SUMMARY
Secretory tissues occur in most vascular plants. Some of these tissues, such as hydathodes, salt glands and nectaries, secrete unmodified or only slightly modified substances supplied directly or indirectly by the vascular tissues. Other tissues secreting, for instance, polysaccharides, proteins and lipophilic material, produce these substances in their cells. The cells of secretory tissues usually contain numerous mitochondria. The frequency of other cell organelles varies according to the material secreted. In most glandular trichomes the side wall of the lowest stalk cell is completely cutinized. This prevents the secreted material from flowing back into the plant.

The salt glands in Atriplex eliminate salt into the central vacuole of the bladder cell but, in other plants, the glands secrete salt to the outside. Different views exist as to the manner in which salt is eliminated from the cytoplasm. According to some authors, the mode of elimination is an eccrine one, while others suggest the involvement of membrane-bound vesicles.

Nectar is of phloem origin. The pre-nectar moves to the secretory cells through numerous plasmodesmata present in the nectariferous tissue. Nectar is eliminated from the secretory cells by vesicles of either KR or dictyosomal origin. In some cases, both organelles may be involved but an eccrine mode of nectar secretion has also been suggested by some authors.

Carbohydrate mucilages and gums are synthesized by dictyosomes but virtually every cell compartment has been suggested as having a role on the secretion of lipophilic substances. Most commonly, plastids are implicated in the synthesis of lipophilic materials but KR may also play a part. In some cases lipophilic materials may be transported towards the plasmalemma in the KR.

Resin and gum ducts of some plants develop normally or in response to external stimuli, such as microorganisms or growth substances. Among the latter, ethylene is the most effective.

During the course of evolution, secretory tissues seem to have developed from secretory idioblasts scattered among the cells of the ordinary tissues. Subsequently ducts and cavities developed and finally secretory trichomes.

Secretory tissues in vascular plants

https://harvardforest.fas.harvard.edu/sites/harvardforest.fas.harvard.edu/files/publications/pdfs/Aloni_Differentiation_1983.pdf

The control of vessel size and density along the plant axis: a new hypothesis

Structure-function relationships in highly modified shoots of cactaceae.

The distribution of mucilage cells in vegetative parts of the dicotyledons is reviewed on the basis of an extensive literature study. Mucilage or slime cells occur in 144 families, belonging to 47 orders as defined in Takhtajan's system of classification. Their systematic and diagnostic value at different levels of the taxonomic hierarchy is discussed. Although mucilage cells are generally diagnostic at the species level, variation within genera and families seriously limits the systematic significance in mostphylads. The core families of the Malvales, which are all mucilaginous, constitute an exception at the ordinal level, while in a number of genera, families, and orders the distribution of mucilage cells tends to be associated with natural groups. In most families and orders of the subclass Asteridae, mucilage cells are absent from the vegetative organs. Development, ultrastructure, histochemistry, and distribution of mucilage cells are briefly reviewed. In almost all well documented cases, m...

A survey of mucilage cells in vegetative organs of the dicotyledons

SUMMARY Drought-induced changes in hydraulic conductivity (Lp) and anatomy were investigated for 1-, 3- and 12-monthold roots of Ferocactus acanthodes (Lem.) Britton & Rose and Opuntia ficus-indica (L.) Miller. Responses were

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.1992.tb01053.x

Drought-induced changes in hydraulic conductivity and structure in roots of Ferocactus acanthodes and Opuntia ficus-indica

The mucilage cells of Opuntia ficus-indica start to differentiate in the apical meristem of the shoot. Six stages of development have been distinguished, based on ER development, Golgi body differentiation, and appearance of mucilage. Cytochemical tests of polysaccharides confirmed that only the Golgi bodies are involved in mucilage secretion and also suggest that the mucilage passes through the plasmalemma by reverse pinocytosis.

A. Fahn

Papers

The Mucilage Cells of Opuntia ficus-indica (L.) Mill.-Development, Ultrastructure, and Mucilage Secretion