useful for studies of chemical taxonomy.

THE GROWTH OF BARLEY MUTANTS AT THE XAN‐B AND XAN‐C LOCI IN THE PRESENCE OF SUCROSE OR l‐LEUCINE IN THE GROWTH MEDIUM

SUMMARYThe effects of additions of leucine or sucrose to the medium on which chlorotic barley mutant seedlings developed were examined and compared with those of corresponding green segregants. These additions often raised their fresh weight to that of the green segregants grown on basal medium; their protein content was also higher. Although the chlorophyll content of the mutants Xan‐b15,18 and Xan‐c23 was increased, it remained substantially below that of the green segregants; that of the mutants Xan‐b22 and Xan‐b54 did not increase.In addition to these abnormal growth characteristics, the soluble amino acid pools of the mutants grown on all media and of green segregants grown on leucine medium showed characteristics of chlorotic growth with high levels of aspartic acid and asparagine; these levels were less marked in the mutants which responded to sucrose supplementation.Levels of ribulose‐1,5‐diphosphate carboxylase remained substantially below those of the green segregants irrespective of the medium supplementation. It was concluded that while these Xantha mutants of barley responded to leucine and sucrose supplementation, this response was different from the pattern associated with strictly auxotrophic growth.

Evidence for Two Photoreactions and Possible Involvement of Phytochrome in Light-dependent Stomatal Opening

Leaves of the xantha mutant of Helianthus annuus have a higher rate of transpiration and a lower diffusive resistance in the light than in the dark. Stomates of this nonphotosynthetic mutant open in the light and close in the dark.Comparative studies of tobacco, xantha mutant, and wild-type sunflower stomatal opening over a range of light intensities in isolated portions of the spectrum reveal two patterns of response: (a) a low intensity opening in the green and far red characterized by partial opening, absence of a threshold, and saturation of the response at low light intensities; (b) a high intensity response in the blue characterized by a threshold (intensities greater than 100 microwatts per square centimeter needed for opening) and a linear opening response at higher incident light intensities. In xantha mutant stomates only the low intensity system appears to be operational, while both low and high intensity systems are present in the wild-type sunflower and tobacco.Red light has an inhibiting effect on stomatal opening in both mutant and wild-type sunflowers. They require prior exposure to far red for opening to occur in red light. This redfar red antagonism suggests the involvement of phytochrome.

Defective synthesis of porphyrins in barley plastids caused by mutation in nuclear genes

Seedlings of certain lethal chlorophyll mutants in barley accumulate precursors of protochlorophyllide upon feeding with δ-aminolevulinate in the dark. The porphyrins accumulated in these mutant shoots and their wild types have been identified by thin-layer chromatography and spectroscopy. Mutants at three xantha loci and one albina locus accumulate mainly protoporphyrin. Mutants at two other xantha loci accumulate, in addition to protoporphyrin, uroporphyrin or magnetism protoporphyrin and its monomethyl ester, respectively. A new method for the quantitative determination of porphyrins in mixtures, utilising regression analysis of the spectra, is described. The total amount of porphyrins accumulated by the shoots of any one of the xantha mutants fed δ-aminolevulinate is the same as the wild type; the albina mutant accumulates less. About 90% of the porphyrin produced in the wild type is protochlorophyllide and the rest protoporphyrin. In mutants at the xan-f, xan-g, xan-h and alb-e loci, 80–97% of the total accumulated porphyrins is protoporphyrin and 3–20% protochlorophyllide. The mutant xan-u 21 produces 35% of the total prophyrins as uroporphyrin, whereas xan-l 35 accumulates 48% as magnesium protoporphyrins. None of the mutants is absolutely blocked in protochlorophyllide synthesis when fed δ-aminolevulinate. It is concluded that mutations in the nuclear genes xan-f, -g and -h of barley block the early steps between protoporphyrin and protochlorophyllide. The mutant xan-l 35 has a metabolic block after magnesium protoporphyrin monomethyl ester, whereas the more pleiotropic mutant xan-u 21 contains a major lesion in the pathway between uroporphyrin and protoporphyrin. The latter mutant is also deficient in the conversion of protoporphyrin to protochlorophyllide as well as in carotenoid synthesis. Besides a general reduction in porphyrin and carotenoid synthesis, alb-e 16 has a specific block in the conversion of protoporphyrin to protochlorophyllide. On the basis of a comparative survey of mutants accumulating chlorophyll precursors in photosynthetic organisms, it is suggested that the chlorophyll-synthesising enzymes of algae and seed-plants occupy at least two compartments in the chloroplast: one containing the enzymes converting δ-aminolevulinate to protoporphyrin and the other forming protochlorophyllide from protoporphyrin. The mutants provide evidence that in seed-plants every intermediate in chlorophyll synthesis can regulate the formation of δ-aminolevulinate, whereas in algae only protochlorophyllide and chlorophyll can be ascribed such a function.

The nature of the leucine requirement of the barley mutant Xan-b61.

SUMMARYContrary to previous reports, evidence has been presented which indicates that Xan-b61, a Xantha mutant of barley, does not have an auxotrophic requirement for leucine. It has been shown that this mutant, when grown under appropriate conditions in the absence of leucine, will synthesize leucine and will continue to grow for an extended period of time.

On the Presence of Para-Crystalline Formations in the Cytoplasm of a Maize Albino Mutant

Seeds of « Bagnolo » variety of maize, exposed to gamma radiation with a dose of 2.104r, gave rise to plants wich by self-fertilisation produced a X2-generation wich included: thoroughly green seedlings, albino seedlings which before maturity died, and of light-green or variegate seedlings, the latter interpretable as heterozigous (cfr. BERTONE 1964).For the present research, mutant albino seedlings obtained from seeds of heterozigous X2-plants, and control seedlings obtained from seeds of normal maize plants, were used.Using the electron microscope it was possible to observe in the mutant cytoplasm the presence of paracrystalline structures with a periodicity of about 120A. The paracrystals were not limited by membrane, were preferably localized close to the nucleus, and can be considered as protein crystals. These crystals were found in a mutant with altered plastid morphology, similar to those described previously for albina or xantha mutants. The accumulation of these crystals may be caused by a defect in the utilization of certain compounds by the abnormal chloroplasts.

Comparisons of Phosphate, Carbohydrate, and Kjeldahl Nitrogen Content of Normal and Xantha Mutant Leaves of Helianthus annuus

AbstractTissues of the xantha mutant of Helianthus annuus have an abnormally high phosphorus content compared to normally pigmented tissues of comparable age and position on the plant. A major portion of the observed differences can be accounted for in the acid‐insoluble “7‐minute” phosphate fraction, a fraction thought to be composed primarily of polyphosphates. Although this suggests that the xantha mutant may possess a mechanism for immobilizing excess phosphates as insoluble polymers, all qualitative tests for polyphosphates in extracts of mutant leaves have been negative.Carbohydrate levels in the mutant are lower than in wild type leaves due to the absence of photosynthesis in the mutant and its inability to form starch. Differences between mutant and wild type in Kjeldahl nitrogen appear to be a consequence of aging effects resulting from propagation by grafting onto physiologically older stocks.

Lipid biosynthesis in chloroplast mutants of barley

The capacity of leaf slices from light-grown seedlings of wild type barley and 10 xantha mutants at six different gene loci to incorporate acetate-(14)C into various lipids has been investigated. The fatty acid composition of the leaf lipids in these lethal mutants was similar to that of the wild type, but the fatty acid labeling pattern in the individual lipid classes can be drastically altered by these mutations, which affect chloroplast differentiation. A genetic block in chlorophyll synthesis, caused by mutations in the xan-f locus, leads to a repression of the formation of chloroplast membranes and of acetate incorporation into phospho-, sulfo-, and galacto-lipids (the acetate being preferentially channeled into a lipid fraction containing steroids and free fatty acids). Two leucine "auxotrophs" at different loci, which in the absence of leucine in the growth medium produce giant grana and accumulate some chlorophyll, differed considerably in the amount of labeling of their polar lipids during incubation. Leaves of xan-a(11), containing plastids with little chlorophyll, highly disorganized membrane systems, and large bodies with osmiophilic deposits, were nonetheless equal to wild type in their capacity to incorporate acetate-(14)C into phospho-, sulfo-, and galacto-lipids. The mutants at the xan-m locus have plastids with undispersed prolamellar bodies and osmiophilic packages of grana-like membranes associations. Leaf slices of these mutants synthesized considerably more linolenic acid-(14)C, which was incorporated into monogalactosyl diglycerides, than did slices of the wild type. This led to a labeling pattern of the fatty acids in the monogalactolipids which was remarkably similar to their endogenous fatty acid composition.

Allagochrome II. Effects of Light and Substrate on Allagochrome and Chlorogenic Acid Levels of Incubated Sunflower Leaf Discs

Sunflower leaf discs incubated in the light on carbohydrate substrates exhibit several-fold increases in amounts of extractable allagochrome and chlorogenic acid. These changes are linear with time, and oxygen is required. The light effect saturates at approximately 600 muW/cm(2) "white" light, roughly the compensation point for photosynthesis. Red light is as effective as white light. Incubation in the dark, or in far red light, produces negligible changes in allagochrome and chlorogenic acid content.Sucrose (0.2 m) has been used as the standard substrate. At this concentration, glucose and fructose are slightly more effective. The optimum temperature range for incubation is 20 to 30 degrees . Allagochrome and chlorogenic acid values of both light and dark incubated samples decrease between 30 and 50 degrees , approaching zero at 50 degrees . Net light effects decrease to zero between 40 and 50 degrees .Of the inhibitors tested, 2,4-dinitrophenol, hydroxylamine and salicylaldoxime have no effect on light enhanced allagochrome and chlorogenic acid values except at high concentrations (which are generally deleterious to leaf tissues and cause decreased values for both dark and light incubated samples). Net light effects are completely inhibited, without changes in values of dark incubated discs, by azide (0.1 to 1 mm) and dichlorophenyldimethylurea (1 to 10 mum).Leaf tissues from the xantha mutant of Helianthus annuus do not exhibit a light effect. The absence of light effects in nonphotosynthetic leaf tissue and the inhibiting effects of photosynthetic poisons suggest that the photosynthetic apparatus is somehow involved.An hypothesis for light regulated metabolism via phenolic synthesis is discussed.