Parenchyma, palisade

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. 

When the fleck is examined closely, the lesion can be associated with contiguous stomata in the upper surface. Often, the first visible symptom of ozone toxicity is the death of the palisade parenchyma cells that line the cavities directly beneath the upper stomata. In the case of beans (Phaseolus vulgaris L.) or tobacco (Nicotiana tabacum L.) and perhaps other plants, the upper stomata lie in patterns of arcs or circles, while the lower stomata are scattered randomly and regularly across the epidermis. 

Fig. 86.—Transverse section through portion of dorsoventral leaf blade of horehound Marrubium vulgare). Upper epidermis devoid of stomata up.ep.) lower epidermis which possesses stomata (1. ep) palisade parenchyma (pal.) spongy parenchyma (sp, p) xylem ( ) and phloem ph) regions of fibrovascular tissue of stronger vein long-pointed non-glandular trichome (I), branched tri-chomes (/(, ft fP) several types of glandular trichomes (gt, gt, gt , gi ).

Fig. 87.—Photomicrograph of cross-section through a portion of the leaf of a xerophyte, Ficus elasHca, showing upper epidermis u.e.), water storage tissue (w.5.), cystolith suspended on stalk within a cystolith sac (c> 5), palisade parenchyma spongy parenchyma (s.p.), vein (v), lower epidermis (l.e.), and...

Pig. 88.—Photomicrograph of a transverse section of a bifaciai leaf of Eucalyptus globulus showing epidermis (ep.), palisade parenchyma (pep.), toward both surfaces, spongy parenchyma (s.p.), vein (r), and oil reservoir (o.r.) lined with secretory epithelium. (Highiy magnified.)... 

Palisade layer A layer of palisade parenchyma (columnar or cylindrical cells rich in chloroplasts) in a leaf. 

The major phytoalexins formed by green tissues (cotyledons, leaves, bracts, and the epicarp of bolls) are the cadal.enes and lacinilines shown in Fig. 2 (12, 18). About 75% of these compounds are methylated in the cultivate 6. hirsutum (19), whereas methylation is either greatly restricted or absenfln the other cultivated cottons (G. arboreum, . herbaceum and Gi. barbadense). These compounds have been demonstFated Tn palisade parenchyma cel Is... 

At a later stage of injury palisade parenchyma cells collapsed adjacent to collapsed epidermal cells. The area of injured epidermis in most lesions increased in diameter so that ten to fifteen epidermal cells comprised the lesion when palisade cells... 

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. 

Ozone Flecking, stippling, bleached spotting, pigmentation conifer needle tips become brown and necrotic Oldest leaves most sensitive youngest least sensitive Palisade or spongy parenchyma in leaves with no palisade 0.03 59 4 hr... 

Cucurbit seeds are exalbuminous or lacking endosperm in the mature state. In such seeds the embryo is large in relation to the seed as a whole. It fills the seed almost completely and its body parts, particularly the cotyledons, store the food reserves for germination. Since the predominant tissue of the seed is cotyledonous, and since cotyledons are leaves, anatomy and histology of typical leaf tissue suffice to describe the preponderant part of the seed. Epidermal cells cover the cotyledonary surface followed by palisade and abundant parenchyma cells that contain the food reserves. Vascular tissues are also present. 

Palisade and spongy parenchyma are less distinct and dense. 

The seed coat is the outermost tissue layer which protects the embryonic structure and consists of approximately 7-8 % of the total dry weight in the mature bean with a protein content of 5% (db) (3 and 4). Two external anatomical features include the hilum and micropyle which each have a role in water absorption. The major components in the seed coat structure include a waxy cuticle layer, palisade cell layer, hourglass cells and thick cell-walled parenchyma cells. The cuticle is the outermost portion of the seed coat and its... 

In a later stage of gall formation, cells of both the palisade and spongy parenchyma areas exhibited hypertrophy and hyperplasia in response to simulated acid rain. These cell abnormalities generally caused elevations on both adaxial and abaxial leaf surfaces. 

Fig. 7. Seed coats of rapeseed. (A) Brown seed (B) yellow seed. X375. ep, epidermis pa, palisade cp, crushed parenchyma al, aleurone (endosperm). From Stringam et a/., 1974.

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