Our understanding of the precise role(s) of polyamines (PAs) in various plant developmental and morphogenetic processes has advanced considerably by the ability to manipulate PA biosynthetic pathways using polyamine biosynthesis inhibitors, PA‐ mutants and by adopting various transgenic strategies. The cDNA for almost every biosynthesis pathway enzyme has been isolated and cloned in a number of systems. This review briefly summarizes our current understanding of the genetic control of PA metabolism in different model plant systems.

In flowering plants, pollen grains are produced in the anther and released to the external environment with the primary function of delivering sperm cells to the female gametophyte. This study was conducted to identify proteins in tomato pollen and to analyse their roles in relation to pollen function. Tomato is an important crop which is grown worldwide and is an excellent experimental system. Proteins were extracted from pollen, separated by two-dimensional gel electrophoresis (2-DE), and identified by matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) and peptide mass fingerprinting. Of the 960 spots observed on Colloidal Coomassie Blue (CCB)-stained 2-DE gels, 190 were selected for analysis. Of these, 158 spots, representing 133 distinct proteins, were identified by searching the NCBInr and Expressed Sequence Tag databases. The identified proteins were classified based on designated functions and the majority included those involved in defence mechanisms, energy conversions, protein synthesis and processing, cytoskeleton formation, Ca(2+) signalling, and as allergens. A number of proteins in tomato pollen were similar to those reported in the pollen of other species; however, several additional proteins with roles in defence mechanisms, metabolic processes, and hormone signalling were identified. The potential roles of the identified proteins in the survival strategy of the small, independent, two-celled pollen grain of tomato, and subsequently in pollen germination and tube growth are discussed.

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Proteome analysis of mature Arabidopsis thaliana (Landsberg erecta ecotype) pollen was conducted using two-dimensional gel electrophoresis and mass spectrometry. A total of 960 spots were resolved on pH 4-7 IPG strips and 110 distinct proteins were identified from 150 spots analyzed. The identified proteins were categorized based on their functional role in the pollen, which included proteins involved in energy regulation, defense-related mechanisms, calcium-binding and signaling, cytoskeletal formation, pollen allergens, glycine-rich proteins (GRPs), and late embryogenesis abundant (LEA) proteins. These proteins potentially play important roles in pollen function at maturity and during subsequent germination and tube growth. Some of the proteins identified were related to known pollen-specific transcripts, while some were similar to proteins found in the seed. In this study, 66 new proteins were identified which were not reported in two other recent studies on Arabidopsis pollen, 17 proteins were common in all three studies, and 35 or 26 proteins reported here had an overlap with one or the other two studies. These differences may be attributed to the methods of protein extraction, spot selection for analysis, and the ecotype used. Together, the three studies provide a broad spectrum of the Arabidopsis pollen proteome.

Proteome analysis of embryo and endosperm tissues from germinating tomato seed was conducted using 1-DE, 2-DE, and MS. Mobilization of the most abundant proteins, which showed similar profiles in the two tissues, occurred first in the endosperm. CBB R-250 staining of 2-DE gels revealed 352 and 369 major protein spots in the embryo and endosperm, respectively, at 0 h. Of these, 75 major spots were selected, excised, in-gel digested with trypsin, and analyzed by MALDI-TOF-MS and/or LC-ESI-Q/TOF-MS/MS. Peptide MS and MS/MS data were searched against publicly available protein and EST databases, and 47 proteins identified. Embryo-specific proteins included a BAC19.13 homologue, whereas four proteins specific to the endosperm were tomato mosaic virus coat proteins related to defense mechanisms. The most abundant proteins both in the embryo and endosperm were seed storage proteins, i.e., legumins (11 spots), vicilins (11 spots), albumin (2 spots). Housekeeping enzymes, actin-binding profilin, defense-related protein kinases, nonspecific lipid transfer protein, and proteins involved in general metabolism were also identified. The roles of some of the proteins identified in the embryo and endosperm are discussed in relation to seed germination in tomato.

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