摘要:

Douglas fir (Pseudotsuga menziesii(Mirb.) Franco) ovules were used to study the method of pollen tube formation and penetration of the nucellus, the movement of the body cell down the pollen tube and development of the archegonia. No pollination drop forms but nucellar tip cells produce a minute secretion that may initiate pollen tube formation. Pollen tubes penetrate the nucellus causing degeneration of nucellar cells in contact with the pollen tube tip. The body cell becomes highly lobed and the tube cytoplasm forms thin sheets between the lobes. This may be the mechanism by which the large body cell is pulled down the narrow pollen tube. Body cell plastids and mitochondria remain unaltered during pollen tube growth, whereas tube cell organelles show signs of degeneration. The pollen tube penetrates the megaspore wall and settles in the archegonial chamber. During pollen elongation and pollen tube growth the egg matured. Egg cell plastids were transformed into large inclusions which filled the periphery of the egg while mitochondria migrated to the perinuclear zone. The neck cells, ventral canal cell and archegonial jacket cells are described. The significance of the body cell and egg cell ultrastructure is discussed in light of recent restriction fragment length polymorphism studies of plastid and mitochondrial inheritance in the Pinaceae.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb13574.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Primary roots ofZea mayscv. Yellow Dent growing in an electric field curve towards the anode. Roots treated with EDTA and growing in electric field do not curve. When root cap mucilage is applied asymmetrically to tips of vertically‐oriented roots, the roots curve toward the mucilage. Roots treated with EDTA curve toward the side receiving mucilage and toward blocks containing 10 mm CaCl2, but not toward “empty” agar blocks or the cut surfaces of severed root tips. These results suggest that 1) free calcium (Ca) is necessary for root electrotropism, 2) mucilage contains effector(s) that induce gravitropiclike curvature, and 3) mucilage can replace gravitropic effectors chelated by EDTA. These results are consistent with the hypothesis that the downward movement of gravitropic effectors to the lower sides of tips of horizontally‐oriented roots occurs at least partially in the apoplast.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb13575.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Morphologically heterophyllous species ofPotamogetonalso commonly display biochemical heterophylly with respect to flavonoid compounds. Generally, floating leaves contain an assortment of flavonoids, whereas submersed leaves often exhibit reduced flavonoid profiles. In strictly submersed (homophyllous) species, two patterns occur. Linear‐leaved species have few flavonoids and their biochemical profiles resemble those of submersed leaves of heterophyllous species. Broad‐leaved homophyllous species possess flavonoid profiles more similar to those of the floating leaves of heterophyllous species. Numerical analysis of these chemical data is consistent with phylogenetic relationships within the genus derived independently on the basis of morphological and chromosomal data. Glycoflavones, which are probably maintained in floating leaves because of their UV filtering ability, exhibit the most pronounced biochemical heterophylly inPotamogeton.The lack of glycoflavones in submersed leaves of heterophyllous species and in linear‐leaved homophyllous species is attributable to the ability of naturally colored water to significantly absorb harmful UV radiation. These observations provide strong support for earlier hypotheses suggesting the importance of flavonoid evolution in the conquest of exposed terrestrial habitats by plants.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb13576.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Vesicular‐arbuscular mycorrhizal fungi (VAMF) were a nearly constant component of the coastal strand of the Hawaiian Islands, occurring in beach sand, driftline debris, in roots of 23 of 31 species of vascular plants examined, and in association with rhizomes of two native species,Sporobolus virginicusandJacquemontia sandwicensis.Mycorrhizae were most frequent and intensity of VAM development was greatest in endemic plants, less in indigenous species, and least in alien species. Spores of VAMF were produced in abundance between the rhizome and the leaf sheaths ofSporobolus.Roots of two strand species, including roots ofSporobolusthat were immersed in seawater for 7 days, functioned as inocula of VAMF in pot‐culture studies. The close association between propagules of VAMF and vegetative fragments of indigenous plants found in the present study suggests a mechanism of codispersal that appears to ensure the maintenance of the symbiosis in nutrient‐deficient sites where it is most beneficial. The codispersal of fungus and plant may explain the high frequency of mycotrophy in strand species in the tropical Pacific.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb13577.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Root anatomy was examined for 15 species, in 6 of the 11 tribes of the Bambusoideae. Wide ranges of anatomical variation were found in epidermis, exodermis, cortex, endodermis, pericycle, phloem, xylem, and pith. Although roots of most species seem to resemble the Panicoid type, our study shows much more variation than was described by Goller (1977). These variations could play a role in characterizing taxa within tribes.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb13578.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Prior field studies have shown that populations of forest herbs on relatively nutrient poor soils have higher vesicular‐arbuscular mycorrhizal (VAM) infection intensity than plants on rich soils. However, the growth responses and ability to take up P against the soil nutrient gradient are often not linearly related to infection intensity. To determine if intraspecific differences among populations of the common VAM fungusGlomus occultumcould differentially affect growth and nutrient uptake,Geranium robertianumseedlings were inoculated withGlomus occultumisolated from four forest types along a gradient of soil fertility, and grown in a greenhouse at P levels typical of the extremes of that gradient. Plants given inoculum from relatively infertile forest sites generally produced greater root, shoot, and total mass than plants given inoculum from fertile sites or uninoculated plants, especially at the low P supply rate. Total P uptake and both P and N uptake efficiency were also highest in plants given inocula from low fertility sites. These results indicate that local adaptation and intraspecific variations in the ability of VAM fungi to induce growth and nutrient uptake effects on host plants may be as important as interspecific differences among VAM fungus species.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb13579.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Atriplexconfertifolia(Chenopodiaceae) consists of ploidy races extending from diploid through decaploid and is dissected into many racial groups by cytological and flavonoid relationships. On the basis of morphology, the species can be divided into two major subdivisions, one centered in western Nevada and inhabiting chiefly the Great Basin, and one centered in the Colorado Plateau. Western Nevada plants are distinguished by smaller and narrower leaves, as well as by darker spines and other charactristics. Because western Nevada is situated in the lee of the Sierra Nevada Range, it received reduced amounts of rainfall during Pleistocene and Holocene times. These reduced leaf dimensions ofA. confertifoliaof the rain shadow zone may thus reflect an evolutionary response to aridity.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb13580.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Scanning electron micrographs of the foliar epidermes of all 17 species ofSorghastrumare presented. A description of foliar epidermal micromorphology for the genus is followed by short descriptions of the individual species, emphasizing their epidermal differences. Papillar morphology is variable but taxonomically informative in distinguishing among the species ofSorghastrum.Based on the absence or presence of papillae, and differences in papillar morphology, three informal groups withinSorghastrumare recognized: 1) the nonpapillate group includingS. balansae, S. rigidifolium, S. setosum, S. contractum, S. minarum, andS. viride; 2) the globose‐papillate group includingS. elliottii, S. incompletum, S. nudipes, S. nutans, S. scaberrimum, S. secundum, andS. trichopus; and 3) the elongate‐papillate group includingS. brunneum, S. stipoides, S. chasae, andS. pellitum.No correlation between papillar development and habitat is evident; however, a correlation exists between papillar development and the geographic distribution of the species ofSorghastrum.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb13581.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

The plastochron age of theLinumleaf that first exhibited lateral leaf vein divergences, the divergent leaf, increased through shoot ontogeny, but the size of the divergent leaf remained constant. There were progressive decreases in the plastochron and relative plastochron rate of leaf elongation, but no significant change in relative chronological rate of leaf elongation, through ontogeny. Thus, divergent leaves of similar sizes occupied different relative positions in the array of leaves on stems of different plastochron ages. These observations are partially consistent with theoretical network model predictions on early leaf vein development. The empirical data of this study suggest additional features of leaf development that should be incorporated into future simulation models for leaf vein development.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb13582.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Three species of shrubs (Ericaceae) were found to segregate upon the northeast and southwest slopes of spur ridges on Brush Mountain, in southwestern Virginia.Rhododendron maximumwas found only in valleys and lower northeast slopes,Rhododendron periclymenoides=R. nudiflorum) was found on northeast slopes whileKalmia latifoliawas most abundant on southwest slopes. Previous vegetation studies indicated that these partially segregated distributions were related to irradiance and water availability. In field studies of water potential,R. periclymenoideshad the lowest diurnal leaf water potentials and the largest seasonal variation in midday leaf water potential.Kalmia latifoliahad the highest leaf conductance in field and phytotron experiments.Rhododendron maximumhad the greatest seasonal osmotic adjustment followed byR. periclymenoidesandK. latifolia.In phytotron experiments, the photosynthetic capacity ofR. maximumwas the most sensitive to water stress followed byR. periclymenoidesandK. latifolia. Kalmia latifoliawas able to modify its conductance rates to reduce water loss and maintain constant leaf water potential minimizing photosynthetic inhibition.Rhododendron periclymenoidesshowed extreme luxury spending of water indicated by high conductance and low photosynthesis. The ecophysiological responses to water and irradiance provided an explanation for the distributions of the three species. For example,R. maximumleaves are sensitive to elevated irradiance, and carbon gain is strongly influenced by water stress. Thus,R. maximumwill perform best in low irradiance environments with ample water, such as valley sites. Each species had a unique set of adaptations for performing best in their optimum habitat.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb13583.x

出版商:Wiley    

年代:1990

数据来源: WILEY