The Cost of Maintenance Processes in Plant Cells

Abstract

The most important maintenance processes in plants are protein turnover and active transport processes to maintain certain ion concentrations in the cells. In this paper an attempt is made to calculate the total energy cost of these processes from what is known about their specific costs and what has been observed about their rates. Because of insufficient reliable data about rates of individual maintenance processes, only approximate values can be obtained.The average turnover rate of leaf proteins may be about 100 mg protein per g proteins per day at normal temperature in leaves assimilating at moderate light intensities. This process consumes 28-53 mg glucose per g protein per day, which equals 7-13 mg glucose per g dry weight per day in leaves. It is likely that the rates of protein turnover and of C0 2 -assimilation are related. The cost of maintaining ion concentrations is estimated to be about 6-10 mg glucose per g dry weight per day in leaves. The sum of these figures is lower than is indicated by measurements of maintenance respiration. One reason for the underestimation may be that the protein turnover rates used in the calculations apply to plants with lower photosynthetic rates than the plants in which the maintenance respiration was measured. Effects of water stress and salinity, temperature and other environmental factors on the rate of maintenance processes are discussed.The consumption of assimilates for maintenance of plant cells is a significant, negative factor in plant productivity. A better understanding of the maintenance processes may give a clue how to manipulate plant characteristics or the environment to reduce the amount of assimilates consumed in these processes. It is suggested that reduction in protein turnover rates may be one such manipulation.

Energy content, storage substances, and construction and maintenance costs of Mediterranean deciduous leaves

“…The construction cost was calculated (as g glucose/g dry matter) according to the method of Willaims et al (1987), using a value for growth efficiency Eo = 0.87 (Pcnning de Vries et al 1974, Penning de Vries 1975McDermitt and Loomis 1981) and considering nitrale as the nitrogen source. The maintenance cost (g glucosc/g dry matter x day) was estimated using the mnintenance coefficients of and the method described by Merino et al (1984).…”

Response of root respiration to changes in temperature and its relevance to global warming

“…the energy necessary for the maintenance of chemical and electrochemical gradients across membranes and the turnover of cellular constituents such as proteins (Penning de Vries, 1975)) are small (approx. 5-10%) in actively growing root systems, under conditions of constant temperature in a controlled environment (Van Der Werf et al, 1988 ;Scheurwater et al, 1998).…”

Photosynthate costs associated with the utilization of different nitrogen–forms: influence on the carbon balance of plants and shoot–root biomass partitioning

“…Penning de Vries, 1975). We use data on E. coli, for which simultaneous protein and mRNA synthesis has been calculated by Dennis & Bremer (1974), to estimate the cost of mRNA turnover.…”