In plants, parenchyma refers to a tissue composed of living cells, usually having only thin, primary cell walls and varying widely by morphology and metabolism. Parenchyma in the primary plant body often occurs as a continuous mass, such as in the cortex or pith of stems and roots, the mesophyll of leaves and the flesh of fruits. In vascular tissue parenchyma cells form axial strands that run along the length of the plant body and, where secondary growth occurs, in radial files that run from the outer tissues towards the pith. The unifying characteristic of all parenchyma cells is that they are living at maturity and capable of cell division, giving them important roles in regeneration and wound healing. Other key functions of these cells include photosynthesis, storage, secretion and transport.

Key Concepts:

  • Parenchyma refers to both a cell type and a simple tissue and is found within all three tissue systems of vascular plants: the dermal, ground (fundamental) and vascular tissue systems.

  • Parenchyma functions are diverse and dependant on both location within the plant and morphological specialisation.

  • Parenchyma forms the bulk of plant ground tissue, where they may be specialised to function in photosynthesis, storage, or transport.

  • Parenchyma is integral to vascular tissue, where it provides a route of exchange for materials within and between the xylem and the phloem.

  • Parenchyma is composed of living cells that retain the ability to divide and hence play a key role in several developmental processes, as well in plant response to wounding.

Keywords: eukaryotic; plant cells; primary cell walls; metabolism; meristematic state; totipotency; vegetative reproduction

Figure 1.

Parenchyma comprise the bulk of the primary plant body, as seen in the cortex of these meadow buttercup (Ranunculus acris) stem (a and b) and root (c and d) cross‐sections. Symbols indicate: c, cortex; chl, chlorenchyma; en, endodermis and p, pericycle. Scale bars show magnification in millimetre. Images of prepared slides from Carolina Biological Supply Company, photo credit: M.L. Pruyn.

Figure 2.

Ray and axial parenchyma in secondary xylem (i.e. wood). (a) Rays (plates of radially oriented parenchyma) in tangential longitudinal section of Fraxinus americana. (b) Ray and axial parenchyma in radial longitudinal section of F. americana (4′,6‐diamidino‐2‐phenylindole (DAPI)‐stained nuclei visible under epifluorescent (UV) illumination). Axial parenchyma [ap] is found adjacent to vessels [v] and intersects ray parenchyma. (c) A single ray in Pinus strobus showing nuclei (arrowheads) and starch‐storing amyloplasts (arrow). The red cellular contents are the product of tetrazolium reduction and indicate active mitochondrial respiration. Scale bar=50 μm. Photo credit: R. Spicer.

Figure 3.

Pigment‐storing plastids in parenchyma. (a) Chlorenchyma from a leaf of Elodea canadensis; cholorplasts are surrounding the vacuoles in each cell and in live specimens are often moving in an orderly fashion around the cell via cytoplasmic streaming. (b) Chromoplasts filled with carotenoid and other pigments from the flesh of red pepper (Capsicum annum). Scale bars=50 μm. Images of fresh mounts, photo credit: M.L. Pruyn.

Figure 4.

Calcium oxalate crystals in vacuoles of storage parenchyma. (a) Druse crystals [d] in parenchyma of the stems of geranium (Pelargonium × hortorum, a complex hybrid largely derived from Pelargonium inguinans and Pelargonium zonale), which are adjacent to vascular tissue [v]. (b) Raphide crystals [r] in parenchyma of snake plant leaves (Sansevieria trifasciata), which are a few cell layers adjacent to the vascular tissue [v]. Chloroplasts are visible as small green discs in the parenchyma in both panels. Scale bars=50 μm. Images of fresh mounts, photo credit: M.L. Pruyn.

Figure 5.

Leaf parenchyma cells from the two perennials: (a) woody oleander (Nerium oleander) and (b) herbaceous water lily (Nymphaea sp.). Cross‐sections show the tightly packed palisade parenchyma [p] above the spacious lobe‐shaped, spongy mesophyll [m], both filled with chloroplasts (stained red in water lily). Vascular cylinders [v] are embedded within the mesophyll to facilitate transport among the cells. Also visible in the oleander are sunken stomata [st] with surrounding protective trichomes [tr], and in the water lily mesophyll is a branched sclereid [s]. Scale bar=50 μm. Images of prepared slides from Carolina Biological Supply Company, photo credit: M.L. Pruyn.



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How to Cite close
Pruyn, Michele L, and Spicer, Rachel(Aug 2012) Parenchyma. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0002083.pub2]