Leaf Senescence can be Induced by Inhibition of Root Respiration

Abstract

Constituting the last stage of leaf development, leaf senescence is a complicated process that involves many senescence-associated genes, and numerous factors can induce leaf senescence. To elucidate the relationship between root respiration and leaf senescence, we treated the roots of Alhagi sparsifolia with nitrogen (N2) with the purpose of inhibiting root respiration (denoted as the N2 group). The results showed that compared with the control group, N2 treatment decreased the root respiration rate, chlorophyll (Chl) a, Chl b and carotenoid (Car) contents, the Chl/Car ratio, stomatal conductance (Gs), photosynthesis rate (Pn), maximum photochemical efficiency (φPo), and performance index on absorption basis (PIabs). In contrast, it increased leaf proline (Pro), malonaldehyde (MDA), and abscisic acid (ABA) contents. Moreover, no significant decline of Chl a/b was found in the N2 group. The results of the present work implied that leaf senescence can be induced by root respiration inhibition. Root respiration inhibition may result in ABA accumulation in leaves and thus induce leaf senescence. Another mechanism may be that root respiration inhibition resulted in the decrease of root water uptake, which subsequently led to water stress-induced leaf senescence. Root respiration inhibition-induced leaf senescence is a highly regulated process that is similar to natural senescence. In this process, no significant decline of Chl a/b was found. Root respiration inhibition-induced senescence is a “mild” process, in which most of the function of the photosynthetic apparatus performed well. Carotenoids play a key photoprotective role in leaf senescence. Overall, root respiration inhibition accelerated leaf senescence. In both types of senescence (root respiration induced senescence and natural senescence), the photosynthetic apparatus maintains a good performance until the last stage of senescence.