Influence of kinetin on protochlorophyll(ide) accumulation and on the Shibata shift in Raphanus seedlings

Regulation of chloroplast development and function by cytokinin

A role of the plant hormone cytokinin in regulating the development and activity of chloroplasts was described soon after its discovery as a plant growth regulator more than 50 years ago. Its promoting action on chloroplast ultrastructure and chlorophyll synthesis has been reported repeatedly, especially during etioplast-to-chloroplast transition. Recently, a protective role of the hormone for the photosynthetic apparatus during high light stress was shown. Details about the molecular mechanisms of cytokinin action on plastids are accumulating from genetic and transcriptomic studies. The cytokinin receptors AHK2 and AHK3 are mainly responsible for the transduction of the cytokinin signal to B-type response regulators, in particular ARR1, ARR10, and ARR12, which are transcription factors of the two-component system mediating cytokinin functions. Additional transcription factors linking cytokinin and chloroplast development include CGA1, GNC, HY5, GLK2, and CRF2. In this review, we summarize early and more recent findings of the long-known relationship between the hormone and the organelle and describe crosstalk between cytokinin, light, and other hormones during chloroplast development.

Fluorescence induction kinetics of green and etiolated leaves by recording the complete in-vivo emission spectra

Complete room temperature fluorescence emission spectra of green and etiolated leaves (Raphanus sativus L., cv. Saxa Treib, Hordeum vulgare L., cv. Villa) are continuously recorded up to 4 min after onset of excitation. In green leaves two emission bands appear, whereas in etiolated leaves only one band is observed. In both cases the emission intensity increases with time, the high-energy band of green leaves decreasing more rapidly than the low-energy band. This phenomenon can be interpreted in terms of energy transfer. During the observation time of the fluorescence induction kinetic no shift of the emission peaks is found within the accuracy of the apparatus (±2nm).