Cytokinin delays dark-induced senescence in rice by maintaining the chlorophyll cycle and photosynthetic complexes.
Cytokinin delays dark-induced senescence in rice by maintaining the chlorophyll cycle and photosynthetic complexes.
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DOI：
10.1093/jxb/erv575
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发表时间：
2016-03
影响因子：
6.9
通讯作者：
Ramanan R
中科院分区：
文献类型：
--
作者：
Talla SK;Panigrahy M;Kappara S;Nirosha P;Neelamraju S;Ramanan R
细胞分裂素通过维持Chl a/b比值和光合复合体的稳定性，诱导水稻在黑暗诱导衰老过程中保持功能性绿色。已知植物激素细胞分裂素（CK）可以延缓植物衰老。研究了CK类似物6-苄基腺嘌呤（BA）对水稻叶片的影响，以暗致衰老（DIS）作为叶片自然衰老的替代，了解CK延缓耐旱耐热水稻品种Nagina22 （N22）叶片衰老的可能机制。N22的留绿突变体N22- h -dgl162叶片和ba处理的N22叶片在DIS过程中表现出叶绿素（Chl）色素的保留、Chl a/b比的维持以及光化学效率和析氧速率降低的延迟。HPLC分析表明，7-羟甲基叶绿素（HmChl）在DIS过程中积累，其积累动力学与衰老进程相关。转录组分析显示，与自然衰老的N22叶片相比，ba处理的N22叶片和保持绿色突变体叶片中几个质体定位基因，特别是与光系统II （PSII）相关的基因的转录水平更高。实时PCR分析显示，与Chl a/b相互转换相关的酶和与光收集复合物相关的蛋白质编码基因在BA处理后的72小时内保持较高的转录水平。在N22- h -dgl162和ba处理的N22叶片中，即使在DIS处理96h后，色素-蛋白复合物仍保持完整。因此，CK通过积累HmChl和上调Chl循环中的基因来延缓衰老，从而维持Chl a/b比值。此外，CK处理还保留了较高的psii相关基因转录水平，导致水稻光合色素复合物的稳定性和功能性保绿。
Cytokinin induces functional stay-greenness by maintaining the Chl a/b ratios and the stability of photosynthetic complexes during dark-induced senescence in rice. The phytohormone cytokinin (CK) is known to delay senescence in plants. We studied the effect of a CK analog, 6-benzyl adenine (BA), on rice leaves to understand the possible mechanism by which CK delays senescence in a drought- and heat-tolerant rice cultivar Nagina22 (N22) using dark-induced senescence (DIS) as a surrogate for natural senescence of leaves. Leaves of N22-H-dgl162, a stay-green mutant of N22, and BA-treated N22 showed retention of chlorophyll (Chl) pigments, maintenance of the Chl a/b ratio, and delay in reduction of both photochemical efficiency and rate of oxygen evolution during DIS. HPLC analysis showed accumulation of 7-hydroxymethyl chlorophyll (HmChl) during DIS, and the kinetics of its accumulation correlated with progression of senescence. Transcriptome analysis revealed that several plastid-localized genes, specifically those associated with photosystem II (PSII), showed higher transcript levels in BA-treated N22 and the stay-green mutant leaves compared with naturally senescing N22 leaves. Real-time PCR analyses showed that genes coding for enzymes associated with Chl a/b interconversion and proteins associated with light-harvesting complexes maintained higher transcript levels up to 72h of DIS following BA treatment. The pigment–protein complexes analyzed by green gel remained intact in both N22-H-dgl162 and BA-treated N22 leaves even after 96h of DIS. Thus, CK delays senescence by accumulation of HmChl and up-regulating genes in the Chl cycle, thereby maintaining the Chl a/b ratio. Also, CK treatment retains higher transcript levels of PSII-related genes, resulting in the stability of photosynthetic pigment complexes and functional stay-greenness in rice.