D. Massimino

Growth of plants at reduced pressures: experiments in wheat-technological advantages and constraints.

Procedures and results are presented concerning the growth of wheat plants with variable partial pressures of O2 and N2. Data demonstrate that some growth occurs in pressures as low as 0.1 atmosphere. The growth was similar or higher at 200 mb (0.2 atmosphere) than in normal atmosphere but the development was different. Advantages of the low pressure cultivation, especially in the absence of nitrogen, are discussed, including better ratio volume/mass of plant cultivation module; lower losses of gases by leakage; easier management of photosynthetic oxygen produced by plants.

The C 2 3A System, an Example of Quantitative Control of Plant Growth Associated with a Data Base

The architecture of the C23A (Chambers de Culture Automatique en Atmosphere Artificielles) system for the controlled study of plant physiology is described. A modular plant growth chambers and associated instruments (I.R. CO2 analyser, Mass spectrometer and Chemical analyser); network of frontal processors controlling this apparatus; a central computer for the periodic control and the multiplex work of processors; and a network of terminal computers able to ask the data base for data processing and modeling are discussed. Examples of present results are given. A growth curve analysis study of CO2 and O2 gas exchanges of shoots and roots, and daily evolution of algal photosynthesis and of the pools of dissolved CO2 in sea water are discussed.

Effect of CO2 and O2 on development and fructification of wheat in closed systems.

The cultivation of wheat (Triticum aestivum L.) was performed in controlled environment chambers with the continuous monitoring of photosynthesis, dark respiration, transpiration and main nutrient uptakes. A protocol in twin chambers was developed to compare the specific effects of low O2 and high CO2. Each parameter is able to influence photosynthesis but different effects are obtained In the development, fructification and seed production, because of the different effects of each parameter on the ratio of reductive to oxidative cycle of carbon. The first main conclusion is that low level of O2, at the same rate of biomass production, strongly acts on the rate of ear appearance and on seed production. Ear appearance was delayed and seed production reduced with a low O2 treatment (approximately 4%). The O2 effect was not mainly due to the repression of the oxidative cycle. The high CO2 treatment (700 to 900 microl l-1) delayed ear appearance by 4 days but did not reduce seed production. High CO2 treatment also reduced transpiration by 20%. Two hypothesis were proposed to explain the similarities and the difference in the O2 and CO2 effects on the growth of wheat.

Photosynthesis and Photorespiration on a Red Macroalga Chondrus crispus, in Relation to the Carbonic System

Some investigations about photorespiration in algae have already been made, but results remain very contradictory because of the common use of indirect techniques as Warburg effect, 14C measurements, compensation points for CO2, etc... Most of the gas exchange measurements on aquatic plants are based upon O2 because CO2 exchanges are interfering with HCO− 3 and CO= 3 pools wich represent a buffer 100 times higher than free dissolved CO2, at seawater pH values. Then, fast and non steady-state experiments are generally carried out in buffered artificial media. The set up we developed makes possible continuous and steady-state measurements of gas exchanges from aquatic plants, as measured by O2, but also by CO2. It allows the use of 18O2 as a tracer in order to measure directly the photorespiration.

Oxygen Exchanges in Marine Macroalgae

Whether photorespiration occurs in marine algae is still very controversial for two main reasons. First, the methods used for its detection are often indirect (O2 sensitivity of photosynthesis), or known to underestimate the process (14CO2 method). In addition, the nature of the external carbon form acquired for photosynthesis (CO2 and/or HCO 3 - ) is still thought to be quite variable among marine species, and is strongly dependent upon the experimental conditions. Since I) the HCO 3 - concentration in seawater is about 200 times greater than the free CO2 concentration, 2) its uptake might drive putative internal DIC accumulation, and 3) the O2 and CO2 substrates interact on Rubisco in a competitive manner, it appears essential to know which DIC form is absorbed in order to understand the photorespiratory phenomenon in these organisms.