Microscopy and chemical analyses reveal flavone-based woolly fibres extrude from micron-sized holes in glandular trichomes of Dionysia tapetodes.

BACKGROUND: Dionysia tapetodes, a small cushion-forming mountainous evergreen in the Primulaceae, possesses a vast surface-covering of long silky fibres forming the characteristic "woolly" farina. This contrasts with some related Primula which instead form a fine powder. Farina is formed by specialized cellular factories, a type of glandular trichome, but the precise composition of the fibres and how it exits the cell is poorly understood. Here, using a combination of cell biology (electron and light microscopy) and analytical chemical techniques, we present the principal chemical components of the wool and its mechanism of exit from the glandular trichome. RESULTS: We show the woolly farina consists of micron-diameter fibres formed from a mixture of flavone and substituted flavone derivatives. This contrasts with the powdery farina, consisting almost entirely of flavone. The woolly farina in D. tapetodes is extruded through specific sites at the surface of the trichome's glandular head cell, characterised by a small complete gap in the plasma membrane, cell wall and cuticle and forming a tight seal between the fibre and hole. The data is consistent with formation and thread elongation occurring from within the cell. CONCLUSIONS: Our results suggest the composition of the D. tapetodes farina dictates its formation as wool rather than powder, consistent with a model of thread integrity relying on intermolecular H-bonding. Glandular trichomes produce multiple wool fibres by concentrating and maintaining their extrusion at specific sites at the cell cortex of the head cell. As the wool is extensive across the plant, there may be associated selection pressures attributed to living at high altitudes.

Are the glandular trichomes in Jacquinia armillaris (Theophrastoideae-Primulaceae) salt glands?

Salt stress is harmful to plants, especially for those that live under conditions of intense salt aport. For this reason, several species present alternatives to prevent or diminish the damages that high salt concentrations may cause to the cells. Salt glands are one of these alternatives once they are specialized structures that secrete salt. Here, we aimed to investigate if the glandular trichomes in the leaves of Jacquinia armillaris are salt glands. Anatomical and ultrastructural observations showed that the glandular trichomes in J. armillaris resemble the salt glands from other recretohalophytes Primulaceae, such as, their occurrence in sunken regions in the leaf epidermis, the presence of a large basal cell that acts as a collecting cell, the detachment of the cuticle from the outer periclinal walls forming a cuticular chamber, the thickness of the cuticle in the stalk portion of the trichome, and the presence of sodium and chloride ions in the secretion and in the xylem. Altogether, the gathered results support the hypothesis that the glandular trichomes in J. armillaris are adapted to salt secretion, thus characterizing as salt glands.

Selection of reference genes for normalization of quantitative real-time PCR in cell cultures of Cyclamen persicum

As a prerequisite for gene expression analyses in cell cultures of the ornamental crop Cyclamen persicum basic parameters for quantitative real-time polymerase chain reaction (qRT-PCR) have been established including the selection of reference genes using the software tools ‘geNorm’ and ‘NormFinder’. Five potential reference genes have been tested (elongation factor tu (Ef-Tu), putative ABC transporter ATPase, putative conserved oligomeric Golgi (COG) complex component, V-ATPase G subunit 1 and Histone H3-K9 methyltransferase 4 (H3-K9-HMTase 4)). ‘NormFinder’ as well as ‘geNorm’ identified Ef-Tu to be the least stable reference gene while the ranking of the most stable genes differed depending on the algorithm. According to ‘NormFinder’ COG complex component displayed the most stable expression whereas ‘geNorm’ indicated V-ATPase G subunit 1 and a putative ABC transporter ATPase to be the most reliable reference genes. Hence, we concluded to use a normalization factor calculated from the four reference genes V-ATPase G subunit 1, ABC transporter ATPase, Histone H3-K9 methyltransferase 4 (H3-K9-HMTase 4) and COG complex component for normalization of qRT-PCR in cell cultures of Cyclamen persicum.