The Anatomy of Zea mays Devin Nichols pmpb program 5/1/06
|
|  Yüklə 23.5 Kb.
|
| The Anatomy of Zea mays
Devin Nichols PMPB Program 5/1/06 Zea mays, commonly called corn in the United States, is a dicotyledonous angiosperm plant and a member of the Poaceae or grass family. Zea mays is the most widely grown crop plant in the United States as well as the most economically valuable. Worldwide, Zea mays is also a very important crop plant. The entire above ground portion of the plant can be utilized with the grain being used as both food and feed and the vegetative shoot sometimes being used for silage. Zea mays grain and shoot tissue can also be used in the production of ethanol fuel. The structure of Zea mays is similar to that of other grasses with the plant having a pattern of opposite leaves lacking petioles attached to the nodes of the main stalk with obvious nodes and internodes. The axillary buds at lower nodes may develop into tillers, although this is uncommon in modern corn hybrids, while the upper buds may develop into female inflorescences known as ear shoots. Zea mays is a determinate plant and the shoot terminates in a male inflorescence called a tassel. The vascular bundles present in Zea mays stems are closed collateral bundles with adjacent xylem and phloem tissues surrounded by schlerenchyma fibers. These bundles are arranged in a scattered pattern throughout the stem with a higher density towards the outside. As previously stated, the leaves of Zea mays are arranged in an opposite pattern with one leaf per node. Zea mays has a parallel venation pattern similar to most monocots with alternating large primary vascular bundles and smaller secondary bundles. These secondary bundles are surrounded by bundle sheath cells containing large chloroplasts. This arrangement, known as Kranz anatomy, is a specialized design to allow for C4 photosynthesis. The remainder of the leaf consists of an upper epidermis, mesophyll cells containing chloroplasts, and a lower epidermis. The stomates are arranged in parallel rows between the veins on both the upper and lower epidermis. The upper epidermis also has two types of trichomes, microhairs and macrohairs. Also on the upper epidermis are bulliform cells which allow the leaves to roll in response to water stress. There are also capitate glandular trichomes present on the leaves. The root system of Zea mays consists of two types of roots, seminal and crown roots. The seminal roots are present in the embryo and are important for early seedling establishment. The main root system of the plant is composed of the crownal roots. These roots make up the fibrous root system of the plant which is characteristic of monocots. Zea mays possess a closed root apical meristem with separate sets of initials for the calyptrogen, protoderm, procambium, and ground meristem. The pericycle of Zea mays roots exhibits a polyarch distribution of vascular tissue. Mature Zea mays plants also have adventitious brace roots which develop from the lower above ground nodes. These roots help to support the large plant and obtain nutrients, especially potassium. Zea mays is a monoecious species with a staminate inflorescence known as the tassel at the top of the plant and a pistillate inflorescence in the axil of one or more of the middle nodes. When pollinated, the female inflorescence develops into an ear containing many single seeded fruits or caryopses usually called kernels. References Esau, Katherine. 1977. Anatomy of Seed Plants Second Edition. John Wiley and Sons, Inc. New York. Freeling, M. and V. Walbot, Editors. 1993. The Maize Handbook. Springer-Verlag. New York. Kiesselbach, T.A. 1980. The Structure and Reproduction of Corn. University of Nebraska Press. Lincoln. |