Chloroplast ultrastructure of sugar beet (Beta vulgarisL.) cultivated in normal and elevated CO₂concentrations with two contrasted nitrogen supplies

Abstract

Sugar beet (Beta vulgaris L., cultivar Celt) plants were grown under simulated field conditions in pots and supplied with adequate or deficient nitrogen (HN and LN, respectively) combined with two C0 2 concentrations, ambient (c. 350/imol mol~1 C0 2-AC), or elevated CO 2 (c. 600 fimo\ mol~1 C0 2-HC). Chloroplast structure in mesophyll palisade cells of mature leaves (leaf number 19 in HN and 9 in LN), sampled at midday on 16 August 1993 was studied by transmission electron microscopy and quantified stereologically. The ultrastructure of palisade parenchyma chloroplasts was affected by the elevated CO 2 concentration and strikingly affected by nitrogen supply. Chloroplast diameter (cross-sectional length) was slightly, but not significantly, greater in HC than AC treatments within an N treatment, but was smaller in LN than HN; chloroplast cross-sectional area also increased with HC in both N treatments, but only significantly so in LN. Elevated C0 2 reduced the proportion of total thylakoids (significant at 5% and 0.1% in HN and LN, respectively) due to decreased granal thylakoids, but the proportion of inter-granal (stromal) thylakoid membranes was not affected compared to chloroplasts from plants grown with ambient CO 2. Chloroplast stroma increased as a proportion of chloroplast volume with elevated compared to ambient CO 2 with HN but not LN. Starch inclusions were not significantly different with elevated compared to ambient C0 2 at HN, but the proportion of starch increased considerably at elevated compared to ambient C0 2 at LN, indicating an overproduction of assimilates. Plastoglobuli in chloroplasts increased with deficient N, but decreased with elevated CO 2. Larger chloroplasts with a greater proportion of stroma, but a smaller proportion of granal thylakoids, suggest increased CO 2 assimilating capacity and decreased light harvesting/PSII capacity with elevated CO 2 .

Plant growth in elevated CO 2 alters mitochondrial number and chloroplast fine structure

“…Qualitatively similar chloroplast fine structure findings were reported for sugar beet (Beta vulgaris L.) cultivated in normal and elevated CO 2 partial pressure (41), although the differences were not highly significant. Here we found highly significant differences, which may be attributed in part to long-term CO 2 exposure period and the denser amount of intergrana thylakoids in our species, thus increasing the sample size and statistical power.…”

Acclimation of photosynthesis to nitrogen deficiency in Phaseolus vulgaris

“…The rate of CO 2 assimilation per Chl unit declines due to decrease in the expression of several key enzymes of the CalvinBenson cycle (Evans and Terashima 1987;Sage and Pearcy 1987;Terashima and Evans 1988;Sugiharto et al 1990). Moreover, N deficiency induces accumulation of starch (Kutik et al 1995;Bondada and Syvertsen 2003), apparently because N deficiency limits the consumption of carbohydrates in anabolic reactions.…”

Effects of plant-growth-promoting bacteria on growth and yield of pepper under limited nitrogen supply

“…This low N supply can alter the rates of cell division and cell expansion in growing leaves and can also induce large changes in N allocation between roots and shoots (Gastal and Lemaire 2002). Nitrogen is a fundamental constituent of the photosynthetic apparatus: chlorophyll concentration, photosynthesis, and growth all decrease with N deficiency (Kutik et al 1995). Our data show that restricted N supply reduced plant growth significantly.…”

“…It is possible that many of the prospective metabolic changes that occur in shoots of N-deficient plants are regulated through transcriptional changes elicited by increased leaf sugar concentrations (Koch 2004). A low N supply can cause ultrastructural changes, due to the accumulation of starch granules in chloroplasts (Kutik et al 1995), which increase in size (Schaffer et al 1986). With sufficient N supply, N can stimulate the mobilization of starch out of the chloroplast to sites of high carbon sink activity, whereas in Ndeficient leaves, starch can build up in chloroplasts (Ariovich and Cresswell 1983).…”