Effects of Phosphorus Deficiency on the Photosynthesis and Respiration of Leaves of Sugar Beet

Abstract

Phosphorus deficiency was induced in sugar beet plants (Beta vulgaris L. var. F5855441), cultured hydroponically under standardized environmental conditions, by removal of phosphorus from the nutrient supply at the ten leaf stage 28 days after germination. C02 and water vapor exchange rates of individual attached leaves were determined at intervals after P cutoff. Leaves grown with an adequate nutrient supply attained net rates of photosynthetic CO2 fixation of 125 ng CO2 cm-2 sec-' at saturating irradiance, 25 C, and an ambient CO2 concentration of about 250 ,l I-'. After P cutoff, leaf phosphorus concentrations decreased as did net rates of photosynthetic C02 uptake, photorespiratory evolution of C02 into C02-free air, and dark respiration, so that 30 days after cutoff these rates were about one-third of the control rates. The decrease in photosynthetic rates during the first 15 days after cutoff was associated with increased mesophyll resistance (rm) which increased from 2.4 to 4.9 sec cm-', while from 15 to 30 days there was an increase in leaf (mainly stomatal) diffusion resistance (r,') from 0.3 to 0.9 sec cm-', as well as further increases in rm to 8.5 sec cm-'. Leaf diffusion resistance (ri') was increased greatly by low P at low but not at high irradiance, rz' for plants at low P reaching values as high as 9 sec cm-'.Much of the phosphorus found in the sugar beet plant is in the inorganic form and has many roles in cell metabolism (2).

Effects of Calcium on the Photosynthesis of Intact Leaves and Isolated Chloroplasts of Sugar Beets

“…Control plants (-O-, -A-). So the effect of Ca on photosynthesis appears to be small compared to deficiencies of other elements such as phosphorus (18), manganese (20), or potassium (19). The actual requirement for Ca by higher plants for metabolic activities in general may be relatively small.…”

“…Measurements of leaf mineral contents and photosynthetic activities of isolated chloroplasts and RuDP carboxylase extracts were carried out at each harvest in all three experiments but gas exchange parameters were determined only in experiments I and II. Details of the procedure followed in the culture of plants, in the determination of gas exchange parameters of individual attached leaves, and in the estimation of the contents of leaf minerals are as outlined in earlier papers (18,19,21). The composition of the culture solutions for experiments I and II (expressed in mmole/l) was: 0.5 Ca(NO,)2, 4 NaNO2, 0.5 KH2PO4, 2.5 KNOs, 1 MgSO4, and 0.5 NaCl, and, in mg/i, comparable to the leaf chosen for gas exchange analysis but was taken from a different plant; it was the largest (150-300 cm2 for a control leaf) of the newly expanded apical leaves and is arbitrarily designated leaf 2.…”

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

“…2B; see also ref. 26). This resulted in slightly lower intercellular CO2 partial pressures in low-P leaves at each PFD level (Fig.…”

Biochemical Basis for Effects of K-Deficiency on Assimilate Export Rate and Accumulation of Soluble Sugars in Soybean Leaves

“…Because ofthe role of K fluxes in stomatal aperture changes (24), it has often been assumed that the influence of K on photosynthesis could be attributed to stomatal closure (17,21). However, more recent studies with sugarbeet (29), alfalfa (22), and cotton (15) have ' suggested that nonstomatal limitations may also be involved. K-nutrition affects the rate of assimilate export and the concentrations ofsugars in leaves, but the relationship between these two parameters is not clear.…”