Basic plasticity of protein expression in tobacco leaf plasma membrane

Highly purified plasma membrane fractions were prepared using top‐, middle‐ or bottom‐leaf sets of tobacco. Plasma membrane polypeptides were analysed by two‐dimensional gel electrophoresis and the abundances of 90 polypeptides non‐washed out by Triton X‐100 were quantified by image analysis. Under constant environmental conditions, the relative abundances of approximately 75% of polypeptides were shown to change during plant development, irrespective of the position of the leaves on the plant. The greatest plasticity of the plasma membrane polypeptide pattern was observed, first during the early stages of plant development, including floral induction, and, to a lesser extent, during the late stages, including seed formation. Some of the leaf plasma membrane polypeptides were abundant only at specific developmental stages and in specific leaf sets. A similar situation existed during the nycthemeron, where the abundances of approximately 75% of the polypeptides were observed to change during a 24 h period. Some polypeptides appeared to be essentially dark‐ or light‐specific. Overall data analysis supports the conclusion that, under constant environmental conditions, approximately 90% of plant plasma membrane polypeptides are simultaneously subjected to both long‐term (day‐scaled) and short‐term (hour‐scaled) dynamics. This unexpected steady‐state dynamics (i) corresponds to a new kind of plasticity which has to be distinguished from the phenotypic plasticity shown by plants in response to various changes in environmental factors, (ii) provides new insights into the functioning of membranes and is proposed to constitute a signature of the plant physiological state.