Photosynthesis and Gas Exchange of Acetabularia Chloroplasts in an Artificial Leaf

Abstract

ISOLATED chloroplast preparations offer great advantages in the analysis of carbon pathways of photosynthesis because the system is not complicated by non-chloroplast metabolism, and kinetic analyses¹ can be made which are difficult with whole leaves². Unfortunately the slow diffusion and equilibration of CO₂, HCO⁻₃ and CO²⁻₃ in the suspension medium is a serious disadvantage in gas exchange or ¹⁴CO₂-¹²CO₂ pulse-chase experiments³, but this difficulty can be overcome by using a thin film of concentrated chloroplast suspension spread on a non-absorbent support in the form of an “artificial leaf”. Recent experiments by Coombs and Baldry have shown that pea and spinach chloroplast preparations supported on filter paper were stable only for periods of up to 10 min⁴. We have used Acetabularia mediterranea Chloroplasts on filter paper to analyse the products of short term (1 s to 5 min) ¹⁴CO₂ fixation, but we found them insufficiently stable for longer experiments or gas exchange measurements. We have overcome this difficulty, however, by supporting Chloroplasts on a non-absorbent grid instead of filter paper.