Maximum and effective PSII yields in the cortex of the main stem of young Prunus cerasus trees: effects of seasons and exposure

Abstract

Seasonal changes in chlorophyll fluorescence parameters of corticular chlorenchyma in the main trunk of Prunus cerasus were followed in the field under ambient temperature and light conditions during bright days. Concomitantly, measurements of periderm light transmittance also allowed the calculation of linear electron transport rates along PSII. Pre-dawn PSII photochemical efficiency was high during late spring, summer and early autumn, but low during winter in the North-facing, permanently shaded, side and extremely low in the South-facing, exposed side. Corresponding mid-day PSII effective yield and linear electron transport rates peaked at late spring and early summer with the exposed side always displaying lower values for effective yield, but higher values for electron transport rate. However, corticular electron transport rates were more than sixfold lower compared to leaves. Nonphotochemical quenching was higher in the exposed side throughout the year while peak values appeared at early autumn. Although a photoinhibitory damage during winter can be claimed, we may note that Mediterranean winter temperatures are mild, while the light reaching the trunk photosynthetic tissues is very low (maximum at 30 and 280 lmol m -2 s -1 in the shaded and the exposed side, respectively) to be considered as photoinhibitory. Based on recent findings for the retention of PSI activity and a concomitant inhibition of PSII under low temperatures in leaves, together with an adequate cyclic electron flow found in bark chlorenchyma, we suggest a temperaturedependent adaptive adjustment in the relative rates of PSI over PSII activity, possibly linked to seasonally changing needs for metabolic energy supply.

Contribution of stem CO₂ fixation to whole-plant carbon balance in nonsucculent species

“…Stems of several species show the F v /F m ratios from 0.71 to 0.81, close to the maximum value (0.83) of healthy leaves under optimal conditions (Björkman and Demmig 1987). In most species, the stem F v /F m ratio decreased to values lower than 0.5 during the winter, suggesting the PSII photoinhibition at low temperatures (Damesin 2003, Berveiller et al 2007, Levizou and Manetas 2008.…”

Analysis of fast chlorophyll fluorescence rise (O-K-J-I-P) curves in green fruits indicates electron flow limitations at the donor side of PSII and the acceptor sides of both photosystems

“…In both fruits and twigs, partial inactivation of PSII is accompanied by extremely low linear transport rates in the light-adapted state [ Fig. 6B and Table 4; see also Borisjuk et al (2005) and Hetherington et al (1998) for other fruits, and Levizou and Manetas (2008) and Manetas (2004) for twigs]. However, the inability of PSII to act as an efficient electron donor to PSI and the reductive pentose phosphate cycle does not necessarily predispose to an equally inactive PSI.…”

Role of corticular photosynthesis following defoliation in Eucalyptus globulus

“…It would appear that stem CO 2 fluxes are influenced by factors other than total light environment such as the recovery time following defoliation and seasonal effects (e.g. Levizou & Manetas 2008). In the present study, only field‐grown seedlings that had been defoliated 1 month after the September defoliation event showed increased rates of corticular net CO 2 flux and re‐fixation.…”