Chlorophyll (Chl) a fluorescence transient and 820-nm transmission kinetic were investigated to explore the development of photosynthetic apparatus in grapevine leaves from emergence to full expansion. In this study, all leaves at various developing stages exhibited typical Chl a fluorescence transient. In newly initiating leaves, the maximum quantum yield of primary photochemistry (ϕP0) was slightly lower (<10 %) than that in fully expanded leaves. Nevertheless, the fluorescence rise from O to J step was clearly speeded up in young leaves compared with that in fully expanded leaves. Additionally, a distinct K step appeared in young leaves at high irradiances. With leaf development, the efficiency that a trapped exciton can move an electron into the electron transport chain further than QA - (Ψ0), the quantum yield of electron transport beyond QA (ϕE0), electron transport flux per excited cross section (ET0/CS0), the amount of active photosystem (PS) 2 reaction centres per excited cross section (RC/CS0), and the performance index on cross section basis (PICS) increased gradually and rapidly. Young leaves had strikingly lower amplitude of transmission at 820 nm. A linear relationship between Ψ0 and the transmission at 820 nm (I30/I0) was evident. Based on these data, we suggest that (1) the primary photochemistry of PS2 may be not the limiting step of the photosynthetic capacity during leaf growth under natural irradiance; (2) oxygen evolving complex (OEC) might be not fully connected to PS2 at the beginning of leaf growth; (3) though there are a few functional PS1 and PS2 at the early stages of leaf development, they match perfectly. and C.-D. Jiang ... [et al.].
UV screening by plant surfaces can be determined by exposing plant organs to UV radiation and measuring the chlorophyll (Chl) fluorescence elicited. From this fluorescence, the UV transmittance can be derived: the more intense the screening the lower the reporter Chl fluorescence and the lower the UV transmittance. The relationships between UV screening at 375 nm, as determined in the field by a portable UV-A-PAM fluorimeter, and UV screening at 314 and 360 nm, measured in the laboratory with the non-portable XE-PAM fluorimeter, were investigated in leaves of grapevine (Vitis vinifera L. cv. Bacchus) and barley (Hordeum vulgare cv. Ricarda), as well as in white grape berries. With leaves, linear trends were observed between XE-PAM measurements at 314 nm and UV-A-PAM measurements at 375 nm but the relationship between transmittance at 360 and 375 nm in barley was curved: a simple model calculation suggests that this curvi-linearity arises from particularly weak absorbance of barley flavonoids at 375 nm relative to absorbance at 360 nm. Transmittance values at 314 nm plotted against 375 nm yielded a much smaller slope in grapevine leaves than in barley leaves, which was attributed to screening in the short-wavelength UV by hydroxycinnamic acids in the former but not in the latter species. With grape berries, a poor correlation was detected between transmittances at 314 and 375 nm which might arise from high scattering of UV radiation at the berry surface. Such artefacts appear to be confined to the UV-B region, as berry transmittance at 360 nm correlated very well with that at 375 nm. Thus, assessment of UV screening in the field at short UV wavelengths using 375 nm readings from a UV-A-PAM fluorimeter is possible provided that information is available on the relationship between the transmittance at the UV wavelength of interest and at 375 nm for the sample tissue being investigated. and C. A. Kolb ... [et al.].