A rapid, whole‐tissue determination of the functional fraction of PSII after photoinhibition of leaves based on flash‐induced P700 redox kinetics

Abstract

Assaying the number of functional PSII complexes by the oxygen yield from leaf tissue per saturating, single-turnover flash, assuming that each functional PSII evolves one oxygen molecule after four flashes, is one of the most direct methods but time-consuming. The ratio of variable to maximum Chl fluorescence yield (F(v)/F(m)) in leaves can be correlated with the oxygen yield per flash during a progressive loss of PSII activity associated with high-light stress and is rapid and non-intrusive, but suffers from being representative of chloroplasts near the measured leaf surface; consequently, the exact correlation depends on the internal leaf structure and on which leaf surface is being measured. Our results show that the average F(v)/F(m) of the adaxial and abaxial surfaces has a reasonable linear correlation with the oxygen yield per flash after varied extents of photoinactivation of PSII. However, we obtained an even better linear correlation between (1) the integrated, transient electron flow (Sigma) to P700+, the dimeric Chl cation in PSI, after superimposing a single-turnover flash on steady background far-red light and (2) the relative oxygen yield per flash. Leaves of C3 and C4 plants, woody and herbaceous species, wild-type and a Chl-b-less mutant, and monocot and dicot plants gave a single straight line, which seems to be a universal relation for predicting the relative oxygen yield per flash from Sigma. Measurement of Sigma is non-intrusive, representative of the whole leaf tissue, rapid and applicable to attached leaves; it may even be applicable in the field.

Eco-physiological evaluation of different scion-rootstock combinations of almond grown in Mediterranean conditions

“…This result confirms that the rootstock type has an influence on PSII efficiency [31]. The slight reductions in F v /F m occurred for almond cultivars on dwarfing rootstocks, indicating that down-regulation of PSII efficiency was associated with a protective increase in non-radiative dissipation of light energy [32].…”

Decreased Photochemical Efficiency of Photosystem II following Sunlight Exposure of Shade-Grown Leaves of Avocado: Because of, or in Spite of, Two Kinetically Distinct Xanthophyll Cycles?

“…Previously, a robust linear correlation was demonstrated between the integrated transient electron flow to P700 after a fully saturating flash and PSII reaction center function assayed by the relative amount of oxygen per singleturnover flash evolved in leaves of herbaceous and woody species, wild-type and chlorophyll b-less barley (Hordeum vulgare), monocots and dicots, and C 3 and C 4 species (Losciale et al, 2008). Importantly, this relationship held in plants subjected to varying extents of photoinactivation of PSII by inhibiting chloroplast D1 protein synthesis (Losciale et al, 2008). This method has emerged as the preferred assay for PSII activity in vivo (Chow et al, 2012), and in avocado sun and shade leaves it delivered the same PSII/PSI ratio whether measured from the upper or lower epidermis.…”

“…Chlorophyll fluorescence analyses based on optimized, nonintrusive rapid light-response curves (RLRC) that minimized V and Lx deepoxidation during the assay (Förster et al, 2011) were used to separate qE (NPQ DpH ) from the three forms of nonphotochemical fluorescence quenching (NPQ AZ , NPQ DLAZ , and NPQ DL ). Very slow rates of photosynthesis in avocado shade leaves prevented accurate estimates of oxygen yield in single-turnover flashes, so another more sensitive method, based on the kinetics of delivery of electrons from PSII to PSI as measured from P700 + rereduction kinetics (Losciale et al, 2008;Chow et al, 2012), was used to estimate independently the functional fraction of PSII centers in vivo (PSII/PSI) and thereby assess NPQ PI .…”

Canopy conundrums: building on the Biosphere 2 experience to scale measurements of inner and outer canopy photoprotection from the leaf to the landscape

“…3g) and to sustained high NPQ PI (>2.0). Independent assays based on delivery of electrons from PSII to P700+ in single turnover flashes (Losciale et al 2008), showed a decline in the functional fraction of PSII (H-S. Jia, W. S. Chow and B. Osmond, unpubl. data).…”