A proteomics approach has been used to study changes in protein abundance during leaf senescence in white clover. Changes in cell ultrastructure were also examined using transmission electron microscopy. The most obvious ultrastructural changes during senescence occurred in chloroplasts, with progressive loss of thylakoid integrity and accumulation of osmiophilic globules in the stroma. Quantitative analysis of 590 leaf protein spots separated by two-dimensional electrophoresis indicated that approximately 40% of the spots showed significant senescence related changes in abundance. Approximately one-third of the protein spots present in mature green leaves were also visible by two-dimensional electrophoresis of an isolated chloroplast fraction, and these spots represented a major proportion of the proteins showing senescence related declines in abundance. Chloroplast proteins that were identified by matrix-assisted laser desorption/ionization-time of flight mass fingerprinting included rubisco large and small subunits, a rubisco activase and the 33 kDa protein of the photosystem II oxygen-evolving complex. These proteins declined in abundance late in senescence, indicating that the photosynthetic apparatus was being degraded. A chloroplast glutamine synthetase showed partial decline in abundance during late senescence but was maintained at levels that may support provision of glutamine for export to other tissues. The results emphasise the importance of proteolysis, chloroplast degradation and remobilisation of nitrogen in leaf senescence.
The total RNA extracted from rye embryos (Secale cereale) and seed of the broad bean (Vicia faba), pea (Pisum sativum) and oil-seed rape (Brassica napus) exhibits low levels of template activity when incubated in a wheat-germ cell-free protein-synthesising system. The RNA from pea, rapeseed and rye embryos was fractionated by chromatography on oligo dT-cellulose columns. Most of the template-active RNA bound to the column at high ionic strength, indicating that it is polyadenylated. The remainder would not bind, even when passed through the column several times. The proteins synthesised in vitro from the template-active RNA migrated as numerous bands in polyacrylamide gels and ranged in molecular weight from 10,000 to 70,000. The banding patterns obtained were quite different for the three species of seed tested. It is concluded that dry seeds contain a store of intact, long-lived mRNA.
A simple, nondestructive physical process was developed for routinely isolating the outermost layers from female, male, and sporophyte fronds of Chondrus crispus Stack‐house. Yields of pure cuticles from apical segments ranged from 0.74 to 2.35% on a dry weight basis after 5–7 d of culture. These undegraded cuticles were examined by electron microscopy (scanning and transmission electron microscopy), spectroscopy (infrared and X‐ray), and chemical means. Cuticles isolated from female or male fronds were characterized by parallel arrays of electron‐dense lamellae (typically 6–14) alternating with more electron‐transparent regions. The thickness and uniformity of these lamellae provide the physical basis for the iridescence characteristic of C. crispus fronds. Sporophyte fronds are not iridescent. This phenomenon may be explained by the fewer electron‐dense cuticular lamellae (usually three to seven) and the fact that these lamellae anastomose freely to form a thin cuticle with a highly irregular substructure. Elements detected by X‐ray analysis, in addition to carbon and oxygen, included Mg, Br, S, and Ca in both gametophyte and sporophyte cuticles. Major features of FTIR spectra of all cuticles were absorbances due to proteins. A strong band, indicative of sulfate ester, occurred near 1250 cm−1 in all cuticle preparations. Gametophyte, but not sporophyte, cuticles absorbed at 935, 846, and 800 cm−1 consistent with the presence of kappa and/or iota carrageenan. Amino acid analyses showed that sporophyte and gametophyte cuticles were generally similar in gross composition. All contained proline as the principal residue together with significant amounts of cysteine, methionine, and lysine. Protein contents calculated from these analyses ranged from 37.6 to 44.4% on a dry weight basis as compared to 51.5–56.7% calculated from total nitrogen values. Up to 75% of the cuticle mass was solubilized by sodium dodecyl sulfate‐β‐mercaptoethanol. Three similar migrating bands were seen in female and male cuticle extracts on sodium dodecyl sulfate–polyacrylamide gel electrophoresis; however, none of the three weaker bands from sporophyte cuticles comigrated with those from gametophytes. Chloroform‐methanol extraction removed < 3.3% of the cuticle mass, suggesting that lipids were minor components.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.