Protection by isoprene against singlet oxygen in leaves

Abstract

Isoprene (2-methyl-1,3-butadiene) protection against effects of singlet oxygen was investigated in Myrtus communis and Rhamnus alaternus. In M. communis, singlet oxygen produced in the leaves by Rose Bengal (RB) led to a 65% decrease in net assimilation rates within 3 h, whereas isoprene emission rates showed either a 30% decrease at ambient CO2 concentrations or a 70% increase under high CO2. In both cases, these changes led to an increase in calculated internal isoprene concentrations. The isoprene protection effect was directly demonstrated by fumigation of young (non-emitting) leaves, treated with RB or bromoxynil (simulating photoinhibition). There was 42% and 29% reduction in the damage to net assimilation compared with non-fumigated leaves for RB or bromoxynil, respectively. In R. alaternus, similar effects of RB on net assimilation were observed, and additional fluorescence measurements showed a significantly smaller decrease in Fv/Fm in isoprene-fumigated young leaves treated with RB (from 0.78 to 0.52), compared with non-fumigated leaves (from 0.77 to 0.27). The internal isoprene concentrations used in this study and possible rate of 1O2 production in leaves indicate that the protective effects observed should be beneficial also under natural conditions.

Figure 1

Seasonal variations (a) and effects of branch age (b) on net assimilation (A) and isoprene emission rates (Is) from a shrub of M. communis. Measurements were performed at leaf temperature of 26°C and light intensity of 1,000 μmol m⁻² s⁻¹. The seasonal variations were measured at intercellular CO₂ concentration (c_i) values between 450 and 500 μL L⁻¹, and the effect of branch age was measured at ambient CO₂ concentrations (approximately 350 μL L⁻¹).

Figure 2

Effects of c_i on net assimilation (a) and isoprene emission rates (b) from branches of M. communis measured at 26°C (circles; two different branches) and 34°C (triangles) and light intensity of 1,000 μmol m⁻² s⁻¹.

Figure 3

Effects of different concentration of RB in the feeding solution on net assimilation (a) and isoprene emission rates (b) of M. communis at leaf temperature of 26°C, light intensity of 1,000 μmol m⁻² s⁻¹, and c_i values of 200 to 250 μL L⁻¹. The vertical line indicates the beginning of RB feeding. Values were normalized to the average before RB feeding.

Figure 4

Effects of singlet oxygen in leaves of M. communis under ambient CO₂ concentration (approximately 350 μL L⁻¹; a and b) and high CO₂ concentration (approximately 800 μL L⁻¹; c and d) on net assimilation and isoprene emission rates (a and c) and on changes in the c_i and isoprene (Isop_i; b and d) at leaf temperature of 26°C and light intensity of 1,000 μmol m⁻² s⁻¹. The vertical line indicates the beginning of RB feeding.

Figure 5

Effect of RB (0.1 μm) on net assimilation rates (full symbols) and chlorophyll fluorescence yield (F_v/F_m; white symbols) in young shade leaves of R. alaternus at leaf temperature of 26°C, light intensity of 1,000 μmol m⁻² s⁻¹. The vertical line indicates the beginning of RB feeding. The fumigation effect was significant at P < 0.04 and P < 0.006 in net assimilation and fluorescence, respectively. The error bars of F_v/F_m before the RB treatment are smaller than the symbols.