秋天樹葉為什么會掉落,？科學(xué)家最新研究發(fā)現(xiàn),，落葉樹通過一種細(xì)胞機理讓樹葉自然脫落，樹葉在夏天扮演著“太陽能電池”的角色,，但是,，在光照不足的冬天，樹葉變得多余了,，所以就在秋天掉落,。這項研究發(fā)表于美國《國家科學(xué)院院刊》（PNAS）上。
研究人員發(fā)現(xiàn),，每片樹葉與樹枝間都有“脫落帶”的特殊層,，秋天這層的細(xì)胞開始膨脹，減緩了樹和葉之間的營養(yǎng)輸送,。一旦“脫落帶”被堵上,，分裂線就開始形成，并向下延伸,，直到整片葉子脫落,。之后，保護層封住“傷口”,，阻止水蒸發(fā)和蟲子侵入,。（生物谷Bioon.com）
生物谷推薦原始出處：
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.
