Xylem abscisic acid accelerates leaf abscission by modulating polyamine and ethylene synthesis in water-stressed intact poplar

Abstract

We investigated the effects of endogenous and exogenous abscisic acid (ABA) on polyamines (PAs) and ethylene synthesis and their relevance to leaf senescence in 1-year-old intact cuttings of a drought-sensitive poplar genotype Populus × euramericana cv. I-214 (cv. Italica) and a drought-tolerant genotype P. popularis 35-44 (P. popularis). P. popularis exhibited a transitory and moderate increase in xylem ABA concentrations in response to water stress and no leaf abscission during the period of drought (30% of field capacity; the soil water potential was -2.108 MPa). In contrast, leaf shedding occurred in stressed cv. Italica following a sustained increase in xylem ABA concentrations (up to 1.73 µM). Application of ABA to the transpiration stream accelerated leaf abscission in both genotypes with a threshold of approximately 1.7-1.8 µM. Initial elevation of xylem ABA concentrations reduced PA levels but enhanced ethylene synthesis simultaneously at the onset of water stress or the ABA treatment. Moreover, sharp increases in ABA concentrations, i.e. over 1.7 µM, severely restricted PA synthesis in aged leaves in the longer term (within 3 days). Leaves abscised following a progressive decline of PA levels, when putrescine decreased below approximately 0.5 µmol g -1 fresh weight, and spermidine and spermine became almost undetectable by HPLC. Therefore, we concluded that a drastic reduction in the level of PAs might increase the sensitivity of the leaf to ethylene, thus accelerating defoliation, even though the ethylene emission of stressed plants returned to prestress values by day 3. Young leaves were not shed during the period corresponding to the increase in xylem ABA, which appeared to result from the lesser reductions of PA. Compared with P. popularis, the inhibitory effect of ABA on PA synthesis was more pronounced in the drought-sensitive genotype cv. Italica. On the other hand, cv. Italica plants typically produced more ethylene than P. popularis. Taken together, these observations might explain our previous finding that ABA-treated plants of cv. Italica experienced more leaf loss than P. popularis .

Population differences in physiological and morphological adaptations of Populus davidiana seedlings in response to progressive drought stress

“…WUE increase, ABA accumulation, plant structural modifications and growth pattern adjustments are useful indices of the consequences of water deficit [5][6][7]12,13,18]. Differences in drought adaptations among populations of P. davidiana were demonstrated and attributed to differences in these morphological and physiological responses to water availability.…”

“…Some of the adaptive responses to water deficit are physiological and morphological changes, Abbreviations: A, net photosynthesis; ABA, abscisic acid content; E, transpiration; Ht, height growth; La, total leaf area; Rs, root/shoot ratio; Sla, specific leaf area; Tb, total biomass; WUE, water use efficiency; WUE i , instantaneous water use efficiency; δ 13 such as changes in plant structure, growth rate, tissue osmotic potential and stomatal conductance [8,9]. On the other hand, abscisic acid (ABA), a well-known stress-inducible plant hormone and growth inhibitor, has long been studied as a potential mediator for induction of drought tolerance in plants [10][11][12][13]. ABA seems to play a predominant role in the conversion of environmental signals into changes in plant gene expression [14,15].…”

Effect of Provenance and Climate on Xylem Anatomy of Haloxylon Ammodendron (C. A. Mey) Bunge in the Gurbantunggut Desert, China

“…This may be because drought stress favored the production of ethylene in the plants (Chen et al, 2002) and ethylene promoted anticlinal division in fusiform initials, increasing the density and/or size of rays (Pramod et al, 2013). The dR and hR were negatively related to average annual precipitation (P < 0.05; Table 5, Eq.…”

The role of free polyamines in the alternate-bearing of pistachio ( Pistacia vera cv. Pontikis)

“…PAs are known to act as anti-senescence agents and counteract the activity of abscisic acid (ABA) and ethylene (Smith 1985;Wang and Steffens 1985;Evans and Malmberg 1989;Chen et al 2002). According to Chen et al (2002), ABA increased levels resulting in membrane leakage and leaf abscission, while it inhibited PA biosynthesis. Ethylene, on the other hand, is the most dominant hormonal factor promoting senescence and exogenous application of ethephon (an ethylene producer) enhanced bud abscission on non-fruiting branches (Crane et al 1982).…”

“…Ethylene, on the other hand, is the most dominant hormonal factor promoting senescence and exogenous application of ethephon (an ethylene producer) enhanced bud abscission on non-fruiting branches (Crane et al 1982). Despite the opposing roles of PA and ethylene they share the same precursor, S-adenosylmethionine (SAM) (Smith 1985;Wang and Steffens 1985;Chen et al 2002). In some cases where the level of SAM is low, there could be direct competition between PAs and ethylene on SAM as a precursor (Evans and Malmberg 1989;Kuznetsov et al 2002), which could lead to senescence and abscission (ethylene biosynthesis dominates) or retardation of senescence (PA biosynthesis prevails).…”