Morphological, histochemical and ultrastructural indicators of maize and barley leaf senescence

This review synthesizes knowledge on dark-induced barley, attached, leaf senescence (DILS) as a model and discusses the possibility of using this crop system for studying senescence and autophagy mechanisms. It addresses the recent progress made in our understanding of DILS. The following aspects are discussed: the importance of chloroplasts as early targets of DILS, the role of Rubisco as the largest repository of recoverable nitrogen in leaves senescing in darkness, morphological changes of these leaves other than those described for chloroplasts and metabolic modifications associated with them, DILS versus developmental leaf senescence transcriptomic differences, and finally the observation that in DILS autophagy participates in the circulation of cell components and acts as a quality control mechanism during senescence. Despite the progression of macroautophagy, the symptoms of degradation can be reversed. In the review, the question also arises how plant cells regulate stress-induced senescence via autophagy and how the function of autophagy switches between cell survival and cell death.

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The role of cytokinins in the development and metabolism of barley leaves. I. The effect of cytokinins on leaf senescence

Acta Societatis Botanicorum Poloniae ◽

10.5586/asbp.1977.028 ◽

2015 ◽

Vol 46 (2) ◽

pp. 357-368 ◽

Cited By ~ 1

Author(s):

A. Woźny ◽

A. Szweykowska ◽

J. Legocka

Keyword(s):

Nucleic Acids ◽

Leaf Senescence ◽

Rna Synthesis ◽

Similar Extent ◽

Mesophyll Cells ◽

Barley Leaves ◽

Barley Leaf ◽

Cytokinin Action ◽

Natural Cytokinin

The loss of chlorophyll during dark-induced ageing of barley leaves was prevented to a similar extent by kinetin and the natural cytokinin, 6-Δ<sup>2</sup>-iso-pentenylarninopurine (2iP). A concentration of 400 μM appeared to be optimal in both cases. In the presence of 2iP the structure of mesophyll cells in dark-incubated leaves was maintained unchanged. A distinct correlation has been found between the retardation by 2iP of the chlorophyll loss, the rate of S2P-incorporation into nucleic acids and the maintaining of the RNase activity at a low level. The importance of the RNA synthesis and the rate of its de-gradation in the cytokinin action in barley leaf senescence will be subjected to future experiments.

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Kinetin affects the level of chloroplast polyamines and transglutaminase activity during senescence of barley leaves.

Acta Biochimica Polonica ◽

10.18388/abp.2009_2457 ◽

2009 ◽

Vol 56 (2) ◽

Cited By ~ 19

Author(s):

Ewa Sobieszczuk-Nowicka ◽

Przemysław Wieczorek ◽

Jolanta Legocka

Keyword(s):

Leaf Senescence ◽

Covalent Bonds ◽

Transglutaminase Activity ◽

Barley Leaves ◽

Tgase Activity ◽

Barley Leaf ◽

Chloroplast Senescence

We analysed the level of polyamines (PAs) bound to thylakoids and the level and activity of thylakoid transglutaminases throughout barley leaf senescence, retarded by kinetin. The level of PAs bound to thylakoids changed in senescing barley leaves: bound putrescine (PU) and spermidine (SD) increased throughout senescence, whereas bound spermine (SM) decreased. Kinetin diminished the increase in thylakoid-bound PU and SD and almost completely abolished the decrease of the bound SM. These data suggest different roles of PU/SD and SM in thylakoid degradation. Immunodetection of transglutaminases (TGase) in thylakoid fraction revealed three bands of 33, 58 and 78 kDa. During senescence the intensity of all bands increased and it was correlated with an increase in TGase activity. Kinetin down-regulated the accumulation of the 58- and 78-kDa TGases and the TGase activity. We postulate that formation of covalent bonds between PAs and proteins by TGase is involved in chloroplast senescence. The kinetin-mediated preservation of low TGase levels and activity throughout leaf senescence may represent an important component of the mechanism of kinetin action in the retardation of leaf senescence.

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