Aspects of programmed cell death during early senescence of barley leaves: possible role of nitric oxide

Abstract

Leaf senescence is a highly coordinated process which involves programmed cell death (PCD). Early stages of leaf senescence occurring during normal leaf ontogenesis, but not triggered by stress factors, are less well known. In this study, we correlated condensation of chromatin and nuclear DNA (nDNA) fragmentation, two main features of PCD during early senescence in barley leaves, with the appearance of nitric oxide (NO) within leaf tissue. With the help of the alkaline version of the comet assay, together with measurements of nDNA fluorescence intensity, we performed a detailed analysis of the degree of nDNA fragmentation. We localised NO in vivo and in situ within the leaf and photometrically measured its concentration with the NO-specific fluorochrome 4-amino-5-methylamino-2',7'-difluorofluorescein. We found that both nDNA fragmentation and chromatin condensation occurred quite early during barley leaf senescence and always in the same order: first nDNA fragmentation, in leaves of 6-day-old seedlings, and later chromatin condensation, in the apical part of leaves from 10-day-old seedlings. PCD did not start simultaneously even in neighbouring cells and probably did not proceed at the same rate. NO was localised in vivo and in situ within the cytoplasm, mainly in mitochondria, in leaves at the same stage as those in which chromatin condensation was observed. Localisation of NO in vascular tissue and in a large number of mesophyll cells during the senescence process might imply its transport to other parts of the leaf and its involvement in signalling between cells. The fact that the highest concentration of NO was found in the cytoplasm of mesophyll cells in the earliest stage of senescence and lower concentrations were found during later stages might suggest that NO plays an inductive role in PCD.

Nitric oxide affecting root growth, lignification and related enzymes in soybean seedlings

“…5) suggesting a cytotoxic effect of SNP. Cytotoxicity and cell death are known actions of NO, especially when it is present in high concentrations (Delledonne et al 1998;Clarke et al 2000;Zottini et al 2002;Víteček et al 2007;Kolodziejek et al 2007). Our findings suggest that a concentration of 1,000 lM of SNP induced soybean root cell death, reducing its growth and lignification.…”

Programmed cell death, antioxidant response and oxidative stress in wheat flag leaves induced by chemical hybridization agent SQ-1

“…Recently, many studies have described the mechanism of PCD during plant leaf senescence, and have mainly focused on biotic and abiotic stress (Lee and Chen 2002;Buchanan-Wollaston et al 2003;Penfold and Buchanan-Wollaston 2014;Potschin et al 2014;Sakamoto and Takami 2014). These stresses are often inextricably linked with reactive oxygen species (ROS), such as dark (Pastori and Delrio 1994a, b;Jimenez et al 1997;del Rio et al 2003), Drought (Hameed et al 2013;Ye et al 2013), heat (Fan and Xing 2004), NO (Kolodziejek et al 2007;Guo et al 2013), O 3 (Pell et al 1999), paraquat and H 2 O 2 (Pastori and Trippi 1993), salt stress (Deng et al 2014), and UV-C irradiation (Danon and Gallois 1998). Increasing evidence has revealed that ROS can also act as a signal molecule or take part in PCD, resulting in delayed growth (Lamb and Dixon 1997;Bowler and Fluhr 2000;Bethke and Jones 2001;Noreen and Ashraf Advanced Online Publication 2015Doi：10.101660977-1 2008).…”

Caffeine-Induced Premature Chromosome Condensation Results in the Apoptosis-Like Programmed Cell Death in Root Meristems of Vicia faba

“…The type of DNA fragmentation can be also distinguished in comet assay [ 28 , 39 ]. Regardless of the method (alkaline or neutral variant), intact DNA remains in the head of the comet and DNA from regions with strand breaks appears in the tail.…”

“…amount of DNA in the comet tail) times tail length (i.e. length of the comet tail measured from right border of head area to end of tail, according to the method described by Olive et al [ 27 ] and Kołodziejek et al [ 28 ]). We analyzed 30 images of nuclei from each experimental series.…”