Ambient levels of UV-B in Hawaii combined with nutrient deficiency decrease photosynthesis in near-isogenic maize lines varying in leaf flavonoids: Flavonoids decrease photoinhibition in plants exposed to UV-B

Abstract

Near-isogenic lines of maize varying in their genes for flavonoid biosynthesis were utilized to examine the effects of foliar flavonoids and nutrient deficiency on maximum net photosynthetic rate (P N ) and chlorophyll (Chl) fluorescence (F v /F m ) in response to ultraviolet-B (UV-B) radiation. Plants with deficient (30 to 70 % lower N, K, Mn, Fe, and Zn) and sufficient nutrients were exposed to four irradiation regimes: (1) no UV-B with solar photosynthetically active radiation (PAR), (2) two day shift to ambient artificial UV-B, 8.2-9.5 kJ m −2 d −1 (21-25 mmol m −2 d −1 ); (3) continuous ambient artificial UV-B; (4) continuous solar UV-B in Hawaii 12-18 kJ m −2 d −1 (32-47 mmol m −2 d −1 ). The natural ratio of UV-B : PAR (0.25-0.40) was maintained in the UV-B treatments. In the adequately fertilized plants, lines b and lc had higher contents of flavonoids and anthocyanins than did lines hi27 and dta. UV-B induced the accumulation of foliar flavonoids in lines hi27 and b, but not in the low flavonoid line dta or in the high flavonoid line lc. In plants grown on deficient relative to adequate nutrients, flavonoid and anthocyanin contents decreased by 30-40 and 40-50 %, respectively, and Chl a and Chl b contents decreased by 30 and 70 %, respectively. The UV-B treatments did not significantly affect P N and F v /F m in plants grown on sufficient nutrients, except in the low flavonoid lines dta and hi27 in which P N and F v /F m decreased by ~15 %. P N , F v /F m , and stomatal conductance decreased markedly (20-30 %) in all lines exposed to UV-B when grown on low nutrients. The decrease in F v /F m was 10 % less in higher flavonoid lines b and lc. The photosynthetic apparatus of maize readily tolerated ambient UV-B in the tropics when plants were adequately fertilized. In contrast, ambient UV-B combined with nutrient deficiency significantly reduced photosynthesis in this C 4 plant. Nutrient deficiency increased the susceptibility of maize to UV-B-induced photoinhibition in part by decreasing the contents of photoprotective compounds.

Developmental phase-dependent photosynthetic responses to ultraviolet-B radiation: damage, defence, and adaptation of primary leaves of wheat seedlings

“…Anthocyanin mitigates the damaging effects on PSA by screening UV-B penetration, while flavonoids, besides their anti-oxidant property, diminish the damaging effect by attenuating UV-B radiation (Holton and Cornish 1995, Mohr and Schopfer 1995, Lau et al 2006. The protection of DNA by anthocyanin and flavonoids was detected by Stapleton and Walbot (1994).…”

UV-B exposure, ROS, and stress: inseparable companions or loosely linked associates?

“…Nutrient supply has also been shown to did not affect well--fertilized plants [40]. UV--B (7.2 kJ m −2 day −1 UV above ambient)…”

Glomus intraradices Attenuates the Negative Effect of Low Pi Supply on Photosynthesis and Growth of Papaya Maradol Plants

“…It has been reported that the negative effect of the nutrient scarcity on the development of many crops is associated with the reduction of Pn, F V /F M , and g s , in corn [20] while in sugar beet, the low Pi reduced CO 2 assimilation by 33% [21]. This negative effect of low Pi supply can be related to many aspects such as reduction of chlorophyll a and b, affecting also, the PSI and PSII efficiency [20].…”

“…This negative effect of low Pi supply can be related to many aspects such as reduction of chlorophyll a and b, affecting also, the PSI and PSII efficiency [20]. Furthermore, Pi is necessary to couple photosynthetic reactions in the dark and light phases, because of its structural and regulatory role in energy conservation and CO 2 assimilation [22].…”