Stomata

Dear students, you will get a thorough knowledge about the stomata.

1. Stomata Dr. K. GANESH KUMARI ASSISTANT PROFESSOR DEPARTMENT OF BOTANY SRIMAD ANDAVAN ARTS AND SCIENCE COLLEGE (AUTONOMOUS) TRICHY - 5

2. Definition of Stomata Stomata (singular - stoma) are minute openings distributed in the epidermis of the leaves and young stems. They bring about gas exchange between leaf tissues and atmosphere. Each stoma remains surrounded by two kidneys or bean shaped epidermal cells the guard cells. The stomata may occur on any part of a plant except the roots. The epidermal cells bordering the guard cells are called accessory cells or subsidiary cells.

3. Cont … Generally the term stoma is applied to the stomatal opening and the guard cells. The guard cells are living and contain chloroplasts in them. They also contain a larger proportion of protoplasm than other epidermal cells. Usually in the leaves of dicotyledons the stomata remain scattered whereas in the leaves of monocotyledons they are arranged in parallel rows .

4. Distribution A leaf of normal mesophyte may have as many six million stomata. Usually, in the leaves of mesophytes , stomata are found in more numbers in the lower epidermis than in the upper epidermis. For instance, leaf of tomato plant contains about 10,000 stomata / cm 2 area in the lower epidermis and about 2300 stomata /cm 2 of its upper epidermis.

5. Position of stomata In stomata, more number of stomata is seen in the upper epidermis than the lower epidermis. For example Leaf of wheat plant contains – Lower epidermis - 1400 stomata / cm 2 area. - Upper epidermis – 3300 stomata / cm 2 area. Woody plants – Lower epidermis of leaves Aquatic plants – Upper epidermis of leaves Monocot stomata

6. Size of the Stomata The size of the stomata varies according to the plant species and even among the stomata of a single leaf. In general, size of the open stomata is 27 - 45µ in length and 23 – 28µ in width, and of closed stomata is 27 - 45µ in length and 10 - 33µ in width.

7. Types of stomata   1. Anomocytic or Type – A   No subsidiary cells are present. Stoma remains surrounded by several irregularly arranged ordinary epidermal cells. This type is also called Ranunculaceous type or irregular-celled type. This type of stomata are found commonly in several dicotyledons, including Tridax , Citrullus, Ranunulus , etc.

8. Cont … 2. Anisocytic or Type – B: i . Stoma remains surrounded by three subsidiary cells. ii.   Of the three subsidiary cells, one is distinctly- smaller than the other two. iii. This type of stomata is also called unequal- celled type or Cruciferous type. iv. This types of stomata are seen commonly in genera such as Brassica, Sedum etc.

9. Cont … 3.  Paracytic or Type – C: i .   One or more subsidiary cells are present. ii.   Subsidiary cells flank the stoma parallel with the long axis of the guard cells. iii.   This type of stomata are also called parallel - celled type or Rubiaceous type. This type is commonly seen in members of Rubiaceae , and genera such as Vigna , etc.

10. Cont … 4.  Diacytic or Type – D: i . Stoma remains surrounded by a pair of subsidiary cells. ii. Common walls of subsidiary cells remain at right angles to the long axis of the guard cells. iii. This type is also called cross-celled type or Caryophyllaceous type. This type of stomata are commonly seen in Ocimum , Caryophyllaceae (e.g., Dianthus ), etc.

11. Cont … 5. Gramineous: The gramineous stoma possesses guard cells of which the middle portions are much narrower than the ends so that the cells appear in surface view like dump-bells. They are commonly found in Gramineae and Cyperaceae of monocotyledons .

12. Cont … 6. Coniferous Stomata: They are sunken and appear as though suspended from the subsidiary cells arching over them. In their median parts the guard cells are elliptical in section and have narrow lumina . At their ends they have wider lumina and are triangular in section. The characteristic of these guard cells is that their walls and those of the subsidiary cells are partly lignified and partly non-lignified.

13. Thank you