Differential expression of a gene for a methionine-rich storage protein in maize

Summary A methionine-rich 10 kDa zein storage protein from maize was isolated and the sequence of the N-terminal 30 amino acids was determined. Based on the amino acid sequence, two mixed oligonucleotides were synthesized and used to probe a maize endosperm cDNA library. A fulllength cDNA clone encoding the 10 kDa zein was isolated by this procedure. The nucleotide sequence of the cDNA clone predicts a polypeptide of 129 amino acids, preceded by a signal peptide of 21 amino acids. The predicted polypeptide is unique in its extremely high content of methionine (22.5%). The maize inbred line BSSS-53, which has increased seed methionine due to overproduction of this protein, was compared to W23, a standard inbred line. Northern blot analysis showed that the relative RNA levels for the 10 kDa zein were enhanced in developing seeds of BSSS-53, providing a molecular basis for the overproduction of the protein. Southern blot analysis indicated that there are one or two 10 kDa zein genes in the maize genome.     

Phylogeny and the patterns of leaf phenolics in gap-and forest-adapted Piper and Miconia understory shrubs

Summary The types and quantities of defense compounds found in plants occupying ecologically distinct habitats have received much theoretical and little empirical attention. Here we characterize the leaf phenolic chemistry of eight species in two genera of tropical rainforest shrubs; four species in each genus are typical of disturbed sites, and four are typical of mature forest understory. Two Miconia species growing in light gaps had significantly higher leaf tannin and total phenolic contents than congenors growing in the primary forest; this pattern was not found among the gap- and forest-adapted Piper species. Tannin patterns were not mirrored by leaf cinnamic acids. These results indicate that plant phylogeny must be considered when predicting plant defense investment.     

Thermal requirements for development of aphidophagous Coccinellidae (Coleoptera), Chrysopidae,Hemerobiidae (Neuroptera), and Syrphidae (Diptera): some general trends

Summary The sum of effective temperatures (SET) and lower development threshold (LDT) were established for eggs and/or pupae of central European populations of 20 species of chrysopid, coccinellid, hemerobiid, and syrphid predators of aphids. LDT ranged between 5.6° and 12.2°C, SET between 38.3 and 140.9 day degrees (dd), with broad overlap among stages and taxa. When LDT was plotted against SET, the data for both eggs and pupae were scattered along a single regression line which predicted a 0.47°C decrease in LDT per 10 dd increase in SET (r=-0.77, p<0.001). A regression calculated from published data from all over the world predicted a 0.24°C/10 dd decrease in LDT, and the data were more scattered (r=-0.38, p<0.01). This is perhaps the first report on the functional relationship between LDT and SET at the interspecific level. The species and stages differed in typical development length (VDL) and in the extent of its deceleration by low temperatures (DD). DD increased with increasing VDL, but the relative effect of low temperature on development length (DD/VDL ratio) reflected thermal adaptations consistent with the life history of the species. Polyvoltine species were less affected by low temperatures than monovoltine species, particularly the thermophilic ones.     

Do holly leaf spines really deter herbivory?

Summary Although spinose teeth of holly leaves have been widely cited as an example of a physical defense against herbivores, this assumption is based largely on circumstantial evidence and on general misinterpretation of a single, earlier experiment. We studied the response of third and fifth instar larvae of the fall webworm, Hyphantria cunea Drury, a generalist, edge-feeding caterpillar, to intact American holly leaves and to leaves that had been modified by blunting the spines, by removing sections of leaf margin between the spines, or by removing the entire leaf margin. The results suggest that the thick glabrous cuticle and tough leaf margin of Ilex opaca are more important than the spinose teeth in deterring edge-feeding caterpillars. Microscopic examination of mature leaves revealed that the epidermis is thickened at the leaf margin, and that the leaf is cirucumscribed by a pair of fibrous veins. In simple choice tests neither domesticated rabbits nor captive whitetailed deer discriminated between spinescent holly foliage and foliage from which spines were removed. Nevertheless, we found little evidence of herbivory by mammals in the field, either on small experimental trees or in the forest understory. While it is possible that spinose teeth contribute to defense by reducing acceptibility of holly relative to other palatable plant species, we suggest that the high concentrations of saponins and poor nutritional quality of holly foliage may be more important than spines in deterring vertebrate herbivores. The degree of leaf spinescence and herbivory was compared at different heights with the tree canopy to test the prediction that lower leaves should be more spinescent as a deterrent to browsers. Leaves on lower branches of mature forest trees were slightly more spinescent than were upper leaves, and juvenile trees were slightly more spinescent than were mature trees. However, there was no relationship between degree of spinescence and feeding damage. The greater spinescence of holly leaves low in the canopy is probably an ontogenetic phenomenon rather than a facultative defense against browsers.The investigation reported in this paper (No. 87-7-8-77) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with the approval of the Dirctor     

Identification of potentially embryogenic microspores in Brassica napus

Studies were undertaken with Brassica napus L. cv. Topas to identify buds containing microspores predisposed to embryogenesis in vitro and to investigate bud and microspore development in relation to this process. No significant correlation was found between the final embryo number and bud components. There appears to be a developmental window of less than 8 h duration during which microspores are very likely to form embryos: over 70% of the microspores can undergo division and up to 70% of these can form embryos. Embryos were mainly obtained from late uninuucleate to early binucleate microspores: the former contained mainly a G2 or M phase nucleus located at the microspore periphery and the latter a generative nucleus (associated with the intine) and a vegetative nucleus. Observations indicated that only the vegetative nucleus contributed to embryo formation. The first embryogenic division occurred between 8 and 16 h for uninucleate- and between 8 and 48 h for binucleate-derived embryos.     

Consequences of a mixed reproductive system in the hog peanut,Amphicarpaea bracteata, (Fabaceae)

Summary The forest annual, Amphicarpaea bracteata L. can reproduce via aerial chasmogamous, aerial cleistogamous, and subterranean cleistogamous flowers. Both plant size and light intensity influenced the utilization of the three modes of reproduction. chasmogamous and aerial cleistogamous flower number and the ratio of chasmogamous flowers to the total number of aerial flowers increased with plant size. The latter demonstrated a shift to xenogamy and outbreeding in larger plants. Light intensity indirectly influenced reproductive modes through its infuence on plant size. Seed set by both types of aerial flowers was low and unrelated to plant size. Subterranean seed number and the total dry weight of subterranean seeds per plant increased with size. The subterranean seeds of Amphicarpaea bracteata are thirty-four times larger than the aerial seeds (fresh weight). Under field conditions, subterranean seeds had greater germination after one year than acrial seeds. The plants arising from subterranean seeds were significantly larger and more fecund than those from aerial seeds. Seeds produced by aerial cleistogamous, hand selfpollinated chasmogamous, and naturally pollinated chasmogamous flowers had equivalent germination rates and produced plants of equal size and fecundity. This suggests that the outbred progeny from chasmogamous flowers have no advantage over the inbred progeny from aerial cleistogamous flowers.     

Uptake and metabolism of benzyladenine in the early stage of flower bud development in vitro in tobacco

Benzyladenine (BA) was found to regulate the number of flower buds regenerated in vitro from pedicel tissue of tobacco. Flower bud induction was particularly sensitive to BA levels in the range of 0.45 to 1.0 μ M , where a two-fold increase in concentration caused a threefold rise in the number of buds. When tissues were fed radioactive BA for 24h, only 9–12% of the counts were recovered in the original compound. The rest was present in metabolites, tentatively identified as the mono-, di- and triribotides, 7- and 9-glucosides and 9-riboside of BA. The amount of growth regulator taken up and the quantities of BA and its metabolites in the explants were all linearly related to the concentration of the medium. The internal BA concentration was ca 60% of the level in the medium after 24 h. When the concentration in the medium was raised, relatively more BA remained in the non-conjugated form. However, this change in the equilibrium between BA and the conjugates is too small to account for the steep rise in the curve representing concentration vs effect between 0.45 and 1.0 μ M .     

The sensitive period for light and temperature regulation of sporangiophore development inPhycomyces

Light and temperature markedly influence sporangiophore development inPhycomyces blakesleeanus. Under normal conditions in the dark, low temperature drastically stimulates the production of dwarf sporangiophores (microphorogenesis) and inhibits that of giant sporangiophores (macrophorogenesis). These effects of low temperature could still be observed if applied only for a short period before sporangiophore initiation. Continuous white illumination strongly inhibits microphorogenesis and slightly stimulates macrophorogenesis. Short exposures to white light noticeably inhibit microphorogenesis and stimulate macrophorogenesis when given to mycelia grown for between 90 and 160 h at 14° C or 150 h or more at 10° C. These results indicate the existence in the mycelium of developmental stages for the regulation of sporangiophorogenesis by environmental signals.     

The source of gibberellins in the parthenocarpic development of ovaries on topped pea plants

The role and source of gibberellins (GAs) involved in the development of parthenocarpic fruits of Pisum sativum L. has been investigated. Gibberellins applied to the leaf adjacent to an emasculated ovary induced parthenocarpic fruit development on intact plants. The application of gibberellic acid (GA₃) had to be done within 1 d of anthesis to be fully effective and the response was concentration-dependent. Gibberellin A₁ and GA₃ worked equally well and GA₂₀ was less efficient. [³H]Gibberellin A₁ applied to the leaf accumulated in the ovary and the accumulation was related to the growth response. These experiments show that GA applied to the leaf in high enough concentration is translocated to the ovary. Emasculated ovaries on decapitated pea plants develop without application of growth hormones. When [³H] GA₁ was applied to the leaf adjacent to the ovary a substantial amount of radioactivity accumulated in the growing shoot of intact plants. In decapitated plants, however, this radioactivity was mainly found in the ovary. There it caused growth proportional to the accumulation of CA₁. Application of LAB 150978, an inhibitor of GA biosynthesis, to decapitated plants inhibited parthenocarpic fruit development and this inhibition was counteracted by the application of GA₃ (either to the fruit, or the leaf adjacent to the ovary, or through the lower cut end of the stem). All evidence taken together supports the view that parthenocarpic pea fruit development on topped plants depends on the import of gibberellins or their precursors, probably from the vegetative aerial parts of the plant.Abbreviations FW flesh weight - GA_n gibberellin A_n - HPLC high-performance liquid chromatography     

The histogenesis of somaclones from tomato (Lycopersicon esculentum Mill.) cotyledons

Summary A histological study ofin vitro cultured cotyledonary expiants of tomato (Lycopersicon esculentum) was performed in order to determine the site (differentiated tissue or developing callus) and the mode of plant regeneration.Results have shown that callus develops at the excision sites of cotyledonary expiants and that shoots are formed exclusively within the unorganized callus: excision areas are the only morphogenetic sites and the proximal excision is the preferred site for plant regeneration.Shoots differentiate by organogenesis within the superficial region of the callus. Few neocambial cells cooperate in the neoformation. Origin from a single cell is highly unlikely since rarely observed single activated cells never developed into shoots.Regenerated plants may be chimeras if invitro culture induces genetic diversity in the initial cells.Abbreviations IAA Indole-3-acetic acid - c callus - d vegetative dome - s shoot - ad adaxial - ab abaxial - t tracheid - p parenchyma - S sieve tube