Palisade mesophyll

Although Ames/A varies with plant species as well as with leaf development, it is usually between 10 and 40 for mesophytes (Bjorkman, 1981 Nobel and Walker, 1985). We can appreciate the large values of Ames/A by examining Figures 1-2, 8-4, and 8-7, which indicate that a tremendous amount of cell wall area is exposed to the air within a leaf for example, the palisade mesophyll is usually 15 to 40% air by volume, and the spongy... 

Suppose that a shade leaf has a layer of tightly packed palisade mesophyll cells with rectangular sides that are externally 30 pm x 100 pm and with square ends 30 pm x 30 pm (the long dimension is perpendicular to the leaf surface). Suppose that there are two spherical spongy mesophyll cells (30 pm in diameter) under each palisade cell. Let the cell wall thickness of mesophyll cells be 0.2 pm, the mean distance from the plasma membrane to the chloroplasts be 0.1 pm, and the average distance that CO2 diffuses in the chloroplasts before reaching the photosynthetic enzymes be 0.5 pm. 

A. We will calculate the total surface area of the palisade mesophyll cells (rectangular parallelepipeds) and spongy mesophyll cells (spheres) and express it per unit area of the leaf surface ... 

A second proof comes from wounding experiment of Pseudowintera colorata Raoul (Gould et al, 2002b). In contrast to green leaves, the red ones, enriched in vacuolar antho-cyanins, flavonols, dihydroflavonols, and HCAs, alleviate intensity and duration of the localized burst of H2O2 induced in palisade mesophyll cells by wounding. Vacuolar phenolics participate to scavenge ROS. 

Air pollutants may enter plant systems by either a primary or a secondary pathway. The primary pathway is analogous to human inhalation. Figure 8-2 shows the cross section of a leaf. Both of the outer surfaces are covered by a layer of epidermal cells, which help in moisture retention. Between the epidermal layers are the mesophyll cells—the spongy and palisade parenchyma. The leaf has a vascular bundle which carries water, minerals, and carbohydrates throughout the plant. Two important features shown in Fig. 8-2 are the openings in the epidermal layers called stomates, which are controlled by guard cells which can open and close, and air spaces in the interior of the leaf. 

The classic ozone symptoms on angiosperms are the upper surface fleck of tobacco and stipple of grape. These classic symptoms were described in plants with differentiated mesophyll and are especially significant, because they were identified with palisade cells, and not with spongy cells. 

Fluorides are readily translocated to the tip and margin of leaves in the transpiration stream. If atmospheric levels of HF are low enough, the intercostal injury will not develop, and the fluoride concentration will increase at the periphery of the leaf. Acute fluoride intoxication at the margin of dicotyledonous plants, according to Solberg et al. (18), is first characterized by a collapse of the spongy mesophyll and lower epidermis, followed by distortion and disruption of the chloroplasts of the palisade cells, and finally, distortion and collapse of the upper epidermis. The injured area soon turns brown during hot, dry weather, but this symptom may be delayed if the weather is cool and damp. 

Representations of mesophyll cells showing how geometry affects Ames/A. Spheres or cylinders with hemispherical ends in an orthogonal (right-angled) array lead to the indicated Ames/A. The length of the lateral walls of the palisade cells in panel c is six times the radius r. 

B. Assume that a sun leaf on the same plant has two layers of palisade cells and half as many spongy mesophyll cells. If the dimensions of the cells are the same as for the shade leaf, what is AmesM for the sun leaf ... 

Nicotine is mainly located in the intercostal areas of the leaf (247, 289, 290). Chojecki (291), by microchemical technique, has arrived at the following depots of nicotine in the tobacco plant given in the order of decreasing concentration leaf epidermis, particularly at the base of the hairs, spongy mesophyll tissue of the leaves, primary cortex of roots, epidermis and parenchymatous tissue of the stem and palisade tissue of the leaves small amounts in the phloem and xylem of the stem, in the veins of the leaves, and in the medulla of the stem and traces in flowers and axial cylinders of the roots. 

The third stage of lesion development was characterized by collapse of spongy parenchyma cells adjacent to epidermal and palisade parenchyma cells (Fig. 9). Initially, spongy mesophyll cells exhibited cell wall distortions. Eventually they collapsed completely. In the last stage of injury, all tissues except vascular tissues were completely collapsed. 

The histological stages of lesion development in leaves of G. max were similar to those in P. aquilinum, P. vulgaris> and H. annuus. Lesions were initiated by collapse of several cells on the adaxial epidermis. Epidermal cell collapse was followed by a distortion of palisade parenchyma cells. This mesophyll tissue layer exhibited extensive hyperplasia. Occasionally, slightly enlarged cells were observed concomitant with this hyperplasia. Hyperplasia and hypertrophy occurred prior to cell collapse. 

Fig. 7-10. Leaf cross sections of Phaseolus vulgaris > hybrids of Populus sp., and Quercus palustris after one to several rainfalls of simulated acid rain of low pH. Fig. 7. Initial injury of epidermal cells near a trichome hydathode. Note injury is greatest at the anticlinal walls of epidermal cells at the base of a hydathode on P. vulgaris. Fig. 8. Initial injury of subsidiary cells near the guard cells of a stoma. The cells of the palisade parenchyma appear normal on P. vulgaris. Fig. 9. A large lesion with an injured adaxial epidermis, palisade parenchyma, and spongy parenchyma near vascular tissues in poplar. Fig. 10. A cross-section of a gall on a leaf of palustris. Note both collapsed epidermal and palisade cells. Hypertrophy and hyperplasia of spongy mesophyll cells are also evident.

Leaves of pin oak showed a different sequence of steps in leaf injury from that seen in other plant species. Initially, injury began with collapse of adaxial epidermal cells. Initial lesions consisted of approximately one to six collapsed epidermal cells which resulted in a slight depression on the leaf surface. At this stage, all cells in the mesophyll layers, and the abaxial epidermis were unaffected. After several more simulated acid rainfalls larger lesions, with increased surface area and depth, developed from smaller lesions. These lesions encompassed five to fifteen collapsed epidermal cells. Penetration of acidic solutions into the mesophyll tissues resulted in collapse of epidermal and underlying palisade parenchyma cells. 

No quantitative changes in relationships of leaf tissue compartments were detected during this ejperiment (Fagerberg, urpubl.). However, because differences in the size of mesophyll cells, tissue compartments for the different sample periods varied. On a per unit of leaf surface (100 mm ) basis shade recovery leaves had larger palisade tissue compartments than fully shaded leaves. 

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