Some further studies on metabolism of acetate-l-14C in potassium deficient rice leaves

Acetate-1-¹⁴C was fed to excised leaves of normal and potassiumdeficient rice plants. The rate of respiratory evolution of¹⁴CO₂ was increased by a potassium deficiency. Malonate, glyoxylateor malate supplied enhanced the metabolism of acetate-l-¹⁴C.These results suggest an accelerated turn of the TCA cycle inpotassium deficient leaves. Malate synthetase activity was notrecognized in either normal or deficient leaves. However, condensingenzyme activity was higher in deficient leaves than in normalones. An addition of DNP to the leaves increased ¹⁴CO₂ productionfrom acetate-l-¹⁴C though its effect was smaller in deficientleaves than it was in normal ones. This result may suggest anincrease in the turnover rate of ATP or loose coupling of electrontransfer with oxidative phosphorylation in deficient leaves.Chromatographic separation of cold acidsoluble nucleotides hasshown that the ATP level was lowered by a potassium deficiency,though the ADP level was not affected. ¹Present address: Sericultural Experiment Station, Suginami-Ku,Tokyo     

RESPIRATION AND ORGANIC ACID METABOLISM IN POTASSIUM DEFICIENT RICE PLANT

Rice seedlings were grown in nutrient solutions containing 5,10, and 100 ppm of potassium (as K₂O) for about one month. Respiratoryrate and mineral, organic acid and amino acid contents of theleaves of those seedlings were determined. At an earlier stageof growth, potassium deficiency induced a marked increase inrespiration. The amounts of cellular constituents were variabledependent on extent of potassium deficiency as well as age ofthe plant. The relationship between the respiration and organicand amino acid contents was discussed in terms of metabolicactivities for these compounds. Acetic and succinic acid contentsin the leaves of the lowest supply of potassium (K₅ leaves)were smaller than those of the other leaves (K₁₀ and K₁₀₀ leaves)at the earlier step of growth. The highest rate of respirationwas observed in K₅ leaves. The distinctive changes were observedin glutamine and asparagine contents by potassium treatment. (Received April 21, 1966; )     

Modulated Degradation of Ribulose Bisphosphate Carboxylase in Leaves on Top-Pruned Shoots of the Mulberry Tree (Morus alba L.)

Yamashita, T. 1987. Modulated degradation of ribulose ftisphosphatecarboxylase in leaves on top-pruned shoots of the mulberry tree(Morus alba L.).—J. exp. Bot. 38: 1957–1964. The effects of pruning shoot tops on the synthesis and degradationof ribulose 1,5–Wsphosphate carboxylase (RuBPCase) inleaves on remaining shoots were investigated in mulberry trees.Leucine labelled with ¹⁴C was fed to leaf discs from field-grownmulberry trees and ¹⁴C incorporation into RuBPCase was examined.Proportion of ¹⁴C in RuBPCase to leucine–¹⁴C absorbedby leaf discs was remarkably lowered by top-pruning, thoughoccasionally a slight increase was observed soon after pruning.Yet RuBPCase content in leaves on top-pruned shoots became progressivelyhigher than that in leaves on intact shoots. Changes in ¹⁴Cin Ru1BPCase in leaves of mulberry saplings previously fed ¹⁴CO₂were followed. Following ¹⁴CO₂ feeding, the attainment of themaximal level of ₁₄C in RuBPCase was retarded by top-pruning.The highest level of ₁₄C in RuBPCase was maintained in leaveson top-pruned shoots but decreased in leaves on intact shoots.Specific radioactivity in RuBPCase continued to increase inleaves on top-pruned shoots even after attaining a maximum levelin the control leaves. These facts suggest that the increasein RuBPCase by top-pruning results from a cessation of its degradationfor the remobilization of nitrogen for newly developing leaveson shoot tops. Key words: RuBP carboxylase, shoot pruning, mulberry (Morus alba)     

Changes in Ribulose 1,5-Bisphosphate Carboxylase Concentration due to External Nitrogen Supply in Mulberry Leaves (Morus alba L)

Effects of external nitrogen supply on quantity and activityof ribulose 1,5-bisphosphate carboxylase (RuBPCase) in mulberryleaves (Morus alba L. cv. Shin-ichinose) were examined. PhotosyntheticCO₂ fixation and the contents of chlorophyll and phosphoruswere increased by the increased N supply. RuBPCase-protein concentrationand its proportion to total soluble-protein or to total-N rosecorrespondingly as the N supply increased. Specific enzyme activityexpressed on a RuBPCase protein basis was not affected by theN supply. Morus alba L. (mulberry), N nutrition, RuBPCase protein content, photosynthesis     

METABOLISM OF ACETATE-1-14C IN EXCISED LEAVES FROM POTASSIUM DEFICIENT RICE SEEDLINGS

Excised leaves from one-month old rice seedlings grown in potassiumdeficient nutrient solution were fed with acetate-l-¹⁴C for20 to 180 min. Rate of respiration of those leaves was significantlyhigher than that of control leaves supplied with sufficientpotassium. Incorporation of UC into organic acid and sugar fractionswere greater in potassium deficient leaves than in normal leaves.The reverse was true as for the incorporation into amino acidfraction. In comparison with normal leaves, potassium deficientleaves acquired much ¹⁴C in succinic acid and glutamine. Therewere distinct differences in the labeling pattern of citrateand in the order of magnitude of specific activities among theorganic acids included in the TCA cycle. From these results,it was assumed that the increase of respiratory rate causedby the potassium deficiency was related to accelerated operationof the TCA cycle. The decreased rate of conversion of organicacids to amino acids and the accumulation of glutamine werealso concluded. (Received April 13, 1967; )