Leaf Phosphate Status, Photosynthesis, and Carbon Partitioning in Sugar Beet

Abstract

Sugar beets (Beta vulgaris L. cv F58-554H1) were cultured hydroponically for 2 weeks in growth chambers with two levels of orthophosphate (Pi) supplied in half strength Hoagland solution. Low-P plants were supplied with 1/20th of the Pi supplied to control plants. With low-P treatment, the acid soluble leaf phosphate and total leaf P decreased by about 88%. Low-P treatment had a much greater effect on leaf area than on photosynthesis. Low-P decreased total leaf area by 76%, dry weight per plant by 60%, and the rate of photosynthesis per area at light saturation by 35%. Low-P treatment significantly decreased the total extractable activity of phosphoglycerate kinase (by 18%) and NADPglyceraldehyde-3-phosphate dehydrogenase (by 16%), but did not decrease the total activities of ribulose-1,5-bisphosphate (RuBP) carboxylase (RuBPCase) and ribulose-5-phosphate kinase. Low-P treatment decreased the initial activities of three rate-limiting Calvin cycle enzymes, but had no effect on the initial activity of RuBPCase. Furthermore, low-P treatment significantly increased the total extractable activities of fructose-1,6-bisphosphatase (by 61%), fructose-1,6-bisphosphate aldolase (by 53%), and transketolase (by 46%). The results suggest that low-P treatment affected photosynthetic rate through an effect on RuBP regeneration rather than through RuBPCase activity and that the changes in Calvin cycle enzymes with low-P resulted in an increased flow of carbon to starch.

Dependence of Photosynthesis of Sunflower and Maize Leaves on Phosphate Supply, Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase Activity, and Ribulose-1,5-Bisphosphate Pool Size

“…The carboxylation efficiency and the apparent quantum yield for CO2 assimilation were two parameters strongly affected by phosphate deficiency, leading to an increase in the relative mesophyll limitation of photosynthetic rate. Similar effects on carboxylation efficiency and quantum yield in phosphate-deficient leaves of spinach, soybean, and sugar beet have been observed in other studies (4,11,19).…”

“…The carboxylation efficiency and the apparent quantum yield for CO2 assimilation were two parameters strongly affected by phosphate deficiency, leading to an increase in the relative mesophyll limitation of photosynthetic rate. Similar effects on carboxylation efficiency and quantum yield in phosphate-deficient leaves of spinach, soybean, and sugar beet have been observed in other studies (4,11,19).Under conditions of a nonlimiting supply of RuBP, the amount and specific activity of Rubisco determine carboxylation efficiency (24), defined as the initial slope of the curve relating A to C1, i.e. dA/dCj when A = 0 (10).…”

“…dA/dCj when A = 0 (10). Phosphatedeficient leaves produce smaller amounts of RuBP and Rubisco (4,19), and the Rubisco has a lower specific activity ( In a previous study (7), we showed that the decrease in A' by leaves of phosphate-deficient sunflower, maize, and wheat 0, 0.5, or 10 mm Pi. The flux of photosynthetically active radiation (400-700 nm) was 350 to 400 umol quanta m-2 s51 for 16 h a day, RH 75 to 85%, and air temperature 22°C day and 20°C night.…”

“…dA/dCj when A = 0 (10). Phosphatedeficient leaves produce smaller amounts of RuBP and Rubisco (4,19), and the Rubisco has a lower specific activity ( …”

Lipid Biosynthesis and Protein Concentration Respond Uniquely to Phosphate Supply during Leaf Development in Highly Phosphorus-Efficient Hakea prostrata

“…In healthy mature leaves, total protein concentrations were highest at 40 mmol Pi plant 21 d 21 . Such large increases in leaf protein concentration with increasing Pi supply have not been reported in other plants, where changes in protein concentrations are relatively small (Lauer et al, 1989;Rao and Terry, 1989). It was also noteworthy that in H. prostrata, increased Pi supply did not lead to an increase in leaf fresh weight (Fig.…”