Photoinhibition of photosynthesis in intact kiwifruit (Actinidia deliciosa) leaves: Effect of temperature

Abstract

Photoinhibition of photosynthesis was induced in attached leaves of kiwifruit grown in natural light not exceeding a photon flux density (PFD) of 300 μmol·m(-2)·s(-1), by exposing them to a PFD of 1500 μmol·m(-2)·s(-1). The temperature was held constant, between 5 and 35° C, during the exposure to high light. The kinetics of photoinhibition were measured by chlorophyll fluorescence at 77K and the photon yield of photosynthetic O2 evolution. Photoinhibition occurred at all temperatures but was greatest at low temperatures. Photoinhibition followed pseudo first-order kinetics, as determined by the variable fluorescence (F v) and photon yield, with the long-term steady-state of photoinhibition strongly dependent on temperature wheareas the observed rate constant was only weakly temperature-dependent. Temperature had little effect on the decrease in the maximum fluorescence (F m) but the increase in the instantaneous fluorescence (F o) was significantly affected by low temperatures in particular. These changes in fluorescence indicate that kiwifruit leaves have some capacity to dissipate excessive excitation energy by increasing the rate constant for non-radiative (thermal) energy dissipation although temperature apparently had little effect on this. Direct photoinhibitory damage to the photosystem II reaction centres was evident by the increases in F o and extreme, irreversible damage occurred at the lower temperatures. This indicates that kiwifruit leaves were most susceptible to photoinhibition at low temperatures because direct damage to the reaction centres was greatest at these temperatures. The results also imply that mechanisms to dissipate excess energy were inadequate to afford any protection from photoinhibition over a wide temperature range in these shade-grown leaves.

Photoinhibition in Vitis californica

“…5), and the associated decline in Kp (Fig. 7), at lower temperatures is consistent with many previous reports (17,18,22,23), and suggests damage to the PSII reaction center as an early event in high-PFD exposure. High temperature may lead to direct inhibition of the Calvin cycle, which could, in turn, cause secondary declines in PSII activity (7,31,32).…”

“…When these processes cooccur, they may confound the interpretation of raw fluorescence signals, especially FO. To resolve this dilemma, we have followed the procedures of Bjorkman (8), Demmig et al (12), and Greer et al (18) and estimated values of the first-order rate constant for deexcitation of Chl molecules by photochemistry (KP):…”

“…where KP is the rate constant for photochemistry, KF is the rate constant for fluorescence, and J is the PFD absorbed by photosynthetic pigments (8,15,18).…”

“…The results of several investigators have supported this prediction (1,8,9,11,12). However, in studies of Actinidia deliciosa, Greer et al (18) found that this relationship was curvilinear and concluded that Fv, which was linearly related to OA, provided a better estimate of the inhibitory effects of high PFD on PSII photochemistry. By examining both Chl fluorescence and OA in V.…”

Some photosynthetic characteristics in the leaves of kiwifruit

“…Most of the published papers are concerned with micropropagation in vitro (Shen et al 1990), the H93087 Received 20 December 1993; accepted 28 July 1994 chemistry or biochemistry of metabolites (Buwalda el al. 1991), the transport of assimilates (MacRae et al 1990), photoinhibition (Greer et al 1988), and water regime (Green et al 1989). Fewer are from the field of anatomy and root structure (e.g., Przywara et al 1988).…”