Nov 30, 2014

Response to Environmental Stress in Plants

The growth of plants depend on nutrition and environmental factors. The absence or short supply of any of the factors in the environment may exert stress on plants affecting their health and survival. If plants are grown without light, they become extremely long and fail to form chlorophyll. They are said to be etiolated. Due to short supply of mineral nutrient in the soil, the plant fail to form sufficient chlorophyll, and becomes yellowish in color. This condition is known as chlorosis.

PLANT’S DEFENSE MECHANISM AGAINST PATHOGENS

Plants can be under attack by several types of pathogens. These include fungi, bacteria, viruses, nematodes. In the absence of induced antibiotics to protect themselves, plants must rely on various structural and anatomical attributes for, either avoid infection entirely or prevent infection initially. There are certain defense structures that are already present in the plants. For example (a) Surface waxes (b) Structure of epidermal cell walls (c) Position of stomata and lenticels (d) Thick cell walls (e) Leaf hairs.

Some defense structures are formed in response to infection by the pathogen. Once infection occurs, the plant may respond by producing structural barriers to further entrance of the parasite. The mechanisms are either at the tissue level, termed histological defense or sub-cellular level known as cellular defense reaction.

Histological Defense Structures

(a)      Formation of cork layers.

(b)      Formation of abscission layer.

(c)      Formation of tyloses (a chemical substance).

(d)      Deposition of gums,

(e)     Cellular Defense Structures

(f)     Callus thickening of the cell wall i.e. a group of cells called callus which         quickly    covers the wound.

(g)      Necrotic defense reaction or hypersensitivity (death of cells surrounding            infection site).


In addition to that some plants exude onto their surface compounds which inhibit the germination of fungi e.g. tomato. Other plants e.g. onion produce phenolic compounds that protect them from infection.

No comments:

Post a Comment