Differential effect of temperature on mitrochondrial activity in shoots from freshly harvested and moderately aged kernels of maize (Zea mays L.)

This paper reports on a study of mitochondrial activity in etiolated shoots of freshly harvested and moderately aged kernels of maize. Activity was investigated after incubation at a favourable temperature (25°C), sub-optimal temperature (13°C) and after a heat shock (46°C for 2h). Although impaired mitochondrial activity in shoots from moderately aged maize kernels was not detected at 25°C, deficiencies became evident under low temperature stress (13°C). State 3 oxygen uptake, cyanide-insensitive oxygen uptake and cytochrome oxidase activity were lower in mitochondria from these shoots at 13°C than in mitochondria from shoots of freshly harvested kernels at this temperature. After a heat shock, cyanide-insensitive oxygen uptake was higher, and cytochrome oxidase activity lower, in shoots of aged kernels than in shoots of fresh kernels. No significant differences in ADP: O ratio or succinate dehydrogenase activity occurred between mitochondria from shoots of the two seed lots in any of the temperature treatments.     

Pollen discounting and the evolution of selfing in Arenaria uniflora (caryophyllaceae)

Although most models of mating system evolution assign a central role to the male transmission advantage of selfing genotypes, empirical data on the male fitness consequences of increased self-pollination are still uncommon. Here, I use measures of pollen import and export by focal plants in genotyped arrays to investigate the effects of floral morphology and pollination environment on self and outcross male function. Plants from an autogamous population of Arenaria uniflora (Caryophyllaceae) exhibit complete pollen discounting relative to closely related outcrossers, as do morphologically intermediate F1 hybrids between the two populations. However, the low cumulative male fitness of hybrids probably results from reduced pollen number or competitive ability, rather than a nonlinear relationship with floral morphology. When surrounded by selfers, plants from the outcrosser population self-fertilize at nearly the same rate as selfers (>80%), but have much lower self male fitness due to reduced fruit set. Because outcross siring success is also extremely low (<8%) in this treatment, these mate-limited outcrossers are at male fitness disadvantage to both pseudocleistogamous selfers and nonlimited outcrossers. The relative male fitness of plants with different mating systems appears dependent on the ecological context, as well as on morphological trade-offs.     

Seed banks of a southern Australian wetland: the influence of water regime on the final floristic composition

The sediments of a southern Australian wetland complex were investigated to determine the germinable seed bank. The number of seeds ranged from 22,000 to 78,000 m^–2. Non-metric multi dimensional scaling (NMS) ordination based upon species composition separated the four basins but each contained the representatives of the major functional groups: terrestrial, amphibious and submerged. To test the influence of water regime on the final floristic composition derived from these seed banks, sediments were positioned at three elevations (0, 30 and 80 cm) and subjected to three hydrologic regimes (static water level, and draw down rates of 2.5 and 7 cm week^–1). Species compositions were analysed after 98 days via ordination. Despite significant differences in the initial seed bank composition the final floristic compositions were correlated with the water regime and independent of the initial seed bank composition. Species groups were segregated on a basis of whether sediments were continuously exposed to the atmosphere, the rate of draw down and the water depth. Moist sediments were dominated by species belonging to all the main functional groups. Sediments subject to rapid drying were dominated by terrestrial species whereas sediments that were flooded for the majority of the time were dominated by submerged species.     

Discrimination of sunflower volatiles by the red sunflower seed weevil

Five principle monoterpenoid and other constituent volatile chemicals of sunflower heads were combined to resemble two lines of sunflower (Helianthus annuus L.): one U.S.D.A. standard line and one French line which was poorly visited by insects (Etievant et al., 1984). Field trials of attraction to red sunflower seed weevils (Smicronyx fulvus Le Conte, Coleoptera: Curculionidae) showed that one was clearly preferred over the other. The more attractive mixture contained -pinene, -pinene, limonene, camphene and bornyl acetate in a ratio resembling that of Flath et al. (1985) rather than that described by Etievant et al. (1984). One or two volatiles were deleted from the optimal blend but only mixtures of five volatiles showed the highest attraction. Substitution of sabinene, another volatile prominent in sunflower, for one of the five in the optimal blend also decreased attraction of seed weevils. When the monoterpenoid components and green leaf volatiles in the traps resembled the ratios of most of the prominent volatiles of sunflower, attraction was significantly greater than controls.     

Nitrogen and phosphorus addition differentially enhance seed production of dominant species in a temperate steppe

Previous studies have demonstrated changes in plant growth and reproduction in response to nutrient availability, but responses of plant growth and reproduction to multiple levels of nutrient enrichment remain unclear. In this study, a factorial field experiment was performed with manipulation of nitrogen (N) and phosphorus (P) availability to examine seed production of the dominant species, Stipa krylovii, in response to N and P addition in a temperate steppe. There were three levels of N and P addition in this experiment, including no N addition (0 g N m⁻² year⁻¹), low N addition (10 g N m⁻² year⁻¹), and high N addition (40 g N m⁻² year⁻¹) for N addition treatment, and no P addition (0 g P m⁻² year⁻¹), low P addition (5 g P m⁻² year⁻¹), and high P addition (10 g P m⁻² year⁻¹) for P addition treatment. Low N addition enhanced seed production by 814%, 1371%, and 1321% under ambient, low, and high P addition levels, respectively. High N addition increased seed production by 2136%, 3560%, and 3550% under ambient, low, and high P addition levels, respectively. However, P addition did not affect seed production in the absence of N addition, but enhanced it under N addition. N addition enhanced seed production mainly by increasing the tiller number and inflorescence abundance per plant, whereas P addition stimulated it by decreasing the plant density yet stimulating height of plants and their seed number per inflorescence. Our results indicate seed production is not limited by P availability but rather by N availability in the temperate steppe, whereas seed production will be increased by P addition when N availability is improved. These findings enable a better understanding of plant reproduction dynamics in the temperate steppe under intensified nutrient enrichment and can inform their improved management in the future.     

In vitro zygotic embryo germination and propagation of an endangered Boswellia serrata Roxb., a source of boswellic acid

This study aims to establish an efficient protocol for development of seedlings of an endangered medicinally important forest tree Boswellia serrata Roxb., for mass plantation and consistent supply of salai guggul. The green mature fruits served as source of seeds. The excised green zygotic embryos were cultured on Gamborg (B5), McCown and Loyd (WPM) and Schenk and Hildebrandt (SH) media fortified with different concentration of sucrose and on Murashige and Skoog (MS) medium containing 3 % sucrose, polyvinylpyrrolidone (PVP) (0–300 mg l^−l), Gibberellic acid (GA₃), Indoleacetic acid (IAA), Naphthaleneacetic acid (NAA), Indole-3-Butyric acid (IBA) or 2,4-dichlorophenoxyacetic acid (2,4 D) and 6-benzylaminopurine (BA) or kinetin (Kin) individually. The highest frequency of embryo germination (96 %) and conversion into seedling was obtained on MS medium containing 3 % sucrose together with 200 mg l^−l PVP; other media were either inferior or induced abnormalities in the seedlings including callus formation from the zygotic embryos. Fully developed seedlings could be successfully established in soil with about 94 % survival. The embryos from mature dry seeds did not respond for germination in any of the experiments. In conclusion, selection of zygotic embryo from green mature seeds and their in vitro germination is important for propagation of B. serrata.     

ABSENCE OF POLLEN DISCOUNTING IN A GENOTYPE OF IPOMOEA PURPUREA EXHIBITING INCREASED SELFING

Throughout southeastern North America, the annual morning glory Ipomoea purpurea exhibits a polymorphism at a locus that influences the intensity of floral pigmentation. Previous studies have shown that when rare, the homozygous white genotype has a greater selfing rate than the homozygous dark genotype. In the absence of pollen discounting (a reduction in transmission of pollen to other plants by genotypes that exhibit increased selfing) and inbreeding depression, this increased selfing rate should favor the white allele. Experiments reported here confirm that the white genotype has elevated selfing rates when rare but indicate pollen discounting is not associated with elevated selfing. Rather, white genotypes contribute more pollen to the outcross pollen pool. The disparity between genotypes in both selfing rates and success at pollen contribution to other plants disappears at intermediate to high frequencies of the white allele. Pollinator movements are consistent with the pattern of selfing. These results suggest that elevated selfing and enhanced success at pollen donation contribute to maintenance of the white allele in natural populations of morning glories.     

CONVERGENT AND CORRELATED EVOLUTION OF MAJOR LIFE‐HISTORY TRAITS IN THE ANGIOSPERM GENUS LEUCADENDRON (PROTEACEAE)

Natural selection is expected to cause convergence of life histories among taxa as well as correlated evolution of different life‐history traits. Here, we quantify the extent of convergence of five key life‐history traits (adult fire survival, seed storage, degree of sexual dimorphism, pollination mode, and seed‐dispersal mode) and test hypotheses about their correlated evolution in the genus Leucadendron (Proteaceae) from the fire‐prone South African fynbos. We reconstructed a new molecular phylogeny of this highly diverse genus that involves more taxa and molecular markers than previously. This reconstruction identifies new clades that were not detected by previous molecular study and morphological classifications. Using this new phylogeny and robust methods that account for phylogenetic uncertainty, we show that the five life‐history traits studied were labile during the evolutionary history of the genus. This diversity allowed us to tackle major questions about the correlated evolution of life‐history strategies. We found that species with longer seed‐dispersal distances tended to evolve lower pollen‐dispersal distance, that insect‐pollinated species evolved decreased sexual dimorphism, and that species with a persistent soil seed‐bank evolved toward reduced fire‐survival ability of adults.