Leaf apex

FIGURE 4.5 Leaf and stem trichomes (A) adaxial surface, falcate and moniliform trichomes pointing toward the leaf apex (B) abaxial surface displaying falcate, moniliform, and glandular trichomes, the orientation of which is more random (C) glandular trichome found only on the abaxial surface (D) falcate and moniliform trichomes and (E) acuminate trichomes on an immature stem. 

The generative tissues are found in the growing apices of plant organs, such as root, stem and leaf apex. By the division and redivisions of their cells they give rise to the mature or adult tissues of plants. 

The questions ought to be applicable to all taxa to be keyed out in that particular part of the key. This seems obvious, but a question on leaf apex being either obtuse or acute is e.g. not applicable to the sausage-shaped leaves of certain speies of 8edum, and also not to emarginate or oblique leaf tops. 

Chloroplast development is coupled to leaf mesophyll cell development and is controlled, in part, by light (rev. 1, 2, 3). The extent of light control over chloroplast development varies considerably between plant species and leaf type. However, a common sequence of events can be discerned in most plants which leads from undifferentiated proplastids to photosynthetically active chloroplasts (1). This sequence of events has been studied extensively in monocots such as barley because of the spatial separation of stages in chloroplast development in these plants (4-7). Barley leaf cells are produced primarily by a meristematic zone located in the leaf base. These undifferentiated dividing cells contain 10 to 15 proplastids (5, 7). Proplastids accumulate 120 to 150 copies of plastid DNA but exhibit low overall transcription activity (7). Once cells in the leaf base stop dividing they are displaced toward the leaf apex due to cell enlargement and continued formation of cells in the leaf base. During the phase of cell... 

Leaf apex Rountieti Acuminate Acuminate Acute to rounded-apiculate... 

Two proteinase inhibitors, Inhibitors I and II, accumulate in leaves of tomato plants when attacked by chewing Insects or mechanically wounded. The accumulation of these two antinutrient proteins is apparently a defense response and is initiated by the release of a putative wound hormone called the proteinase Inhibitor inducing factor (PIIF). The direction of flow of PIIF out of wounded leaves is primarily towards the apex and transport occurs maximally about 120 min following wounding. After a single severe wound, the vitro translatable tomato leaf mRNA specific for Inhibitors I and II Increases to a maximum within four hours and remains constant for about five hours when it decreases rapidly to about 50% of the maximum. 

Cuneate Leaf A leaf truncate at the apex and tapering to a point at the base so that they appear wedge-shaped. 

The bioassay with dwarf peas is similar. Six to 7 days after the seed was planted the seedlings were about 4 cm. high. The first leaf infolded the growing point at the apex of the plant. The test solution was introduced onto the apical region with a 0.1-ml. pipet. Each treated plant received 0.05 fig. of gibberellic acid in a total volume of 0.01 ml. Five to 7 days after the time of treatment measurements were obtained for the shoot length from the point of seed attachment to the epicotyl. 

Figure 4. Sketches of representative leaves showing various leaf characteristics, (a) illustrates a lobed leaf with an acute apex, a round base, and no teeth (like (b) and (c)). (b) illustrates an ovate shaped leaf with an attenuated apex (drip-tip), and a cordate base, (c) illustrates an obovate shaped leaf with a round and emarginate apex, and an acute base, (d) illustrates a leaf margin with teeth that are compound, acute, closely spaced, and regularly spaced, (see Wolfe (1995)) [Used by permission of Geological Society of America, from Forest et al. (1999), Geol. Soc. Am. Bull., Vol. Ill, Fig. 6, p. 505.]...

Leaf size varies with position on the plant (Figure 4.1B), clone, and agronomic practices (Pas ko, 1973). Leaves are smaller at the base of the plant, largest midway up the stem, and then decline in size toward the apex. Leaf size on lateral branches depends upon the branches position relative to light inception. Leaves on flowering branches are typically considerably smaller than on the stems and lateral branches. 

Secondary metabolites can accumulate in the same cell and tissue in which they are formed, but intermediates and end-products can also be transported to other locations for further elaboration or accumulation. For example, TAs and nicotine are typically produced near the root apex, but mostly accumulate within leaf cell vacuoles. Even TA biosynthesis itself involves intercellular transport of several pathway intermediates (Fig.7.9A). P-Glucuronidase (GUS) localization in A. belladonna roots transformed with a PMT promoter-GUS fusion showed that PMT expression is restricted to the pericycle.144 Immunolocalization and in situ RNA hybridization also demonstrated the pericycle-specific expression of H6H.145,146 In contrast, TR-I was immunolocalized to the endodermis and outer root cortex, whereas TR-II was found in the pericycle, endodermis, and outer cortex.85 The localization of TR-I to a different cell type than PMT and H6H implies that an intermediate between PMT and TR-I moves from the pericycle to the endodermis (Fig.7.9A). Similarly, an intermediate between TR-I and H6H must move back to the pericycle. The occurrence of PMT in the pericycle provides the enzyme with efficient access to putrescine, ornithine, and arginine unloaded from the phloem. In the same way, scopolamine produced in the pericycle can be readily translocated to the leaves via the adjacent xylem. 

The size and shape of the blade are often characteristic of a species, and are useful in species identification. However, the leaf blades of some species, such as those of oaks Quercus), exhibit great variation in size and shape, sometimes even when on the same tree. Botanists use a large vocabulary of specialized terms to describe the leaf outline, margin, apex, base, and vestiture (surface covering). For example. Pine Pinus) leaves are considered acicular, meaning they are shaped like a needle Aspen (Populus) leaves are considered ovate, meaning they resemble a two-dimensional projection of an egg May apple Podophyllum) leaves are considered peltate, meaning they are shaped like a shield, and are attached to the stalk on the lower leaf surface. 

An adventitious bud is one which occurs on some position of the stem other than at its apex or in the axil of a leaf. Such buds may be seen developing along the veins of a Begonia leaf or along the margin of a Bryophyllum leaf after these have been planted in moist soil for several days. 

Vernation.—Prefoliation or Vernation relates to the way in which leaves are disposed in the bud. A study of the individual leaf enables u to distinguish the following forms. When the apex is bent inward toward the base, as in the leaf of the Tulip Tree, it is said to be... 

Apex of Leaf.—Acute, when the margins form an acute angle at the tip of the leaf. Examples Eriodictyon, Digitalis. 

A Lobed leaf is one in which the indentations extend toward the mid-rib, or the apex of the petiole, the segments or sinuses, or both, being rounded. Example Sassafras. 

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