Senescence induced by nitrogen deprivation in wheat leaves

CRIADO, M.V.; ROBERTS, I.N.; ECHEVERRÍA, M.E.; BARNEIX, A.J.

Journal of Plant Growth Regulation

Springer

Año: 2007 vol. 26 p. 301 - 307

0721-7595

The sequence of events and the signals that regulate the remobilization of nitrogen (N) reserves during senescence induced by N starvation were studied in leaf 3, the last fully expanded leaf, in 17 d-old wheat (Triticum aestivum L) plants. The first event observed was a fast decrease in the isopentenyl adenosine (iPA) concentration during the first 24 h of N starvation. No differences in Zeatin riboside (t-ZR) and dihydrozeatin riboside (DHZR) concentrations were observed until the end of the assay. During the following 6 days, there was a decrease in soluble amino acids, chlorophyll and protein, mainly Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), as well as an increase in soluble sugar concentration and endoproteolytic activity. On the other hand, at day 3 of the experiment, the abscisic acid (ABA) concentration in the leaves of N-deprived plants started to increase. After six days of N deprivation, there was a rise in oxidative stress, as indicated by the increase in the malondialdehyde concentration, as well as a decrease in the activities of antioxidant enzymes catalase and ascorbate peroxidase. Then, the first, second, third and fourth leaves were studied, observing a decrease in the iPA concentration for all the leaf stages, including the leaf 4, which was not fully expanded. A lineal correlation between iPA and protein concentration was determined. These results suggest that the sharp fall in iPA could be the earliest event that induce protein degradation during the development of senescence induced by N deficiency, and that only later is ABA accumulated and oxidative stress developed.