THE IMPORTANCE OF THE RATIO UV-B PHOTOSYNTHETIC ACTIVE RADIATION (PAR) DURING LEAF DEVELOPMENT AS DETERMINING FACTOR OF PLANT-SENSITIVITY TO INCREASED UV-B IRRADIANCE - EFFECTS ON GROWTH, GAS-EXCHANGE AND PIGMENTATION OF BEAN-PLANTS (PHASEOLUS-VULGARIS CV LABEL)/
G. Deckmyn et al., THE IMPORTANCE OF THE RATIO UV-B PHOTOSYNTHETIC ACTIVE RADIATION (PAR) DURING LEAF DEVELOPMENT AS DETERMINING FACTOR OF PLANT-SENSITIVITY TO INCREASED UV-B IRRADIANCE - EFFECTS ON GROWTH, GAS-EXCHANGE AND PIGMENTATION OF BEAN-PLANTS (PHASEOLUS-VULGARIS CV LABEL)/, Plant, cell and environment, 17(3), 1994, pp. 295-301
To evaluate the effect of different naturally occurring irradiation co
nditions on the sensitivity of bean (Phaseolus vulgaris cv. Label) to
increased UV-B levels, plants were grown under six different light tre
atments. In the control series (at ambient levels of UV-B), UV-B and v
isible light were decreased in parallel, resulting in three different
total irradiation treatments with the same UV-B/PAR ratio. A second se
ries with a 15% increase in UV-B irradiation at each PAR level was use
d to investigate the effect of UV-B under the varying total irradiance
levels. The different total irradiance levels resulted in large diffe
rences in total dry weight, specific leaf weight, photosynthesis-light
response and pigment concentrations. Nevertheless, the 15% increase i
n UV-B resulted in equal reductions in total dry weight (from 24.5 to
34.3%) and effective photosynthesis for all light levels. The accumula
tion of protective pigments in the primary bean leaves was strongly co
rrelated to the total irradiance level (200% increase from the lowest
to the highest light level), but was not influenced by increasing UV-B
levels. As the UV-B/PAR ratio outside increases with decreasing total
irradiance (when induced by cloud cover) this implies that low radiat
ion levels are potentially dangerous to some plants, even though the U
V-B levels may seem negligible.