What are the two conditions necessary for the opening of stomata?
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Answers
The four factors affecting opening and closing of stomata are: (1) Light (2) Water Content of Epidermal Cells (3) Temperature and (4) Mineral Elements.
The aforementioned details pertain to the mechanism of opening and closing of photoactive stomata (i.e., stomata that open during day time), but in some plants (e.g., succulent plants like Opuntia) stomata open during night {i.e., when light is absent). Such stomata are called scotoactive stomata. According to Nishida (1963), in these plants there is incomplete oxidation of carbohydrates leading to the accumulation of malic acid without release of CO2.
According to Pallas (1969) and Ehrler (1972) when there is deficiency of O2 it leads to the formation of organic acids which result in intake of K+ ions (rest of the reactions are like those in photoactive stomata).
Factors affecting opening and closing of stomata:
1. Light:
Among external factors, light plays predominant role in the movement of guard cells. Blue and red light are effective in both photosynthesis and stomatal opening. However, blue light is found to be more effective (relative to red light) in causing stomatal opening than in photosynthesis.
At low light levels, blue light may cause stomatal opening when red light has no effect at all. Blue light causes movement of K+. It is now thought that blue light promotes the breakdown of starch into the PEP molecules that can accept CO2 producing malic acid.
2. Water Content of Epidermal Cells
The movement of guard cells is turgor phenomenon and guard cells derive water from the adjoining epidermal cells and hence water content of the latter is bound to effect this phenomenon.
3. Temperature:
Increase in the temperature causes stomata to open. Temperature has significant effect on the permeability of the wall of the guard cells and therefore greatly affect the osmotic phenomenon which is responsible for the movement of these cells.
4. Mineral Elements:
Deficiency of certain mineral elements like nitrogen, phosphorus and potassium has some effect on the opening and closing of stomata (Desai, 1937).
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Answer:
water ,chlorophyll ,corbon dioxide , sunlight