NECTARY STRUCTURE OF PEAR CULTIVARS AND ITS RELATION TO FIRE BLIGHT SUSCEPTIBILITY

Morphological features of nectaries of some species of the genus Rosa (Rosaceae)

Results are presented of our study of nectaries of 13 species of the genus Rosa from the collection of the M.M. Gryshko National Botanical Garden of the National Academy of Sciences of Ukraine. Using light microscopy, we described and illustrated their morphological features in details. Nectaries of all studied species were floral, hypanthial, symmetrical, non-septally structural, mesenchymatous, and persistent. Based on location of the androecium, nectaries were intrastaminal, and only Rosa henryi was found to have amphistaminal nectary. Each species was morphologically differentiated from others by one or more characters. We analyzed morphological features (diameter of nectary and throat of hypanthia, thickness of nectary tissue around throat of hypanthia and on the edge, form of nectary on the longitudinal section), on that basis we allocated groups of nectaries based on their shape – convex (cone- and dome-shaped), curved, and flat ones. The latter is typical for Rosa roxburghii, which, according to a number of other morphological features, is separated by taxonomists in a monotypic (monospecific) subgenus. Based on surface characteristics of the nectary, Rosa xanthina with papillary growns and Rosa henryi with a uniformly humped relief stood out the most examined species. We emphasized reduction of thickness of nectary tissue in radial direction, except for Rosa spinosissima, in which thickness was almost even throughout the whole area of the nectary. The listed morphological differences can be used as additional diagnostic characters at the species level. Such features as the outline of the nectary throat and edges are quite variable within species and were not taxonomically significant. We present original figures and photographs of nectaries in an outline and on a longitudinal section.

The major nectar protein of Brassica rapa is a non-specific lipid transfer protein, BrLTP2.1, with strong antifungal activity

Nectar is one of the key rewards mediating plant-mutualist interactions. In addition to sugars, nectars often contain many other compounds with important biological functions, including proteins. This study was undertaken to assess the proteinaceous content of Brassica rapa nectar. SDS-PAGE analysis of raw B. rapa nectar revealed the presence of ~10 proteins, with a major band at ~10 kDa. This major band was found to contain a non-specific lipid transfer protein encoded by B. rapa locus Bra028980 and subsequently termed BrLTP2.1. Sequence analysis of BrLTP2.1 predicted the presence of a signal peptide required for secretion from the cell, eight cysteines, and a mature molecular mass of 7.3 kDa. Constitutively expressed BrLTP2.1-GFP in Arabidopsis displayed accumulation patterns consistent with secretion from nectary cells. BrLTP2.1 was also found to have relatively high sequence similarity to non-specific lipid-transfer proteins with known functions in plant defense, including Arabidopsis DIR1. Heterologously expressed and purified BrLTP2.1 was extremely heat stable and bound strongly to saturated free fatty acids, but not methyl jasmonate. Recombinant BrLTP2.1 also had direct antimicrobial activity against an extensive range of plant pathogens, being particularly effective against necrotrophic fungi. Taken together, these results suggest that BrLTP2.1 may function to prevent microbial growth in nectars.

Review: Nectar biology: From molecules to ecosystems

Plants attract mutualistic animals by offering a reward of nectar. Specifically, floral nectar (FN) is produced to attract pollinators, whereas extrafloral nectar (EFN) mediates indirect defenses through the attraction of mutualist predatory insects to limit herbivory. Nearly 90% of all plant species, including 75% of domesticated crops, benefit from animal-mediated pollination, which is largely facilitated by FN. Moreover, EFN represents one of the few defense mechanisms for which stable effects on plant health and fitness have been demonstrated in multiple systems, and thus plays a crucial role in the resistance phenotype of plants producing it. In spite of its central role in plant-animal interactions, the molecular events involved in the development of both floral and extrafloral nectaries (the glands that produce nectar), as well as the synthesis and secretion of the nectar itself, have been poorly understood until recently. This review will cover major recent developments in the understanding of (1) nectar chemistry and its role in plant-mutualist interactions, (2) the structure and development of nectaries, (3) nectar production, and (4) its regulation by phytohormones.