photorespiration; instead, higher amounts of assimilates, larger leaves, and a better leaf carbon balance
leading to improved light absorption and carbon accumumlation with a resulting increase in dry matter
production have been discussed [124]. Thus, the interpretation still appears valid that high reaction rates
of photorespiration seem indispensable for an agriculturally relevant C3 plant and that this process should
not be the principal (negative) target for plant breeding and/or physiological experiments aimed at in-
creasing the average yield of crops.
Interesting and promising models have been presented by Marcelis et al. [125] for horticultural crops.
Most of the models presented refer to photosynthesis with respect to leaf area development, light inter-
ception, and interrelationship with growth and maintenance respiration. Following reports on increases in
vegetative growth and the net yield of crops together with a decrease in water use with the spray applica-
320 BADER AND ABDEL-BASSETFigure 15 Effect of selenium on physiological parameters of Emiliania huxleyi: changes in cell number (A
and F), the concentration of chlorophyll (B and G), net photosynthesis (C and H), gross photosynthesis (D and
I), and dark respiration (E and J) from the first (A–E) and second (F–J) cultures. Aliquots from cells grown for
170 hr in selenium-deficient medium (first culture) were taken and inoculated into fresh deficient medium (sec-
ond culture). Filled and open symbols represent the presence and the absence of 10 nM selenite, respectively.
Lines were drawn according to curve fit functions of Deltagraph 4.0 (Deltapoint Inc. Monterey, CA). (From
Ref. 121.)