Strands of bundle sheath cells isolated from the NADP malic enzyme type C4 species, Zea mays, rapidly decarboxylate malate via NADP malic enzyme. The present studies show that these cells also decarboxylate aspartate, but at much lower rates. Aspartate decarboxylation is dependent upon added 2-oxoglutarate, is partially light dependent, and apparently proceeds via the following reaction sequence: aspartate ͛4 oxaloacetate ͛4 malate ͛4 pyruvate + CO2. Studies of the activity, properties, and location of enzymes indicated that these reactions are catalysed by a mitochondrial aspartate aminotransferase, mitochondrial or cytoplasmic NAD malate dehydrogenase, and chloroplast-located NADP malic enzyme, respectively. A mitochondria preparation isolated from Z. mays bundle sheath cells converted aspartate to oxaloacetate (with 2-oxoglutarate) and also pyruvate to alanine (with glutamate); the preparation did not reduce oxaloacetate to malate or decarboxylate malate at significant rates. Bundle sheath strands of Z. mays have a relatively limited capacity for HCO3- plus ribose 5-phosphate dependent oxygen evolution and rates were almost as high with aspartate plus 2-oxoglutarate. We suggest that amongst NADP malic enzyme type C4 species there may be a direct relationsip between the capacity of bundle sheath cells to decarboxylate aspartate and their potential for the photosystem II-mediated oxygen evolution.

The response of potato (Solanum tuberosum L.) cultivars Russet Burbank and Kennebec to soil and fertiliser potassium (K) was studied on basaltic krasnozems of north-west Tasmania. Yield increases in response to fertiliser K were recorded at sites with up to 300-400 mg/kg of bicarbonate extractable soil K. The close correlation between relative yield and soil K indicated that soil K can reliably predict fertiliser requirements. Petiole K concentrations at early tuber set increased with fertiliser K at responsive sites; maximum yields were achieved with 12-14% petiole K for Kennebec and 11-13% for Russet Burbank. Petiole K concentrations provide an excellent indication of the K status of a growing crop. Tuber K concentrations increased with both soil and fertiliser K, and yields of 50-80 t/ha removed 180-380 kg K/ha in the tubers. At severely deficient sites specific gravity and crisp colour increased with low rates of fertiliser K, but the general trend was for fertiliser K to reduce specific gravity and crisp colour. Bruising susceptibility decreased with fertiliser K at some sites but the physiological disorder, 'hollow heart', was not influenced by fertiliser K. There were consistent differences between the 2 cultivars. Russet Burbank required higher soil K, had lower petiole and tuber K concentrations and removed less K in the marketable tubers.

Sterile embryos of barley (Hordeum vulgare) and cultures of Lemna perpusilla have been labeled with 'Pi and the chromatin proteins prepared and separated by acid-urea and sodium dodecyl sulfate gel electrophoresis. Under these conditions chromatin proteins became labeled and the gel radioactivity profiles which were complex indicated a probable minimum of 15 to 20 proteins phosphorylated with molecular weights ranging from 10' to 10'. The majority of the radioactivity, 80 to 90% of the total, is found in the acidic protein fraction and this can be recovered as serine phosphate after partial acid hydrolysis.Nuclei have been isolated from Lemna and barley and found to possess endogenous kinase activity. In vitro labeling of these nuclei with 'P-adenosine triphosphate indicated that similar proteins appear to become labeled as in vivo labeling with 'Pi but the proportions of label in each protein were different.Protein phosphorylation is an important element in the molecular basis of animal hormone action (6). We have already reported the presence of ribosomal protein phosphorylation in Lemna and pea and its catalysis by a kinase attached to the ribosomes (9, 15). As part of a continuing program to examine the presence and possible function of this regulatory system in plants this paper describes the presence of phosphorylated chromatin proteins and indicates that the phosphorylation may be carried out by endogenous kinases in the nucleus. 50 j,Ci/ml; (b) for 18-hr labeling, to 50 /tM with '2Pi at 25 /Ci/ ml; and (c) for 8-days labeling, to 1 uM with uPi at 4 XCi/ml. Growth, measured as frond number, continued normally on these media for the duration of the different labeling periods. MATERIALS AND METHODSHordeum vulgare L. cv. COHO seeds were dehusked by soaking for 3 hr in 50% HS04, and subsequently sterilized for 5 min in 1% sodium hypochlorite. They were then washed five times and imbibed for 3 hr in sterile distilled H20. Embryos were removed with a sharp spatula, sterilized 10 min in 0.2% sodium hypochlorite, and stored in sterile distilled H20 at 2 C.Sterility was checked in the same way as for Lemna.Barley embryos were labeled in vivo with 200 uCi/ml 3'Pi in the basal medium of Joy and Folkes (7), in which the phosphate concentration was reduced to 1 0' M. Amino acids were supplied in the form of 600 ,ug/ml of an enzymic hydrolysate of casein. Sterilized embryos were placed in 2 ml of the above medium in a 50-ml conical flask, left at 2 C overnight, and further incubated at 25 C for 3 hr.Isolation of Chromatin. Chromatin was isolated by a modification of the procedure of Huang and Bonner (5). Lemna was ground in 10 volumes 0.05 M tris-HCl, pH 8, 0.25 M sucrose, 10 mm MgCI1, 0.12 M mercaptoethanol, 1 mm NaHSO, at 0 C. The homogenate was filtered through two and four layers of gauze and two layers of Miracloth on a Buchner funnel under suction. The combined filtrates were immediately made 2% in Triton X-100 and centrifuged at 2,000g for 30 min. The precipitate was resuspended in 1 volume of grinding m...

Four field experiments were conducted to examine the yield response and cadmium (Cd) concentration of potatoes (Solanum tuberosum L. cv. Russet Burbank) grown with banded or broadcast phosphorus (P) fertiliser at rates up to 240 kg P/ha. The Cd content of the triple superphosphate (TSP) was 151 mg/kg. All 4 sites were on intensively cropped, high P-fixing krasnozem soils in north-western Tasmania, with concentrations of Colwell-extractable P ranging from 112 to 210 mg/kg. All sites showed economic yield responses to banded P, but broadcast P was much less effective except at the site where the response to banded P was least. Yield responses came mostly through increased tuber number, but at 1 site the tubers were also bigger. There was no effect of P on tuber size distribution or specific gravity. Increasing rates of banded TSP increased tuber Cd concentrations by 50-300% at the 3 sites where they were measured; broadcast TSP had little effect. Tubers from the site with pH 6.0 had much higher Cd concentrations than those from the sites with pH 6.5 and 6.6. Petiole Cd concentrations were about 5 times greater than tuber concentrations.

Thirteen field trials were conducted on ferrosols and tenosols in Tasmania to assess the response of potatoes (Solanum tuberosum L., cv. Russet Burbank) to basal (up to 250 kg/ha) and topdressed (up to 100 kg/ha) nitrogen fertiliser. Economic yield responses to basal nitrogen were obtained at 9 sites. Topdressing did not increase yield compared with equivalent rates of basal nitrogen, and often failed to compensate for a lack of nitrogen applied at planting. This lack of response may reflect the inability of the potato crop to make use of nitrogen applied during tuber bulking. Nitrogen fertiliser decreased tuber specific gravity at several sites. The effects of nitrogen on misshapen tubers, bruising susceptibility, crisp colour and hollow heart were inconsistent and often of no practical importance. However, at 2 sites, nitrogen fertiliser increased yields of misshapen tubers at the expense of processing tuber yields. At 1 of these sites, nitrogen topdressing decreased the yield of misshapen tubers. Otherwise, topdressing had similar effects on tuber quality to those of basal nitrogen. Growers should fertilise with nitrogen to optimise their yields. Optimum rates were greater in paddocks that had been continuously cropped for more than 10 years (average rate 193 kg/ha), than in those that had been in pasture (average rate 48 kg/ha).