Kumagai Etsushi, Hamaoka Norimitsu, Araki Takuya, Ueno Osamu
Graduate School of Bioresource and Bioenvironmental Science, Kyushu University, Hakozaki 6-10-1, Higashi-ku, Fukuoka 812-8581, Japan; NARO Tohoku Agricultural Research Center, Akahira 4, Shimokuriyagawa, Morioka 020-0198, Japan.
Physiol Plant. 2014 Aug;151(4):533-43. doi: 10.1111/ppl.12145. Epub 2014 Jan 29.
Rice is believed to show photosynthetic symmetry between adaxial and abaxial leaf sides. To verify this, we re-examined dorsoventral asymmetry in photosynthesis, chlorophyll fluorescence and anatomical traits in flag leaves of two Oryza sativa cultivars that differ in nitrogen (N) response and in leaf angle: 'Akenohoshi', a cultivar that can adapt to low-N (LN), with low leaf angle (more erect leaves), and 'Shirobeniya', a cultivar that is unable to adapt to LN, with higher leaf angle. Plants were grown under standard-N (SN) and LN conditions. LN leaves of both cultivars became more erect than SN, but LN Akenohoshi still had more erect ones than Shirobeniya. Contrary to results of previous studies, leaves of both cultivars showed an asymmetry in photosynthetic rate between adaxial and abaxial sides (higher on the adaxial side) under SN. SN leaves of both cultivars showed lower susceptibility to photoinhibition on the adaxial side than on the abaxial side. However, leaves of Akenohoshi showed less asymmetry in these traits under LN than under SN, whereas leaves of Shirobeniya had similar degrees of asymmetry in these traits under both SN and LN. Both cultivars also showed dorsoventral asymmetry in anatomical traits of mesophyll tissue regardless of N level, but the degree of asymmetry was lower in LN Akenohoshi. These data reveal that rice leaves exhibit dorsoventral asymmetry in photosynthetic and anatomical features, and that the degree of asymmetry varies with cultivar and N level. It is suggested that lower leaf angles (particularly in Akenohoshi) in the presence of LN represent a light acclimation to prevent photoinhibition.
水稻被认为在叶片的近轴面和远轴面之间呈现光合对称性。为了验证这一点，我们重新研究了两个在氮（N）响应和叶角方面存在差异的水稻品种剑叶光合作用、叶绿素荧光和解剖学特征的背腹不对称性：“秋之星”，一个能适应低氮（LN）、叶角较小（叶片更直立）的品种，以及“白米丹谷”，一个不能适应低氮、叶角较大的品种。植株在标准氮（SN）和低氮条件下生长。两个品种的低氮叶片都比标准氮条件下的叶片更直立，但低氮条件下的“秋之星”叶片比“白米丹谷”的更直立。与之前的研究结果相反，在标准氮条件下，两个品种的叶片在近轴面和远轴面之间的光合速率存在不对称性（近轴面更高）。两个品种标准氮条件下的叶片在近轴面比远轴面表现出更低的光抑制敏感性。然而，“秋之星”叶片在低氮条件下这些特征的不对称性比在标准氮条件下更小，而“白米丹谷”叶片在标准氮和低氮条件下这些特征的不对称程度相似。无论氮水平如何，两个品种在叶肉组织的解剖学特征上也表现出背腹不对称，但低氮条件下的“秋之星”不对称程度更低。这些数据表明，水稻叶片在光合和解剖学特征上表现出背腹不对称，且不对称程度随品种和氮水平而变化。研究表明，在低氮条件下较小的叶角（特别是“秋之星”）代表了一种光适应，以防止光抑制。
