Overview Photosynthesis is the process by which plants use light energy to convert carbon Since respiration does not require.60 Science and Children Q: How does photosynthesis work?
Pathogens also affect , both directly and indirectly. Pathogens that cause defoliation rob the plant of photosynthetic tissue, while necrotrophs decrease the photosynthetic rate by damaging chloroplasts and killing cells. Biotrophs affect photosynthesis in varying degrees, depending on the severity of the infection. A biotrophic infection site becomes a strong metabolic sink, changing the pattern of nutrient within the plant, and causing net influx of nutrients into infected leaves to satisfy the demands of the pathogen. The depletion, diversion and retention of photosynthetic products by the pathogen stunts plant growth, and further reduced the plant's photosynthetic efficiency. In addition, pathogens affect water relations in the plants they infect. Biotrophs have little effect on rate until sporulation ruptures the cuticle, at which point the plant wilts rapidly. Pathogens that infect the roots directly affect the plant's ability to absorb water by killing the root system, thus producing secondary symptoms such as wilting and defoliation. Pathogens of the vascular system similarly affect water movement by blocking xylem vessels. Growth and development in general are affected by pathogen infection, as a result of the changes in source-sink patterns in the plant. Many pathogens disturb the hormone balance in plants by either releasing plant hormones themselves, or by triggering an increase or a decrease in synthesis or degradation of hormones in the plant. This can cause a variety of symptoms, such as the formation of adventitious roots, gall development, and epinasty (the down-turning of petioles).
While some parasites colonise the outside of the plant (ectoparasites), pathogens may also enter the host plant by , through a natural opening (like a stomatal pore) or via a wound. The symptoms of the diseases produced by these pathogens result from the disruption of respiration, photosynthesis, translocation of nutrients, transpiration, and other aspects of growth and development.
While necrotrophs have little effect on plant physiology, since they kill host cells before colonising them, biotrophic pathogens become incorporated into and subtly modify various aspects of host physiology, such as respiration, photosynthesis, translocation, transpiration and growth and development. The rate of plants invariably increases following infection by fungi, bacteria or viruses. The higher rate of glucose catabolism causes a measurable increase in the temperature of infected leaves. An early step in the plant's response to infection is an oxidative burst, which is manifested as a rapid increase in oxygen consumption, and the release of reactive oxygen species, such as hydrogen peroxide (H2O2) and the superoxide anion (O2-). The oxidative burst is involved in a range of disease resistance and wound repair mechanisms . In resistant plants, the increase in respiration and glucose catabolism is used to produce defence-related metabolites via the pentose phosphate pathway. In susceptible plants, the extra energy produced is used by the growing pathogen.