PHOTOMORPHOGENESIS PHOTOSYNTHESIS AND EARLY GROWTH OF PRIMARY LEAVES OF PHASEOLUS VULGARIS

The response of leaf tissue to white, blue, red, and far-red light has been examined. Leaves on plants grown in darkness show increased cell number, cell volume, and area when exposed to long periods (up to 48 h) of low-intensity red, blue, or far-red radiation. This is believed to be a photomorphogenic response which does not involve photosynthesis. Leaves from plants exposed to white light during germination do not usually respond to red, blue, or far-red light. An exception to this was found for leaf discs which showed a larger increase in area than the dark controls following exposure to far-red light for 24 h. Leaf tissue from light-grown plants responds to high-intensity white light, probably through photosynthesis. Discs cut from dark-grown plants and cultured in white light grow equally well in air and CO2-free conditions. Application of the photosynthetic inhibitor DCMU reduces growth and chlorophyll formation, however.It is concluded that light, perhaps acting through the phytochrome mechanism, has initially a number of morphogenic effects including initiation of development of the photosynthetic apparatus. The responses to photomorphogenically active radiation do not persist and light effects through photosynthesis are rapidly initiated and dominate the later stages of leaf growth. © 1968 OXFORD UNIVERSITY PRESS.