Characterisation of cell death in bagged baby salad leaves

Baby leaf salads are gaining in popularity over traditional whole head lettuce salads in response to consumer demand for greater variety and convenience in their diet. Baby lettuce leaves are mixed, washed and packaged as whole leaves, with a shelf-life of approximately 10 days post-processing. End of shelf-life, as determined by the consumer, is typified by bruising, water-logging and blackening of the leaves, but the biological events causing this phenotype have not been studied to date. We investigated the physiological and ultrastructural characteristics during postharvest shelf-life of two lettuce varieties with very different leaf morphologies. Membrane disruption was an important determinant of cell death in both varieties. although the timing and characteristics of breakdown was different in each with Lollo rossa showing signs of aging such as thylakoid disruption and plastoglobuli accumulation earlier than Cos. Membranes in Lollo rossa showed a later, but more distinct increase in permeability than in Cos. as indicated by electrolyte leakage and the presence of cytoplasmic fragments in the vacuole, but Cos membranes show distinct fractures towards the end of shelf-life. The tissue lost less than 25% fresh weight during shelf-life and there was little protein loss compared to developmentally aging leaves in an ambient environment. Biophysical measurements showed that breakstrength was significantly reduced in Lollo rossa, whereas irreversible leaf plasticity was significantly reduced in Cos leaves. The reversible elastic properties of both varieties changed throughout shelf-life. We compared the characteristics of shelf-life in both varieties of bagged lettuce leaves with other leafy salad crops and discuss the potential targets for future work to improve postharvest quality of baby leaf lettuce. (C) 2007 Elsevier B.V. All rights reserved.

The pgip family in soybean and three other legume species: evidence for a birth-and-death model of evolution

Background Polygalacturonase-inhibiting proteins (PGIPs) are leucine-rich repeat (LRR) plant cell wall glycoproteins involved in plant immunity. They are typically encoded by gene families with a small number of gene copies whose evolutionary origin has been poorly investigated. Here we report the complete characterization of the full complement of the pgip family in soybean (Glycine max [L.] Merr.) and the characterization of the genomic region surrounding the pgip family in four legume species. Results BAC clone and genome sequence analyses showed that the soybean genome contains two pgip loci. Each locus is composed of three clustered genes that are induced following infection with the fungal pathogen Sclerotinia sclerotiorum (Lib.) de Bary, and remnant sequences of pgip genes. The analyzed homeologous soybean genomic regions (about 126 Kb) that include the pgip loci are strongly conserved and this conservation extends also to the genomes of the legume species Phaseolus vulgaris L., Medicago truncatula Gaertn. and Cicer arietinum L., each containing a single pgip locus. Maximum likelihood-based gene trees suggest that the genes within the pgip clusters have independently undergone tandem duplication in each species. Conclusions The paleopolyploid soybean genome contains two pgip loci comprised in large and highly conserved duplicated regions, which are also conserved in bean, M. truncatula and C. arietinum. The genomic features of these legume pgip families suggest that the forces driving the evolution of pgip genes follow the birth-and-death model, similar to that proposed for the evolution of resistance (R) genes of NBS-LRR-type.