THE USE OF UV-RADIATION TO CONTROL THE ARCHITECTURE OF SALVIA SPLENDENS PLANTS .1. EFFECTS ON PLANT-GROWTH, WATER RELATIONS AND GAS EXCHANGED

In experiments with Salvia splendens plants grown in the greenhouse we evaluated the possible use of irradiation with unfiltered UV (UVA + U VB + UVC) lamps for the control of plant growth. The effect of UV irra diation on the growth of S. splendens plants in the greenhouse was clo sely dependent on the growing season and the level of available photos ynthetically active radiation. In summer UV treatments were ineffectiv e, but in the low light conditions of winter UV irradiation inhibited the growth via both photomorphogenic and photosynthetic effects. The r eduction of stomatal conductance and expansion growth, which in turn d epressed photosynthesis and dry matter accumulation, were not a conseq uence of an impairment of plant water status but appeared to be a dire ct UV effect on stomata and cell wall rheological properties. Our find ings suggest that the use of unfiltered UV irradiation could become an effective tool for the regulation of growth in greenhouse crops, part icularly during the poor light conditions of the winter season.