Characterization of a calcium/calmodulin-dependent protein kinase homolog from maize roots showing light-regulated gravitropism

Roots of many species respond to gravity (gravitropism) and grow downward only if illuminated. This light-regulated root gravitropism is phytochrome-dependent, mediated by calcium, and inhibited by KN-93, a specific inhibitor of calcium/calmodulin-dependent protein kinase II (CaMK II). A cDNA encoding MCK1, a maize homolog of mammalian CaMK, has been isolated from roots of maize (Zea mays L.). The MCK1 gene is expressed in root tips, the site of perception for both light and gravity. Using the [³⁵S]CaM gel-overlay assay we showed that calmodulin-binding activity of the MCK1 is abolished by 50 M KN-93, but binding is not affected by 5 M KN-93, paralleling physiological findings that light-regulated root gravitropism is inhibited by 50 M KN-93, but not by 5 M KN-93. KN-93 inhibits light-regulated gravitropism by interrupting transduction of the light signal, not light perception, suggesting that MCK1 may play a role in transducing light. This is the first report suggesting a physiological function for a CaMK homolog in light signal transduction.Abbreviations CaM calmodulin - CaMK (II) Ca²⁺/calmodulin-dependent protein kinase (II) - CBP CaM-binding protein - CDPK Ca²⁺-dependent protein kinase - MCK1 maize homolog of mamalian CaMK This work is supported by the National Aeronautics and Space Administration grant No: NAGW 238.     

Relationship of photocarotenogenesis to other behavioural and regulatory responses inPhycomyces

The effect of light on carotene accumulation was studied by analyzing the -carotene content of 4--old mycelia continuously exposed to illumination of different intensities. The wild-type, mutants defective in phototropism, mutants defective in carotene regulation, and newpic mutants specifically defective for photocarotenogenesis were examined. The results indicate that photocarotenogenesis depends on a single sensory pathway which shares its earlier steps (governed by genesmadA andmadB) with the sensory pathway for phototropism. It shares its later steps (probably governed by genescarA andpicB) with one of the pathways for carotene regulation, and includes at least one specific step (governed by genepicA) not known to be involved in other responses.     

Light dependence of sexual agglutinability in Chlamydomonas eugametos

The mating activity of mating-type plus gametes of Chlamydomonas eugametos depends on light. Cells lost their ability to agglutinate with mating-type minus gametes after a dark period of 30 min. They regained their agglutinability after 10 min exposure to light. Other mating reactions, such as tipping and flagellar tip activation, were not dependent upon light. Since cycloheximide and tunicamycin did not affect the light-induced activation of flagellar agglutinability, no protein synthesis or glycosylation is involved in this process. Equal amounts of biologically active agglutination factor could be extracted from cells placed either in light or in darkness. A minor portion of the active material was found to be located on the flagellar surface of illuminated cells. No active material was found on the flagellar surface of dark-exposed cells, whereas their cell bodies contained the same amount of active material as the cell bodies of illuminated cells. Since a light-induced flow of agglutination factors from the cell body to the flagella could not be detected and dark-exposed cells could be slightly activated by amputation or fixation by glutaraldehyde, we propose that light affects flagellar agglutinability by an in-situ modification of the agglutination factor on the flagella. When mt ⁺ and mt ^- strains were crossed and the progeny examined for light-sensitivity, it was apparent that this phenomenon is not mating type-linked.Abbreviations and symbols FTA flagellar tip activation - mt ^+/- mating type plus or minus - WGA wheat-germ agglutinin     

Distribution of growth regulators in relation to the light-induced geotropic responsiveness in Zea roots

Growth regulators were measured in extracts from the upper and lower halves of 7-mm apical segments of horizontally oriented, red-light-irradiated and non-irradiated roots of Zea mays L. cv. Golden Cross Bantam 70 which exhibit a georesponse only after an exposure to light. Abscisic acid (ABA) was measured by gas-liquid chromatography, auxin (indole-3-acetic acid, IAA) by the Avena straight-growth assay, and an unidentified growth inhibitor by a Zea root-growth assay. The ratio of ABA in the upper and lower halves was 1.6 in the irradiated roots and 1.0 in the non-irradiated ones. The total amount of ABA after irradiation was increased by a factor of ca. 1.8. The ratio of IAA in the upper and lower halves of irradiated and non-irradiated roots was 1:3.4 and 1:2.9, respectively. The content (or activity) of an unidentified growth inhibitor was highest in the lower halves of horizontally oriented roots which had been irradiated with red light. The unidentified growth inhibitor, rather than IAA or ABA, may be the major factor in the light-induced geotropic responsiveness in Zea roots.     

The relationship between carbon-dioxide-limited photosynthetic rate and ribulose-1,5-bisphosphate-carboxylase content in two nuclear-cytoplasm substitution lines of wheat,and the coordination of ribulose-bisphosphate-carboxylation and electron-transport capacities

Photosynthesis in two cultivars of Triticum aestivum was compared with photosynthesis in two lines having the same nuclear genomes but with cytoplasms derived from T. boeoticum. The in-vitro specific activity of ribulose-1,5-bisphosphate carboxylase (RuBPCase; EC 4.1.1.39) isolated from lines with T. boeoticum cytoplasm was only 71% of that of normal T. aestivum. By contrast, the RuBPCase activities calculated from the CO₂-assimilation rate at low partial pressures of CO₂, p(CO₂), were the same for all lines for a given RuBPCase content. This indicates that both types of RuBPCase have the same turnover numbers in-vivo of 27.5 mol CO₂·(mol enzyme)^–1·s^–1 (23°). The rate of CO₂ assimilation measured at normal p(CO₂), p _a =340 bar, and high irradiance could be quantitatively predicted from the amount of RuBPCase protein. The maximum rate of RuBP regeneration could also predict the rate of CO₂ assimilation at normal ambient conditions. Therefore, the maximum capacities for RuBP carboxylation and RuBP regeneration appear to be well-balanced for normal ambient conditions. As photosynthetic capacity declined with increasing leaf age, the capacities for RuBP carboxylation and RuBP regeneration declined in parallel.Abbreviations PAR photosynthetically active radiation - RuBP(Case) ribulose-1,5-bisphosphate (carboxylase)     

Influence of light on the morphological changes that take place during the development of the <Emphasis Type="Italic">Flammulina velutipes</Emphasis> fruit body

We show that fruit bodies of Flammulina velutipes can be induced in complete darkness after a sharp temperature reduction (23° to 16°C). However, the fruit bodies that form in complete darkness have a long stipe with an undeveloped pileus on the top (pinhead fruit bodies) and are thinner and whiter than the normal fruit bodies which are formed in the light. This finding suggests that F. velutipes fruit bodies cannot mature in complete darkness. However, when we irradiated the fruit bodies that had formed in complete darkness, a pileus developed immediately, and 4 days later the separation between the stipe and the pileus could be observed. Immediately after light exposure, the stipe also thickened and became increasingly pigmented. The stipe elongation was inhibited until 8 days after light exposure, although stipe elongation progressed very quickly thereafter. Basidospores were also visible in the gills 8 days after light exposure. We consider that the basidiospore development is involved in this rapid stipe elongation, which aids the effective dispersal of basidiospores.     

The effect of transfer from low to high light intensity on electron transport in Rhodospirillum rubrum membranes

The effects of transfer from low to high ligh intensity on membrane bound electrontransport reactions of Rhodospirillum rubrum were investigated. The experiments were performed with cultures which did not form bacteriochlorophyll (Bchl) for about two cell mass doublings during the initial phase of adaptation to high light intensity. Lack of Bchl synthesis causes a decrease of Bchl contents of cells and membranes. Also, the cellular amounts of photosynthetically active intracytoplasmic membranes decrease.In crude membrane fractions containing both cytoplasmic and intracytoplasmic membranes the initial activities of NADH oxidizing reactions increase only slightly (about 1.2 times) per protein, but the initial activities of succinate oxidizing reactions decrease (multiplied by a factor of 0.7). On a Bchl basis activities of NADH oxidizing reactions increase 3.4 times while activities of succinate dependent reactions increase 1.9 times. With isolated intracytoplasmic membranes activities of NADH as well as succinate dependent reactions increase to a comparable extent on a Bchl basis (about 1.8 times) and stay nearly constant on a protein basis. Cytochrome c oxidase responds like succinate dependent reactions. The data indicate that in cells growing under the conditions applied NADH oxidizing electron transport systems are incorporated into both, cytoplasmic and intracytoplasmic membranes, while incorporation of succinate oxidizing systems is confined to intracytoplasmic membranes only.Activities of photophosphorylation and succinate dependent NAD⁺ reduction in the light increase per Bchl about 1.8 times. On a Bchl basis increases of the fast light induced on reactions at 422 nm and increases of soluble cytochrome c ₂ levels are comparable to increases of photophosphorylations and succinate dependent activities. But increases of slow light off reactions at 428 nm and of b-type cytochrome levels become three times greater then increases of cytochrome c ₂ reactions and levels. These results infer that although electrontransport reactions of intracytoplasmic membranes change correlated to each other, Bchl, cytochrome c ₂ and b-type cytochromes cellular levels are independent of each other. Furthermore, the data indicate that cytochrome c ₂ rather than b-type cytochrome is involved with steps rate limiting for photophosphorylation.Abbreviations Bchl bacteriochlorophyll - DCIP 2,6-dichlorophenolindophenol     

Hedgerows as an environment for forest plants: a comparative case study of five species

Many areas in Europe are dominated by agricultural land use, and as a consequence, many typical forest plant species suffer from habitat loss and fragmentation. Hedgerows, one of the common elements of rural landscapes, have been considered as potential refuges for these species. The main objective of this study was to examine whether forests and hedgerows differ in environmental conditions, and whether important life-history attributes of the populations differ between the two habitat types. We selected five species commonly found in the region in both forests and hedgerows (Adoxa moschatellina, Anemone nemorosa, Circaea lutetiana, Polygonatum multiflorum and Stellaria holostea), and sampled data on 10 populations of each species in each habitat type, including measurements of light and various soil factors. Hedgerows had higher relative light availability and tended to have higher soil nutrient contents and lower soil water values than forests. The comparison of plant performance values between habitat types did not show consistent patterns across species. Anemone and Polygonatum performed equally well in hedgerows and forests, whereas Stellaria appeared to have a higher fitness in hedgerows. In contrast, Circaea showed a higher reproduction under forest conditions. For Adoxa, the results were somewhat contradictory: whereas the reproductive output of this species was higher in forests, population density was higher in hedgerows. The abiotic factors most closely related to the performance values were relative light and soil water availability. The majority of plant performance values did not differ between hedgerows and forests. We therefore conclude that the tested forest species are capable of growing also in hedgerows and will survive equally well in forest and its “surrogate” habitat.     

Light measurement for entomology in the field and laboratory

ABSTRACT. Light units weighted for human vision (e.g. lux) are unsuitable for work on insects which have good sensitivity in the blue and UV. We have built and calibrated two light meters - a portable field unit and a mains operated laboratory device-which measure illumination in physical units over a wavelength range suitable for insect vision. Both meters share a single photocell, so field and laboratory measurements are strictly comparable. The field meter covers a range from starlight to tropical sunlight on a single scale, and can be used in conditions when the operator has no effective vision. The laboratory meter is linear over five decade ranges, of which the most sensitive has a full-scale deflection of 1 mW m^-2.