Schumaker M A, Bassman J H, Robberecht R, Radamaker G K
Plant Gene Expression Center, University of California, Berkeley/U.S. Department of Agriculture, 800 Buchanan Street, Albany, CA 94710, USA.
Tree Physiol. 1997 Oct;17(10):617-26. doi: 10.1093/treephys/17.10.617.
We compared the physiological and morphological responses of rooted cuttings of Populus trichocarpa Torr. & Gray and P. trichocarpa x P. deltoides Bartr. ex Marsh. grown in either near-ambient solar ultraviolet-B (UV-B; 280-320 nm) radiation (cellulose diacetate film) or subambient UV-B radiation (polyester film) for one growing season. Midday biologically effective UV-B radiation was 120.6 and 1.6 mJ m(-2) s(-1) under the cellulose diacetate and polyester films, respectively. Gas exchange, leaf chlorophyll, light harvesting efficiency of photosystem II, and foliar UV-B radiation-absorbing compounds (i.e., flavonoid derivatives) were measured in expanding (leaf plastochron index (LPI) 5), nearly expanded (LPI 10), and fully expanded mature (LPI 15) leaves of intact plants of plastochron index 30 to 35. Plants were then harvested and height, diameter, biomass allocation and leaf anatomical attributes determined. Net photosynthesis, transpiration, and stomatal conductance were significantly greater in mature leaves exposed to subambient UV-B radiation than in mature leaves exposed to near-ambient UV-B radiation. Concentrations of UV-B radiation-absorbing compounds (measured as absorbance of methanol-extracts at 300 nm) were significantly greater in mature leaves exposed to near-ambient UV-B radiation than in mature leaves exposed to subambient UV-B radiation. The UV-B radiation treatments had no effects on chlorophyll content or intrinsic light harvesting efficiency of photosystem II. Height, diameter, and biomass were not significantly affected by UV-B radiation regime in either clone. Leaf anatomical development was unaffected by UV-B radiation treatment in P. trichocarpa x P. deltoides. For P. trichocarpa, leaf anatomical development was complete by LPI 10 in the near-ambient UV-B radiation treatment, but continued through to LPI 15 in the subambient UV-B radiation treatment. Mature leaves of P. trichocarpa were thicker in the subambient UV-B radiation treatment than in the near-ambient UV-B radiation treament as a result of greater development of palisade parenchyma tissue. We conclude that exposure to near-ambient UV-B radiation for one growing season caused shifts in carbon allocation from leaf development to other pools, probably including but not limited to, UV-B absorbing compounds. This reallocation curtailed leaf development and reduced photosynthetic capacity of the plants compared with those in the subambient UV-B radiation treatment and may affect growth over longer periods of exposure.
我们比较了毛果杨（Populus trichocarpa Torr. & Gray）以及毛果杨与三角叶杨（Populus trichocarpa x P. deltoides Bartr. ex Marsh.）杂交种的带根插条在近环境太阳紫外线B（UV-B；280 - 320纳米）辐射（二醋酸纤维素膜）或亚环境UV-B辐射（聚酯膜）下生长一个生长季的生理和形态响应。在二醋酸纤维素膜和聚酯膜下，午间生物有效UV-B辐射分别为120.6和1.6毫焦·平方米⁻²·秒⁻¹。在叶龄指数（LPI）为30至35的完整植株的伸展叶（叶龄指数5）、近伸展叶（LPI 10）和完全伸展成熟叶（LPI 15）中，测定了气体交换、叶片叶绿素、光系统II的光能捕获效率以及叶片UV-B辐射吸收化合物（即类黄酮衍生物）。然后收获植株，测定株高、直径、生物量分配和叶片解剖学特征。与暴露于近环境UV-B辐射的成熟叶相比，暴露于亚环境UV-B辐射的成熟叶的净光合作用、蒸腾作用和气孔导度显著更高。暴露于近环境UV-B辐射的成熟叶中UV-B辐射吸收化合物的浓度（以甲醇提取物在300纳米处的吸光度衡量）显著高于暴露于亚环境UV-B辐射的成熟叶。UV-B辐射处理对叶绿素含量或光系统II的内在光能捕获效率没有影响。两个无性系的株高、直径和生物量均未受到UV-B辐射处理的显著影响。在毛果杨与三角叶杨杂交种中，叶片解剖学发育不受UV-B辐射处理的影响。对于毛果杨，在近环境UV-B辐射处理中，叶龄指数10时叶片解剖学发育完成，但在亚环境UV-B辐射处理中一直持续到叶龄指数15。由于栅栏薄壁组织发育更充分，在亚环境UV-B辐射处理下，毛果杨的成熟叶比在近环境UV-B辐射处理下更厚。我们得出结论，在一个生长季暴露于近环境UV-B辐射会导致碳分配从叶片发育转移到其他库，可能包括但不限于UV-B吸收化合物。与亚环境UV-B辐射处理的植株相比，这种重新分配抑制了叶片发育并降低了植株的光合能力，并且在更长时间暴露下可能影响生长。
