Meristem aging is not responsible for age-related changesin growth and abscisic acid levels in the Mediterranean shrub, Cistus clusii

摘要

To obtain new insights into the mechanisms underlying aging in perenni-als, we measured abscisic acid levels, growth and other stress indicators in leaves of Cistus clusii Dunal plants of different ages grown under Mediter-ranean field conditions. Recently emerged leaves from 9-year-old plants were compared to those of 1-year-old plants (obtained from cuttings from 9-year-old plants) to evaluate the effects of meristem aging on plant aging. Rooting and successful establishment of the cuttings allowed us to com-pare the physiology of plants with old meristems, but of different size. Plants obtained from cuttings were rejuvenated, with new leaves displaying a higher leaf area and chlorophyll content, but smaller leaf mass per unit area ratios and endogenous abscisic acid levels than those of 9-year-old plants. A comparative study in 1-, 4- and 9-year-old plants revealed that abscisic acid levels increase during the early stages of plant life (with increases of 90% between 1- and 4-year-old plants), but then remain con-stant at advanced developmental stages (between 4- and 9-year-old plants). Although leaf biomass was 53% smaller in 9-year-old compared to 4-year-old plants, the dry matter produced per shoot apical meristem was equiva-lent in both plant groups due to an increased number of leaves per shoot in the former. It is concluded that (i) C. clusii plants maintain the capac-ity to rejuvenate for several years; (ii) newly emerged leaves accumulate higher amounts of abscisic acid during early stages of plant life, but the levels of this phytohormone later remain constant; and (iii) although plant aging leads to the production of smaller leaves, the amount of biomass produced per shoot apical meristem remains constant at advanced develop-mental stages.