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UNDERSTANDING PHOTOSYNTHESIS, PIGMENT AND GROWTH RESPONSES INDUCED BY UV‐B AND UV‐A IRRADIANCES
Author(s) -
Middleton Elizabeth M.,
Teramura Alan H.
Publication year - 1994
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1994.tb03940.x
Subject(s) - photosynthesis , pigment , photosystem ii , irradiance , irradiation , phytochrome , photosynthetic pigment , chlorophyll , biology , botany , photosystem , chlorophyll a , photochemistry , horticulture , chemistry , biophysics , optics , physics , red light , organic chemistry , nuclear physics
—Plant response to UV‐B (0.290–0.320 μm) irradiation in controlled environments has been difficult to assess, possibly because plants also respond to UV‐A (0.320–0.400 μm) and visible radiation. Photosynthetic dysfunction is often reported, but effects on photosynthetic pigments have been equivocal. Because UV‐A/blue radiation is involved in pigment synthesis, the experimental UV‐A irradiation was controlled and this study was conducted under high ambient photosynthetic photon flux (mid‐day PPF > 1400 pmol m –2 s –1 ). Two biologically effective UV‐B irradiances (10.7 and 14.1 kJ m ‐2 day ‐I ) were utilized and the UV‐A irradiances were matched in controls (˜5 and 9 kJ m ‐2 day ‐1 ). Normal and two mutant pigment isolines (chlorophyll‐deficient, flavonoid‐deficient) of soybean cultivar Clark were utilized for comparisons. Many pigmedgrowth variables exhibited a statistical interaction between spectral quality and quantity. UV‐A/blue photoregulation was demonstrated in the UV‐A controls. The pigmentlgrowth pattern observed at the lower UV‐B irradiance was interpreted as a photosystem II response similar to shade adaptation, suggesting phytochrome involvement in UV‐B irradiation responses. On the other hand, two variables most commonly observed to manifest UV‐B‐induced effects—decreased photosynthesis and increased leaf flavonoid content—exhibited no interactions due to UV exposure or spectral quality. In general, the observed response patterns indicated either moderation of UV‐B‐induced responses by UV‐A/blue radiation, or coaction between them, and provides an explanation for the common failure to demonstrate fluence‐related responses in UV‐B experiments.