Ontogeny of glyoxysomes in maturing and germinated cotton seeds?a morphometric analysis

Abstract

Morphometric procedures were used with light and electron microscopy to examine glyoxysome number, volume, shape and distribution as well as mesophyll cell volume, in cotyledons of mature (50 d postanthesis), imbibed (5h) and germinated (24 and 37 h) cotton (Gossypium hirsutum L.) seeds. Additionally, activities of five glyoxysomal marker enzymes in cotyledon extracts were assayed at each of the above ages. Cell volume was determined from photomicrographs of Epon-embedded sections by the point-counting procedure. Analysis of variance showed that cell volume was not different among the tissue segments studied. Glyoxysomes were cytochemically stained for catalase (EC 1.11.1.6) activity with the 3,3'-diaminobenzidine-tetrahydrochloride procedure. Analyses involving both phase and electron microscopy, and two separate sterologic calculations for determining the number of glyoxysomes per cell, indicate that glyoxysomes are numerous in mature seeds, persist through desiccation and imbibition, then increase dramatically in volume (seven fold) but not number (a maximum of 1.5-fold), when enzyme activities increase two to six times (depending on the enzyme). During the entire period of increase in glyoxysomal enzyme activities, no ultrastructural evidence was found for glyoxysome formation or destruction. Our data, in contrast to some proposals in the literature, indicate that cottonseed glyoxysomes form during seed maturation, then develop following seed imbibition into pleomorphic organelles by posttranslational accumulation of proteins from the cytosol and transfer of membrane components probably from the endoplasmic reticulum.

Heterogeneity of Catalase in Maturing and Germinated Cotton Seeds

“…We previously found using morphometric procedures that peroxisomes of cotton cotyledons persist through seed desiccation and increase dramatically in volume (but not number) during postgerminative growth (17). No evidence was found for autophagy or turnover of entire organelles during the entire period studied (17).…”

“…Plant Material. Cotton plants, Gossypium hirsutum L. (AD), cv Deltapine 62 (Delta and Pine Land Co., Lubbock, TX) were grown under the conditions described previously (17), and flowers were tagged at anthesis to determine the age ofthe developing embryos. For studies with germinated seeds, acid-delinted seeds were surface sterilized in 1% (v/v) NaOCl for 10 min, rinsed thoroughly, soaked in distilled H20 for 6 h at 30C with aeration, then scrolled in moistened filter paper.…”

“…during imbibition, sowing, and harvesting) were performed under a green safelight, although it was determined later that these operations could be done in dim white light without consequence. For studies with green cotyledons, cotton seedlings were grown in moist vermiculite for 10 d in a glasshouse under conditions described previously (17 Nondenaturing PAGE. Nondenaturing PAGE was performed using the discontinuous buffer system of Davis (4), except the stacking gel and separating gel consisted of 3% polyacrylamide (2:0.5, acrylamide:bis-acrylamide) and 5% polyacrylamide (30:0.8, acrylamide:bis-acrylamide), respectively.…”

Five Arabidopsis peroxin 11 homologs individually promote peroxisome elongation, duplication or aggregation

“…In plant cells, there are numerous examples of terminal peroxisome elongation at different stages of growth and development. Specifically, peroxisomes in cotyledon cells of germinated oilseed seedlings, greening leaves and developing root nodules all undergo dramatic increases in spherical or cylindrical volume, but do not increase in number (Gruber et al, 1973;Wanner and Theimer, 1978;Kunce et al, 1984;Newcomb et al, 1985). Exposure of Arabidopsis suspension cells to ultraviolet (UV) irradiation induces extensive peroxisomal elongation without subsequent multiplication (proliferation) (our unpublished observations).…”

“…Collings et al observed horseshoe-and dumbbell-shaped peroxisomes at the cell plate within the phragmoplast of dividing onion-root meristem cells (Collings et al, 2003). Kunce et al documented elongation of glyoxysomes in cotyledons of growing cottonseed seedlings (Kunce et al, 1984). Significantly, no efforts were made in any of these studies to identify molecular elements or machinery related to these proliferative events.…”