Latency of Botrytis cinerea Pers.: Fr. and Biochemical Studies During Growth and Ripening of Two Grape Berry Cultivars, Respectively Susceptible and Resistant to Grey Mould

Latency and development of Botrytis cinerea were assessed under field conditions and after artificial inoculation of two grape varieties, Gamay (susceptible) and Gamaret (resistant). When the percentage of latent Botrytis was the same for both varieties, severity of visible grey mould remained very low in Gamaret berries, while Gamay clusters were destroyed by the disease to a high percentage. Some biochemical parameters were measured in berries, such as constitutive and induced anti‐fungal compounds, polymeric proanthocyanidins and lipid peroxidation products as markers of senescence. Differences were observed in polymeric proanthocyanidins (PPRA) of Gamaret compared with those of Gamay. Concentration and mean degree of polymerization (mDP) of PPRA were always higher in the berries of the resistant variety. The inhibitory effect of Gamaret PPRA on enzyme activity remained until harvest whereas Gamay PPRA lost their inhibitory activity at the beginning of véraison. Based on these results, resistance to B. cinerea seems to be linked to the maintainance of the fungus in its latent form in berries, mainly due to the ability of Gamaret PPRA to inhibit macerating fungal enzyme activities.     

Initiation and maintenance of long term somatic embryogenesis from anthers and ovaries of Vitis longii ‘Microsperma’

Anthers and ovaries of Vitis longii Microsperma produced embryogenic callus when cultured on solidified Murashige and Skoog medium with 5M 2,4-dichlorophenoxyacetic acid (2,4-D) and 1M benzyladenine (BA). The initial callus was short-lived. However, long-term embryogenesis from callus was maintained through serial transfers by careful selection of clustered embryos with subtending callus. Alternatively, long term culture maintenance was through secondary embryogenesis which occurred directly from previously formed embryos on medium lacking growth regulators. Somatic embryos were white, exhibited frequent pluricotyly and tended to be larger than zygotic embryos. Histology of embryogenic callus demonstrated the presence of lipid-like substances and abundant starch. Somatic embryos were attached to callus by narrow to wide suspensor-like structures and possessed typical epidermal, cortical, and vascular tissue. Embryo cells contained abundant lipid-like accumulations but no starch. Embryos germinated when placed on medium containing 1M BA and produced plants of normal appearance.     

Nucleic acids in mummified plant seeds: screening of twelve specimens by gel-electrophoresis,molecular hybridization and DNA cloning

Summary Twelve seed specimens of varying ages and from different archaeological sites were analyzed for the presence of polymerized DNA and RNA. Amongst the samples tested, one of Vitis vinifera from an archaeological site in Iran (2,000–3,000 B.C.) was found to be completely devoid of nucleic acids. Zea mais seeds of Precolumbial age from Peru (about 800 A.D.) contained depolymerized DNA and RNA. Samples of Vitis vinifera and Rubus sp. from a Lombard archaeological site (800 A.D.) as well as radiocarbon dated seeds from the site of the Spring Sanctuary near Metaponto (I–IV century B.C.) were found to contain polymerized DNA and rRNA bands. However the electrophoretic properties of the rRNAs in one case and hybridization experiments performed with cloned seed DNA in the other, clearly demonstrated that the polymerized nucleic acids were not of plant origin.     

Photoinhibition of white clover seed germination at low water potential

Photosensitivity of germination of white clover ( Trifolium repens L. cv. Podkowa) seeds was studied under water deficit (low water potential) conditions at 25°C. The seeds showed negative photoblastism, which was most pronounced at -0.03 MPa polyethylene glycol solution. Inhibition was observed at two different wavelength bands with maxima at 660 nm (R) and around 730 nm (FR). Red light acted identically to white light (maximum inhibition ca 50%). The effect of far-red illumination was less inhibitory (20–30%). The photoresponse required long illuminations (3 h exposures); saturation level was at 0.1 W m⁻², independently of the light quality. White clover seed germination showed no reversibility of the effects of R and FR light. Prolonged illumination with R and FR increased the inhibition, and intermittent illumination had a higher effect than a continuous one. It was concluded that the photoinhibition of germination of seeds of Trifolium repens involves a reaction dependent on the rate of phytochrome interconversion, a property that is characteristic for the high irradiance reaction.     

Artificial seeds in barley: encapsulation of microspore-derived embryos

Summary An in vitro culture system has been developed for barley (Hordeum vulgare), which yields high frequencies of high quality microspore-derived embryos without an intervening callus phase. The embryos are very similar to zygotic embryos with regard to their morphology and germination capacity. These embryos were encapsulated in sodium alginate to produce individual beads containing one embryo each. In accordance with the literature, these beads are denoted artificial seeds. The artificial seeds germinated well and with a root system superior to that of non-encapsulated embryos. The artificial seeds also maintained their germination capacity for at least 6 months, whereas non-encapsulated embryos did not survive more than 2 weeks in storage. Artificial seeds, thus, probably provide a simple and universal delivery system of in vitro plantlets to greenhouse or field.     

Fruit photosynthesis

Abstract. In addition to photosynthesis as in the leaf, fruit possess a system which refixes CO₂ from the mitochondrial respiration of predominantly imported carbon. This pathway produces malate by the action of phosphoenolpyruvate carboxylase, PEPC, (E.C. 4.1.1.31) and appears to be regulated primarily by the cytosolic concentration of HCO₃/CO₂ and malate. Malate is stored in the vacuole as malic acid, constituting a major carbon pool and a potential substrate for respiration. The PEPC in apple fruit proves to be an efficient form of the enzyme with low Michaelis constants, i.e. Km = 0.09 mol m^-3 PEP and 0.2 mol m^–3 HCO₃, and large Ki= 110 mol m^-3 HCO³. In fleshy fruit, chlorophyll and chloroplasts are unevenly distributed; they resemble the C₃ sun-type and arc concentrated in the perivascular tissue, with smaller chloroplasts, fewer grana per chloroplast and a larger degree of vacuolation than commonly found in a leaf of the same species. Fruit photosynthesis often compensates for respiratory CO₂ loss in the light. However, due to respiration in the dark, CO₂ loss is in excess of photosynthetic gain in the light, such that a continual loss of CO₂ was observed in the diurnal cycle and which is maintained throughout fruit development. The rate of CO₂ exchange decreases on a fresh weight or surface basis, but increases with fruit ontogeny on a per fruit basis, causing accumulation of several percent CO₂ in the internal cavity. Stomata are present in the outer epidermis of those fruits examined, but with a 10-to 100-fold lesser frequency than in the abaxial epidermis of leaf of the same species. The number of Stomata is set at anthesis and remained constant, while the stomatal frequency decreases as the fruit surface expands. Stomata are as sensitive as in leaves in the early stages of fruit development, but often are transformed into lenticels during fruit ontogeny, thereby decreasing the permeability of the outer epidermis. The discrepancy between the CO₂-concentrating mechanism provided by PEPC analogous to C₄/CAM Photosynthesis and the kinetics of fruit PEPC, characteristic of C₃/non-autotrophic tissue, suggests the definition of a new type of ‘fruit photosynthesis’ rather than its categorization within an existing type.     

Survey of the mycoflora and mycotoxins of cotton seeds and cotton seed products in Egypt

Thirty-nine species and 16 fungal genera were isolated from Egyptian cotton seeds, cotton seed meal and cotton seed cake on 1% glucose-Czapek's agar medium incubated at 28 °C. Aspergillus was the most frequent genus and it emerged in 87–100% of the samples contributing 70–98% of total fungi in the three substrates tested. The most common species were A. niger, A. flavus, A. fumigatus, A. terreus and Rhizopus stolonifer; A. niger, A. fumigatus and Penicillium corylophilum; and A. niger, A. flavus, A. terreus, A. nidulans and Rhizopus stolonifer, respectively. Cotton seeds and cotton seed products were naturally contaminated by aflatoxin B₁ and B₂. About 16% of the different substrates tested were positive for aflatoxin contamination. No citrinin, ochratoxin A, patulin, sterigmatocystin, diacetoxyscirpenol, T-2 toxin or zearalenone were detected in the samples assayed.     

Induction of secondary dormancy in sunflower seeds by high temperature. Possible involvement of ethylene biosynthesis

High temperature (45°C) inhibits seed germinition and seedling sunflower ( Helianthus annuus L. cv. Mirasol). Treatment of imbibed seeds at 45°C for more than 48 h induces a secondary dormancy, which is associated with progressive decrease of germination ability at optimal temperature (25°C) as well as with abnormal seedling growth. Ethylene (55μl l⁻¹) and 2-chloroethylphosphonic acid (ethephon) (2.5 m M ) improve germination of thermodormant seeds at 25°C. but the abnormal growth of the seedlings remains. O₂-enriched atmosphere and dry storage improve germination and normal seedling growth. The induction of thermodormancy in sunflower seeds seems associated with loss of their ability to convert 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene. Possible effects of high temperature on membranes and ethylene forming enzyme (EFE) are discussed.     

Buried seed population in the herbaceous lomas on Loma Ancon in the coastal desert of central Peru

Herbaceous lomas in the Peruvian coastal desert, of South America establish in spring, and its habitat is limited to the southern or southwestern slopes along the coast that are affected by thick fog. The time of appearance, the duration and the thickness of the fog vary greatly from year to year, so the lomas can grow only in habitats with enough water to, sustain seed germination and plant growth. This paper studies the species composition and density of the buried seed population, of the herbaceous lomas of Loma Ancon in order to clarify the mechanisms of the lomas' establishment. The mean number of species with viable seeds was about, 12 spp. m⁻² and that of dead seeds was about 22 spp. m⁻². The dominant species wereSolanum tuberiferum, S. pinnatifidum andNolana humifusa, both in viable and dead seeds. Viable seed density was about 5000–8000 seeds m⁻², which is comparable with the seed densities of other herbaceous communities. Dead seed density was about 15000–27000 seeds m⁻², or nearly three times the viable seed density, because the rate of decomposition was slow in the extremely dry conditions. The net increase of viable seeds by seed production was estimated at about 5000 seeds m⁻² in 1980, and the increase in the number of dead seeds was 2200 seeds m⁻².