الفهرس 
Altered photosynthetic performance of a natural Arabidopsis 17Only 14 pages are availabe for public view
 |  | from | 134 |  |  |
| | | from | 134 | | |
Abstract
Plant performance depends on the acquisition of raw material (carbon fixation and
mineral uptake), the distribution of such materials over the plant organs, and the ability to
cope with environmental stresses. Plant performance is viewed as the result of input
(photosynthesis and mineral nutrition), allocation, and storage or use (respiration), under a
given set of environmental conditions. Functionally a plant can be divided into sources and
sinks. Sources are the parts of the plant where net fixation of carbon dioxide occurs, and sinks
the sites where assimilates are stored and/or used. Allocation of assimilates between plant
parts occurs via transport in the phloem. For total biomass production, photosynthetic carbon
dioxide fixation is by far the most important process.
Growth of autotrophic plants depends on photosynthetic activity. Photosynthesis is a
metabolic process that is highly integrated and regulated in order to maximize the use of
available light, to minimize the damaging effects of excess light and to optimize the use of
limiting carbon and nitrogen resources (Paul and Foyer, 2001). Photoassimilates can be either
used directly for growth or respiration, or stored for a short period (e.g. in leaves, diurnal) or
for a long period (e.g. in seeds or roots). Already in 1868, Boussingault (quoted by Paul and
Foyer, 2001), assumed that the accumulation of photoassimilates in leaves has a role in
regulating photosynthetic rate. As the accumulation of end products is a function of the
balance between photosynthesis and the use by the growth processes of the plant,
Boussingault`s hypothesis essentially pointed out that there is an interrelationship between
photosynthesis and growth rather than a one-way relationship. A metabolic signaling network
involving information on the carbon and nitrogen status of different tissues interacts with
phytohormone signaling pathways and redox signals to control photosynthetic gene
expression and leaf development. This highly integrated signal transduction network, which
forms the basis of the source-sink interaction, regulates photosynthetic activity by
determining the amount of photosynthetic apparatus present during leaf development and
senescence, overriding direct control of photosynthesis by light and CO2 (Paul and Foyer,
2001).