Ribulose Bisphosphate Carboxylase Activity and Photosynthesis during Leaf Development in the Tomato

Besford, R. T., Withers, A. C. and Ludwig, L. J. 1985. Ribulosebisphosphate carboxylase activity and photosynthesis duringleaf development in the tomato.—J. exp Bot. 36: 1530–1541. The carboxylase activity of ribulose-1,5-bisphosphate carboxylase/oxygenaseand of phosphoenolpyruvate carboxylase, and the light saturatedrate of net photosynthesis were measured in the developing 5thleaf of tomato plants. Values for light saturated net photosynthesiswere also calculated from the measured carboxylase activitiesand estimates of internal CO₂ and oxygen concentrations. Thecalculated rate using the activity of ribulose bisphosphatecarboxylase alone for net CO₂ assimilation in 300 mm³ dm^–3CO₂ was greater than the measured rate at 80% and full expansionbut less than the measured rate in younger leaves. When theactivities of both the carboxylases were taken into accountbetter agreement was evident for young leaves but the rate wasfurther overestimated for older leaves The calculated rate forphotosynthesis in 1200 mm³ dm^–3 CO², assuming saturationof ribulose bisphosphate carboxylase with RuBP, was an overestimatefor young leaves but was close to the observed values for leavesnear full expansion. The results are discussed in terms of measuredconductances for CO₂ and the availability of RuBP in the leaf Key words: Tomato, leaf development, photosynthesis, RuBP carboxylase, oxygenase     

Participation of the Mehler Reaction and Catalase in the Oxygen Exchange of Chloroplast Preparations

We have reinvestigated several aspects of the Mehler reactionin isolated chloroplasts. We have confirmed that the rate ofoxygen uptake is accelerated by a number of biological and artificialelectron carriers. The Mehler reaction also responds to uncouplingagents and exhibits photosynthetic control with ADP. In thepresence of catalase, steady-state oxygen exchange may be establishedand lead to such apparent anomalies as oxygen uptake in thelight followed by oxygen evolution in the dark. The steady stateis a function of catalase concentration, light intensity, andthe presence and concentration of electron carriers, etc., whichaffect the rate of the Mehler reaction.     

An analysis of the vegetation pattern in a semi-arid Eucalyptus populnea woodland in north-west New South Wales

Shrub invasion of Eucalyptus populnea woodland is of concern to the pastoral industry. As part of an ecosystem study, different analyses were used to identify spatial pattern and associations in the tree and shrub species, with the aim of identifying what factors were most influential on the ecosystem. The results suggested that there were no strong edaphic or topographic influences on the distribution of plants. The principal influence on the arrangement of trees and shrubs was the large Eucalyptus trees, which were randomly arranged, and the canopy of which covered 15% of the area. It is concluded that any disturbance of the large Eucalyptus trees would have intense effects on the whole ecosystem. Qualitative and quantitative measurements of the plant species in sample quadrats were subjected to a variety of pattern analyses including association analysis (DIVINF), correlation analysis, principal components analysis and several classification programs including POLYDIV and MULCLAS. A criticism of such analyses is that positive results are both inevitable and not subject to statistical proof, whilst their strength is that they can simplify complicated sets of data. In this case the patterns suggested by the results were visually apparent and no additional insights were achieved. The dangers inherent in relying on a single pattern analysis were revealed when the groups of quadrats produced by the different analyses were mapped. Even when the groupings derived from different analyses were based on a similar species content, their spatial arrangement was dissimilar.