Judith A. Jernstedt

Influence of Cell Integrity on Textural Properties of Raw, High Pressure, and Thermally Processed Onions

UNLABELLED The integrity of onion cells and its impact on tissue texture after high pressure and thermal processing was studied. The contribution of cell membranes and the pectic component of cell walls on the texture properties of onion tissue were analyzed. Neutral red (NR) staining of onion parenchyma cell vacuoles was used for the evaluation of cell membrane integrity and microscopic image analysis was used for its quantification. The content of methanol in tissue as a result of pectin methylesterase activity was used to evaluate the pectin component of the middle lamella and cell walls and the hardening effect on the tissue after processing. High pressure treatments consisted of 5-min holding times at 50, 100, 200, 300, or 600 MPa. Thermal treatments consisted of 30-min water bath exposure to 40, 50, 60, 70, or 90 °C. In the high pressure treatments, loss of membrane integrity commenced at 200 MPa and total loss of membrane integrity occurred at 300 MPa and above. In the thermal treatments, membrane integrity was lost between 50 and 60 °C. The texture of onions was influenced by the state of the membranes and texture profiles were abruptly modified once membrane integrity was lost. Hardening of the tissue corresponded with pressure and temperature PME activation and occurred after membrane integrity loss. PRACTICAL APPLICATION The texture of vegetables is an important quality attribute that affects consumer preference. Loss of textural integrity also indicates that other biochemical reactions that affect color, flavor, and nutrient content may occur more rapidly. In this study, we analyzed changes in the texture of onions after preservation with heat and high pressure.

Pollen exine development precedes microtubule rearrangement inVigna unguiculata (Fabaceae): A model for pollen wall patterning

SummaryAlthough patterns on pollen exines are highly conserved, heritable traits, there is no prevailing explanation for control of pattern development. InVigna unguiculata (Fabaceae), the exine reticulum is unusually coarse so that development of the reticulum can be followed by light microscopy. Developing exine patterns were compared with the arrangement of microtubules in the microspore using immunofluorescence labeling of microtubules. Exine pattern developed in microspores at stages with a regular microtubule pattern. At later stages of exine formation, microtubules were arranged in patches under the lumina of the reticulum. We conclude that microtubules do not determine exine pattern. The developing exine appears to rearrange microtubules. We interpret this as evidence for the selfpatterning of exine based on intrinsic properties of the matrix between the microspore and the callose wall.

Rhizophore and root development in Selaginella martensii : meristem transitions and identity

Rhizophores arise from angle meristems located at shoot branch points in many species of Selaginella and produce roots at their distal ends. We reinvestigated the origin and development of rhizophores and roots in Selaginella martensii using a nondestructive sequential replica technique for scanning electron microscopy and anatomical studies of sectioned material. We followed development in excised branch systems containing undetermined ventral angle meristems Analysis of patterns of division and expansion of cells on the surface of apical meristems and in transverse and longitudinal sections showed that the outgrowth from a ventral angle meristem had three distinct developmental phases: rhizophore, aerial root, and subterranean root, each with a distinctive apical meristem structure and activity. Rhizophore formation involved division of all cells in the angle meristem and establishment of multiple surface initial cells from which rhizophore growth ensued. The aerial root phase began with formation of two internal root meristems, each with a single prominent apical cell, replacing the multiple surface initials. From these meristems, dichotomously branched aerial roots formed, which continued to grow and branch internally. Eventually, subterranean roots formed, bearing root hairs and root caps. Formation of subterranean roots was induced at any time after aerial roots reached 0.5-1 cm in length when the tip of the organ touched a substrate. Our data provided support for the original concept of the rhizophore as a unique root-bearing organ in S. martensii, as well as for a developmental succession of apical meristem structure and activity, specific forms of which characterized the rhizophore and true root stages of angle meristem outgrowth.

Root contraction in hyacinth. III: Orientation of cortical microtubules visualized by immunofluorescence microscopy

SummaryCortical microtubules (MTs) were visualized in root cortex cells ofHyacinthus orientalis L. using immunofluorescence techniques. Cellular MT orientation was determined adjacent to radial longitudinal and transverse walls of root tip, uncontracted, contracting, and fully contracted regions. As seen in longitudinal views, MTs formed parallel, apparently helical arrays which were oriented transversely, axially or obliquely depending upon the region. Transverse sectional views showed that MTs adjacent to transverse cell walls formed a variety of patterns which varied with developmental stage and cell location. Microtubules were oriented in crisscross or parallel arrays. The parallel arrays were oriented either parallel, perpendicular or oblique to the radius of the root. There was an apparent temporal progression in MT reorientation from outer cortical to inner cortical cell layers. A resultant progression of reoriented cell growth could account for root contraction. These findings corroborate earlier electron microscopic observations of changing MT orientation accompanying root contraction, and provide cytological evidence to test mathematical and biophysical models of the mechanics of cell expansion.

Root contraction in hyacinth. II: Changes in tubulin levels, microtubule number and orientation associated with differential cell expansion

Root contraction in hyacinth (Hyacinthus orientalis L.) is marked by reoriented cell growth in the cortex of the contractile region. Cellular volume of the inner cortex enlarges fourfold during root contraction. This is associated with large increases in the radial and tangential dimensions and decreases in the longitudinal dimension of the cells. In order to determine the possible role of microtubules (MTs) in these changes we compared tubulin levels and MT numbers and orientation in contracted and non-contracted regions of hyacinth roots. Tubulin content was analysed by a radioimmunoassay; MT numbers and orientation were analyzed by counting profiles in sectioned material using transmission electron microscopy. Contracted tissue was found to have significantly higher levels of tubulin on a per-cell basis than non-contracted tissue, and also increased tubulin levels relative to total protein. The spatial MT frequencies were the same in contracted and non-contracted tissues, indicating a proportional increase in MT numbers in the expanded cells. Although the absolute spatial frequency of MTs was constant, the orientation, as determined by morphometric analysis of MT profiles, was not. While in the longitudinal section plane 42% of the MTs in the non-contracted cells were oblique, in the contracted cells the percentage of MTs presenting oblique profiles increased to 87%. Additionally, a qualitative difference in MTs was observed in contracted cells; electron-opaque material was seen peripherally associated with the MTs of the inner cortex. The changes in tubulin levels and in MT numbers as well as the qualitative differences in the MTs of contracted and non-contracted root regions indicate that, in hyacinth, reoriented cellular enlargement associated with root contraction cannot be explained simply by shifts in the arrangement of preexisting cortical MT arrays, but involves more complex changes in the cytoskeleton.

Cytochemistry of developing cotton fibers:: A hypothesized relationship between motes and non-dyeing fibers

Abstract Developing lint fibers from normally developing seeds and from motes of Upland cotton ( Gossypium hirsutum L. cv Acala SJ2 and cv Acala Maxxa) were compared with respect to cell wall cytochemistry. Fibers from motes (unfertilized ovules or aborted seeds) were used as a model for non-dyeing fibers, a contributor to poor quality textiles. Primary and secondary fiber walls were stained for pectin, cutin, suberin, callose, and cellulose. Up to 25 days post-anthesis (DPA), mote fibers had pectinaceous primary walls with a thin layer of cellulose, indistinguishable from primary walls of normally developing fibers. However, secondary walls in mote fibers had scanty, irregularly deposited cellulose, while secondary walls in normal fibers were well developed with thick cellulosic layers. At 29 DPA and at later stages of development, fibers on normal seeds had well-developed secondary walls, which were proportionally less developed on medium-sized and small motes. Nonetheless, fibers, which varied in diameter and cell wall thickness, were found on all normal seeds, on medium-sized and on small motes; most fiber cell walls were smaller in thickness at the chalazal than at the micropylar end. Regardless of their thickness, fibers on seeds and motes had cellulosic secondary cell walls. As most industrial dyes are specific for cellulose, the paucity of cellulose in mote fibers is consistent with the suggested causal relationship between lack of cellulose and the non-dyeing nature of some fibers. There were indications that immature fibers at the chalazal end of seeds may also contribute to dye imperfections in fabrics.

Spatial congruence between exine pattern, microtubules and endomembranes in Vigna pollen

The role of microtubules and endomembranes in pollen wall pattern formation in Vigna vexillata L. was examined using fluorescence laser scanning confocal microscopy. Indirect immunofluorescence using anti-β-tubulin antibodies revealed that the arrangement of the cortical microtubular cytoskeleton in microspores resembled the reciprocal of the reticulate ektexine ornamentations of mature V. vexillata pollen. Patches of microtubules in cortical cytoplasm corresponded in location with the lumina of the exine reticulum and with apertural sites. Microtubules were absent from cytoplasm under muri (ridges) of the exine reticulum. Labeling of microspores during the mid-tetrad stage with the endomembrane-specific fluorochrome DiOC6 produced a pattern similar to that of the microtubules; i.e., DiOC6 staining was localized in cytoplasm underlying lumina and absent from cortical cytoplasm underlying sites of muri. This report represents the first observation of congruence of the pattern of occurrence of any subcellular organelles with exine pattern and, in particular, the congruence of both microtubules and endomembranes in cortical cytoplasm with the lumina of the reticulate exine.

Texture, composition and anatomy of spinach leaves in relation to nitrogen fertilization

BACKGROUND The postharvest quality and shelf life of spinach are greatly influenced by cultural practices. Reduced spinach shelf life is a common quandary in the Salinas Valley, California, where current agronomic practices depend on high nitrogen (N) rates. This study aimed to describe the postharvest fracture properties of spinach leaves in relation to N fertilization, leaf age and spinach cultivar. RESULTS Force-displacement curves, generated by a puncture test, showed a negative correlation between N fertilization and the toughness, stiffness and strength of spinach leaves (P > 0.05). Younger leaves (leaves 12 and 16) from all N treatments were tougher than older leaves (leaves 6 and 8) (P > 0.05). Leaves from the 50 and 75 ppm total N treatments irrespective of spinach cultivar had higher fracture properties and nutritional quality than leaves from other N treatments (P > 0.05). Total alcohol-insoluble residues (AIR) and pectins were present at higher concentrations in low-N grown plants. These plants also had smaller cells and intercellular spaces than high-N grown leaves (P > 0.05). CONCLUSION Observed changes in physicochemical and mechanical properties of spinach leaves due to excess nitrogen fertilization were significantly associated with greater postharvest leaf fragility and lower nutritional quality.

Reproductive short-shoots of Ginkgo biloba: A quantitative analysis of the disposition of axillary structures

Ginkgo biloba, the only living representative in an otherwise extinct clade, is of pivotal importance to understanding seed plant phylogeny. Although G. biloba and its fossil relatives have been studied for over two centuries, there are both gaps and contradictions in the information available. We present data documenting the distributions of strobili and consider what an understanding of the disposition of strobili along short-shoots in Ginkgo adds to knowledge of the evolution of reproductive structures in seed plants in general. The megasporangiate strobili are found at and around the boundary between bracts and foliage leaves, while the expanse of microsporangiate strobili centers on the fifth bract back from that boundary. Quantitative analysis of the locations of the strobili along the short-shoot finds that increases in numbers of strobili are the result of recruitment of adjacent axils into morphogenetic activity. Gaps in the series of strobili are exceedingly rare. Further, while increased numbers of megasporangiate strobili arise from the symmetrical addition of axils into the fertile zone, increased numbers of microsporangiate strobili arise from a distinctly asymmetrical, basipetally biased, addition of axillary positions. This accurate morphological framework should orient molecular genetic studies that probe gymnosperm development itself or that consider gymnosperms as the proximate sources of gene expression redeployed in the origin of the angiosperm flower.

Root contraction in hyacinth IV. Orientation of cellulose microfibrils in radial longitudinal and transverse cell walls

SummaryCellulose microfibrils (MFs) were visualized on the inner surface of root cortex cell walls ofHyacinthus orientalis L. using a replica technique. Microfibril orientation was determined in radial longitudinal and transverse cell walls of the root tip, uncontracted, contracting, and fully contracted regions of the root. In longitudinal walls, the innermost MFs were ordered and parallel to one another and were oriented transversely, axially or obliquely, depending upon the developmental stage of the region. In transverse walls MFs in a single layer formed crisscross or ordered parallel arrays, depending upon the region. Parallel arrays were oriented either parallel, perpendicular, or oblique to the radius of the root. Inner walls of certain cells in the contracting region had MFs which appeared interrupted over their lengths. In general, these findings parallel earlier immunofluorescence and electron microscopic observations of changing cortical microtubule (MT) orientation accompanying root contraction. The major exception to MT-MF congruence occurred in cells of the actively contracting region. In middle and outer cell layers, MFs appeared short and partially obscured, while MTs in these cells occurred in conspicuous laterally aggregated strands parallel to one another over the length of the cells or were absent. This alteration in MF-MT parallelism may be related to the reorientation in cell growth occurring in the contractile zone or to the collapse of specific cells during the process of root contraction.