ATP - Adenosine triphosphate. ATP is the major source
of chemical energy in cellular processes. When hydrolysed it loses
one phosphate to become adenosine diphosphate (ADP) and releases usable
energy.
Bundle sheath cells - Special cells found in leaves
of C4 plants in which the 4 carbon acids formed initially in the mesophyll
cells are decarboxylated and CO2 is fixed by Rubisco.
These cells are characterized by thick walls which increase CO2
concentrations near the Rubisco sites, prevent CO2 from
leaking out of the cells and enhance carbon fixation over photorespiration.
C3 plants - Carbon fixed from CO2 is assimilated
during the first stage of the PCR pathway into two identical three-carbon
products (3-phosphoglycerate, 3PGA). Found in all major plant families
or in about 300,000 species. Typical C3 plants include: barley, sunflower,
rice, tomatoes, wheat, peanuts, cotton, sugar beet, oats, and most trees.
C4 plants - In C4 plants, the first stable products of carbon
assimilation are 4-carbon carboxylic acids produced. Cellular differentiation
occurs which spatially regulates carbon assimilation. The 4 carbon acids
are formed in the mesophyll cells and are then transferred to special cells
(bundle-sheath cells) where they are decarboxylated and the CO2
released is then fixed by Rubisco in the PCR cycle.
Carboxylase - An enzyme incorporating CO2 into
an organic compound with a carboxyl group.
Chlorophyll a - The major pigment of photosynthesis. Found
in all plants.
Decarboxylate - Removal of a carboxyl group (COOH) from a molecule.
CO2 is produced.
Gross photosynthesis (Pg) - The total fixation of energy by photosynthesis.
Guard cells - Cells in the leaves of higher plants surrounding the
stomatal pores. Changes in the shape of the guard cells causes the stomata
to open or close.
Hatch Slack pathway - Pathway of carbon fixation in C4 plants.
Carbon is assimilated into C4 Discovered and described by Marshall
Hatch and Roger Slack
Krantz anatomy - Characteristic of C4 plants. Plant veins are encased
by thick-walled photosynthetic bundle-sheath cells that are surrounded
by thin-walled mesophyll cells.
Light-compensation point - The amount of light at which photosynthesis
and respiration balance (i.e. net photosynthetic rate of a plant = 0).
For a plant like wheat this is about 5 Wm-2.
NADP/NADPH - Nicotinamide adenine dinucleotide phosphate.
A coenzyme that functions as an electron acceptor/donator in many of the
redox reactions within cells. Obtained in the light-reactions of
photosynthesis and used to reduce carbon dioxide.
Net photosynthesis (Pn) - The actual rate of production
of new biomass . This is essentially gross photosynthesis minus the
rate of respiration.
PEP carboxylase (PEPCASE) - The enzyme responsible for
the carboxylation of CO2 in the mesophyll cells of C4
plants into oxaloacetate.
Photorespiration - Uptake of oxygen in the light by Rubisco
(which also acts as an oxygenase) and the consumption of carbohydrate.
This process competes with photosynthetic CO2 uptake and
carbohydrate synthesis. Photorespiration increases in dry hot climates
when conditions limit CO2 availability and favor high
oxygen concentrations.
Primary productivity - The rate of biomass production per
unit area by plants.
Redox reaction - A reaction that involves reduction (gain
of electrons or hydrogens – gain of oxygen) and oxidation (loss of
electrons or hydrogens – loss of oxygen).
Respiration - The breakdown of organic molecules such as sugars
and starches into smaller components releases stored energy. In plants,
this process, the reverse of photosynthesis, consumes oxygen and releases
CO2 .
Rubisco - Ribulose bi-phosphate carboxylase/oxygenase . A
bifunctional enzyme that can fix carbon dioxide or molecular oxygen, which
leads to photosynthesis or photorespiration, respectively. Rubisco
is the most abundant enzyme on earth.
Stomata - Intracellular openings mostly found on the underside
of leaves and act as valves to allow CO2 in and out of
the cells.
Transpiration - The process by which water vapor is lost from
plants, evaporating from cell walls just below the surface of the leaf
and diffusing into the air through small stomatal pores.
The
Woodrow Wilson National Fellowship Foundation
CN 5281, Princeton NJ 08543-5281 - Tel:(609)452-7007
- Fax:(609)452-0066
Technical contact: lpt@woodrow.org