Antibodies against Yariv's reagent for immunolocalization of arabinogalactan-proteins in aerial parts of Echinacea purpurea.

Arabinogalactan-proteins are glycoproteins that occur in higher plants and are involved in important processes like cell differentiation and plant growth. In the medicinal plant Echinacea purpurea L., they belong to the putative immunomodulating compounds and are structurally well characterized. For microscopic localization of arabinogalactan-proteins, synthetic (ß-D-Glc)3 Yariv phenylglycoside that specifically binds to most plant arabinogalactan-proteins was used to label arabinogalactan-proteins in fresh cut sections of stems and petioles of Echinacea purpurea. Polyclonal antibodies against (ß-D-Glc)3 Yariv phenylglycoside were used to detect the arabinogalactan-protein-(ß-D-Glc)3 Yariv phenylglycoside complex. After addition of fluorescein isothiocyanate-conjugated secondary antibodies, the sections were analyzed by confocal laser scanning microscopy. Arabinogalactan-proteins are localized mainly in the central cylinder in the collateral vascular bundles, especially in the area of the xylem. In cell walls of fully differentiated vessels and tracheids, arabinogalactan-proteins have been detected mainly at the inner area of the wall close to the cell lumina. Intense labeling occurs around pit canals connecting adjacent vessels. Furthermore, arabinogalactan-proteins are present in the lumina of cells of the sclerenchyma caps and in companion cells of the phloem.

Floral nectar production and nectary anatomy and ultrastructure of Echinacea purpurea (Asteraceae).

BACKGROUND AND AIMS: In spite of the impressive species diversity in the Asteraceae and their widespread appeal to many generalist pollinators, floral-nectary ultrastructure in the family has rarely been investigated. To redress this, a study using Echinacea purpurea, a plant of horticultural and nutraceutical value, was undertaken. Nectar secretion of disc florets was compared with floral nectary ultrastructure taking into account nectar's potential impact upon the reproductive success of this outcrossing species. METHODS: Micropipette collections of nectar in conjunction with refractometry were used to determine the volume and nectar-sugar quantities of disc florets throughout their phenology, from commencement of its production to cessation of secretion. Light, scanning-electron and transmission-electron microscopy were utilized to examine morphology, anatomy and ultrastructure of nectaries of the disc florets. KEY RESULTS: Florets were protandrous with nectar being secreted from anthesis until the third day of the pistillate phase. Nectar production per floret peaked on the first day of stigma receptivity, making the two innermost whorls of open florets most attractive to foraging visitors. Modified stomata were situated along the apical rim of the collar-like nectary, which surrounds the style base and sits on top of the inferior ovary. The floral nectary was supplied by phloem only, and both sieve elements and companion cells were found adjacent to the epidermis; the latter participated in the origin of some of the precursor cells that yielded these specialized cells of phloem. Companion cells possessed wall ingrowths (transfer cells). Lobed nuclei were a key feature of secretory parenchyma cells. CONCLUSIONS: The abundance of mitochondria suggests an eccrine mechanism of secretion, although dictyosomal vesicles may contribute to a granulocrine process. Phloem sap evidently is the main contributor of nectar carbohydrates. From the sieve elements and companion cells, an apoplastic route via intercellular spaces and cell walls, leading to the pores of modified stomata, is available. A symplastic pathway, via plasmodesmata connecting sieve elements to companion, parenchyma and epidermal cells, is also feasible. Uncollected nectar was reabsorbed, and the direct innervation of the nectary by sieve tubes potentially serves a second important route for nectar-sugar reclamation. Microchannels in the outer cuticle may facilitate both secretion and reabsorption.