Plant Transport and Physiology

Sayre reported that stomata open when pH is higher (7) and close when pH is low (5), i.i., high pH favours stomatal opening.

Stomata opens by increasing solute concentration in guard cells. The guard cells contain chloroplasts, so they can manufacture food by photosynthesis. The epidermal cells don't have chloroplast. Due to the presence of chloroplast, guard cell synthesizes glucose during the day time by the process of photosynthesis and so its osmotic potential increases and it withdraws water from the epidermal cell and turns turgid and the stomata opens and transpiration takes place.

Stomatal movement is primarily regulated by K+ ion flux, CO2 concentration, and ABA levels, which change the turgor pressure of guard cells.

When the concentration of the potassium ions and malate ions increase guard cells form potassium malate and stores it in vacuoles of the guard cells. This increases the osmotic concentration and hence water enters the guard cells by endosmosis. The turgor pressure of the guard cells increases due to endosmosis which finally leads to the opening of the stomata.

The increased concentrations of potassium ions are balanced by malate ions that form potassium malate. This is stored in the vacuoles of the guard cells, increasing the osmotic concentration. Hence, the water enters the guard cells by endosmosis. The turgor pressure of the guard cells also increases due to this endosmosis causing the stomata to open.

When guard cells become turgid the inner wall cannot move in vertical direction or along the longitudinal axis. Neither it can move or stretch on inner side. This is because of extra cellulose deposition on inner wall and radial microfibrils emerging from the inner wall.
So as guard cells become turgid and pressure builds up, the outer wall is pushed outside, which pulls the inner wall towards outside, or radially outwards. This opens the stomatal pore.

Scotoactive stomata are the stomata, which open in dark and close during the day time. Scotoactive stomata occur in succulents, e.g., cactus and bryophyllum. Succulents perform crassulacean acid metabolism or CAM in their photosynthesis. Nishida explained, that in succulents during night there is accumulation of organic acids, whereas, during day time the organic acids breakdown releasing carbon dioxide, which keeps stomata closed. During night, because of formation of organic acids carbon dioxide is consumed and concentration of carbon dioxide is less.

Stomata are tiny openings present on the epidermis of the leaves and young stem. These structures help in transpiration as well as uptake of carbon dioxide. The carbon dioxide is utilised in the process of photosynthesis. Since carbon dioxide is not utilised during the night, its concentration increases which inhibit the uptake of the potassium ions and closing of stomata takes place.

Deficiency symptoms of Ca, K, Mg and P appear initially as localized tissue necrosis leading to stunted plant growth, necrotic leaf margins on young leaves or curling of the leaves, and eventual death of terminal buds and root tips.

Phosphorus deficiency leads to lower leaves turning purplish due to anthocyanin accumulation, potassium causes marginal discoloration, manganese causes chlorosis in patches or stripes, and calcium affects cell walls causing dead tissues around margins.

Potassium (K) is essential for various physiological processes, including the activation of enzymes and the maintenance of turgor pressure, which is critical for cell division and apical meristematic activity.

Heart rot in beet root is a deficiency in the minor, nonmobile element Boron, $B$. It shows necrotic cross-hatching inside the leaf petiole. Young leaves turn brown and die, resulting in a rosette of small dead leaves at the top of the beet. In the fleshy root, internal and external black spots of necrotic tissue develop.

Phosphorus deficiency is a plant disorder associated with an insufficient supply of phosphorus. Darker green leaves and purplish or red pigment can indicate a deficiency in phosphorus. It is most common in lower leaves that are older. This condition is associated with the accumulation of sugars in P-deficient plants. Stems are thinner and leave acquire a leathery texture and tend to curl upwards, sometimes shedding prematurely. 

Plants absorb water and mineral salts simultaneously through root hairs, not sequentially. The statement that plants absorb one thing at a time is incorrect because absorption of water and minerals occurs concurrently through the same root tissues. Mineral absorption does primarily occur through active transport methods.

Buds of potato are a type of vegetative reproductive part of the potato. These buds can individually be grown as a whole new plant with proper habitat and nutrition.