Flower Bud Development in Some Varieties of Tulip

A study is being made of the time of initiation and development of the flower bud in three classes of tulips. All floral organs are present in November. The flower bud is twice as large in the earliest (Mendel) class than in the latest (Darwin) class, but the cytological condition in the anthers and ovules is strikingly similar; pollen is in the late quartet to early microspore stage, ovules are very small primordia with no evidence of integuments or megaporocyte. Expansion of flower bud size is in proportion to earliness, pollen development is virtually parallel, and megagamentophyte development is slightly more rapid in the earliest class

The Cytological Basis For Homothallism And Heterothallism In The Agaricaceae

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141249/1/ajb209513.pd

Some Meiotic Irregularities in Cultivated Lilies

Refinements of the paraffin technique make it possible to demonstrate critical details of meiosis. The process yields figures that are comparable to the results of the smear process. Progressive synapsis during amphitene, and the tetrad structure of the chromosome at strepsiphase can be readily demonstrated

Development of Axillary Buds of the Tillers of Zea

An inbred line of popcorn and a line that contained teosinte germ plasm were compared with respect to the inflorescences of the numerous tillers produced by plants of these lines. In both lines, all terminal and axillary apices of the tillers initiated inflorescences. No axillary tassels were found on the tillers of either line. On a popcorn tiller, a terminal inflorescence was either a tassel, a tassel that bore a few scattered kernels, an ear, or an ear that had basal tassel branches. Every tiller of the teosinte-contaminated corn had a terminal tassel

A Twin-Embryo Abnormality in Maize

A mutant strain of corn obtained by ultra violet treatment has twin growing points in the embryo. The flattened emerging coleoptile is a continuous sheath, containing two distinct stem apices, each of which lays down a series of leaf primordia. Each growing point becomes encircled by its laterally overlapping young leaves. The procambium strands of the two young axes converge into the stele of the mesocotyl (first internode), which is common to the two potential stems

Histolytic Polyploidy in Root Tips of Maize

A sample of Hopi Indian maize from an unknown locale in New Mexico was brought into the writer\u27s laboratory for the preparation of sections of the radicle for the study of the histogens. The sample consisted of a mixture of creamy white kernels, black kernels and kernels of intermediate shades of gray. Some of the paraffin ribbon of radicles was discarded because of the presence of a large cavity behind the root cap. The shape and consistent position of the cavity did not resemble the results of faulty infiltration, and a study of finished preparations showed that the cavities are the result of a cytohistological aberration in the meristem. The present report describes the salient features of the abnormality

The Critical Period for Floral Initiation in Tulipa (Abstract)

During June and most of July, the apical meristem in the tulip bulb lays down the primordia of foliage leaves. Toward the end of July, or early in August, perianth primordia are initiated, followed rapidly by stamen and pistil primordia. The late Darwins lag behind the early classes in the initiation of floral organs. In view of slight variations of stage of development in each variety tested, and in view of possible effect of seasonal conditions, August first is suggested as an approximate critical date for floral initiation

The Development of Ear Prirnordia of Zea In Relation to Position on the Plant

The development of auxiliary buds of a yellow dent maize hybrid was studied. Seven buds at acropetally successive nodes survived at least to 68 days after planting and became pistillate inflorescences, potential ears. Meiosis occurred in the basal ovaries of the upper two ears after 68 days, when the styles were 2 mm. long, and complete embryo sacs were present by 71 days. The two upper ears attained approximately the same morphological and cytological stage between 68 and 71 days. The top bud invariably became the harvestable ear. The failure of complete development of the second ear is not ascribed to inadequate ovule development by the time of anthesis, nor to failure of pollination of this ear, but to factors associated with competition prior to, and after anthesis. 13. A comparison of the mode-The time required for floral abscission in Lizard\u27s Tail variety is less and more uniform than in Little Turkish. Factors which affect abscission in general and which cause a varying effect in the two varieties include auxin concentration, leaves (sources of carbohydrates), methyl donors, and pectic enzymes. Concentrations of 100 ppm, 1,000 ppm, and 10,000 ppm IAA are more effective in retarding abscission in Little Turkish variety; low concentrations (5 ppm) tend to accelerate abscission slightly in Little Turkish and retard the process in Lizard\u27s Tail. It is suggested that carbohydrate levels are higher in Little Turkish and have a varying effect upon abscission in the two varieties. A lack of a methyl donor is more limiting in Little Turkish. Addition of 0.01 percent methionine resulted in a 32 percent decrease in time of abscission in Little Turkish and a 19 percent decrease in Lizard\u27s Tail. Response to higher concentrations is much the same in both varieties. Pectin-methylesterase activity is higher in Little Turkish, and since this enzyme prevents abscission, its greater abundance aids in explaining differences between the two varieties. The results indicate that abscission is controlled by the interaction of many factors and that a variation in the concentration, activation, or transport of any one or any combination affects the mode of abscission generally

Structural determinants of PINK1 topology and dual subcellular distribution

<p>Abstract</p> <p>Background</p> <p>PINK1 is a mitochondria-targeted kinase that constitutively localizes to both the mitochondria and the cytosol. The mechanism of how PINK1 achieves cytosolic localization following mitochondrial processing remains unknown. Understanding PINK1 subcellular localization will give us insights into PINK1 functions and how mutations in PINK1 lead to Parkinson's disease. We asked how the mitochondrial localization signal, the transmembrane domain, and the kinase domain participate in PINK1 localization.</p> <p>Results</p> <p>We confirmed that PINK1 mitochondrial targeting signal is responsible for mitochondrial localization. Once inside the mitochondria, we found that both PINK1 transmembrane and kinase domain are important for membrane tethering and cytosolic-facing topology. We also showed that PINK1 dual subcellular distribution requires both Hsp90 interaction with the kinase domain and the proteolysis at a cleavage site downstream of the transmembrane domain because removal of this cleavage site completely abolished cytosolic PINK1. In addition, the disruption of the Hsp90-PINK1 interaction increased mitochondrial PINK1 level.</p> <p>Conclusion</p> <p>Together, we believe that once PINK1 enters the mitochondria, PINK1 adopts a tethered topology because the transmembrane domain and the kinase domain prevent PINK1 forward movement into the mitochondria. Subsequent proteolysis downstream of the transmembrane domain then releases PINK1 for retrograde movement while PINK1 kinase domain interacts with Hsp90 chaperone. The significance of this dual localization could mean that PINK1 has compartmental-specific functions.</p

Meeting Report: Hazard Assessment for Nanoparticles—Report from an Interdisciplinary Workshop

In this report we present the findings from a nanotoxicology workshop held 6–7 April 2006 at the Woodrow Wilson International Center for Scholars in Washington, DC. Over 2 days, 26 scientists from government, academia, industry, and nonprofit organizations addressed two specific questions: what information is needed to understand the human health impact of engineered nanoparticles and how is this information best obtained? To assess hazards of nanoparticles in the near-term, most participants noted the need to use existing in vivo toxicologic tests because of their greater familiarity and interpretability. For all types of toxicology tests, the best measures of nanoparticle dose need to be determined. Most participants agreed that a standard set of nanoparticles should be validated by laboratories worldwide and made available for benchmarking tests of other newly created nanoparticles. The group concluded that a battery of tests should be developed to uncover particularly hazardous properties. Given the large number of diverse materials, most participants favored a tiered approach. Over the long term, research aimed at developing a mechanistic understanding of the numerous characteristics that influence nanoparticle toxicity was deemed essential. Predicting the potential toxicity of emerging nanoparticles will require hypothesis-driven research that elucidates how physicochemical parameters influence toxic effects on biological systems. Research needs should be determined in the context of the current availability of testing methods for nanoscale particles. Finally, the group identified general policy and strategic opportunities to accelerate the development and implementation of testing protocols and ensure that the information generated is translated effectively for all stakeholders