Dihydrogen monoxide (DHMO)
Hydrogen hydroxide (HH or HOH)
In plants, the transpiration stream is the uninterrupted stream of water and solutes which is taken up by the roots and transported via the xylem vessels to the leaves where it evaporates into the air/apoplast-interface of the substomatal cavity. It is driven in by capillary action and in some plants root pressure. The main driving factor is the difference in water potential between the soil and the substomatal cavity caused by transpiration.
Transpiration can be regulated through stomatal closure or opening causing water to move out and evaporate on the leaf, while air flows in. It allows for plants to efficiently transport water up to their highest body organs, regulate the temperature of stem and leaves during heat-generating photosynthesis and it allows for upstream signaling such as the dispersal of an apoplastic alkalinization during local oxidative stress.
Hydraulic redistribution refers to the mechanism by which some vascular plants redistribute soil water. It occurs in vascular plants that commonly have roots in both wet soil and extremely dry soil, especially plants with both taproots that grow vertically down to the water table, and lateral roots that sit close to the surface.
During hot, dry periods, the surface soil dries out so much that the lateral roots tend to exude whatever water they contain; thus the roots die unless the water is replaced. In plants that exhibit hydraulic redistribution, there are xylem pathways from the taproots to the laterals, so the loss of water from the laterals creates a pressure potential analogous to that of transpirational pull. Ground water is thus drawn up through the taproot to the laterals, only to be exuded into the surface soil.
Plant physiology is a subdiscipline of botany concerned with the functioning, or physiology, of plants. Closely related fields include plant morphology (structure of plants), plant ecology (interactions with the environment), phytochemistry (biochemistry of plants), cell biology, genetics, biophysics and molecular biology.
Fundamental processes such as photosynthesis, respiration, plant nutrition, plant hormone functions, tropisms, nastic movements, photoperiodism, photomorphogenesis, circadian rhythms, environmental stress physiology, seed germination, dormancy and stomata function and transpiration, both parts of plant water relations, are studied by plant physiologists.