Endogenous hormones and expression of senescence-related genes in different senescent types of maize

Abstract

Levels of cytokinins and abscisic acid (ABA) and the expression of senescence-related genes were investigated in two maize (Zea mays L.) cultivars of different senescence type, cv. P3845 (stay-green) and cv. Hokkou 55 (earlier senescent), in a field study. The delay in leaf senescence in P3845 was correlated with increased levels of chlorophyll and nitrogen and a higher photon-saturated photosynthetic rate (P(sat)). Compared with the earlier senescent Hokkou 55, P3845 showed enhanced contents of cytokinins (trans-zeatin riboside, t-ZR; dihydrozeatin riboside, DHZR; isopentenyladenosine, iPA) and reduced levels of ABA in its leaves. In roots, P3845 had increased levels of t-ZR, DHZR, and ABA, but decreased concentrations of iPA. It was concluded that a higher rate of cytokinin transport from roots to leaves contributes to the delay of senescence in P3845. By contrast, the translocation of ABA from roots to shoots may be blocked in the stay-green cultivar, which also results in retarded leaf senescence. P3845 ear leaves contained more malondialdehyde (MDA) and higher catalase (CAT) and superoxide dismutase (SOD) activities than Hokkou 55. Since the accumulation of the mRNAs for Rubisco small subunit (rbcS), phosphoenolpyruvate carboxylase (PEPC), and SOD peaked after Chl content and P(sat) had reached their maxima, it is speculated that when leaf senescence is initiated, Chl contents decrease first, followed by the degradation of the photosynthetic apparatus and of photosynthesis-related enzymes. See1 and See2 encode senescence-related cysteine proteases; their mRNAs were most abundant in yellowing leaves, suggesting that these proteins are involved in the process of senescence rather than its initiation. mRNAs of both genes were more abundant in Hokkou 55 than in P3845, which suggests a regulation of leaf senescence at the transcriptional level.

Transcription Factor ATAF1 in Arabidopsis Promotes Senescence by Direct Regulation of Key Chloroplast Maintenance and Senescence Transcriptional Cascades

“…ABA is one of the most effective plant hormones known to promote senescence (Zacarias and Reid, 1990;Lee et al, 2011;Finkelstein, 2013), and increases in endogenous ABA levels during senescence have been reported in several plant species, including oat (Avena sativa; Gepstein and Thimann, 1980), rice (Oryza sativa; Philosophhadas et al, 1993), maize (He et al, 2005a), and Arabidopsis (Breeze et al, 2011). As expression of ATAF1 is well induced by ABA treatment (Lu et al, 2007;Wu et al, 2009), we tested whether ATAF1 plays a role in the hormonal control of senescence.…”

Plough Pan Impacts Maize Grain Yield, Carbon Assimilation, and Nitrogen Uptake in the Corn Belt of Northeast China

“…The conspicuous visual symptoms of leaf senescence are the loss of chlorophyll pigments, desiccation, and eventual abscission (He and Wasaki, 2005). The initiation and progression of leaf senescence can be modulated by internal factors (such as plant hormones and plant growth regulators) and various environmental factors, such as temperature or drought status, mineral supplying capacity (Masclaux et al, 2008b;Kosgey et al, 2013), soil water conditions (Széles et al, 2012;Thoiron and Briat, 1999), and soil compactions .…”

Application of abscisic acid regulates antioxidant enzymes activities and modulates endosperm cell division in winter wheat

“…Stay-green mutants have been reported to maintain leaf greenness longer than their wild types during senescence (Hortensteiner 2009). In stay-green maize, the delay of senescence was associated with higher CAT and SOD levels (He et al 2005). Hui et al (2012) suggest that the higher antioxidant defense system may be one of the most important mechanisms underlying the expression of the delayed senescence phenotype in staygreen wheat.…”

“…The stay-green phenotype can be the result of alterations in hormone metabolism and signaling, particularly affecting networks involving cytokinins and ethylene (Thomas and Ougham 2014). Stay-green cultivar may have a defect in ethylene biosynthesis or signaling (Shirzadian-Khorramabad et al 2008) and show enhanced contents of cytokinins and reduced levels of ABA in leaves (He et al 2005).…”