Nuclear (DNA, RNA, histone and non-histone protein) and nucleolar changes during growth and senescence of may apple leaves

Genetic mechanisms of aging in plants: What can we learn from them?

Plants hold all records in longevity. Their aging is a complex process. In the presented review, we analyzed published data on various aspects of plant aging with focus on any inferences that could shed a light on aging in animals and help to fight it in human. Plant aging can be caused by many factors, such as telomere depletion, genomic instability, loss of proteostasis, changes in intercellular interaction, desynchronosis, autophagy misregulation, epigenetic changes and others. Plants have developed a number of mechanisms to increase lifespan. Among these mechanisms are gene duplication ("genetic backup"), the active work of telomerases, abundance of meristematic cells, capacity of maintaining the meristems permanently active and continuous activity of phytohormones. Plant aging usually occurs throughout the whole perennial life, but could be also seasonal senescence. Study of causes for seasonal aging can also help to uncover the mechanisms of plant longevity. The influence of different factors such as microbiome communities, glycation, alternative oxidase activity, mitochondrial dysfunction on plant longevity was also reviewed. Adaptive mechanisms of long-lived plants are considered. Further comparative study of the mechanisms underlying longevity of plants is necessary. This will allow us to reach a potentially new level of understanding of the aging process of plants.

Apoptosis-like cell death of Brassica napus leaf protoplasts

•   The cleavage of nuclear DNA into oligonucleosomal fragments that is the hallmark of apoptosis in animal cells occurs during the culture of Brassica napus leaf protoplasts. •   The changes in nuclei of cultured Brassica napus leaf protoplasts were studied by propidium iodide (PI) and 4', 6-diamino-2-phenylindole, dihydrochloride (DAPI) staining, transmission electron microscopy, flow cytometry analysis, and DNA laddering staining with ethidium bromide and Southern hybridization. •   Free 3'-OH termini of nuclear DNA fragments were labelled with DIG-dUTP, catalyzed by terminal deoxynucleotidyl transferase (TdT), and used as probes for Southern hybridization. This method (TUNEL on membrane) allowed visualization of DNA fragments with 3'-OH termini on a nylon membrane. •   These results suggest that loss of viability of protoplast with culture time is accompanied by apoptosis-like cell death. However, the forms or processes undergoing to apoptotic cell death in B. napus leaf protoplasts appears to be different in some details to those in animal cells.

The comet assay: a tool to study alteration of DNA integrity in developing plant leaves

DNA integrity of Nicotiana tabacum L. and Vicia faba L. leaves in different stages of growth was analysed with the single cell gel electrophoresis (comet) assay. With this test DNA of individual cells is stretched by electrophoresis and the migration is measured, which gives an image of the nuclear DNA organisation. Nuclei were sampled when the plants had developed an apical bud, five true leaves and cotyledons. To get an idea of the kind of lesions observed, three different comet protocols were used. The neutral protocol with electrophoresis in a neutral buffer and the semi-alkaline or alkaline assay with alkaline unwinding followed by electrophoresis in neutral alkaline buffer, respectively. For V. faba there was a successive increased cellular DNA mobility with age of the leaves. The percentage DNA migration in control cells of fully developed leaves from N. tabacum almost reached the same level than after irradiation of not fully developed leaves with 50 Gy X-rays. The increased stretching of DNA with leaf age was most obvious if the DNA duplex was converted to single strands by alkali treatment before electrophoresis. Therefore, it could be concluded that with the ageing of leaves there is a decrease in DNA integrity, which could be the result of rising amounts of DNA single-strand breaks and 'alkali-vulnerable sites'.