秋天树叶为什么会掉落？科学家最新研究发现，落叶树通过一种细胞机理让树叶自然脱落，树叶在夏天扮演着“太阳能电池”的角色，但是，在光照不足的冬天，树叶变得多余了，所以就在秋天掉落。这项研究发表于美国《国家科学院院刊》（PNAS）上。
研究人员发现，每片树叶与树枝间都有“脱落带”的特殊层，秋天这层的细胞开始膨胀，减缓了树和叶之间的营养输送。一旦“脱落带”被堵上，分裂线就开始形成，并向下延伸，直到整片叶子脱落。之后，保护层封住“伤口”，阻止水蒸发和虫子侵入。（生物谷Bioon.com）
生物谷推荐原始出处：
PNAS，vol. 105 no. 40 15629-15634，Sung Ki Cho，John C. Walker
Regulation of floral organ abscission in Arabidopsis thaliana
Sung Ki Cho, Clayton T. Larue, David Chevalier, Huachun Wang, Tsung-Luo Jinn, Shuqun Zhang, and John C. Walker
Abscission is a developmental program that results in the active shedding of infected or nonfunctional organs from a plant body. Here, we establish a signaling pathway that controls abscission in Arabidopsis thaliana from ligand, to receptors, to downstream effectors. Loss of function mutations in Inflorescence Deficient in Abscission (IDA), which encodes a predicted secreted small protein, the receptor-like protein kinases HAESA (HAE) and HAESA-like 2 (HSL2), theMitogen-Activated Protein Kinase Kinase 4 (MKK4) and MKK5, and a dominant-negative form of Mitogen-Activated Protein Kinase 6 (MPK6) in a mpk3 mutant background all have abscission-defective phenotypes. Conversely, expression of constitutively active MKKs rescues the abscission-defective phenotype of hae hsl2 and ida plants. Additionally, in hae hsl2 and ida plants, MAP kinase activity is reduced in the receptacle, the part of the stem that holds the floral organs. Plants overexpressing IDA in a hae hsl2 background have abscission defects, indicating HAE and HSL2 are epistatic to IDA. Taken together, these results suggest that the sequential action of IDA, HAE and HSL2, and a MAP kinase cascade regulates the programmed separation of cells in the abscission zone.
