Increases in the terrestrial levels of ultraviolet-B (UV-B) radiation (280 to 320 nm) due to diminished stratospheric ozone have prompted an investigation of the protective mechanisms that contribute to UV-B tolerance in plants. In response to UV-B stress, flowering plants produce a variety of UV-absorptive secondary products derived from phenylalanine. Arabidopsis mutants with defects in the synthesis of these compounds were tested for UV-B sensitivity. The transparent testa-4 (tt4) mutant, which has reduced flavonoids and normal levels of sinapate esters, is more sensitive to UV-B than the wild type when grown under high UV-B irradiance. The tt5 and tt6 mutants, which have reduced levels of UV-absorptive leaf flavonoids and the monocyclic sinapic acid ester phenolic compounds, are highly sensitive to the damaging effects of UV-B radiation. These results demonstrate that both flavonoids and other phenolic compounds play important roles in vivo in plant UV-B protection.

Increases in the terrestrial levels of ultraviolet-B (UV-B) radiation (280 to 320 nm) due to diminished stratospheric ozone have prompted an investigation of the protective mechanisms that contribute to UV-B tolerance in plants. In response to UV-B stress, flowering plants produce a variety of UV-absorptive secondary products derived from phenylalanine. Arabidopsis mutants with defects in the synthesis of these compounds were tested for UV-B sensitivity. The transparent testa-4 (tt4) mutant, which has reduced flavonoids and normal levels of sinapate esters, is more sensitive to UV-B than the wild type when grown under high UV-B irradiance. The tt5 and tt6 mutants, which have reduced levels of UV-absorptive leaf flavonoids and the monocyclic sinapic acid ester phenolic compounds, are highly sensitive to the damaging effects of UV-B radiation. These results demonstrate that both flavonoids and other phenolic compounds play important roles in vivo in plant UV-B protection.

Six-year-old ‘Gala’/‘Malling26’ (‘M.26’) apple (Malus ×domestica Borkh.) trees grown in sand culture were provided with a total of 30 g of N per tree as enriched 15N-NH4NO3 in Hoagland's solution via fertigation to determine the magnitude and seasonal patterns of accumulation of macro- and micronutrients and the demand-supply relationship of N. Crop load was adjusted to 8.2 fruit/cm2 trunk cross-sectional area, at king fruit diameter of 10 mm by hand-thinning. At each of seven key developmental stages throughout one annual growth cycle, four trees were excavated and destructively sampled for complete nutrient analysis. Nutrient concentrations in leaves and fruit fell within the recommended optimal range, and the fruit yield was 18.8 kg/tree (equivalent to 52.45 t·ha−1) with an average fruit weight of 181 g. The net accumulation of N, P, K, Ca, Mg, and S from budbreak to fruit harvest was 19.8, 3.3, 36.0, 14.2, 4.4, and 1.6 g/tree, respectively, and that for B, Zn, Cu, Mn, and Fe was 93.6, 60.9, 46.5, 184.8, and 148.7 mg/tree, respectively. Nutrient accumulation by new growth (fruit plus shoots and leaves) accounted for over 90% of the net gain for N, P, K, Mg, S, and B in the whole tree and a large proportion of the net gain for Ca, Zn, Mn, and Fe (from 58.1% for Zn to 87.2% of Fe) from budbreak to fruit harvest. Differential nutrient accumulation patterns were found in shoots and leaves and fruit. The most rapid accumulation of all nutrients in shoots and leaves took place during active shoot growth from bloom to the end of shoot growth. The accumulation pattern of most nutrients corresponded well with the accumulation of dry matter, with continued accumulation observed only in total Ca and Mn in shoots and leaves after the end of shoot growth. Nutrient accumulation in fruit largely followed its dry matter accumulation, and a large proportion of the nutrient accumulation (from 58.1% for Zn to 77.4% of K) occurred from the end of shoot growth to fruit harvest. At harvest, fruit contained more P, K, B, and Fe, whereas shoots and leaves had more N, Ca, Mg, S, Zn, and Mn. Most of the N demand by new growth at bloom was provided by tree reserve N. Remobilization of N from perennial parts of the tree was found to support rapid fruit expansion from the end of shoot growth to fruit harvest. The most rapid uptake from current season's N supply occurred from bloom to the end of shoot growth, corresponding to the highest tree N demand. At harvest, 62.4% of the total N in new growth was in shoots and leaves, with the balance in fruit. Reserve N and current season's N uptake each contributed about 50% to the total N in the whole tree at harvest.

Winter wheat (cultivar Vona) was exposed to four levels of 03 (7-hr accelerated thfe loss of moisture from the heads. Ozone significantly exposure period averages of 0.027, 0.054, 0.076, and 0.096 ppm) and four reduced stomatal conductances of flag leaves, net photosynthesis of whole levels of SO 2 (4-hr exposure period averages of 0, 0.039, 0.166, and 0.363 plants and individual heads, and seed dry weights per head as a result of ppm) and all combinations of the two pollutants from anthesis until reduced seed size but not seed number. Reductions in seed weights caused harvest. Sulfur dioxide did not affect net photosynthesis or yield but by ozone were highly correlated with measured reductions in whole-plant temporarily reduced stomatal conductances of flag leaves. No interactions and individual head photosynthesis. Exposure of Vona winter wheat to ambient between SO 2 and 03 were found for any variables measured. Ozone and higher 03 concentrations from anthesis until harvest resulted in yield accelerated the senescence of flag leaves, stalks, and heads and also losses caused by reductions in net photosynthesis.