Discrete character of the development of the photosynthetic apparatus in greening barley leaves

Biogenesis of the photosynthetic apparatus in greening etiolated leaves of barley (Hordeum vulgare L) was investigated by an approach permitting investigation of this process under conditions that minimize differences in plastid development. Distributions of barley leaves greening for 24 h as to chlorophyll content and of chloroplast grana as to number of thylakoids were shown to be of a multimodal character. The shape of time-course curves of chlorophyll accumulation in local sites of greening etiolated leaves was of a stepped or (at the end of greening) undulated character. The stepwise accumulation of chlorophyll was accompanied by wave-like changes in chlorophyll b/a ratio, intensity of low-temperature chlorophyll fluorescence and photosynthetic activity with minima at the time points of transition to accelerated chlorophyll accumulation. It is assumed that (1) development of the photosynthetic apparatus in local sites of greening etiolated leaves occurs stepwise, from one steady level to another, but not as gradually as is generally accepted, and (2) every separate step in development of the photosynthetic apparatus seems to begin with formation of photosystem cores and to end with the synthesis of light-harvesting complexes.